4. Pipeline Coatings Notes

Pipeline Coatings Inspector I.Corr level 2

PIPELINE

COATINGS

INSPECTOR

INSTITUTE

OF

CORROSION

LEVEL II

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Pipeline

Coatings

Inspector

I.Corr Level II

Part A

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Section PageENAMEL COATINGS………………………………………………….. 1 4FUSION BONDED EPOXY……………………………………………. 2 7POLYOLEFINS & OTHER PLASTIC COATINGS………………… 3 12ELASTOMERIC COATINGS…………………………………………. 4 16MULTI-COMPONENT LIQUIDS – MCL’s………………………….. 5 19WRAPPING TAPES……………………………………………………. 6 22

Hot applied tapes………………………………………………….. 6-1 23Cold applied laminate tapes………………………………………. 6-2 24Grease based tapes………………………………………………... 6-3 26Self adhesive overwrap tapes…………………………………….. 6-4 27

BRUSHING MASTICS…………………………………………………. 7 28FILLERS (MASTICS & PUTTIES)…………………………………… 8 29INTERNAL PIPE COATINGS………………………………………… 9 29TESTING OF COATINGS AND WRAPPINGS……………………… 10 30

Factory / laboratory based tests…………………………………… 10-1 30Tests performed by inspection personnel (factory/site)…………… 11 33Awareness of other tests…………………………………………... 11-1 34

INSPECTION……………………………………………………………. 12 34Duties of a pipeline inspector……………………………………… 12-1 34Reports and records………………………………………………... 12-2 38Examples of possible contractor malpractice……………………… 12-3 39

HANDLING, TRANSPORT, STORAGE OF COATED PIPE……….. 13 39DITCHING AND BACK FILLING…………………………………….. 14 40PEARSON SURVEY…………………………………………………….. 15 41

PIPELINE COATING INSPECTOR………………………………PART B 42

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1 ENAMEL COATINGS

When using the term enamels in relation to pipe coatings we are referring to coal tar or bitumen (asphalt) based coatings, which are applied as a hot liquid.FBE and polyolefin coatings have, largely superseded coal tar and bitumen enamel coatings for full pipe lengths; however, many pipeline users do still specify the use of enamels. Pipeline coating inspectors are also likely to encounter these materials on maintenance work.Bitumen and coal tar enamels must not in any circumstances be mixed or applied on top of one another. Loss of properties and poor adhesion respectively will be the result.Both materials are black and are very similar in texture. A simple test can be conducted to distinguish between the two materials.(Note 1) Take a very small ball, about 3mm dia of the unknown enamel and place onto a sheet of

white blotting paper of filter paper. Put two or three drops of xylene or toluene onto the ball. The ring of liquid running from the enamel and soaking into the paper will show yellow for coal tar and brown for bitumen enamels.

Enamel coatings are normally reinforced with two layers of fibreglass to provide a rigid durable coating.

Constituents Coal tar enamelsPlasticised coal tar pitch from coal, distilled in coke ovens, is the main constituent to which is added various amounts of coal oil (plasticizer), which modifies the material for viscosity properties and temperature tolerance. Fillers are added, usually in the form of talcum powder or slate flour. Proportions of 25% - 35% and these are classed as inert mineral fillers.

Bitumen enamelsBitumen (asphalt) is a heavy reside from the distillation of crude oil. Inert mineral fillers are added, usually in the form of talcum powder or slate flour as for coal tar. Adding certain waxes and increasing refinement can reduce the viscosity of bitumen. Herbicides are also added to bitumen enamels to discourage root growth.

Advantage and limitationsAdvantages

1. Low cost system – low material cost and pipe is not heated.2. Relatively simple system.3. Widely known system – users have a good knowledge of application and performance properties.

Limitations1. Overall – poor performance properties when compared to more modern systems; higher CP

currents required.2. Labour intensive, at least three operatives will be required for site applications.3. For site work, bulky melting pots are required.4. Coating needs reinforcement.5. Safety hazards – (1) toxic fumes from liquid state; (2) danger of burns from hot enamels,

especially during field application on welded butt joints; (3) flammable constituents.6. Thermoplastic nature of coating can lead to coating damage during handling, storage and

ditching.7. Susceptible to breakdown in UV light.8. Easy disbondment due to impact.9. Bitumen’s need herbicides incorporated.10. Susceptible to coating damage during soil stressing – compaction.11. Limitations on bending, due to brittle nature of material.12. Enamels of both types are not suitable for use over plastics of any type – no adhesion.Note 1 – Many other solvent types will also give the desired result when carrying out an enamel identification test.

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Surface preparationFactory Surface preparation in a factory is normally carried out by dry abrasive blast cleaning, using totally enclosed centrifugal blast cleaning units. Chemical cleaning, usually using the Footner process, is an alternative.Typical requirements (blast cleaning)

Abrasive used – steel grit and shot mix. Profile requirements – Sa 21/2, medium profile or 50 - 70μm. Inspect blasted areas for surface laminations (slivers0; if any exist then remove with a grinder,

check for correct contour and wall thickness, then re-blast the area.

SiteWelded joints are blast cleaned using pressure blasting equipment and dry expendable abrasive.Typical requirements

Remove solar protective coating and all extraneous material from the existing coating (150mm is typical requirement).

Degrease only if necessary. Chamfer coating by 50m or 100mm as specified, using a blowtorch and scraper. Blast clean using dry expendable abrasive – profile requirements – Sa21/2, medium profile or 50-

75μm. Inspect blasted areas for surface laminations (slivers) – if any exist, remove with a grinder, check

for contour and wall thickness, then re-blast area. Check for disbanded coating, if any exists then remove and re-blast area.

Coating applicationFactory (note 1)In a pipe coating factory (mill) the enamel coating process is often done as a continual process by using spacer collars placed between the pipes, so that in effect one long continuous pipe length is being coated. Some coating factories will treat each pipe separately.

The sequences of events for coating (showing typical requirements) are as follows1. Residual dust from the blast cleaning operation is removed from the pipe by soft brush and/or

clean dry compressed air, or by vacuum suction.2. As the pipe is rotating and moving forward an overhead spray applies the appropriate primer. For

coal tar enamel, a fast drying synthetic primer (chlorinated rubber) type B would be used. For bitumen enamels a synthetic or bitumen based primer would be used. In both cases the d.f.t required would be around 15-25μm. The primers are low volume solids materials and dry in approximately 5-15 mins, sometimes facilitated by blowing warm air through the pipe.

3. When the primer is dry, a flood coating of hot enamel is applied using a flood box. The enamel should be constantly agitated and should not exceed 205˚C generally, especially when there is a delay in application.Maximum application temperature for coal tar enamel: 250˚C, discard enamel if temperature exceeds 260˚C.Maximum application temperature for bitumen enamel, 230˚C, discard enamel if temperature exceeds 240˚C.

4. Simultaneously, two reinforcements are applied in a spiral fashion, using a 150mm wide strip of glass fibre and a 150-230mm wide strip of impregnated glass fibre outer wrap. The spiral overlap on each wrap should be at least 25mm. The inner wrap should be embedded approximately half way into the enamel and should not be within 1 mm of the pipe surface. The outer wrap should be visible on the surface of the pipe coating.

5. The wrapping (enamel plus reinforcement) should be trimmed back 150mm from each end of the pipe and possibly bevelled, e.g. by at least 25mm.

Note 1 - Full pipe lengths along with welded joints may also be prepared and coated on site with purpose built equipment to allow for continuous operation.

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6. A solar protective coating should be applied, whilst the pipe is still warm. White wash for coal tar enamels, blue wash for bitumen enamels. The washes should terminate from each end of the wrapping.

Typical thickness requirement 4-7mm

Site application (welded joints)In the field enamels can only be used on welded butt joints, when the adjoining pipes are enamel coated.The sequence of events is essentially a manual reproduction of the factory system, except the pipes cannot be rotated or moved in any way.Sequence of operations

1. Blast clean to Sa21/2.2. Remove dust.3. Apply primer by brush.4. When primer is dry, apply 1st flood coat of enamel. This is poured from a bucket and the coating

is smoothed off (preventing icicles) by using a sling, which is pulled back and forth around the joint by two operatives.

5. Apply 2nd flood coat of enamel simultaneously with the application of a fibreglass inner wrap overlapping the existing coating by at least 75mm.

6. Apply a 3rd flood coat of enamel and apply an enamel impregnated outer wrap.

Typical thickness requirement, minimum 4mm.

SafetyWhen using coal tar enamels, due respect should be paid to the hazardous and irritant fumes. Barrier creams should be applied to all areas of bare skin and ideally masks worn. Contact with coal tar can cause warts. Medical attention should be sought at the first suspicion. It is not advisable to use enclosures during inclement weather because of the fumes.Coal tar and bitumen enamels should normally be used at temperatures below their spontaneous ignition temperature, but even so, the vapour space is frequently within the flammable range. Therefore smoking or naked flames should not be allowed in the vicinity of a tank or drum containing hot material. No source of ignition should be put into a tank or drum that has contained this material until the tank or drum is gas free.

TestingTests on the primer

1. Viscosity measurement, using a flow cup at a specified temperature.2. Film thickness measurement.

Tests on the enamel material1. Enamel temperature measurements.2. Softening point (ring and ball).3. Penetration.4. Viscosity measurement using a Zahn flow cup at 230˚C

Tests on the enamel coating1. Preliminary adhesion.2. Tapping to check for laminations.3. Holiday detection.4. Bond strength test5. Thickness of wrapping6. Visual check for uniformity of coating contour, e.g. no icicles, ensure that the outer wrap is not

disbonded and bleed through has taken place, ensure no coking exists.7. Coupons taken to ensure inner wrap is correctly positioned in enamel. Laminations may also be

evident.

Determination of filler fineness, filler content, enamel specific gravity, peel resistance, sag resistance, flexibility, (bend tests), low temperature disbondment/cracking, impact resistance and cathodic

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disbondment. Other tests are carried out at less frequent intervals, e.g. once a year or at the start of a project. The inner and outer wraps must also meet specified requirements for various tests.

RepairsRepairs to enamel coatings can be carried out by various methods, depending on the nature and size of the coating fault. Pinholes are sometimes repaired using a hot knife, whereas extensive damage would normally require full circumferential removal of the wrapping over the effected area. The bare area may then be repaired with the same enamel (normally incorporating reinforcement), heat shrinkable material, hot applied tape, cold laminate tape or a grease based tape, over-wrapped with a self adhesive overwrap tape as specified. Multi-component liquids could also be used. The method employed should be governed by the specification. Patch type repairs with tapes are not advisable; if tapes are specified then full circumferential wraps will be required.

2 FUSION BONDED EPOXY

Fusion bonded epoxy (FBE) is a common coating material used on pipelines throughout the world. It is applied in factories on full pipe lengths and on fittings. In the field it is used for coating welded joints, but only when the adjacent pipes/fittings are coated with the same material.These coatings are sometimes referred to as Resin powder coatings (RPC)(note 1) and are thermo-setting, which means when heat is applied to a cured coating it will not return to a liquid state, they therefore chemically cure by cross-linking.The material is applied as a powder to components which a re heated to a specified temperature, governed by the powder type being used. The application temperature range will not normally exceed 215˚C, e.g. 218˚C to 246˚C for 3M’s powder Scotchkote 206N. When the powder makes contact with the hot component it melts and forms a coating typically between 350 - 650μm thick, which can become fully cured in approximately three minutes.There are four main stages of transformation from a powder to a cured coating:

1. Flow time powder to semi-liquid.2. Wetting time powder to liquid.3. Gel time powder to gel (to the start of solidification).4. Cure time powder to completion of cross-linking.

Constituents of coating materialIn common with other coating materials, several components are used to give the required finished product, these typically include:

a. 50 – 60% binder (base resin and curing reagent).b. 35 – 50% pigment and extenders (fillers).c. 2 – 4% other additives such as anti-foaming agents, wetting agents and flow control agents.

The base resin and curing reagent are essentially high melting point resins, which are solids at normal ambient temperatures. Technically they should have a softening point of above 70˚C (note 2) , but generally are in the range of 85˚ - 90˚C.

During powder manufacture, all the required components are heated together and as soon as possible, when liquid (note 3), they are mixed into a homogenous mixture and then frozen to halt the reaction. This material is then micronized into a powder. Powder particle sizes are typically in the range of 25-75μm and each particle contains the required components to affect a cure when returned to a liquid state.

Advantages and limitationsAdvantages

I. No solvent – no global warming potential (GWP) no ozone depletion potential (ODP)II. Low health risk.

Note 1 – powder coatings (not epoxy) can be made from thermoplastic materialsNote 2 – Lower softening points require lower storage temperaturesNote 3 – when the materials are melted they have a molecular freedom, the molecules can move about and cross-link. The warmer the material, the more molecular freedom (lower viscosity). As the mixture is cooled and eventually solidifies, the curing reaction is stopped.

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III. Low fire risk – although loose powder particles in the air are highly flammable.IV. Low processing time.V. Good film properties – especially chemical resistance.

VI. Low dust pick up (~ 3 mins to full cure).VII. Good edge coverage (no shrinkage therefore good on sharp corners).

VIII. Clean to use.

LimitationsI. Heating of components can be costly.

II. Achieving thin films, e.g. <25μm can be difficult to achieve if ever requested.III. Different powders cannot be mixed with each other, e.g. powders with different colours, from

different generic types of from other manufacturers.IV. Prone to chalking when exposed to UV light.V. Prone to chipping damage due to brittle nature.

VI. High storage temperatures can cause sintering.

Surface preparationFactory

Surface preparation in a factory is normally carried out by dry abrasive blast cleaning, flowed by the application of a conversion coating (phosphoric acid wash and/or chromating (Note 1)). Sometimes the conversion coating is omitted.It is essential to remove any oil or grease prior to blast cleaning. The client’s specification or contractors procedures should clarify this, but a typical clause would state, ’before surface preparation commences, any oil/grease shall be removed using a suitable solvent’.Typical requirements

Abrasive used – steel grit or grit and shot mix. Profile requirements – Sa21/2, medium profile or 50-75μm. No more than X hours to elapse before powder application after the conversion coating has been

applied.

SiteWelded joints are blast cleaned using pressure blasting equipment and dry expendable abrasive. Conversion coatings are not used.In a factory, long pipes can be manoeuvred and spun in front of blast nozzles or centrifugal blast units as required. Once the pipes are welded together to form a string in the field, a different situation arises. The heat generated during welding often causes a certain amount of damage to the edge of the factory coating and scorches and disbonds the coating. These damaged areas need to be removed.

Typical requirements Remove all extraneous material and any loose or blistered coating. Degrease the welded area and onto the existing coating each side of the joint, using a suitable

solvent. Abrasive used – dry expendable abrasive. Profile requirements – Sa21/2, medium profile, or 50-75μm Overlap blast pattern onto the existing coating by 30mm – only roughen the coating. Inspect the blast cleaned areas for surface laminations (slivers) – if any exist then remove with a

grinder, check for correct contour and wall thickness, then re-blast area. Check for disbanded coating, if any exists, remove and re-blast.

Note 1 – the phosphoric acid wash and/or chromating is done to passivate the surface, by forming a relatively stable strongly adherent corrosion inhibiting layer and to provide a surface to which coatings will readily adhere.

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Coating application

Factory applicationThe components to be coated are heated before the application of the powder. The method of heating can be either by the use of induction coils or gas flames. Coils are usual for pipe lengths, whereas flame systems can be used for awkward shapes, i.e. bends and other fittings. Coils may also be used inside fittings.The components are usually heated to a temperature slightly above the maximum application temperature for the powder, to allow for heat loss during transit from the heating area to the powder application area.When the components are within the application temperature range the powder is applied by either flock spray or as is usual, by electrostatic methods.When using electrostatic spray methods, charging of the particles is achieved by corona discharge or ion bombardment (note 1) . This is achieved in the spray gun head, where the discharge electrode is situated. The powder becomes charged (+ve) when it passes through the ionised air surrounding the electrode.The component to be coated is earthed (into the same circuit) and becomes negatively charged, thus attracting the charges particles. Earthing is achieved on full pipe lengths through metal wheels making contact with the pipe ends, which are not coated. During powder application the pipes normally move past the spray guns whilst rotating on the wheels.On impact with the hot surface, the particles melt and start to cure. When sufficient material has been attracted to an area, the coating acts as insulation and the charges particles are more strongly attracted to other areas.

Complex shapes, i.e. fittings or bends, may be coated in fluidised beds. This is a system whereby low-pressure air is passed upwards through vats of powder. As the air is passed upwards through the powder particles, it allows the particles to move about, giving the properties of a fluid and so allowing total immersion of a component. When fluidised beds are operating, the surface of the agitated powder has a rippling effect, giving the appearance of a liquid.To allow for handling and inspection, pipes that have just been coated are often quenched with water. If carried out to soon, water quenching can stop the cure reaction; therefore careful control should be exercised.Typical DFT requirement; 350-650μm for pipes. Fluidised bed applications on fittings can produce thicknesses up to 1500μm.

Site applicationField application of powder onto welded pipe butts is usually done as the third stage of a continual operation, carried out from one vehicle: (1) blast clean, (2) heat, (3) apply powder.A flat back trailer or similar carries a compressor, which provides air for grit blasting and powder application, a generator for providing power, an induction heater, a powder application control unit, a small blast pot and the consumables needed.In the first part of the operation the grit blasting operative prepares the butt as previously described, he then moves to the next butt, whilst the heating coil moves onto the butt just prepared.

HeatingThe induction coil (note 2) is clipped into position and the generator supplies an 110V alternating current. The induction coil itself does not touch the pipe and only gets warm from the radiated heat from the pipe.The coil sets up a field that causes the metal particles to excite, the resulting in friction causes the metal to heat up. Heating time can vary from 1 – 8 minutes, with an average time of 4 –5 minutes, depending upon starting temperatures, induction heat procedures, wall thickness and pipe diameters.When the specified temperature is reached, (checked with touch pyrometer or temperature indicating crayons (note 3)) the heating is stopped, the coil disconnected and moved to the next butt. The specified temperature would normally be slightly higher than the maximum powder application temperature.Note 1 – by increasing or decreasing the voltage, the thickness of the coating can be controlled. A typical voltage for a system of this type is 65kV. When running in well controlled conditions these systems are quoted as being 95% efficient. A typical output rate would be 6-12kg of powder per hour.Note 2 – the coils can be built to cater for different butt joint widths.Note 3 – If temperature-indicating crayons are used, then the affected area should be wire brushed prior to powder application.

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It is usual and necessary to state a temperature over which the pipe must not be heated, e.g. 300˚C. over the stated temperature the steel may lose certain mechanical properties and blueing of the steel is likely, a cut-out is likely to be requested if it occurs.

Powder applicationPowder application commences using a spraying technique when the metal temperature drops down to the specified powder application temperature range, e.g. 218˚ - 246˚C. The specification may state the regions where the temperature has to be checked.The equipment used for coating, which is usually semi-automatic, normally has two coating heads, which rotate around the welds at a uniform rate, constantly spraying the epoxy powder. When the powder comes into contact with the hot metal surface it melts to form a liquid film that solidifies and cures within approximately three minutes.To reduce the differential curing of the epoxy resin, the required coating thickness is applied in as few passes as practicable, e.g. six. However the use of only two or three passes can be detrimental to film formation and adhesion characteristics.The fluidised bed, which contains the powder, should be frequently checked by the contractor to ensure there is enough powder to complete the application process.Typical DFT requirement, minimum 400μm.

Powder storage

Epoxy powder is usually supplied in polyethylene lined cardboard boxes and should be kept dry at all times. It should not be stored in direct sunlight or be left overnight in the application container. Otherwise the curing of the coating may be affected. Batches should be used in strict rotation and faulty batches should be placed in quarantine, until the written authority to use or destroy is gained.

Safety requirements

Any sources of ignition should be kept away from the area where epoxy powders are being used. When the powder is in the air it becomes highly flammable. Masks and goggles should also be worn.

Testing

Factory/laboratory testsTests on the powder

a. Infrared scan – gives a fingerprint of the powder for comparison purposes.b. Gel time.c. Particle size analysis – optimum size depends on method of powder application. Test sieves are

used complying with BS410.d. Density.e. Moisture content – less than 0.5% by weight.f. Thermal analysis – DSC is used.g. Stability – age for 120 days at 25 ± 1˚C in a sealed container, no significant change in properties

should occur.

Tests on the detached filma. Micro-sectioning – for homogeneity.b. Tensile strength – for maximum strength and strength at break.c. Elongation.d. Dielectric strength – quoted in kV/mm.e. Water permeability.f. Water absorption – after three months immersion at 20˚C.

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Tests on the attached cured coatinga. Cissing and pinholing.b. Blistering and appearance test.c. Sagging test.d. Thermal analysis – DSC is usede. Flexibility test.f. Impact resistance test.g. Adhesion test.h. Hardness test.

Environmental tests on the attached cured coatinga. Cathodic disbondment test.b. Strain / polarization cracking test.c. Water immersion test.d. Hydrostatic pressure expansion test (rare).e. Thermal stability test.f. Natural weathering test.g. Humidity resistance test.h. Slat spray test.i. Artificial weathering test.

Site testinga. Gel time test (rare on site).b. Dry film thickness.c. Holiday detection.d. Adhesion test.e. Cure test – DSC (sample taken and despatched to laboratory).

RepairsMinor damaged areas; pinholes and areas found with low DFT are marked for repair by using an indelible material, by drawing a circle around the unacceptable area. In factories, repairs are not normally permitted within200mm of the end of pipes, because heating in the field prior to joint coating would destroy the repaired areas. Repair materials used are usually two pack solvent free compounds (epoxy or urethane) and should be mixed and applied according to the manufacturers instructions. It is a rare occurrence for a pipe, fitting or a welded joint to be fully stripped of an FBE coating in order to have the powder re-applied.

A typical repair procedure on a small unacceptable area would be:1. Abrade the affected area using coarse grit emery, e.g. 100 grit2. Remove dust with a clean lint free cloth.3. Repair using specified 2-pack material – using spatula or blade.4. Check thickness if required and holiday detect when the coating is hard dry.

Specifications applicable to field application will usually allow small field repairs to be carried out using materials that harden quickly, e.g. blister pack urethanes or fast cure epoxies, supplied in two tubes.A typical repair procedure on a large unacceptable area using more conventional 2-pack products would be.

1. Blast clean – to original specified requirements.2. Remove dust.3. Repair using specified material – spray, brush and/or trowel.4. Check thickness and holiday detect when the coating is hard dry.

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3 POLYOLEFINS & OTHER PLASTIC COATING.

The term plastic, when used with reference to a material is a loose term but generally means a synthetic polymeric material that is usually pliable. Can be formed into a usable shape by moulding, extruding, heating or by using a similar process.

The term plastic can also include materials, which may also be referred to as resins.There are many types of plastic and many types of coating systems employed, which use plastics. This unit deals with the following broad categories of plastic coatings:

1. Extruded plastic coatings – mainly polyolefins (polyethylene and polypropylene).2. Spray applied plastics.3. Heat shrinkable plastics.

Plastic coatings are commonly used on pipelines nowadays and can be applied in both the factory and on site. The thickness of plastic coatings vary widely, but are typically between 1mm – 6mm.

Materials

Plastic TypesThere are a large number of plastics that may be used as anti-corrosion coatings. Some plastic materials are listed below, but not all of them are currently used to coat pipe or fittings used on pipelines.

1. Polyolefins (alkenes) – low density polyethylene (LDPE – 0.916 – 0.934 g/cm3), medium density polyethylene (MDPE – 0.935 – 0.940 g/cm3), high density polyethylene (HDPE - >0.941 g/cm3) and polypropylene (PP). PP coatings are more rigid and harder than PE coatings. There are two main groupings for polyolefins (1) aliphatic and (2) aromatic, within each group there are many types of material other than PE and PP.LDPE is widely used, although HDPE and PP may be chosen because they can withstand higher service temperatures.Carbon black is usually added to the polyolefin to protect against UV.

2. Polyvinyl chloride (PVC).3. Thermoplastic polyester.4. Polyamide (nylon).5. Ethylene vinyl alcohol copolymer (EVA).6. Fluoroplastics.

The physical form of the raw materials will usually be in pellet, granular or powder form, depending on the specific requirements for application (Note 1 )

Adhesives

There are three main groupings of adhesive used:1. Mastics.2. Copolymers – various types, but usually based on the polyolefin type in the top coat; in the form

of powder for spraying and pellets for extrusion.3. Copolymers of the grafted (interactive) type, in the form of powder for spraying and pellets for

extrusion.

Fusion bonded epoxyFBE may be used with 3-layer coating systems involving polyolefins. There are various types of FBE with different windows of reactivity and different application temperatures. (Note 2)

The FBE is applied to the steel substrate in all cases where FBE is used with a polyolefin coating system. The FBE layer is usually thinner than FBE coatings used as stand alone systems.

Note 1 – For composition of heat shrinkable plastic materials see page - 15Note 2 – Some coating systems use 2-pack liquid epoxy rather than FBE powder.

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Coating systems

There are various coating systems used that involve plastic materials, the main systems involve polyolefins and are listed below:

Factory1. Fused single layer PE2. 2-layer PE with soft adhesive (usually termed a mastic adhesive).3. 2-layer PE with hard adhesive.4. 3-layer PE with hard adhesive of either the normal copolymer type or the newer grafted

copolymer type. FBE is applied as the first layer.5. 3-layer PP with hard adhesive of either the normal copolymer type or the newer grafted

copolymer type. FBE is applied as the first layer. (Note 1)

Site1. Heat shrinkable plastics.2. Flame spray applied PP.3. 3-layer PP with hard adhesive of the grafted type followed by the application of a co-extruded

sheet of PP. Epoxy is applied as the first layer.4. Injection moulded PP.

Advantages and limitations

Advantages1. Polyethylene is non-oxidising.2. Resistant to penetration.3. Good elongation properties.4. Good ageing properties.5. Extremely impermeable.6. High electrical resistance.7. Excellent resistance to micro-organisms.8. Damage to coating is limited during handling and pipeline operations.9. Not susceptible to damage during soil stressing.10. Multi-layer coatings give excellent service performance results.11. Multi-layer coatings reduce the cost of cathodic protection.

Limitations1. Polyproylene needs additives to retard oxidation.2. Cost of heating for application (as with FBE).3. Multi-layer processes are complicated and require careful control.

Surface preparationFactoryThe surface preparation requirement on the steel will obviously be governed by the type of initial coating. Dry abrasive blast cleaning to Sa21/2 is the most likely, amplitude requirements vary but the range specified would normally fall within 40μm to 100μm.SiteAs for factory application for most systems, except an expendable abrasive is likely to be used. However some specifications may allow heat shrinkable plastics to be applied onto surfaces prepared to St3 in certain circumstances.It is important to be aware that surface preparation procedures may not be as straight forward as for other coatings. Limitations on methods used to roughen the existing coating and additional surface preparation requirements will exist especially for multi-layer coatings.Note 1 – 3-layer coating systems combine the excellent chemical resistance properties of epoxy with the excellent mechanical

properties of the polyolefins.

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Coating application

Factory applicationPolyolefins are applied in factories using either side extrusion, (winding) or annular extrusion (sleeving)(note 1) methods. Side extrusion is used on large diameter pipes and annular is used on pipes of diameters up to ~ 500mm.In both cases the raw material (in powder, granular or pellet form) is melted using temperatures, which will vary, depending on the specific type of material used, the screw type in the extruder and the extrusion rate (200 - 220ºC is typical). The powder form is only melted when it hits the pipe (like FBE).The granular or pellet form of the material are initially fed into a hopper and past the heating units and as it melts it is fed towards the nozzle(s) on the extruder by a rotating screw (or screws).Pressure is usually applied to the coating shortly after it has been applied in order to improve adhesion and force out any entrapped air. With side extrusion a non-sticking pressure roller may be used, whereas with annular extrusion a vacuum system plus a roller system may be employed.There are a large number of coating systems involving plastics and also many variations in the materials and application methods used within some of these systems. Typical options are shown below for a 3-layer coating procedure, this should demonstrate some of the basic principles that will also apply to other systems.

3-layer PE or PP1. Blast clean – remove dust.2. Inspect.3. Phosphoric acid treatment and/or chromate wash (not always applied).4. Heat pipe using either induction coil or gas fired oven to specified temperature. The temperature

range used depends on the type of epoxy used, but is likely to fall within the 160º to 250ºC.5. Apply epoxy by using a method recommended for the material – electrostatic spray, twin feed hot

airless spray or conventional airless spray (depending also on the form of material). Thickness requirements vary, but usually come within 50-100μm.

6. Apply adhesive (tie-coat) by either extrusion or by powder spray (extrusion usually gives superior properties). 300 - 400μm is a typical thickness requirement.

7. Apply PE or PP by extrusion. The thickness requirement is determined by the pipe diameter and service conditions.

8. Cool pipe by water spray (after sufficient time has elapsed for polymerisation and cross-linking of the epoxy first coat).

9. Inspect.

Site application

3-Layer PPThe welded joints connecting pipes coated with a 3-layer PP system can be coated using a similar system to that adopted in the factory. This system will require a procedure similar to the following:

1. Cut back existing PP, using bevelling machine, to reveal existing FBE (25mm or as otherwise specified).

2. Mask off existing FBE and blast clean joint area to specified standard, e.g. Sa21/2 at 50-100μm. Remove masking and abrade existing FBE using emery cloth.

3. Heat joint area using an induction coil to the temperature specified, e.g. 240-250˚C.4. Apply FBE powder when the joint is at the specified application temperature and introduce PP

adhesive (copolymer) powder during the final passes to produce what is essentially a 2-layered sintered FBE/PP coating, which will cross-link at the interface. The PP adhesive must be applied within the gel time of the FBE. Typical thickness requirements; 300μm for the FBE and 200μm for the PP adhesive (tolerances will apply).

Note 1 – Annular extrusion may also be referred to as ‘cross-head die extrusion’ or ‘ring extrusion’. ‘Side extrusion’ uses ‘slot dies’ and may also be referred to as ’lateral extrusion’.

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5. Apply preheated co-extruded PP sheet, which is normally the same thickness as the existing coating, around the joint and apply a hinged clamp in position around the coating during the cool down period. The sheet should butt up to the existing PP – overlap onto the existing PP is not desirable. Remove the clamp when temperature has dropped below 120˚C or as otherwise specified.

6. After cleaning away any adhesive material, weld the circumferential seams of the PP sheet using a special welding extruder gun, which may be attached to a machine that travels circumferentially around the joint. The plastic welding filler material should be the same material brand as the PP sheet.

7. Finally, the longitudinal seam is welded with an extruder gun using a manual technique.

A modification to the above procedure that may be encountered is to apply the PP layer by injection moulding in lieu of using a wrap around PP sheet.

Heat shrinkable plastics

Heat shrinkable plastic materials may be supplied in many pre-expanded forms, some of which will fit tees, flanges and similar components. The common types encountered on pipelines for use on welded joints are supplied either as short continuous sleeves, slightly larger than the pipe diameter, or in bandage type form to wrap around the joint and overlap onto itself. Heat shrinkable tapes also exist.Heat shrinkable products have an adhesive layer composed of either, a pressure sensitive mastic or a thermoplastic hot melt type adhesive. (note 1)

Materials are available in standard and heavy-duty forms and are therefore available in different thicknesses.The plastic material is a radiation cross-linked polyolefin, which is elastic in nature. Once it has shrunk onto the area to be coated by the application of heat, it will not return to an expanded state on the re-application of heat.

Primers are not recommended for mastic systems, but at the other end of the scale, these coatings may be used as part of a 3-layer system, where the first layer is usually a 2-pack epoxy. The heat shrinkable material is applied over the epoxy when it is still tacky.When the heat shrinkable material is in position, heat is applied, usually by using a long yellow flame from a propane torch, working from the centre of the wrapping outwards. Induction heating may also be used in some circumstances.Note; Manufacturers of these products issue very detailed step by step instructions on how they should be applied. These instructions should always be followed unless the specification, procedures or instructions issued state otherwise.

Testing

Tests on polyolefinsa. Density.b. Melt index.c. Elongation at break.d. Maximum moisture content.e. Softening point.f. Impact resistance.g. Indentation resistance.h. Electrical insulation resistance.i. Resistance to UV energy.j. Thermal stability.k. Cathodic disbondment.

Note 1 – hot melt type adhesives have a slightly higher lap shear strength than mastic type adhesives and would be preferable for certain applications such as thrust boring.

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l. Flexibility.m. Peel strength.n. Thickness.o. Holiday detection.p. Visual inspection – blisters, general contours.q. Weld integrity – coupons cut from seam welds on site-applied systems involving wrap around PP

sheets.

RepairsThe repair materials and procedures used would have to be approved prior to use as applicable to any other coating system. Most standards and draft standards, which apply to polyolefin coatings, do not identify specific materials or detailed procedures to use. They do however state the obvious, that is to say that any repair material and procedure used shall be compatible with the existing coating and satisfy service conditions.Repairs in the factory or on site can be affected using copolymer PE or PP, which after surface preparation, is melted into the problem area, using a special extruder gun or by using a melt stick. Heat shrinkable plastics in patch or bandage form may also be used – especially on site.When repairs to plastic coatings are necessary on site and on the lower integrity plastic systems, cold applied laminated tapes may be permitted.Elastomeric pipeline coatings are very flexible and have good insulation properties over a range of temperatures and can be applied in substantial build thicknesses. They elongate under stress and return to their original relaxed condition without any adverse results.

4 ELASTOMERIC COATINGS

Elastomer typesEPDMEPDM (ethylene propylene diene monomer) is an elastomer that is not widely used nowadays due to required additions of carbon black (pigment). The addition of carbon black improves the materials abrasion and impact resistance properties, although too much adversely affects CP current, which is conducted away from the coated structure.EPDM is essentially a mixture of ethylene and propylene. When polymerised, ethylene C2H4 (E) gives E-E-E-E in varying numbers of ethylene molecules, hence the different grades, e.g. LDPE, MDPE etc. Propylene C3H6 (P) when polymerised gives P-P-P-P. A mixture of ethylene and propylene produces a material that is rubber-like in appearance and properties, very unlike the original materials.

Polychloroprene (Neoprene) – DupontManufactured by the chlorination of isoprene, the material looks like rubber. It is supplied in pellet form compounded with fillers for reinforcing, e.g. silica and carbon black, to improve impact and abrasion resistance. Neoprene has the property of being fire retardant, because of the chlorine content (Cl2).Conductivity problems do not occur (compare EDPM) and the material has excellent abrasion resistance.

Bituseal – ShellBituseal is a polymer bitumen and a trade name of a Shell product. This material is thermoplastic and has excellent low temperature flexibility.The softening point is much lower than conventional bitumen (85˚C compared to 120˚ - 130˚C for conventional materials), therefore as the limitations for usage are at the upper end of the temperature scale, it is not recommended for use above 85˚C, but has the excellent properties for use on land at temperatures of less than -20˚C.Conventional asphalt and bitumen are brittle at ambient temperatures but Bituseal can be cold bent at temperatures in the range of -20˚C.

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Elastomeric polyurethaneThe reaction between a polyol and an isocyanate produces polyurethane. Different reactions and formulations give materials with different properties. These vary from elastic to rigid solids. All polyurethane’s are thermoset materials and do not soften with the application of heat.Syntactic polyurethane’s are of a similar structure to cake, with a tiny closed cell structure and are formed in-situ. The closed cell structure significantly improves the normally poor insulation properties.Glass micro-spheres are sometimes used as fillers to improve abrasion resistance with this material.


1. Excellent insulation properties.2. Thick coatings can be applied in a single layer.3. Flexible, e.g. materials can be used on pipes to be laid by reel barge.4. Excellent abrasion resistance.5. Good impact resistance.6. Good heat stability.7. EPDM has relatively high operating temperatures, e.g. 125˚C.

Disadvantages1. Cross-linking polyurethane’s use toxic isocyanates.2. Polychloroprenes require vulcanising (heat treatment).3. Some Elastomeric coating systems are not feasible for site application.4. EPDM needs carbon black as a constituent (adverse affect for CP).5. EPDM is difficult to stick to anything, especially itself.

Surface preparation

FactoryDry abrasive blast cleaning to Sa21/2 is the most likely. Amplitude requirements vary, but the range specified would normally fall within40-100μm.

SiteRarely applicable. Synactic polyurethane’s may be cast on site, but over a primed area.

ApplicationApplication methods vary from extruded spiral layering over anti-corrosive (FBE) layer, to inter-layering with closed cell p.v.c foam for extra insulation.In most cases a primer or a bonding agent (adhesive) would be used prior to application to the Elastomeric system.

EPDM and NeopreneThese materials are applied at up to 180˚C and extruded over the primed surface in a continuous sheath.Neoprene is sometimes extruded in a thin strip and spiral wound onto the pipe. The whole pipe is then wrapped with fibreglass or nylon tape and placed in an autoclave for approximately two hours at 140˚C for vulcanisation. After vulcanising the support tape is removed, leaving an indented replica pattern. The ends are trimmed back and any required tests are done at this stage.

Elastomeric polyurethane’sTwo-part polyurethane’s can be applied by casting or by controlled rotational drip and pour (sometimes referred to as controlled rotational casting).Casting on pipe lengths is done by placing the pipe central in a female mould, tilting to an angle of about 30-45˚ and filling the cavity through a filling point at the bottom and of the mould. A vent at the top of the tilted pipe allows air to escape before the excess product. De-moulding time is approximately twenty minutes.

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Controlled rotational casting is done by ejecting a stream of the mixed components onto a rotating pipe; this is done from a position in line with dead centre of the pipe bore and the 12 o’clock position. The rotation and feed speed are adjusted so that no overlap or voids occur, leaving a slightly corrugated surface. The material quickly achieves a degree of cure, which allows another layer to be applied, following behind at approximately 1 metre away.

BitusealBituseal is applied hot at approximately 190˚C by extrusion, usually over an anti-corrosive primer. Brittle bitumen and coal tar enamels need temperatures in excess of 200˚C, but have correspondingly higher softening points of 120-130˚C.Unlike the conventional bitumen enamels, the Elastomeric Bituseal does not have an inner layer of reinforcement. Atypical thickness range is 4-6mm with usually an impregnated outer wrap for abrasion resistance.

Testing

ThicknessMagnetic or electromagnetic induction

CureBituseal/EPDM – hardness (shore, barcol, needle penetration).Neoprene – hardness (shore), cure (rheometer).

AdhesionPeel adhesion (on pipe ends).

DisbondmentUltrasonic methods.Tapping (sounding).

PinholesHigh voltage holiday detection.

5 MULTI-COMPONENT LIQUIDS – MCL’s

Multi-component liquid (MCL) is not a standard terminology, but it may be used to describe any coating products that are supplied in two packs or more.MCL’s used are usually solvent free, two-pack materials using an epoxy or urethane base. Depending on the particular product, MCL’s may be spray applied, brush/trowel applied or applied with a palette knife or similar to repair areas.A MCL may be used to coat pipe lengths, but are more likely used to coat fittings, welded joint areas and to repair defects in certain coating materials.

Constituents

EpoxiesBase resin in one container with amine or amide reagents supplied separately, either in tubes or cans.

UrethanesUrethane or urethane and pitch, supplied in drums or cans with modified isocyanate or di-isocyanate curing agent in another can or drum. Sometimes provided in blister packs for small repair jobs.

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Advantages and limitationsAdvantagesEpoxies

1. Supplied in various pack sizes to avoid waste.2. User friendly.3. No solvent – DFT same as WFT; no significant compatibility problems.4. Very good film properties.5. Fast drying rates (typically 7 days to full cure).6. No toxic hazards.

Urethanes1. Supplied in various pack sizes to avoid waste.2. No solvent – DFT same as WFT; no significant compatibility problems.3. Excellent film properties – especially abrasion resistance.4. Fast drying rates (typically 7 days to full cure).

DisadvantagesEpoxies

1. Short pot life.2. Very poor adhesion to plastics.

Urethanes1. Short pot life.2. Very poor adhesion to plastics.3. Toxic components.4. Some types are very moisture sensitive.

Surface preparation

FactoryOnly fittings such as bends and tees are likely to be prepared and coated with MCL’s in a factory environment.Surface preparation is normally carried out by dry abrasive blast cleaning.

Typical requirements (blast cleaning) Abrasive used – steel grit or grit and shot mix. Profile requirements – Sa21/2, medium profile or 50-75μm. (note 1)

Inspect blasted areas for surface laminations (slivers); if any exist then remove with a grinder, check for correct contour and wall thickness, then re-blast the area.

SiteWelded joints are blast cleaned using pressure blasting equipment and dry expendable abrasive.Typical requirements (welded joints)

Remove any solar protective coating and all extraneous material from the existing coating (150mm is typical requirement).

Degrease only if necessary. If existing pipe coating is thick, e.g. if coated with an enamel, chamfer coating by 50 or 100mm

as specified, using a blowtorch and scraper. Blast clean using dry expendable abrasive. Profile requirements; Sa21/2, medium profile or 50-

75μm. Inspect blasted areas for surface laminations (slivers); if any exist then remove with a grinder,

check for correct contour and wall thickness, then re-blast the area. Check for disbonded coating, if any exists then remove and re-blast the area.Note 1- Amplitude requirements may be up to 100μm for some urethanes.

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Coating application.

FactoryUrethane MCL’s are sometimes used for coating pipeline fittings and special fabrications, for subsequent delivery to site. Because urethanes (two-pack) are isocyanate cured, application by spray can only be carried out under closely controlled conditions.When using moisture sensitive material, the maximum RH% requirement during application may be as low as 70%. The minimum air/steel temperature requirement during application may be 10˚C in some instances. It is therefore a common requirement that heaters and dehumidifiers have to be used.Multi-component spray grade urethanes are usually applied using a twin component hot airless system. These use twin airless pumps, skid mounted and specially set to dispense pre-set amounts of base and activator. Coils around the container heat the components, usually and the pre-set flow rate measures out the correct ratio of base and activator into a mixing chamber. The mixing chamber is usually tube shaped and contains a series of baffles, through which the two components pass, so accomplishing the mixing. There is also a solvent feed line entering the chamber.Because the chemical reaction rate increases as the temperature rises, the pot life is considerably shortened, in some cases to a few minutes. Spray lines are usually kept to a limited length. Tip blockages or hold ups of any kind are critical, because the material may gel in the lines and gun resulting in loss of equipment – usually costing over £1000. If there is any such occurrence, the pump lines are immediately closed, the solvent line opened and the system flushed out. On resumption of work, the solvent has to be completely flushed out with produce before coating recommences, otherwise pinholing and blistering may occur.Typical thickness requirements for urethane MCL coatings – 1mm or 1.5mm minimum, for epoxy MCL coatings 500μm minimum.

SiteMCL’s are likely to be brush and/or trowel applied on site. The material will be supplied in cans in any situation other than for minor damage and pinhole repair where epoxy or urethane are likely to be supplied in tubes or blister packs respectively. Because of the short pot life consideration and the requirement that both components be thoroughly mixed in the correct ratio, mechanical mixing is desirable, when components are supplied in cans. For urethanes, ambient conditions may be more stringent than for epoxies.Application should be in accordance with the manufacturers instructions and for urethane, will usually require application in two layers, the second layer being applied at right angles to the first after a specified time lapse.

SafetyWhen using MCL’s, especially urethanes, it is advisable to wear protective clothing with a positive air supply face mask (isocyanates).If welding of coated components is required, a suitable uncoated margin should be left, e.g. 150mm. Heat should not be used to remove urethanes because various cyanide gases will be released. Removal of faulty coatings should be by prolonged blasting only.

Testing

Factory/laboratory testsTests on the unmixed components

a. Total non-volatile content.b. Viscosity.c. Specific gravity.d. Mixing ratio.e. Pot life.f. Flash point.g. Stability.

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Tests on the detached filma. Micro-sectioning – for homogeneity.b. Tensile strength – for maximum strength and strength at break.c. Elongation.d. Dielectric strength – quoted in kV/mm.e. Water permeability.f. Water absorption – after three months immersion at 20˚C.

Tests on the attached cured coating.a. Cissing and pinholing.b. Blistering and appearance test.c. Sagging test.d. Flexibility test.e. Impact resistance test.f. Adhesion test.g. Hardness and cure test.

Environmental tests on the attached cured coatinga. Cathodic disbondment test.b. Strain/polarization cracking test.c. Water immersion test.d. Hydrostatic pressure expansion test.e. Thermal stability test.f. Natural weathering test.g. Humidity resistance test.h. Salt spray test.i. Artificial weathering test.

Site testinga. Dry film thickness.b. Holiday detection.c. Adhesion test.d. Hardness cure test.

RepairsRepairs to MCL coatings are usually made using the same material as the original coating or, especially on site, by using a fast drying product with the same base material and from the same manufacturer.A typical repair procedure on a small unacceptable area would be:

1. Abrade the affected area using coarse grade emery cloth, e.g. 100 grit.2. Remove dust with a clean lint free cloth.3. Repair using specified 2-pack material – using spatula or blade.4. Check thickness if required and holiday test when coating is hard.

Specifications applicable to field application will usually allow small field repairs to be carried out using materials that harden quickly, e.g. blister pack urethanes or fast cure epoxies supplied in two tubes.A typical repair procedure on a large unacceptable area using more conventional 2-pack products would be:

1. Blast clean – to original specified requirements.2. Remove dust3. Repair using specified material – brush and/or trowel.4. Check thickness and holiday test when coating is hard dry.

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6 WRAPPING TAPES

Several types of wrapping tapes are used in the pipeline industry; the main categories are as follows:1. Hot applied tapes2. Cold applied laminate tapes.3. Grease based tapes.4. Self-adhesive overwrap tapes.5. Heat shrinkable tapes.

Whenever tapes are used on risers and similar, care should be taken to ensure spiralling and terminations create a watershed, otherwise disbonding may occur.

When spiralling a tape around a pipe the following should be observed.a. Correct tensioning of the tape.b. Correct overlap distance onto itself – typically 55% of tape width (referred to as double wrap) or

25mm for thicker tapes.c. Correct overlap distance onto existing coatings – 75mm minimum is typical.d. The tape should face downwards at the start and finish.

Specifications do not normally specify DFT requirements when tapes are used because of the tape and overlapping requirement will be known.

6-1 Hot applied tapesHot applied tapes are not often used nowadays. Their main application is for welded joints when the existing pipe coating is an enamel, i.e. coal tar or bitumen. They are used in conjunction with a primer.

ConstituentsA synthetic fibre bandage, e.g. woven nylon, coated with plasticised coal tar or bitumen. The coal tar or bitumen is sometimes applied to one side of the bandage only. In this instance the coated side is placed against the pipe.


1. High resistance to mechanical damage.2. Available in several widths.

Limitations1. Needs a blowtorch or similar for application.2. Toxic fumes.3. Unpleasant working environment.4. Limited use due to compatibility problems with existing coatings (used with enamels only).5. Application requires a minimum of two operators.6. Susceptible to soil stressing.

Surface preparation.FactoryNot normally applied in factories.

SiteWelded joints are blasted using pressure blasting equipment and dry expendable abrasive.Typical requirements (welded joints):

Remove solar protective coating and all extraneous material from the existing coating (150mm is a typical requirement).

Degrease only if necessary.

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Chamfer coating by 50mm or 100mm as specified, using a blowtorch and scraper. Blast clean using dry expendable abrasive – profile requirements – Sa21/2, medium profile or 50-

75μm. Inspect blasted areas for surface laminations (slivers), if any exist then remove with a grinder,

check for correct contour and wall thickness, then re-blast the area. Check for disbonded coating, if any exists then remove and re-blast the area.

Coating application. (Site)Hot applied tape based on coal tar should only be used when existing pipes are coated with coal tar enamel. Hot applied tape based on bitumen (asphalt) should only be used when existing pipes are coated with bitumen (asphalt) enamel.Although mainly used for the wrapping of welded butt joints, hot applied tape may be used for wrapping complete pipe lengths.Appropriate primers are considered essential and are usually applied to an area that is slightly larger than the area to be wrapped. When the primer is dry, Operator 1 applies the correct tension and positions the tape to give a spiral wrap with a neat consistent overlap of usually 55% (this ensures double tape thickness over the wrapped area). Operator 2 applies the blowtorch to the contact areas of the tape and any existing enamel, melting both materials and allowing them to fuse together to form one homogenous layer.Problems arise with over and under heating. Overheating results in combustion and/or coking, under-heating results in lack of fusion, kinks and voids.Areas that may consistently give cause for extra vigilance are 12 o’clock and 6 o’clock, especially on larger pipes, where a handover to a second crew may be required.

Safety requirementsGenerally as required for site application of enamels.


1. Viscosity measurement using a flow cup at a specified temperature.2. Visual check for coverage.3. Measure DFT of primer if requested.

Tests on the final wrapping1. Tapping to check for laminations.2. Holiday detection.3. Bond strength test.4. Visual check for uniformity of coating contour and ensure no coking exists.

RepairsRepairs to hot applied tape wrappings can be carried out by various methods depending on the nature and size of the coating fault. Pinholes are sometimes repaired using a hot knife, whereas extensive damage would normally require full circumferential removal of the wrapping over the affected area. The bare area may then be repaired with either hot applied tape, heat shrinkable material, cold applied laminate tape or a grease-based tape over wrapped with a self-adhesive overwrap tape as specified. Multi-component liquids could also be used. The method employed should be governed by specification. Patch type repairs with tapes are not advisable; if tapes are specified then full circumferential wraps will be required.

6-2 Cold applied laminate tapes

Cold applied laminate tapes (CALT) are commonly used to wrap welded joints, primarily because they are easy and relatively clean to use. They may also be used to wrap fittings, full pipe lengths and may be used for full circumferential repairs. Patch repairing with these tapes should be avoided.

Constituents

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Cold applied laminate tapes are made up from a polyethylene (PE) or polyvinyl chloride (PVC) carrier tape, with a coating of self adhesive, anti-corrosive bituminous compound or self-adhesive synthetic rubber compound.Over width silicone coated or wax coated interleaving paper exists in each tape roll to make it easier to unroll the tape during application and it reduces the amount of dirt contaminating the edges of the rolls.


Advantages1. Available in many widths2. No extensive training required for application.3. Very few compatibility problems and will adhere to virtually any coating.4. Can be applied manually or by a special application machine.

Limitations1. More difficult to apply at lower temperatures (needs heating).2. User-unfriendly at high temperatures (mastic viscosity).3. Can be over tensioned.4. Susceptible to wrinkling during soil stressing – poor lap shear strength.5. Does not adhere well to sharp contours, e.g. edges of welds.

Surface preparationFactoryNot commonly applied in factories – if done, blast cleaning or chemical cleaning may be encountered.

SiteWelded joints are blast cleaned using pressure blasting equipment and dry expendable abrasive.

Typical requirements (welded joints): Remove solar protective coating and all extraneous material from the existing coating (150mm is

a typical requirement). Degrease only if necessary. Chamfer coating by 50mm or 100mm as specified, using a blowtorch and scraper. Blast clean using dry expendable abrasive – profile requirements – Sa21/2, medium profile or 50-

75μm. Inspect blasted areas for surface laminations (slivers), if any exist then remove with a grinder,

check for correct contour and wall thickness, then re-blast the area. Check for disbonded coating, if any exists then remove and re-blast the area.

Substrates other than steel are usually wire brushed or abraded to give a key and then appropriate primers applied as per specification or manufacturers instructions.

ApplicationFactoryWhen CALT is applied at a factory as the primary corrosion protection system, machine application with a static roller rig is likely to be the method used. The pipe lengths are rotated and geared to the rig which carry’s the spool of tape, correctly tensioned to wrap neatly and evenly along the pipe.A primer as specified by the tape manufacturer would be used before tape application. The primer usually has to be in a dry state before the tape can be applied.

SiteAlthough line travel machines do exist for CALT, application is more likely to be manual. A primer as specified by the tape manufacturer would be used before tape application. The primer usually has to be in a dry state before the tape can be applied.

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The tape is applied in a spiral fashion, usually with a 55% overlap, maintaining a uniform tension. Under tension can result in unsightly creases and wrinkles, which if left will lead to early failure (or their existence will increase the CP current used).Over tension shows up as a discolouration of the (normally black) tape. The tape stretches and narrows and shows up light blue/grey in the area of stress.

Safety requirementsThere are no significant hazards associated with CALT.


1. Viscosity measurement using a flow cup at a specified temperature.2. Film thickness measurement.

Tests on final wrapping1. Holiday detection.2. Bond strength/adhesion test.3. Visual check for uniformity of coating contour.

RepairsRepairs to CALT wrappings, e.g. after adhesion tests, can be carried out by overwrapping with CALT. Patch type repairs are not advisable, full circumferential wraps are normally specified.

6-3 Grease based tapes

ConstituentsGrease based tapes usually consist of a bandage of woven or non-woven synthetic material or glass-fibre. This carrier is impregnated with petroleum grease – refined petroleum condensates, to which are added moisture displacing agents and sometimes inhibitors.


1. Compatible with all pipeline coatings.2. Easily mouldable for awkward shapes.3. Very low standard of surface preparation requirements.4. Very simple to apply.

Limitations1. Can be very messy to use.2. Does not give a coating of high quality.3. Usually requires overwrapping, especially on buried pipelines.

Surface preparationFactoryNot normally applicable.

SiteBlast cleaning would not normally be carried out, when grease based tapes are used. In most instances, as long as loose and flaky material is removed that will suffice. Wire brushing to St2 or St3 is commonly specified. All traces of moisture should be removed.

ApplicationFactoryNot applicable

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SiteGrease based primers are normally recommended but not always specified.The tape is applied in a spiral fashion usually with a 55% overlap. Grease based tapes can also be applied double or twisted to fill in sharp contours, because of its mouldablity and may sometimes be used in place of more conventional filler materials, i.e. mastics and putties.

Safety requirementThere are no significant hazards associated with grease-based tapes.TestingThere are no testing requirements other than visual examination for contour. Holiday detection and DFT measurements are not practical propositions unless grease based tape is over wrapped. Even if over wrapped these tests are not always carried out, because it will be very likely that any specification deviation will be found. Holiday detection on over wrapped grease based tapes that have been in service is a normal requirement.

RepairsRepairs to grease based tapes are easily applied by using the same product. Patch type repairs are not advisable, full circumferential wraps are normally specified.

6-4 Self-adhesive overwrap tapes

As the title suggests these tapes are usually used to overwrap other coatings such as grease based tapes and cold laminate tapes.

ConstituentsA strong pressure sensitive adhesive is bonded to a tough carrier tape of PE or PVC. This medium is not designed as a corrosion protection system, but to add mechanical strength to other mediums and to stop migration of constituents in grease based tapes and mastics and fillers.


Advantages1. Clean to use.2. Simple to use.3. Available in various widths.4. Excellent adhesion to itself and other smooth surfaces.5. Compatible with al other coatings.

Limitations1. Not a suitable anti-corrosion coating system in it’s own right.2. Wide tapes are physically difficult to apply – correct tensioning is important.3. Not tolerant of uneven surfaces.

Surface preparationBlast cleaning would not normally be specified when grease tapes are used. In most instances, as long as loose and flaky materials are removed that will suffice. Wire brushing to St2 or St3 is commonly specified. All traces of moisture should be removed.

ApplicationFactoryNot normally applicable but could be applied mechanically or manually as over wraps for other mediums.

SitePrimers are sometimes recommended but not always specified.

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The overwrap tape is applied in a spiral fashion usually with a 55% or 25mm overlap. It may be specified that the direction of spiralling must be made in the opposite direction of the spiralling of the existing tape wrapping.

If welded joints or repairs are being made with either grease based tape or cold laminate tape, the overwrap tape must be firstly adhered to the existing coating before over wrapping the joint wrap and beyond onto the existing pipe coating on the other side of the joint. Overlap requirements on either side of the joint wrap is typically a minimum of 50mm, 75mm or 100mm depending on the specification.

Safety requirementsThere are no significant hazards associated with self-adhesive over wrapping tapes.


1. Viscosity measurement using a flow cup at a specified temperature.2. Visual check for coverage – DFT is not normally measured.

Tests on the final wrapping1. Holiday detection.2. Bond strength/adhesion test (in rare circumstances).3. Visual check for uniformity of coating contour.

RepairsRepairs to overwrap tapes are easily applied by using the same product assuming the underlying coating material is not significantly affected. Patch type repairs are not advisable, full circumferential wraps are normally specified.

7 BRUSHING MASTICS

Brushing mastics are high viscosity coatings that may be built up to the required thickness, as specified by the manufacturer, by way of a number of applications (usually two) after primer application. Each layer must have an appropriate thickness as specified by the manufacturer. For most products a total dry film thickness of 500μm will give satisfactory results.The following points should be taken into consideration when using brushing mastics:

a. Not suitable for overlapping onto polyolefin pipe coatings.b. Ideally suitable for components of complex shape.c. Very susceptible to rock/stone damage and will normally require the use of sand or similar

padding around the finished coating if buried.d. Not suitable for overlapping onto certain tapes, although tapes may overlap onto the mastic. See

manufacturers data sheet for compatibility.e. Damage due to scuffing may be easily patch repaired.

ApplicationThe following text shows a typical application procedure:

1. After surface preparation, apply primer by brush, over lapping onto the factory applied coating to attain a dry film thickness of approximately 25μm.

2. As soon as the primer has dried, e.g. after 1 hour at 20˚C, apply one coat of the specified mastic, laid on evenly by brush to give an appropriate dry thickness specified by the manufacturer, over lapping onto the existing factory applied coating by a minimum of 75mm.

3. Allow to dry for at least 4 hours at 20˚C before applying a second coat of the specified mastic, by brush to a minimum dry film thickness specified by the manufacturer.

4. Before the coated components can be handled or buried, a specified time must elapse, which can be anything from 24 hours to 7 days, depending on the product type and ambient conditions.

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8 FILLERS (MASTICS AND PUTTIES)

Fillers are based upon a range of materials, e.g. petroleum grease, bitumen and rubber. They are also available in a number of forms such as tape, extrusion or bulk packaged in containers or sacks.They are normally intended to be used for modifying the contours of valves, flanges and similar components, in such a manner that allows for the components to be wrapped with conventional cold applied tapes or heat shrinkable materials.Primers are normally used. Application of the filler is normally carried out by hand, although trowels and knives may also be used.The following points should be taken into consideration when using fillers:

a. Materials must be carefully chosen having due regard to their suitability for use with any existing coating and the over wrapping tape to be used.

b. Suitability for use on components operating at elevated temperatures or in situations where soil stressing might occur will be related to the base product of the material.

c. Some material will not exhibit particularly good adhesion to the primed surface, therefore reliance will be placed upon the over wrapping to provide an impervious barrier.

d. Material containing bitumen or petroleum grease should also contain biocides to prevent microbial degradation.

9 INTERNAL PIPE COATINGS

Internal pipe coatings may be applied for the following reasons:

a. Prevents corrosion during pipe storage.b. Aids gas flow – reduces friction.c. Reduces vibration caused by turbulence.d. Reduces fatigue stress – which could cause failure.e. Reduces noise pollution.

The coating chosen is normally two-pack polyamide cured epoxy; therefore the inspection approach is similar to that for a painting inspector.Many of the following requirements have been taken from the draft standard identified in (note 1.)

Surface preparationSurface preparation is normally carried out by dry abrasive blast cleaning to Sa21/2, medium grade. Slivers, laps etc. to be removed by grinding. Dust removal to class 0 in accordance with ISO 8502-3.Use high-pressure water to remove contaminants such as salt and dirt. Any organic contaminant such as grease or oil to be removed by using detergent or an approved organic solvent.The remaining salt level and methods for measurement should be agreed between contracting parties.Other standard specifications may specify chemical cleaning (pickling) as the preparation method, especially on small diameter pipes where blasting would be impractical.

Coating applicationTemperature shall be at least 3˚C above the dew point – heat the pipe if necessary. Other ambient requirements would be as specified by the coating manufacturer.Paint will be spray applied.An accelerated curing procedure may be used by heating the pipe up to a maximum of 100˚C.

Note 1 – an example of a standard which deals with internal pipe coatings is – BS ISO/CD 15741 –‘Internal paint coating of pipelines for the conveyance of non-corrosive gas.

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TestingTests on the wet paint

a. Viscosity.b. Density.c. Solid content (by weight).d. Solid content (by volume).e. Drying time (to handle).f. Pot-life.g. Pinholes (porosity) – using glass plates.h. Ash content.i. Fineness of grind.j. Sieve retention.k. Flash point.

Tests on cured paint filma. Buchholz hardness.b. Adhesion test (cross-cut test).c. Salt spray resistance.d. Bend test (conical mandrel).e. Water resistance.f. Methanol/water 1:1 resistance.g. Methanol resistance.h. Gas blistering.i. Hydraulic blistering.j. High temperature resistance.k. Dry film thickness.l. Visual – sagging.

RepairsSignificant defects are repaired using the same procedure as used with the original coating, except that pinholes and small damaged areas may be wire brushed instead of blast cleaned. In both cases lightly abrade onto the existing coating by at least 10mm.Damaged internal coatings are not often repaired when found on site.

10 TESTING OF COATINGS / WRAPPINGS

Overall there are a large number of tests that are carried out on raw coating materials and the resultant coatings. Tests may be carried out for fitness for purpose reasons or for quality control.Coating inspectors especially if working of behalf of a client/ customer, would not normally conduct any test associated with raw materials other than the Gel time test, associated with FBE or possibly viscosity tests for quality control reasons. A test associated with the final coatings is more likely to be performed by a coating inspector, but not if it is a laboratory type test.However a coating inspector requires a certain degree of knowledge about laboratory type tests, because the inspector working on behalf of the client/customer may be required to verify that the test results meet the specification requirements.

10-1 Factory / laboratory based tests

Viscosity (see also PI notes) (note 1)

All liquids in use in the coatings industry would be subject to viscosity tests at some stage of a production and sometimes prior to application.For ambient temperature application primers, either rotational viscometers or flow cup types could be used, e.g. ISO or Ford flow cups.Note 1 - Viscosity is defined as a fluids resistance to flow.

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For hot application enamels (coal tar and bitumen) and hot melt type mastics and adhesives, the Zahn cup or Frikmar cup are most likely.If a cup is being used, the correct selection of flow cup type, hole size and test temperature are important factors.Viscosity test are sometimes carried out on site.

Gel time (FBE) powderThe gel time test is a test that may be conducted on epoxy powders prior to application to ensure that the powder is in a suitable condition to be used. In order to achieve the correct degree of cure from the final coating, i.e. in order to obtain the expected properties from the coating.The gel time will be affected by the age of the powder, i.e. there will be limited shelf life. During transport and storage, the raw material will be subjected to different temperatures and compaction forces. This allows sintering and a small degree of molecular freedom, resulting in chemical action (cross-linking). This means that when the powder is applied, the cure on the substrate will not allow full wetting, may entrap gases/air and will cure too quickly or improperly.If test results show that the gel time is below the stated minimum time then the powder must not be used, because the curing of the coating would probably be adversely affected.

To determine gel time:1. Measure the temperature of a hot plate to ensure it meets the requirements of the data sheet

specification.2. Apply a small amount of epoxy powder (approximately half a teaspoonful) onto the hot plate

using a spatula.3. Start the stopwatch when the powder hits the hot plate.4. Stir the epoxy (now liquid) using the spatula and lift. Epoxy liquid will be runny, but after a

number of repeated attempts the liquid will gel (string like toffee); at this point stop the stopwatch.

The indicated time is the gel time at the recorded temperature.The manufacturer of the material will state a gel time on the product data sheet and the time achieved at test must be longer than that stated on the product data sheet, or it must lie within a specified time range for acceptance.The gel time test may be conducted on site, e.g. in a cabin or site office, but it will rarely be a requirement.

Differential scanning calorimetry (DSC)DCS is a type of differential thermal analysis (DTA). It is a method assessing the degree of cure of an FBE coating by using the thermal characteristics of the supposedly cured coating material.When FBE is heated, by application to a hot substrate, it melts and cross-linking starts immediately (due to molecular freedom). The reaction rate drops with a corresponding drop in temperature, until eventually no reaction at all is occurring. Hence the material can be at various degrees of cure depending on temperature loss rates.Material at differing degrees of cure will be composed of different chemical compounds and have different molecular structures and therefore will display different thermal characteristics.By comparing two glass transition temperatures (Tg’s) of a supposedly cured material, obtained by testing the same sample twice, it is possible to determine the degree of cure. The two Tg’s should be the same, however, providing that Tg2 comes within a specified temperature range of Tg1 the degree of cure will be accepted. The range specified may include a tolerance to allow for the sensitive nature of the test.

The test procedure basically entails micronizing and conditioning a small coating sample, approximately 10-15mg as required, and placing it in a small aluminium pan and applying heat at a rate of 20˚C per minute, up to 240˚C. The sample is cooled to room temperature then the test repeated, although it is not necessary to attain a temperature too far above the glass transition temperature for the second run. (Note 1)

Note 1 – The glass transition temperature (Tg) of a material is defined as being the temperature at which the substance changes its physical state fro m a brittle (glassy) solid to a rubbery solid.

Penetration

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Most coating materials, especially those that are thermoplastic (enamels, polyethylene, laminate tapes etc.), are subjected to penetration tests.The penetration test simulates contact with sharp objects, e.g. stones or welding electrodes, which the coating may make contact with when in service.The test apparatus consists of a metal rod, weighted and machined to a contact diameter of typically 2.5mm. This is placed through a collar through which it can freely move. The rod is placed touching a panel that is coated with the material under test. A shoulder on the rod to monitor accurately any vertical movement of the rod operates a fixed static gauge.The weight used can be varied accordingly to specification requirements and the profile of the contact point can also be changed by using a different metal rod. A sharp point is specified for coal tar enamel, because the material oxidises quickly and forms a tough skin; a flatter profile would be used for bitumen.After a specified time at a set load, the amount of penetration is measured from the gauge and compared to specification requirements.

Softening pointThis is a test conducted on raw materials for thermoplastic systems, e.g. enamels and polyolefins.Ring and ball apparatus is used to determine the temperature at which the two steel balls pass through prepared discs of the test material, by virtue of the material softening to allow displacement.

Water soak (absorption)Coated panels are totally immersed in water at a stated temperature for a given length of time. The panels are then removed and re-weighed. The amount of water absorbed is then calculated.Maximum requirements are usually specified as a percentage by weight, e.g. max. 5%.

ElongationThis test is mainly on plastics, e.g. tapes, polyethylene cladding and polypropylene. Also used on detached films of FBE and fibreglass reinforcements.The test is done to determine how far a material will stretch before it breaks, sometimes called elongation at break and is expressed as a percentage.A bar bell shaped sample is used and is clamped at both ends. A pulling force is applied at a specified rate (expressed in mm per minute). Two lines are scribed on the narrow section of the bar bell and the distance between them measured before and after the test.A minimum elongation would normally have to be achieved, e.g. at least 350% for a material such as polyethylene.

Tensile strengthFibreglass reinforcements, detached epoxy coatings and most plastic coatings are subjected to a tensile test.The test is similar to the elongation test, except that the maximum load the sample withstands before failure is recorded. Applicable units N/mm2 of MPa.

Impact resistanceMost pipeline coatings are subject to this test.An impact tool with a specified end profile of a specified weight is dropped over a specified distance onto the coating sample. The area is then assessed for damage using a holiday detector.Each material had its own energy absorption impact rating measured in joules (J).A typical requirement for FBE is 5J for 0.5kg, dropping from a height of 1m.

Cathodic disbondment test (see unit 27 page 67 )

Strain polarisation test

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During cold bending operations, large stresses are imposed on the coating. The result of this imposing stress is strain. When cathodic protection is applied, these areas of strain may fail prematurely, therefore this test is performed to determine whether a strained coating is susceptible to breakdown because of the application of cathodic protection.To conduct a strain polarisation test, test samples are prepared by forcing a curved mandrel onto a coated test plate; the coating is on the larger radius produced (on the outside of the bend).The coated samples are then subjected to a current to make it cathodic, usually using the same procedure as described for he cathodic disbondment test, but without the hole in the coating. After a specified period has elapsed, the sample is then tested by holiday detection to determine any areas of breakdown.

11 TESTS PERFORMED BY INSPECTION PERSONNEL(FACTORY AND SITE)

ThicknessMost coatings are subject to thickness tests usually performed manually using specified gauges (magnetic, electromagnetic or ultrasonic). Automatic systems do exist in some factories, e.g. for use on polyethylene cladding.The methods used to determine thicknesses vary because of limitations associated with each method. When trying to deal with a huge range of thicknesses a coating inspector may encounter, e.g. 20˚μm for a primer and 25μm for a thick elastomer type coating. A destructive check performed by taking a coupon or using a heated needle on a needle type gauge may be specified for some thicker coatings.

Adhesion(see also P)Various forms of adhesion tests exist for different types of material and situations. Qualitative and quantitative type tests may be specified according to procedural requirements. Adhesion tests that may be encountered on pipeline coating systems include:

a. Vee cut tests.b. X-cut tests.c. Bond tests.d. Primary bond tests – enamels (factory).e. Dolly test.f. Hydraulic adhesion test.g. Peel creep (usually identified as a separate type of test).

Only selected tests are briefly described below.Vee cut testThis is a quick and easy qualitative test for thinner coatings, e.g. primers, MCL’s and FBE.X-cut testA test more likely to be used on FBE.This test is not the same as the X-cut tape test.This is a test with the same principle as the vee cut test but uses an X instead of a V. A metal bar or similar is used to provide a fulcrum and attempt is made to peel the coating off by using the point of a utility knife at the intersection. The intersection is then assessed for damage and rated against a standard set of diagrams in the applicable specification.

Bond testA qualitative test done on enamels on coated pipes, similar principle to the Vee cut, but uses a rectangular test area, e.g. 300mm wide, 100mm long.

Peel creepUsed largely on polyolefins and other plastic coatings.

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A method of measuring the average force required to peel off a coating from a substrate at a constant rate of pull.A strip typically 20mm wide is cut circumferentially into the pipe coating, e.g. 100mm long or as otherwise specified. The end of the strip is lifted and placed in the jaws of the pull off mechanism. A rate of pull is specified, e.g. 10mm per minute and the force required to maintain this rate is recorded; alternatively, some specifications require the time taken to peel off a stated length at a given force.Other variables are the test temperature and the angle of pull, which can be perpendicular or tangential.

Holiday detection(see unit 28 page 68)

11-1 Awareness of other testsA pipeline coating inspector is less likely to have any involvement in tests not mentioned above. Other tests or test results, which may be encountered, are listed in the mentioned units, which apply to the coating/wrapping materials.

12 INSPECTION12-1 Duties of a pipeline coating inspectorThe duties of inspection personnel are essentially those inspection duties which the client or employer wants them to perform. A significant problem in industry is that different organisations use inspection personnel in different ways, or the use of inspectors for functions additional to inspection. For some, this has lead to a misunderstanding as to the defined role of inspection.The definition of inspection to BS EN 28402: 1991: Quality Vocabulary – “Activities such as measuring, examining, testing, gauging one or more characteristics of a product or service and comparing these with the specified requirements to determine conformity”.A definition of inspection to BS EN 28402: 1991: Standardisation and Related Activities – “Evaluation for conformity by measuring, observing, testing or gauging the relevant characteristics”…”Evaluation for conformity” is defined in the standard as: “Systematic examination of the extent to which a product, process or service fulfils specified requirements”.Inspection may be performed for fitness for purpose or quality control purposes and may be carried out by the contractor, client or a third party.Inspection is not supervision and inspection is not a substitute for supervision.

It is not the duty of an inspector to deviate from the specified requirements; generally speaking, if the specification (Note 1) is inadequate the work will be inadequate. Inspector qualification schemes do not require, or test for a sufficient depth of corrosion engineering, paint technology or design knowledge, which would enable an inspector to pass judgement on the correctness of an application specification. It could be argued that experienced senior inspectors may be in a position to take certain engineering decisions, but it is dangerous to generalise on this point.There was a situation where a client’s senior representative became irritated because a painting inspector under his control would not allow painting to take place because the relative humidity and dew point were outside the specified requirements. Adverse environmental conditions had persisted over a period of a few days and production was suffering. The client’s representative argued that the painting inspector should have allowed painting to continue because it was “common sense to do so”.The inspector had not been given an instruction, either verbally or in writing, to allow this specification deviation. It was being argued that the painting inspector should allow deviations from the agreed specification t his discretion. Examples like this lead to confusion regarding inspector’s duties and authority. Inspectors are usually taught never to deviate from the agreed specification unless given written permission to do so from the client or supervisor.Note 1 – the agreed specification(s) for the contract may consist of a combination of one or more of the followingNational/International specifications, client specifications, job specifications, procedure specifications.Accurate reporting is an important duty for any inspector, but what constitutes an accurate report can differ between organisations and projects. Who the inspector actually reports to is also an important consideration.

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It should be made clear to all workers, including inspectors, as to what is expected of them for the activities they are to perform – this is a basic quality assurance requirement.This is not to say a pipeline coating inspector should not perform duties outside the scope of inspection, this may be acceptable providing the person is competent to perform the work and providing it has been made clear what is required from the outset.Ideally, pipeline coating inspection personnel should be issued with relevant procedures and work instructions to enable them to carry out inspection and associated activities in accordance with the clients or organisations requirements. The procedures should leave the inspector in doubt as to what is to be done. Unfortunately, this documentation rarely exists!

Typical inspectors dutiesBefore work commences

1. Determine your duties and responsibilities. Duties may include those, which relate to health and safety aspects, taking into consideration mandatory requirements. You may also be required to check that rejected paint or used abrasive is disposed of correctly or quarantined.

2. Ensure the contractor’s supervisor is aware of your duties and authority.3. Ensure you have correct applicable specifications and data sheets. Also ensure you at least have

access to relevant referenced normative documents.4. Determine the order of precedence for normative documents if the specification does not make it

clear.5. Learn the specification, procedures, work instructions etc.6. Approach the senior inspector or supervisor if you are not sure what is intended of any

requirement.7. Ensure you have copies of any applicable documentation, e.g. correspondence, minutes of

meetings, concessions etc.8. Liase with the contractor’s supervisor to determine whether the contractor’s personnel are

familiar with the work requirements.9. When required, confirm that the contractor’s operators are properly trained and conversant with

the equipment, materials and application techniques being used.10. Agree with the client/supervisor the level of liaison that is required and determine

reporting/recording requirements.11. Ensure you have test instruments etc. that are required and that they are properly calibrated and in

working order.

Surface preparation1. Check the specification, procedures and/or work instructions to establish:

Standard against which work is to be measured Methods by which the work is to be assessed, e.g. surface comparator Degree of surface cleanliness Surface profile requirements (where applicable) Any special tests to be carried out, e.g. for detecting/measuring degree of surface

contamination, sieve analysis of abrasives. Requirements regarding equipment and consumables Ambient conditions required Recording/reporting requirements

2. Check the condition of the substrate before cleaning and make a note of rust grade, general condition of pipe/fitting, spatter, flux residue on welds, etc. Any areas suspected to be defective, e.g. cracked or laminated or mechanically damaged, should immediately be reported to the supervisor or client.

Note: Do not allow surface laminations, cracks and similar to be dressed without the permission of the supervisor or client.

3. Ensure ambient conditions allow surface preparation to take place. The following may have to be measured/assessed.

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Air temperature Steel temperature Relative humidity Dew point Moisture on substrate Potential sources of contamination, i.e. chemicals, salt spray, fumes, dust Potential changes in the weather to adverse conditions.

4. Ensure any areas requiring protection from abrasive damage are shielded or masked off.5. Identify pipes/fittings/welds being prepared.6. Check that the correct materials and equipment are being used, e.g. correct type, correct size,

consumables are free from contamination. Etc. Examples:a. Abrasive type, size and cleanliness. No re-use of expendable material.b. Correct wire brushes.c. Correct chemicals for chemical cleaning.

7. Carry out inspection of prepared surfaces as required by the specification, including any Overlap requirement onto existing coating.

8. Record the results of the inspection. The areas inspected must be identified in the report, ensuring that it is clear what has been accepted and what has been rejected. The reasons for any rejections should be clearly identified.

9. Ensure that all concerned are clear about the reasons for any rejections.10. Where remedial work has been necessary, re-inspect for conformance to the specification.

Coating/wrapping material1. Check the specified requirements.2. Check that the materials delivered to the work place correspond to the requirements of the

specification and data sheets. The specification may require certain information to be displayed on each paint container.

3. Check that any primer or liquid material is the correct type for the application method being used, i.e. brush grade or spray.

4. Check material storage conditions against manufacturers recommendations.Note: Any warranty on the material is likely to depend on proper handling and storage.5. Especially when dealing with materials having a short shelf life, determine whether the material is being withdrawn from the store in proper rotation, i.e. usually on a first in,, first out basis.6. Ensure material is not being used beyond its shelf life.7. Monitor material usage to determine whether there is sufficient paint in storage for the

completion of the job (or part job). (This is not always a responsibility of the inspector).8. Check that liquid coating materials are being mixed and stirred correctly. Any permitted addition

of thinners must be monitored to ensure correct type and amount. For two-pack coating materials: Check that the materials are mixed strictly in accordance with the manufacturers data

sheets, e.g. add Part B to Part A in the correct ratio; Confirm that any induction time is strictly adhered to or time is allowed for gas bubbles

to escape. Confirm that mixed material is not used after its pot life.

9. Ensure/confirm that all necessary sampling procedures and tests have been carried out prior to the commencement of work. Record batch numbers of materials tested.

Coating/wrapping application

1. Check the specified requirements.

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2. Check that the surface to which the coating/wrapping is being applied is free from contamination, i.e. oil/grease, dust, spent abrasive, corrosion products etc. Any areas suspected as being defective, e.g. cracked, laminated or mechanically damaged, should be immediately reported to the supervisor or client.

Note Do not allow surface laminations, cracks and similar to be dressed without the permission of the supervisor/client, (usually not the remit of the painting inspector).3. Ensure hat the ambient conditions allow coating/wrapping to take place. The following may have

to be assessed/measured: Air temperature Steel temperature Relative humidity Dew point temperature Moisture on substrate Potential sources of contamination, i.e. chemicals, salt spray, fumes, dustNote: Check that the material being applied does not have any special restrictions on its application.

4. Confirm that coating/wrapping material is not being applied to coated substrates either before or beyond the specified overcoating times for the existing coating.

5. Check that the correct application method is being used.6. Check the correct application temperatures are being used (where applicable).7. Identify areas being coated/wrapped.8. Carry out inspection of coated/wrapped surfaces as required by specification. For example:

a. Check that primers and coatings/wrappings used on field joints or repairs overlap onto the existing coating by the correct distance.

b. Check that tapes are applied on risers from the bottom upwards.c. Check that tapes are being applied in a spiral fashion with 55% overlap or as otherwise

specified.d. Check that coatings/wrappings possess uniform contours after application.e. Measure the dry film thickness (D.F.T.) where required.f. Carry out holiday detection.g. Carry out adhesion/bond tests.

9. Take any test samples required.10. Ensure that any areas of defective coating are identified for remedial work.11. Ensure that all concerned are clear about the reasons for any rejections12. Re-inspect any remedial work carried out to ensure that it conforms to the specified requirements.13. Record the result of the inspection. The areas inspected must be identified in the report ensuring

that it is clear what has been accepted and what has been rejected. The reasons for rejections should be clearly identified.

Miscellaneous1. Check that the handling, transport and storage of coated/wrapped pipes and fittings is carried out

in a manner approved by the specification, which does not cause damage to the coating.2. When required, attend appropriate meetings, such as periodic on-site meetings, or those meetings

called to provide solutions to a particular problem that has arisen. You may also be in a position where you need to arrange a meeting to resolve problems that have arisen.

3. Ensure that you effectively organise your time so that you are available for inspections when required. Do not give the contractor an excuse to say, “ we were waiting for the inspector to carry out inspection”.

4. Check the work area housekeeping. For example, equipment and consumables should be cared for (correctly handled, stored and maintained) and the site or shop should be tidy (free from empty containers, worn brushes, spent abrasive) etc.

5. On completion of the work/contract, ensure all records (specifications, procedures, work instructions, permits, concessions, plans, report sheets etc.) are collated and filed in the appropriate location. This is only required when it is your designated responsibility.

6. Do not seek confrontation. Try to avoid arguments. Never be condescending, patronising or

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arrogant. Remember the main duty of an inspector is to inspect against specified requirements and report findings. If the specification is not clear on a particular requirement, seek advice from the supervisor or client. Do not accept or reject work based on your opinion alone. Be objective at all times.

12-2 Records and reports

The reporting requirements of quality control associated with painting work and the actual information recorded can differ considerably from job to job. The daily inspection report is common to most jobs and is often written out on a Daily inspection Report From which has a format designed by the organisation that you are representing, i.e. the inspection agency, contractor or client.Progress reports are often required and these may have to be produced on plain paper or on specially designed forms.Ideally, the exact reporting and recording requirements should be specified in a procedure or in the job specification itself. Always liase with the supervisor or client, verify what is required to be recorded or reported.Regardless of the specification requirements, the inspector should always make a detailed log of work performed, observation, relevant conversations and similar; include applicable times, dates, people involved etc. You may find this information very useful in future disputes.The following list shows the documentation that may exist on a project involving painting inspection and that which the senior painting inspector is more likely to be responsible for collating and controlling effectively, until final completion of the work.

1. The applicable specifications2. Procedures and related work instructions3. Quality plans4. Method statements5. Concessions (waiver or variation orders)6. Daily inspection report forms7. A daily log (this may be a stand-alone document or one in addition to a daily inspection report)8. Lists of remedial action9. Progress reports10. Minutes of meetings11. Correspondence12. Calibration certificates13. Copies of work permits14. Site instructions15. Mechanical completion certificates (hold point release forms or inspection request forms)

16. Audit reports Internal External

17. Non-conformance reports18. Certificates of conformity

12-3 Examples of contractor malpractice

1. Use of unskilled operators. This may relate to surface preparation, application of coating/wrapping or safety considerations, e.g. unsafe scaffolding.

Note: The inspector cannot normally report an unskilled operator as something that does not conform to specification. (report the work observed as out of specification)2. Use of unsuitable equipment, which may be worn brushes, poorly maintained and leaking

compressors, contaminated equipment.

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3. Coating/wrapping on site or preparing surfaces during inclement weather conditions, such as rain, snow fog, mist etc.

4. Re-using expendable abrasives.5. Insufficient cleaning or poor coating in difficult access areas such as under pipes.6. Coating/wrapping before inspection of substrate preparation or previous coat.7. Missing out the primer (when a primer is specified).8. Use of wrong solvent to clean application tools/equipment.9. Not filling irregular contours when using wrapping tapes.10. Not enough tensioning when using wrapping tapes.11. Incorrect material application temperatures (or hold temperatures) when using hot applied

materials.12. Storing coating/wrapping materials incorrectly, e.g. where the specification requires material to

be stored in a temperature controlled environment.13. FBE or liquid paint materials used outside the expiry date.14. Applying a thickness of coating, which is outside the specified range.

13 HANDLING, TRANSPORT AND STORAGE OF COATED PIPES

Pipes and fittings must be handled, transported and stored in accordance with specified requirements. The following text offers some typical requirements.

HandlingThe two main considerations for handling pipe correctly are (1) personnel safety and (2) prevention of damage to the pipe or coating.Where practicable pipes should be lifted using a spreader beam, with suitable slings (nylon type) as this is the safest method. Where a spreader beam is not practicable, two leg chain slings (brothers) could be used, these should be fitted with properly designed profiled hooks, fitted with guide ropes and the inner edge of the hooks should be coated in nylon of soft alloy. The use of vacuum lifts and magnetic devices may be permitted.Chains must not be slung around pipes, even if padded.When handling large bends or tees, a nylon sling should be passed through the bore.

TransportWhen chains or straps, pipe cradles, batten carriers or stanchions are being used during transport, they must be padded, e.g. with at least 12mm of rubber at contact points.Pipes may be stacked in pyramid or parallel fashion when transporting. Stacking in parallel fashion will require the use of padded pipe cradles or battens between the pipe layers.

Stacking at permanent or temporary storage sitesPipes are stacked pyramid fashion on either hard standings or soft standings.Hard standings, which may only be used on flat firm ground, consist of bearers (skids or runners) padded with wood wool mats or similar.The number bearers required for each pipe on the base layer will be governed by the size of the pipe (weight) and the type of coating applied.Soft standings consist of two parallel sand rows, separated by approximately ¾ of the pipe length. Polyethylene sheeting is often required between the sand and the pipes.Stacking should be done in such a way as to avoid accumulation of water inside the pipes, a fall of ~150mm is desirable.The maximum number of tiers and any requirements for preventing pipe-to-pipe contact between tiers should be specified.

14 DITCHING AND BACKFILLING

Ditching is the lowering in of a pipe or string of pipes, into a trench.

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Side booms are normally used for ditching, the number of which depends on size, weight and number of pipes to be ditched. It is good practice to have the booms (jibs) lined with rubber, e.g. car tyres, to prevent damage to the pipe coating, if the pipe comes into contact with the boom.If the trench is excavated rock, a well-rammed bed of approved sand/gravel mixture would be applied to the base of the ditch to a depth required by the specification, e.g. at least 150mm.The base of the ditch must be evenly bedded and the inspector must make sure there are no stones, welding electrodes, etc. present in the ditch, which could cause damage to the coating, or interfere with the cathodic protection.When thermoplastic coatings have been used, e.g. coal tar enamel, lowering in should not take place if the ambient temperature is high, e.g. above 27˚/c, or as otherwise specified.When the pipes are lifted from the skids prior to lowering in, the coating must be checked by holiday detection to ensure freedom from skid damage. It is normal to ensure earth has been achieved by testing the bare bevel ends of the pipe string.

BackfillingThe important considerations when backfilling are as follows:

The pipe and pipe coating must not be damaged. Foreign material, which may cause damage to the coating or interfere with cathodic protection

must not be placed in the trench. The backfill should be well compacted, otherwise the pipeline may not be adequately protected

by the CP system, or a much higher current may be required to achieve adequate protection. Environmental considerations may apply – ideally the excavated material should be returned in

layers, which correspond to how it was originally. When the excavated material contains rocks/stones, it will not be permissible to return this material in the layers around the immediate vicinity of the pipe.

Backfill material consisting of either the excavated material or imported fill is placed into the trench in layers of specified depth, e.g. 300mm each layer. Each layer must be well compacted with hand rammers or mechanical vibrators, prior to the deposition of the next layer.Stone free layers are deposited until the backfill material is a specified distance above the pipe, e.g. at least 300mm. The remaining excavated material is then returned to the trench in layers and compacted as above.The minimum depth of cover between the top of the pipe and the surface of the normal ground will be specified. Water courses and road crossings, railway crossings and similar require special considerations.Note: To protect the coating against stones and soil stressing, a plastic grid mesh is sometimes wrapped around the pipe prior to backfill.

15 PEARSON SURVEY

The Pearson survey is an above ground survey technique used primarily to locate coating defects in buried pipelines. Pearson survey equipment may be used to determine:

1. The presence of holidays/damage.2. The existence of metallic objects.3. The depth of the pipe.4. The position/direction of the pipe.

The survey compares the potential gradients along the pipeline measured between two movable electrical ground contacts. The potential gradients result from an injected a.c. signal leaking to ground at coating defects or metallic objects located near the pipeline.A transmitter is electrically connected with one lead to the pipeline, e.g. at a cathodic protection test point and the other lead to a good remote earth and then energised.The receiver can be used in a pipe-locating mode only. The section of pipe to be surveyed should first be located and identified to enable the survey operators to follow the route of the pipeline. Stakes can then be inserted at measured intervals if required.

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The receiver is connected via a cable harness to earth contacts worn or held by the tow operators, such that at all times earth contact is maintained. A connecting cable provides a separation of 6 – 8 metres between the operators.The tow operators follow the route of the pipeline; when the leading man (front contact) passes over a defect, a higher signal level is indicated in the headphones by an increase in volume and also visually on the receiver if a signal level meter is fitted. As the front contact passes the defect, the signal fades and then increases again as the rear contact passes over the defect.Where the signal is not easily interpreted or where there may be more than one defect within a span of operators, this may be clarified by surveying at right angles to the pipeline, i.e. one operator walks over the pipeline and the second walks parallel to the pipeline, 6-8 meter from the pipeline. In this mode each defect is indicated, as the operator over the pipeline traverses the fault.The survey may be carried out with an impressed current cathodic protection system energised. However sacrificial anodes, bonds to other structures or similar should be disconnected prior to the survey as these can mask defect areas or drastically reduce the length that may be surveyed from one injection point

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Pipeline

Coatings

Inspector

I.Corr Level II

Part B

TABLE OF CONTENTSPART B

41


Section PageCORROSION……………………………………………………………………. 16 43GRAPHITISATION…………………………………………………………….. 17 44BASIC CHEMISTRY…………………………………………………………… 18 44SURFACE PREPARATION……………………………………………………. 19 47

Dry abrasive blasting……………………………………………………… 19.1 47Wet blasting……………………………………………………………….. 19.2 54Hand and power tool cleaning…………………………………………….. 19.3 54Flame cleaning…………………………………………………………….. 19.4 55Chemical cleaning………………………………………………………… 19.5 56

TESTS TO DETECT SURFACE CONTAMINATION………………………. 20 57Soluble iron salts…………………………………………………………... 20.1 57Mill scale………………………………………………………………….. 20.2 58Dust………………………………………………………………………... 20.3 58Oil or Grease………………………………………………………………. 20.4 58

FLASHPOINT……………………………………………………………………. 21 58VISCOSITY………………………………………………………………………. 22 59DENSITY………………………………………………………………………… 23 60WET FILM THICKNESS (WFT)……………………………………………… 24 62DRY FILM THICKNESS (DFT)……………………………………………….. 25 63

Non-destructive test gauges……………………………………………….. 25.1 63Destructive test gauges……………………………………………………. 25.2 64Test panels………………………………………………………………… 25.3 65Calculation………………………………………………………………… 25.4 65

ADHESION……………………………………………………………………… 26 65Vee cut test……………………………………………………………….. 26.1 66Cross-cut test (cross hatch test)…………………………………………… 26.2 66X-cut tape test…………………………………………………………….. 26.3 66Dolly test………………………………………………………………….. 26.4 66Hydraulic adhesion test…………………………………………………… 26.5 67

CATHODIC DISBONDMENT TEST…………………………………………. 27 67HOLIDAY DECTECTION ……………………………………………………. 28 68

High voltage holiday detectors…………………………………………… 28.1 68Wet sponge pinhole detectors…………………………………………….. 28.2 69

WEATHER CONDITIONS…………………………………………………….. 29 69Relative humidity (RH%) and dew point…………………………………. 29.1 69Metal temperature………………………………………………………… 29.2 70

HEALTH & SAFETY…………………………………………………………… 30 70COSHH Regulations 1994………………………………………………… 30.1 70Occupational Exposure Limits (EH40)…………………………………… 30.2 71Volatile organic compounds…………………………………………….… 30.3 72Health & Safety data sheet………………………………………………… 30.4 73

FLAWS ON THE SUBSTRATE………………………………………………… 31 73CATHODIC PROTECTION (Introduction)…………………………………… 32 75QUALITY ASSURANCE………………………………………………………... 33 76NORMATIVE DOCUMENTS………………………………………………….. 34 78

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16 CORROSIONCorrosion is generally an electro-chemical process which results from an anodic reaction and at least one cathodic reaction. The corrosion of steel takes place at the anode.The anodic reaction is expressed as follows: M M+n + ne

Where: M = element involved n = a number e = electron(s)

At least one of the following cathodic reaction(s) takes place at the cathode:1. Oxygen reduction in acid solutions: O2 + 4H+ + 4e 2H2O2. Oxygen reduction in neutral and

Alkaline solutions: O2 + 2H2O + 4)H-

3. Hydrogen evolution: 2H+ + 2e H2

4. Metal ion reduction: Fe+3 + e Fe+2

5. Metal deposition: Cu+2 + 2e Cu

Iron ore is an oxide of iron in chemical balance with the environment; when this iron ore is converted to iron, the chemical balance is changed and the iron becomes active, i.e. it corrodes on contact with the natural environment and tries to convert back to it’s natural inert state. The natural environment usually contains moisture (which provides the (electrolyte)(Note -1) giving the following simultaneous reactions:Anodic reaction: Fe Fe++ + 2ei.e. iron gives ferrous (iron) ions(Note-2) and electrons.

Cathodic reaction: 2H2O + O2 + 4e- 4OH- i.e water + oxygen + electrons give hydroxide ions.The products of these reactions take part in further reactions with the immediate environment leading to the formation of corrosion products, the most familiar being rust: Fe++ + 2OH- Fe(OH)2

i.e. ferrous ions plus hydroxide ions gives iron hyroxide. 4Fe(OH)2 + O2 Fe2)3H2O + 2H2Oi.e. iron hydroxide plus oxygen gives rust.Corrosion reactions can be accelerated by the existence of certain criteria including:

1. variations in oxygen content on the materials surface;2. chlorides and sulphates;3. other metals or metal compounds of higher nobility (more electro-positive) in contact with the

steel, e.g. mill scale(Note 3);4. acids or alkalis;5. certain types of bacteria near the materials surface.

The following list shows some metals / metal compounds in their order of nobility in sea water at ambient temperature. The relative positions of the metals / metal compounds in the list can change in electrolyte type or temperature; this list is known as the galvanic series. The galavanic series may show the potential of each metal / metal compound measured in volts against a specified type of reference electrode. If the absolute potential values of metal elements only are shown, which are independent of the electrolyte used, the list becomes known as the electrochemical series(Note 4).Note: 1 An electrolyte is a substance which when in solution (usually) water or in its fused (molten) state), will be broken down by it.

2 A positive ion may be called a cation, whereas a negative ion may be called an anion. These terms can cause confusion because cathodes are thought of as being negative and anodes positive.

3 Mill scale is an oxide of iron produced when the steel is manufactured; it is a result of the hot steel coming into contact with air and forming an oxide composed of three layers: FeO nearest the steel, Fe3O then Fe2O3 on the outside. Mill scale has a total thickness of between approximately 25m and 100m.

4 The electrochemical series is produced under standard conditions and is useful for theoretical assessments or in laboratory situations

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Nobility Table

Gold NOBLE (ELECTRO-POSITIVE) Silver Nickel Copper Mill scale Mild steel Aluminium Zinc Magnesium IGNOBLE (ELECTRO-NEGATIVE)Example: If steel was in intimate contact with zinc or attached to zinc via a wire in an electrolyte, e.g.. soil or water, the zinc would corrode first because the steel is more noble than zinc.In this example the zinc becomes the anode and the steel the cathode, i.e. the steel is being cathodically protected and the zinc is acting as the sacrificial anode.

17 GRAPHITISATIONCarbon and graphite are inert in many corrosive environments, their tensile strengths are very low, e.g. 500 to 3000psi, impact resistance is nil and abrasion resistance is poor. Resistance to alkali’s and most acids is good but oxidising acids such as nitric acid (HNO3), sulphuric acid (H2SO4) and chromic acid (H2CrO4) attack it. They also have a low resistance to reaction with halides and halogens (fluorine, Chlorine, bromine and iodine).Graphitisation is the process where the iron component is removed from the metal leaving a network of carbon particles – a de-alloying process.The residual carbon retains the shape of the original object, unless the weak structure is fractured.The mechanism of this corrosion process is believed to be based on cathodic depolarisation caused by the removal of hydrogen from the surface, thereby reducing iron sulphate (FeSO4

(-2) to iron sulphide (FeS) which is itself corrosive.This leads to bacterial attack from sulphur reducing bacteria (SRB) called Desulphovibrio Vulgaris, sometimes referred to as metal eating microbes (MEM) of which there are two types – aerobic and anaerobic.Graphitisation most commonly occurs in salt waters, acidic mine waters, dilute acids and those soils containing sulphates and SRB. It is possible to mimic these conditions and cause graphitisation in a laboratory by immersing in diluted H2SO4.Graphitisation usually progresses directly into the surface in a uniform manner, leaving a porous matrix of the remaining alloy element carbon. There is no outward appearance of damage but affected material loses mass and becomes porous and brittle.The porous residues may retain appreciable tensile strength and also have moderate resistance to corrosion, e.g., a completely graphitised pipe may continue to hold water until fractured by impact.It is essential that all graphitisation is removed because the exterior of a structure or pipe containing graphitisation becomes very noble in any galvanic coupling; therefore any other metal in contact or in close proximity will have its corrosion rate accelerated.Anti-graphitisation measures include efficient barrier coatings and for new systems the addition of several percent of nickel during manufacture.

18 BASIC CHEMISTRYTypes of chemistryChemistry is essentially the study of the composition of substances that are made up of elements and the changes that substances undergo.The subject of chemistry is usually divided into three main branches; organic chemistry, inorganic chemistry and physical chemistry.Organic chemistry is the study of carbon that has the unique ability to bond with itself to form long chains of atoms e.g. polyethylene. Most of the chemistry involved in paints is organic chemistry.Inorganic chemistry is the study of non-organic aspects of chemistry i.e. the elements and their compounds.

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Physical chemistry is the study of the physical properties of elements and compounds.Common termsAtomsThe smallest part of an element that can have the elements properties. All matter is composed of atoms that are tiny particles, so small that 100 million placed end to end would measure 1cm. An atom as a whole is electrically neutral.MoleculeWhen atoms are bonded together in a fixed whole ratio, they are known as molecules. A molecule is defined as the smallest particle of an element or compound. Examples of molecules are: O2 CO2 H2O HCLOxygen Carbon dioxide Water Hydrogen ChlorideElementAn element is said to be a pure substance that cannot be broken down into anything simpler by chemical means.There are 110 elements known to man. Below is a table of the elements most commonly encountered in paint technology and corrosion technology.

Atomic Number Symbol Element1 H Hydrogen6 C Carbon7 N Nitrogen8 O Oxygen

12 Al Aluminium16 S Sulphur17 Cl Chlorine26 Fe Iron30 Zn Zinc

CompoundA pure substance, which is made up of two or more elements chemically bonded together, is called a compound.The chemical bonds by which the elements are joined together may be either ionic or covalent.Examples of compounds are: CH4 H2O NaCl Methane Water Sodium ChlorideIonsWhen a compound such as sodium chloride is dissolved in water it dissociates into ions i.e.: NaCl Na+ + Cl-

An ion is a positively or negatively charged particle. Positively charged Ions are called cations e.g., Na+, and negatively charged ions are called anions e.g., Cl-.Groups of atoms can also possess a charge e.g. hydroxide OH -, sulphate SO4 and these are known as radicals.Chemical BondingAtoms are held together in molecules and large chemical structures, such as a cross-linked epoxy, by chemical bonds.There are various kinds of bonds such as co-ordinate, covalent, double hydrogen, ionic, triple.These bonds are the forces that exist between the atoms and are produced by electrons.Electrons are either shared between atoms, or atoms gain or lose electrons forming ions.The sharing of electrons is called covalent bonding and this occurs when similar atoms bond together. Losing or gaining electrons occurs when different types of atoms bond together, e.g., a metal such as sodium Na+ and a none-metal such as chlorine Cl-. This form of bonding is known as ionicCovalent bondingCovalent bonds are formed by two similar atoms coming together and sharing their electrons, e.g., hydrogen, which has only one electron.

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The two hydrogen atoms form a molecule of hydrogen (H2) by the two electrons coming together to form a bond.

Covalent bonds are usually found in compounds which only contain non-metallic elements, for example: CO2 HCl O2 NH3

Carbon dioxide Hydrogen chloride Oxygen AmmoniaCovalent bonds that contain two electrons are called single bonds. Many molecules such as unsaturated fatty acids contain double bonds. Some molecules such as acetylene H-C C-H, contain triple bondsCovalent bonds are not as strong as ionic bonds.Ionic bondsThese chemical bonds occur because of the electrostatic attractive forces between negatively and positively charged ions, i.e. between anions and cations.Ionic bonds are found in compounds of certain non-metals, e.g. Na+Cl- and also in compounds involving radicals; for example:

Cu2+SO42- K+NO3

-

Copper sulphate Potassium nitrate

Chemical formulaeA chemical formulae is a way of representing a substance or compound by using the symbols of the elements present in the formulae.There are two commonly used forms of chemical formulae: (1) molecular and (2) structural.

The molecular formula of a substance shows the number and types of atoms in the molecule, but it does not show how the atoms are arranged, for example C3H6O Acetone.A structural formulae is one that shows the bonds between atoms and the position of the atoms with respect to each other, for example:

CH3

C = O Acetone

CH3

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Hydrogen atoms

Hydrogen molecule


Structural formulae are sometimes written in an abbreviated form, for example: CH3 CO CH3 Acetone

To summarise, it will be seen that the formulae for acetone can be written in any of the following ways, all of which are correct:

CH3

C3H6O C = O CH3 CO CH3

CH3

19 SURFACE PREPARATION

Correct surface preparation is a vitally important stage for most coating systems, it is often the process which governs the service life of the coating system.There are various ways to prepare a surface prior to coating:

Abrasive blast cleaning Wire brushing Scraping Needle gunning Chemical cleaning Water blasting Weathering Flame cleaning Vapour degreasing

The quality of a surface preparation is governed by the amount of surface contaminant remaining on the substrate after cleaning, although it may also relate to the resultant surface texture, e.g. the surface profile on a substrate after abrasive blast cleaning.

19.1 Dry abrasive blastingDry abrasive blasting is carried out by projecting a highly concentrated stream of small abrasive particles on to the substrates surface at speeds of up to 720km/h (450mph) The operation removes rust, scale, dirt and any other extraneous material from the substrate and also leaves an irregular profile that provides the ideal key for coating adhesion. Dry abrasive blasting is often the best method of surface preparation for long-term protection coating systems.

AbrasivesThe degree of surface roughness and the rate of cleaning is partially governed by the characteristics of the abrasive used; these being: AbrasivesThe degree of surface roughness and the rate of cleaning is partially governed by the characteristics of the abrasive used; these being:

Size Hardness Density Shape

Effect of abrasivesGrit is angular in profile with sharp cutting edges; it shatters mill scale and undercuts any surface contaminant resulting in a clean surface with an irregular profile. The amplitude tends to be quite erratic with a large occurrence of rogue peaks, especially when blasting in one area for too long. Many materials both metallic and non-metallic are used to manufacture grits.

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Shot(Note 1) is spherical, it shatters mill scale, but does not have sharp cutting edges to cut into a surface, however, the visual appearance of a shot blasted finish is similar to a grit blasted finish although there is less roughness to the touch. Shot blasting work hardens a steel surface to a greater degree than grit, which has the effect of reducing the chance of any stress corrosion cracking which could otherwise occur in the future. Shot also reduces the occurrence of rogue peaks nut may press impurities into the surface.Shot is usually made from cast steel although a natural mineral called staurolite is also available in shot (spherical) form.It is common practice to mix metallic shot and grit to obtain a blast finish close to the ideal (a typical mix being 70-80& shot and 20-30% grit).Chilled iron gritUsed in enclosed blast mills and open blasting where recovery systems can be employed. The abrasive is relatively cheap and efficient in use. On impact, small chips are removed from the abrasive which exposes new cutting surfaces fro the next cycle. Because of this factor, excessive wear can occur due to larger quantity of fines which need to be extracted.Cast steel gritUsed mainly in blast pens and grit recycling systems. Tends to round off during use as the sharp edges wear down and is therefore not as efficient as the chilled iron varieties but is easier on moving parts. High-carbon steel is used because low-carbon steel cannot be crushed into a grit.Cast steel shotFor use mainly in enclosed recovery systems because of the ricochet characteristics (some mechanised floor blasting systems employ this). It has a tendency to impress impurities into the surface as it peens or work hardens the top few nanometres. Available in high-carbon steel (HCS) and low-carbon steel (LCS).Cut wire steelNormally used in enclosed systems only to facilitate recovery and cleansing. Sharp cutting edges round off quickly and evenly as the steel abrasives mentioned above.Synthetic slags and fused aluminium oxideSynthetic slags include copper refinery slag, nickel refinery slag, iron furnace slag (calcium silicate slags), coal furnace slags (aluminium silicate slag). These are expendable abrasives all having a grit profile and are used in open blasting systems. Cheap with no silicosis hazards (typically less than 1% free silica). Breaks down quickly to fine particles. Extremely fine particulate matter embeds into the profile resulting in slight discolorationNatural mineral abrasivesThis type of abrasive includes garnet, silica sand, olivine sand and staurolite. All are available in grit form, although staurolite is also available in shot form. Natural mineral abrasives are used mainly in open blast systems and give a high degree of surface cleanliness.Note: The Control of Substances Hazardous to Health Regulations 1994 (COSHH Regulations) do not allow the use of sand(Note-2) containing free silica in dry blasting operations because of the associated health hazard of silicosis.Agricultural by-product abrasivesThis classification includes corncob, walnut shell, eggshell, peach husk, coconut shell and many more. Used for stone cleaning or sensitive substrates and has a tendency to absorb water Abrasive analysisThe use of large particle sizes does not increase blasting efficiency or economy. The large particles tend to bounce and ricochet along the blast hose losing speed and hence impact energy. Also large particles cannot always clean out the corrosion pits within the substrate or clean out the pits of the profile cut by abrasive that has already impacted. The most efficient medium contains a controlled mix of large and small particles known as a working mix. Because non-metallic abrasives are normally expendable, the working mix should be as required on supply.Note 1. Both metallic shot and metallic grit particles tend to ricochet and so the blasting area needs to be totally enclosed for efficient recovery and cleansing.Note 2. Sand is not dangerous unless it is in dust form when it can be inhaled e.g. after fragmentation during dry blasting operations.

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Metallic abrasives, being recyclable, gradually reduce in size cycle by cycle until the particles are small enough to be drawn out by the air cleansing system. It therefore becomes necessary to do as an analysis of the abrasive particle sizes to ensure that the optimum mix is being used.Procedures for laboratory sieve tests for the determination of particle size distribution of metallic abrasives are detailed in BS 7079 : Part E7 (ISO 11125-2), for metallic abrasives – BS 7079 : Part F12 (ISO 11125-2).Because non-metallic abrasives are usually expendable and are supplied as an ideal working mix, tests for the determination of particle size distribution are very rarely required in the field. Conversely, abrasive analysis is often required when using recyclable metallic abrasives.In order to obtain a representative sample of recycled abrasive, it is advisable to use a sample point near to the point of reapplication on a gravity feed line e.g. immediately before the top hat on a Wheelabrator or on a free-fall area into the blast pot.A simple test to determine working mix would be as follows(note-1):

1. Select the sieves as specified in the relevant standard for the abrasive size denomination and assemble, in descending order of mesh size – largest at the top – and ensure there is a receiver under the smallest.

2. Weigh out a 200g sample taken from the points as suggested above and place into the top sieve; position the lid and shake well for 5 minutes.

3. Separate the sieves and remove any abrasives remaining on top of each individual mesh. It is essential to remove every single particle entrapped in the mesh by brushing with a stiff short bristled brush. Weigh the abrasives remaining on each sieve and if applicable, any falling through the smallest.

4. Divide the weight in grams by 2 (because of the 200g sample) to express as a percentage.5. Consult the relevant specification/standard to check compliance with the required size ratios.

Note: Generally, this analysis conducted on a recycled working mix will indicate a shortage in large particle ratios and is likely to require addition of new abrasives.

Checking for contamination of abrasivesAbrasive blasting is done to remove contaminants from the substrate and to increase the surface area, which in turn improves adhesion and the life of the coating. If contaminants are present in an abrasive mix, the substrate can actually be coated rather than being cleaned. Several tests can be done to ensure that this does not occur although some are intended for laboratory use, e.g. tests for the determination of moisture content and the amount of soluble chlorides present.Tests for compressed air cleanlinessPass the compressed air through a white cloth (at reduced pressure) for several seconds. Discolouration of the cloth indicates contamination. Wet stain shows oil or water (water will dry off, oil will not)Excessive dust or finings in a working abrasive mixA simple test is merely to toss a handful of abrasives into the air and observe the dust carried away on the breeze.A more definite test is to drop a handful of recycled abrasives into a beaker of water. The finings/dust etc will float (held by surface tension) and so can be roughly quantified.A laboratory test also exists for the determining the foreign matter present in metallic abrasives to BS 7079 : Part E11 (ISO11125 : Part 6)Oil or grease in a working mixA quick and simple test for this is to place an amount of abrasive into a beaker, pour on sufficient water to just cover and stir vigorously for a few seconds. Observe the surface of the water for the purple/blue/green sheen characteristic of oil on water.Another test is to pour hydrocarbon solvent (typically xylene) into the abrasive, agitate, and then pour some of the solution onto a clean glass plate. Any residual smear indicates oil or grease in the mix after he solvent has evaporated.Note 1 The laboratory method requires mechanical agitation. 15 minutes for angular abrasives and 10 minutes for spherical abrasives

Surface profileThe shape of a cross-sectioned blast finish is known as the surface profile or anchor pattern.

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The size of the profile as measure from the peaks to the troughs is known as the amplitude or peak to trough height, and is primarily governed by the size of abrasive used, although other factors are important, e.g. angle of impingement, hardness of surface and other characteristics of the abrasive itself. Maximum amplitudes or amplitude ranges would normally be quoted in the specifications, a typical amplitude range for liquid paints would be in the region of 30 - 75m (Note 2)

The amplitude of a blasted surface may be measured by a number of Methods, including the use of a surface profile needle gauge, surface replica tape, e.g., Testex tape or surface comparator.Surface profile needle gauge (Note 3)

This relies on a needle reaching the bottom of the troughs on the surface profile. Because there are so many troughs of different depth, it is normal and necessary to take ten or twenty readings and calculate the average amplitude. Before taking any readings it is necessary to zero the gauge on a flat piece of glass.

Note 1. Rogue peaks are peaks which stand out above the required profile and should be avoided if applying thin coatings as they may lead to spot or flash rusting.2.Blast finishes should not be touched with the bare hands otherwise contamination will result. 3.All accurate measuring equipment e.g. dial micrometers, should be issued with calibration certificates of conformance to give assurance that the readings obtained are going to be correct within a stated margin of error.

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Amplitude

PeakTrough

Rogue Peak (Note 1)

Surface Profile

Surface Profile gauge


Surface replica tapeTestex tape is a trade name of a commonly used surface replica tape. It is used in conjunction with a dial micrometer and although quite costly, has the advantage of providing a permanent record. The procedure for carrying out this test is as follows:

1. Zero micrometer ensuring the flat contact points are clean.2. Remove paper backing and stick testex tape to the surface to be measured.3. Rub the Testex paste into the troughs using a blunt instrument, until the peaks can be seen

abutting up to the transparent plastic.4. Remove the Testex tape from the surface and measure the overall thickness with the dial

micrometer.5. Deduct 50m (2 thou”) from the reading to obtain the amplitude. The plastic (Mylar) to which the

soft compound is attached is 50m thick.

Surface comparator(Note 1)

The roughness of the surface to be assessed is compared to the different areas on the comparator by visual examination and if necessary by scraping with a fingernail, small wooden stick or similar – never the fleshy part of the finger as this will contaminate the blast.A profile grading can be given when the area under assessment is rougher than the smoothest of the two adjacent areas on the comparator, but not as rough as the rougher of the two areas. The profile is then graded according to the following:

Fine profile Equal to or rougher than area1 but not as rough as area 2. Medium profile Equal to or rougher than area 2 but not as rough as area 3 Coarse profile Equal to or rougher than area 3 but mot as rough as area 4

If the profile is finer than area 1 it is termed finer than fineIf the profile is coarser than area 4 it is termed coarser than coarse.

Blasting gradesThe grade of a blast finish relates to the amount of contaminant remaining after blasting. The grade of a blast finish is primarily governed by blasting time and the velocity of the abrasive particles.BS 7079 : Part A1 (Note 2)

BS 7079 – Preparation of steel substrates before application of paints and related products. Part A1 of this standard is pictorial and shows rust grades prior to blasting and the degree of surface cleanliness after blasting.The surface under examination is visually compared with high quality photographs in the standard both before and after blasting. The preparation is then given a coding e.g. C SA2 1/2 which can be interpreted using the following extract from the standard:Rust gradesA – Steel surface largely covered with adherent mill scale but little if any rust.B - Steel surface has begun to rust and from which the mill scale has begun to flake.C - Steel surface on which the mill scale has rusted away or from which it can be scraped, but with slight pitting under normal vision.D - Steel surface on which the mill scale has rusted away and on which general pitting is visible under normal vision.Preparation grades – blast cleaningPrior to blast cleaning, any heavy layers of rust shall be removed by chipping. Visible oil, grease and dirt shall also be removed.After blast cleaning, the surface shall be cleaned from loose dust and debris.Sa1 – Light blast cleaning. When viewed without magnification, he surface shall be free from visible oil, grease and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter.

Note 1 – It is important to note that needle gauges, surface replica tape and surface comparators only give the degree of roughness and not the degree of cleanliness.Note 2 - BS 7079 : Part A1 is the same as ISO 8501 – 1 and SS 05 59 00.

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Sa2 - Thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease, dirt and from most of the mill scale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.Sa21/2 - Very thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease, dirt and from mill scale, rust, paint coatings and foreign matter Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.Sa3 – Blast cleaning to visually clean steel. When viewed without magnification, the surface shall be free from visible oil, grease, dirt and shall be free from mill scale, rust, paint coatings and foreign matter. It shall have a uniform metallic colour.

Comparison of Blasting Grades

SSPC BS 7079(SS 05 59 00)

NACE

White metal (SP5) Sa 3 Grade 1Near white metal (SP10) Sa21/2 Grade 2Commercial finish (SP6) Sa 2 Grade 3Light blast and brush off (SP7)

Sa1 Grade 4

SSPC = Steel Structures Painting CouncilNACE = National Association of Corrosion Engineers

EquipmentCentrifugal blast unitsBlasting in factories is often carried out using rotating wheels, which throw the abrasive at the component. These units, known as centrifugal blast wheels, are usually fixed installations and are commonly used for large production runs, e.g. on pipes in pipe mills and large steel plates in shipyards.The main advantages of this system compared to air blasting systems are as follows:

a. Lower cleaning timeb. Lower abrasive consumptionc. Lower energy consumptiond. Less labour usede. More consistent and uniform blast finishesf. More environment friendlyg. Safer to implement – closed system

The abrasive is fed into the centre of the wheels and to the inner edges of the attached blades by means of an impeller. The abrasive is then accelerated to the end of the blades and onto the component by centrifugal force at speeds typically between 250-350 km/h (160-220 mph)For cost reasons the abrasive used would normally be reusable. The abrasive is recycled up to twenty times providing it is free from grease or oil contamination. An air-wash separator removes dust contaminants from the recycled abrasive before it is fed back into the wheels.Air blastingPressure blasting, which is a type of air blasting system, would normally be used on site work. Vacuum blast and suction blast equipment also come under the category or air blasting but are not as widely used due to lower efficiency.

Pressure blasting equipment basically consists of: A compressor, providing an air supply of approximately 0.7 Mpa (100psi) A pressurised pot containing the abrasive Liquid separators, i.e. moisture filters (knock-out pots) A carbon impregnated hose A venturi shaped blasting nozzle A dead mans handle for direct operator control

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The velocity of abrasive particles leaving the blast nozzle is primarily governed by the pressure at the nozzle; the higher the pressure the higher the velocity and therefore the higher the cleaning rate.There is a point at which an increase in pressure does not increase the velocity substantially, this is at approximately 0.7Mpa (100psi) depending on the abrasive used. Limiting pressures to 0.7Mpais also advantageous for safety reasons. It is important to keep the pressure at the nozzle as close to 0.7Mpa as possible because for every 1% loss in pressure there is approximately a 11/2% loss in efficiency. The pressure at the nozzle may be measured using a hypodermic needle gauge, this is placed through the hose near the nozzle, with the hole in the needle facing the nozzle.

Blasting nozzlesBlasting nozzles are available in a variety of materials and orifice sizes. Sometimes the nozzles are lined with relatively abrasive resistant materials, e.g. tungsten carbide, for a longer working life.Two types of nozzle, which exist, are the straight bore nozzle and the Venturi shaped nozzle. Straight bore nozzles are rarely used for blasting large surface areas because they are not as efficient as Venturi shaped nozzles. The velocity of the abrasive leaving a straight bore nozzle at 0.7Mpa is approximately 350km/h, whereas the velocity for a venturi shaped nozzle under similar conditions would be 720km/h.

Venturi shaped nozzles also produce a larger blast pattern with the hole area receiving a relatively equal amount of abrasive, whereas, a straight bore nozzle concentrates most of the abrasive in the central area of the blast pattern, resulting in a fringe area of lower blasting efficiency.SafetyCentrifugal blast unit’s area closed system, i.e. human access to the blasting area is limited. When using an open system e.g. for site blasting applications using pressure blasting equipment, access is not usually restricted, therefore warning signs are necessary and regular inspection of equipment is required.Other safety considerations relating to pressure blasting are as follows:

Use of carbon impregnated hose to reduce the chance of static shock Use of a dead-mans handle to stop the flow of abrasive when the operator lets go of the nozzle. Keeping hoses as straight as possible to prevent kinks which may lead to a blow out. Use of hoses of the correct type, i.e. reinforced.

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Straight Bore Nozzle

Venturi shapednozzle


Use of external couplings if joining hoses together. Internal couplings reduce the bore and the eroding action of the abrasive could lead to a blowout.

Restricting the pressure to 0.7Mpa The wearing of protective clothing, including an air fed helmet, boots leather apron and gloves.

19.2 WET BLASTING

Wet blasting methods are good for removing soluble salts such as chlorides from the surfaces and are good for the removal of toxic coatings, e.g., red lead paint films, because they do not create dust.However, all wet blasting methods have similar disadvantages over dry abrasive blasting; including:

a) The availability and drain age of water;b) The production and disposal of sludge (particularly with abrasive injection);c) The extra cost of supplying and mixing a corrosion inhibitor (assuming the specification allows

the use of an inhibitor)d) The problems associated with drying large surface areas or the higher cost of water miscible

primers compared to conventional primers.High pressure water jettingOperates at pressures sometimes in excess of 140 MPa (20,000psi), which can be extremely dangerous. The advantages of this method area as follows.

Simple to operate Highly flexible and mobile in use Suitable for removing soluble salts Will remove mill scale at high pressures

High pressure water plus abrasive injectionOperates at pressures up to 140 MPa, which can be extremely dangerous. The advantages of this method are the same as for high pressure pure water blasting, but will also remove firmly held contamination and will create a surface profile.Low pressure water plus abrasive injectionOperates at 0.7 MPa It is claimed that this technique is very controllable and will remove one coat of paint if required. Disadvantages include high cost an low efficiency.Steam blasting, with or without abrasive injectionOperates at 0.7MPa This method is ideal for surfaces contaminated with oil, grease etc, Disadvantages include high cost and low efficiency.Air blasting with water injectionWater with or without an inhibitor is injected into an air/abrasive stream.

19.3 HAND AND POWER TOOL CLEANINGHand and power tool cleaning, relates to scraping, chipping, wire brushing, sanding, grinding and needle gunning.

This method of cleaning although not as effective as blast cleaning is often used for short-term protection coating systems, maintenance work, or where access for blasting is restricted or damage from abrasive to the surrounding environment would occur.Wire brushing is a widely used surface preparation method but it only cleans up an existing surface, it does not re-cut a new profile. BS7079 Part A1 defines standards of wire brushed finishes along with other hand and power tool cleaning methods as follows:Prior to hand or power tool cleaning, any heavy layers of rust shall be removed by chipping. Visible oil, grease and dirt shall also be removed.St2 – Thorough hand and power tool cleaning When viewed without Magnification, the surface shall be free from visible oil, grease and Dirt and from poorly adhering mill scale, rust, paint coatings and foreign matter.

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St3 – Very thorough hand and power tool cleaning. As for St2, but the surface shall be treated much more thoroughly to give a metallic sheen arising from the metallic substrate.

St3 is usually obtained from mechanical wire brushing and St2 from hand wiring brushing. Care must be taken to avoid over brushing a particular area, causing burnishing, a condition with a highly polished surface, which has an adverse effect on coating adhesion.

For safety reasons, it may be specified that wire brushes used must be of the non-sparking type i.e. phosphor-bronze or beryllium-bronze.(Note 1)

Note 1. Bronze brushes may not be permitted because of the possibility of galvanic corrosion. Plastic bristles with embedded abrasives are available as an alternative.

Needle GunA needle gun or Jasons hammer as it is sometimes referred to, consists of many operated reciprocating tungsten needles. It is usually preferable for the needles to have a small cross-section. Needle guns are useful for cleaning difficult surfaces such as rivet heads and welds, they also peen (hammer) and stress relieves the surface. Their disadvantages are that they can leave sharp edged craters and rogue peaks and they also have a tendency to push impurities into the surface.

19.4 FLAME CLEANINGThe application of an oxy-acetylene flame to the steel surface to be cleaned is an efficient method of removing rust, mill scale and other contamination. The effectiveness of the process is due to a number of factors:Differential expansionThe mill scale on contact with the intense heat expands at a faster rate than the steel to which it is attached and flakes off.DehydrationRust is a combination of iron oxide and moisture. As the moisture is rapidly driven off the rust is dehydrated and converted to a dry powder, which can be removed by wire brushing.Heat penetrationThe heat from the flame penetrates all the surface irregularities and removes all traces of moisture, oil and grease etc.The flame cleaning of any form of fastener, e.g. rivets or bolts should be avoided as a loss of mechanical strength may be caused.Flame cleaning often requires three operatives who work in a team as follows:No 1 – flame cleans the surface, this gives a light grey appearance on the surface when finished.No 2 – Wire brushes the surface to remove all the dry powder.

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Reciprocating needles

Compressed air

Needle Gun


No 3 - Primes the surface; it is often necessary to apply the paint while the metal is still warm, around 40C (hand warm)The warmth of the plate lowers the paint viscosity enabling it to flow more easily into the irregularities and also ensures that condensation will not form on the surface.BS 7079 : Part A1 shows a minimum flame claeining standards according to rust grades, i.e. A Fl, B Fl, C Fl, and D Fl

19.5 CHEMICAL CLEANINGPickling and phosphatingPickling is a chemical cleaning process, which is widely used in a factory environment for preparing items such as pipes and steel plates.The process usually involves immersing the steel in a bath of hot acid such as sulphuric acid (H2SO4), which has been inhibited to reduce attack by the acid on the steel. Te acid dissolves a thin oxide layer at the interface with the steel causing rust or mill scale to be removed.

Procedure (H B Footner’s duplex process)

1. Degrease Removes surface contaminants such as grease and oil by the use of a suitable solvent, e.g. xylene, usually applied with a cloth.

2. Pickle Total immersion in a tank of acid, e.g. 5-10% sulphuric acid at 65-70 C to remove mill scale, rust etc, the time taken is variable and depends upon the type and degree of contamination. An inhibitor is also present in this tank.

3. Wash a clean water wash to remove acid and surface residues, usually applied by hose or spray.4. Phosphate The technique involves a final treatment in a 1-2% phosphoric acid solution held at

80C for 1-2 mins. This leaves a thin rust inhibitive phosphate coating on the steel surface to which the coating should be preferably applied while it is still warm, possibly after a final wash.

Hydrocarbon solvent cleanersThe removal of oil or grease from a substrate using hydrocarbon solvents involves proprietary brands of de-greasers, which usually are solvents such as xylene, toluene and solvent naphtha. Other solvents known as halogenated hydrocarbon solvents such as perchloroethane and perchloroethylene are also used.Note; Halogenated hydrocarbons such as 1,1,1, trichloroethane, trichloroethylene and carbon tetrachloride were commonly used as de-greasers but their use has declined, or been completely restricted due to high toxicity. Heavy vapours of all chemical solvents are a hazard in enclosed areas, e.g. inside tanks.A thin film of oil invariably remains after solvent cleaning but he more solvent used and the more frequent the operation, the less residual matter there is present.Xylene is a commonly used de-greaser, but its use on painted surfaces is limited due to solvent strength and compatibility considerations.Emulsion cleanersEmulsion cleaning uses oil emulsifying agents (soaps) which form a suspension of oil droplets within a liquid. It is usual to follow emulsion cleaning with water or steam cleaning to remove the soap and emulsified oil or grease.

Alkali cleanersEconomic and efficient in use and therefore popular but operator safety is a serious consideration. Vegetable oils are saponified and mineral oils emulsified. This category is designed to preferentially wet the substrate, thus displacing any contaminants.

20 TESTS TO DETECT SURFACE CONTAMINANTS

Tests to detect surface contamination may be qualitative or quantitative. Qualitative tests will determine whether or not contamination is present but they will not show the exact quantity, although an idea of the

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extent of the contamination will normally be determined. There are many tests for detecting contamination but some of these require a chemist or other suitably qualified person to perform; these tests tend to be mainly quantitative i.e. a quantity is determined, e.g. in mg/m2, although even this value may not be the exact amount actually present.

20.1 SOLUBLE IRON SALTSColourless soluble iron salts may be present in pits within the substrate after blast cleaning. If salts are present, they will accelerate corrosion causing rust spots that may in turn break the bond of any applied coatings leading to the failure of the coating system.Some specifications state the maximum levels of salts permissible on a surface and express the quantity in milligrams per square metre (mg/m2 or mg.m2).The maximum requirement may be as low as 10mg/m2 although other specifications may state that 30mg/m2 is the critical level. Only quantitative tests could be used to determine whether these requirements are met.Note: Test results may be misleading or totally wrong if chromate or nitrate inhibitors have been used, for example in wet blasting.

Potassium ferricynaide test (Note 1)

1. Spray fine mist of distilled water onto a small area of the blast cleaned surface using a scent-spray type of bottle.

2. Wait a moment for any water droplets to evaporate then apply a potassium ferricyanide test paper by pressing down for 2-5 seconds.

3. Remove the test paper and check to see if any salts have been drawn by capillary action. They should show as Prussian blue spots.

Merckoquant testThis test is also known as the Eisen test and is a colourmetric quantitative test claimed to be 85% accurate down to 30mg/m2.Small test pads on plastic strips are soaked in a solution of 2,2’ bipyridine which reacts with Fe ++ to produce a red colour. A colour change through white to dark red is shown on the test kit container with corresponding values in parts per million (ppm).ProcedureIt is generally accepted that by using the areas and quantities mentioned below, a direct conversion to mg/m2 can be obtained.

1. Tape off an area of 150mm x 150mm using masking tape or similar.2. Soak swab of cotton wool in a pre-measured 22.5ml of distilled water and swab the

masked off area, replacing the cotton wool into the distilled water.3. Dry off the area using afresh piece of cotton wool, removing as much moisture as

possible and place this second swab into the distilled water.4. Stir the water containing the cotton wool swabs well and immerse the test strip into the

solution, after approximately ten seconds, shake to remove the excess water and monitor the resulting colour change with the master chart.

Bresle sample patch(Note 2)

This is a mercury (II) nitrate (mercuric nitrate) titration test claimed to be 95% accurate down to 10mg/m2 (reference ISO8502 : Part 6)

Note 1 The potassium ferricyanide test may also be referred to as the potassium hexacyanoferrate (III) test.Note 2 There is a laboratory test to determine the quantity of chlorides on a cleaned surface to BS7079 : Part B2 which also involves mercury (II) nitrate.

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Salt contamination metersThese normally give a digital readout by directly measuring the ionised metal salts dissolved in a quantity of water.

20.2 MILL SCALEMill scale is cathodic with respect to steel. This means that if any traces of mill scale are present on the surface after preparation they can accelerate the corrosion of the underlying steel and disbond, leading to the eventual failure of any coating system applied.To test for the presence of any mill scale particles left behind after blast cleaning to BS7079 grade Sa3 the copper sulphate test may be used.ProcedureA fine mist of slightly acidic copper sulphate solution is sprayed onto a localised area of approximately 100mm diameter. The steel turns a bright copper colour and any mill scale particles show as black spots.

20.3 DUST

Applying transparent pressure-sensitive adhesive tape to the test surface and then removing may determine the presence of dust. The tape is examined using a magnifying glass and an assessment of the degree of contamination is made. Standards do exist which standardize the test conditions and the way in which the results are assessed. For example, the pressure applied to the tape and its degree of stickiness will partly govern the results. (reference BS7079 : Part B3)

20.4 OIL & GREASE

Simple visual assessment may reveal the presence of oil or grease; however, a cotton wool swab wiped over the surface may reveal oil or grease that was not directly visible when on the surface. The use of an ultraviolet lamp may also detect oil or grease by causing it to fluoresce, but a dark environment is required for this method. Another method is to drip several drops, using an eyedropper, of a solvent such as xylene onto the suspect area. After a few moments remove some of the solvent with the dropper and drip the solvent onto a tissue or filter paper. When the solvent has evaporated any oil or grease removed by the solvent will show up on the paper as a brown ring.

21 FLASHPOINTFlashpoints give an indication of fire risk and are defined as, ‘the lowest temperature at which solvent vapour from the product under test in a closed cup gives rise to an air/vapour mixture capable of being ignited by an external source of ignition’.Flashpoint determination of paints or solvents may be carried out in accordance with BS 3900 part A9 using a closed cup of the Abel type.Procedure:

1. Fix an Abel cup containing the substance for the assessment into a water bath.2. Apply a heat source to the water bath and monitor the temperature of the substance in the Abel

cup.3. Activate the source of ignition every 1/2C rise in temperature.4. The flashpoint temperature is identified when a blue(Note 1) flame flashes over the substance being

assessed.

Note 1 If an orange flame is observed, the temperature is too high and overheating has occurred. The material under test should be cooled or replaced and the test restarted,

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22 VISCOSITY

Viscosity is a measure of a fluids resistance to flow (Note 1).A fluid with a high viscosity has a high resistance to flow and therefore has a thick consistency; the frictional forces between the molecules are greater. The opposite is true with a low viscosity fluid.Temperature effects viscosity, therefore any comparative tests must be carried out at a specific temperature eg 20±0.5ºC.The S.I. unit for dynamic viscosity is the Pascal second (PaS) which is equivalent to Newton-second per square metre (N.s/m2). The old c.g.s unit, the poise, is still commonly used.The viscosity of water is approximately 1 centi-poise.Another c.g.s. unit which may be encountered relating to kinematic viscosity is the stoke. A fluid having a viscosity of one poise and a density of 1 g/cm3 has a viscosity/density ratio of one stoke.The instruments used for measuring viscosity are known as viscometers of which there are many types. Viscometers in paint laboratories are usually of the rotational type and include the Krebs-stormer viscometer, the cone and plate viscometer and the rotathinner.Note 1 The study of the flow of liquids is known as rheology.

A simple method for measuring the viscosity of free flowing paints is by using flow cup, types include: ISO, Ford and Zahn flow cups.

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Rotathinner

Krebs stormer

Cone and plate

Paint

Flow cup

Broken paint stream


Procedure for measuring viscosity using a Ford flow cup No.4:1. Bring the temperature of the paint to within 20±0.5ºC.2. Level the apparatus, and then with the end of one finger over the orifice of the cup, rapidly fill it

with paint.3. Allow a moment for air bubbles to rise, and then draw a flat edge across the top of the cup to

wipe off the paint level with the edges.4. Remove the finger from the orifice and start the stopwatch simultaneously with the

commencement of the paint stream. The watch is stopped when the first distinctive break in the paint stream occurs.

5. The time in seconds is taken as the viscosity.This procedure can be used to determine the quantity of any added thinners. There is no direct relationship between the time value obtained and the percentage of added thinners. A comparison has to be obtained by preparing a number of control samples using different percentages of thinners added to the paint taken from a freshly opened can.A Thixotropic paint needs to be worked to reach the free flowing stage, therefore the viscosity cannot be assessed with a flow cup; a rotation viscometer or another type of viscometer which works the paint must be used.

23 DENSITY

Density is weight per unit volume and is therefore found by the following formula: Density = weight VolumeThe unit for measuring the density of paint is usually grams per cubic centimetre (g/cm3) 1 cm3 of water = 1 millilitre = 1 gram 1000cm3 of water = 1 litre = 1 kilogramThe density of a paint will be high that of water; the density of a solvent will be lower that of water; the density of a curing agent may be higher or lower that of water.

Density CupProcedure for measuring density using a 100cm3 density cup:

1. Weigh the cup to the nearest decigram using a laboratory balance, with a 1000g capacity and a sensitivity of ±0.1g.

2. Remove the cover and fill the paint to within 2.5mm of the brim.3. Carefully replace the cover so that any air and excess paint is expelled through the vent.4. Wipe off surplus paint from the cover and reweigh.5. Determine the weight of the paint by subtraction.6. Divide the weight by 100 if the density in g/cm3 is required.

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100cc

Vent


This procedure can be applied to determine the quantity of any added thinners. The weight of the sample of paint taken cold be compared with control samples which have been prepared by adding different percentages of thinners to the paint taken from a freshly opened can. There is a relationship between the obtained weight and the percentage of added thinners if the pre-mixed density of thinners and density of paint is known.It is also possible using this procedure to determine whether two-pack paints have been mixed in the correct proportions.

Relative densityRelative density or specific gravity is the density of any substance compared to the density of water.

Specific gravity (SG) = density of x density of water

Because density of water is 1 g/cm3 the figure obtained from the SG formula will be the same as that obtained from the density formula, the difference is that the answer for the SG formula will have no units i.e. it is a dimensionless ratio.Example formula

1. What is the density of a paint if 5 litres weighs 7.35kg?

a. Density = weight Volumeb. Density = 7.35 kg 5 litresc. Density = 7.35 x 1000grams 5 x 1000cm3

d. Density = 1.47 g/cm3

2 A two-pack paint is mixed at a ratio of seven parts base to two parts curing agent; the densities are 1.59g/cm3 and 0.78g/cm3 respectively. What is the density of the paint after mixing?

a. 7 parts base 1.59 * 7 = 11.13 b. 2 parts curing agent 0.78 * 2 = 1.56 c. 9 parts combined 11.13 + 1.56 = 12.69 d. Density 12.69 ÷ 9 parts = 1.41g/cm3

note SG would be 1.41

24 WET FILM THICKNESS

The wet film thickness is taken immediately after a coating has been applied so that any deviation from the specified thickness range can be immediately rectified while the paint is still wet, thereby reducing the amount of dried coatings that are outside the specified thickness tolerances. Also any calculations based on volume solids will be meaningless if a lot of solvent has evaporated.

The wet film thickness may be found using a comb gauge or eccentric wheel

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Procedure for measuring w.f.t.(Note 1) using a comb gauge.1. Immediately after application of the paint, the comb gauge should be placed firmly onto

the substrate in such a way that the teeth are normal to the plane of the surface.2. The gauge should then be removed and the teeth examined in order to determine the

shortest one to touch the wet paint. The film thickness should be recorded as lying between the last touching tooth and the first non-touching tooth as shown on the tooth calibrations marked on the gauge.

3. At least two further readings should be taken in different places in order to obtain representative results over the full coated area.

Note 1 The w.f.t. is sometimes recorded as the average between the last touching tooth and the first non- touching tooth.

The wet film thickness may be found by calculation:

w.f.t. = volume area w.f.t. = 100 x d.f.t. v.s. (%)

25 DRY FILM THICKNESS

There are four methods of determining the dry film thickness of a paint: Non-destructive test gauges Destructive test gauges Test panels Calculation

25.1 NON-DESTRUCTIVE TEST GAUGES

Measuring the d.f.t. directly with a non-destructive test gauge is the most widely used method; there are a variety of gauges available with various scale ranges:

Magnetic film thickness (banana) gauge Pull-off gauge or Tinsley pencil

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COMB GAUGESubstrate

w.f.t

Scale in μm51102152203254

ECCENTRIC WHEEL


Magnetic horseshoe gauge Eddy current/electromagnetic gauge

Magnetic film thickness (banana) gaugeThe banana gauge, as it’s most widely referred to, may only be used for measuring the thickness of non-ferromagnetic coatings applied over ferromagnetic substrates. Prior to use, the gauge must be calibrated.

Calibration procedure:a. Choose a magnetically insulated shim of known thickness, close to the thickness of the paint you

expect to find, eg don’t choose a 25μm shim to calibrate if you expect the coating thickness to be in excess of 300μm; this will reduce the accuracy.

b. Place the shim on the same substrate surface finish as the surface finish on which the paint to be measured is attached, eg, if the paint is on a blasted surface, calibrate the gauge on an uncoated blasted surface.

c. Place the magnet onto the shim and press firmly on the instrument, wind the scale wheel forwards (away from yourself) until the magnet is definitely attached to the shim/substrate.

d. Gradually wind the wheel backwards slowly until the magnet detaches itself. At this point, move the cursor on the instrument to the thickness of the shim as shown on the scale wheel. With some instruments the scale itself must be moved to line up with a fixed cursor. When using the latter type of instrument, rotate the wheel to zero to locate the position of the scale adjustor.

The instrument is now calibrated and may be used to measure the d.f.t. of any non-magnetic paint films to within a claimed accuracy of ±5% in some cases.

Pull-off gaugeThis type of gauge may only be used for measuring the thickness of non-ferromagnetic coatings applied over ferromagnetic substrates. They are not very accurate compared to other non-destructive test gauges.

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Ferromagnetic Substrate

Paint

Magnet

Scale wheelCursor

Tinsley Pencil

Scale

Magnet


The pull-off gauge or Tinsley pencil as it’s most widely referred to, consists of a magnet at the tip of the instrument, which attaches itself to the coated substrate. The gauge is then slowly pulled away from the coated substrate at normal incidence until the magnet detaches itself; at this point the indicator on the body of the gauge is read (you have to be quick because the magnet and indicator are spring loaded!). Calibration is required before use.

Magnetic horseshoe gaugeThe magnetic horseshoe type gauge works be measuring the change in magnetic flux between the two poles of a magnet, the change in magnetic flux depends on the coating thickness. The accuracy of these instruments is claimed to be ± 10% and as with the other magnetic gauges, may only be used for measuring the thickness of non-ferromagnetic coatings applied over ferromagnetic substrates.

Eddy current/electromagnetic gaugesThe most accurate of the non-destructive gauges for measuring d.f.t. are the eddy current and electromagnetic gauges, of which there are many types. If calibrated correctly, accuracy is likely to be within ±5%.Eddy current gauges are used on non-ferromagnetic conductive substrates; electromagnetic gauges are used on ferromagnetic substrates such as steel. Many eddy current/electromagnetic gauges also have statistical capabilities and some will download and upload information from computers.

25.2 DESTRUCTIVE TEST GAUGES

Destructive test gauges cut into the paint film and should therefore only be used where necessary due to the cost of repairing the damaged coating.They are sometimes used on paint films containing M.I.O. pigment; M.I.O. is ferromagnetic and therefore non-destructive test gauges, which rely on a non-magnetic coating, cannot be used.The paint inspection gauge (P.I.G.) is one such type of destructive test gauge. A small vee shaped channel is cut into the coating at a fixed angle governed by a cutter fixed into the gauge. The width of the channel is then measured on a graticule scale by means of a microscope, which is also built into the instrument.Other destructive thickness gauges are the Saberg thickness drill or Erichsen thickness drill, which work on a similar principle to the paint inspection gauge.25.3 TEST PANELS

Test panels, eg metal plates of a known thickness, may be used to measure the d.f.t. indirectly, by coating them in the same way as the work being carried out and measuring the d.f.t. with a micrometer.

25.4 CALCULATION The d.f.t. may be assessed indirectly by measuring the w.f.t. of the paint and providing the volume solids (v.s.%) content of the paint is known, calculating the d.f.t. as follows:

d.f.t. = v.s. x w.f.t. 100

example: What would be the d.f.t. if 15 litres of paint with a volume solids content of 44% is used to cover an area of 12m x 7m.

to find d.f.t.a. d.f.t = v.s.%

w.f.t. 100b. d.f.t = v.s.% x w.f.t.

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100c. d.f.t. = 44 x ? 100

to find w.f.t.:d. w.f.t. = volume w.f.t. is not given directly in the question, therefore must be found by calculation areae. w.f.t. = 15 litres 12m x 7 mf. w.f.t. = 15 x 1000cm 3 convert all existing units to common units i.e. cm. 1200cm x 700cmg. w.f.t. = 15cm 840h. w.f.t. = 15 x 10,000μm Convert to um(10,000um = 1cm) 840i. w.f.t. = 179μm

return to d.f.t. formula:j. d.f.t. = 44 x 179μm 100k. d.f.t. = 79μm

26 ADHESION

Adhesion failures more often occur between uncoated substrate and the primer due to inadequate wetting of the substrate which may be a result of insufficient surface preparation, insufficient dust removal after surface preparation or contamination.All paints within a system should have compatibility between coats and with the substrate. It is advisable to obtain all the components for a paint system from one manufacturer, otherwise it may not be possible to guarantee the system, when compatibility is lacking it is often the adhesion that suffers.

ADHESION / COHESION

26.1 VEE CUT TEST

With a sharp knife, cut a vee using approximately 12mm cuts forming a 30˚ angle, through the paint film and down to the substrate. Insert the tip of the knife blade under the tip of the vee and attempt to lever the paint away from the substrate. If the integrity of the coating is sound it should not peel cleanly from the surface.

26.2 CROSS CUT TEST (CROSS HATCH TEST)

Using a sharp knife or multi-blade cutter, cut 6 lines vertically and horizontally, 2.0mm apart, to produce 25 square. Cover the area with adhesive tape and snatch off; the amount of segments remaining may on the tape be multiplied by four (4) and then given as a percentage value, or a value given based on a scale in accordance with the applicable specification.

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SUBSTRATE

Paint system

Cohesive failure

Adhesive failure between paint films

Adhesive failure between primer and substrate


The tapes degree of stickiness will be relevant to this test and the number and size of the squares may vary, therefore always consult the relevant specification for precise instructions.

26.3 X-CUT TAPE TEST

A sharp knife or similar is used to make an X shaped cut with the smaller angle between 30˚ and 45˚. The cuts must be made down to the substrate in a single action and are approximately 40mm in length. A piece of specified pressure sensitive tape approximately 75mm long and 25mm wide is place over the cut and pressed down in the central area first using a finger. An eraser on the end of a pencil is then used to firmly rub the tape so full adhesion is achieved. Within 1 to 2 minutes the tape is pulled off rapidly at an angle as close to 180˚ as possible. The X-cut area is then examined and the adhesion rated using a scale from 5A = no peeling or removal through to 0A = removal beyond the area of the X.

26.4 DOLLY TEST

A more technical adhesion test, the pull-off adhesion test or dolly test, may show:1. Adhesive failure between primer and substrate (most likely)2. Adhesive failure between paint films3. Cohesive failure within an individual paint film.

PULL OFF DOLLY TEST

Procedure for carrying out pull-off adhesion test

1. Clean and degrease the surface to be tested and the dolly contact surface.2. Roughen both surfaces with fine/medium grade emery cloth.3. Mix regular araldite (Note1) and stick dolly to the surface, leave for 24hrs at 25˚C.4. Cut paint around the dolly down to the substrate using special cutter.5. Attach pull-off instrument and apply full force.6. Take a reading from position of cursor when dolly detaches itself. Values will be typically

obtained in either MPa, N/mm2 or p.s.i.

A minimum pull-off value for the paint type used should ideally be specified in the specification(s) for the work being carried out. In absence of such criteria, a minimum pull-off value should be obtained from the paint manufacturer who should also state categorically whether or not all values less than the minimum pull-off value are deemed a failure.

Note 1 Alternative adhesives are possible, see test procedure sheets

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Dolly

Substrate

Paint film

Dolly puller

Load indicator

Load adjustment


26.5 HYDRAULIC ADHESION TEST

This test uses a similar principle to the dolly tester, but usually gives more accurate test results. The dollies used are reusable and contain a hole down their centre through which a hydraulically operated rod applies force directly to the coated surface in order to pull the dolly away from the surface. The opposing force is supplied by the end of the adhesion tester, which grips the top of the dolly.

27 CATHODIC DISBONDMENT TEST

This test may be performed on a sample cut from the coated structure or coated samples that simulate the coating applied to a structure which is cathodically protected.The test will indicate whether the coating system is susceptible to disbondment if hydrogen gas bubbles are given off from the surface of the substrate – which is likely to be the case in service if the substrate is excessively cathodic, i.e. an excessive amount of cathodic protection to a coated surface can lead to disbondment of the coating.Cathodic disbondment is a significant problem when coating defects are present due to a stripping action caused by the hydrogen bubbles and is especially prominent when the impressed current is way in excess of the corrosion current; this condition is purposely produced for the cathodic disbondment test.The test incorporates a coated test panel (or sample taken from the coated structure) with a hole drilled into the coating that simulates the coating defect. Surrounding the hole a plastic tube is glued down and filled with a specified electrolyte, e.g., a 3% w/v sodium chloride solution. Wires from a battery or transformer are attached to the test panel and to an inner electrode, e.g., platinum rod, set into the lid of the plastic tube and making contact with the electrolyte. A current is then impressed to make the test panel cathodic. The potential required will be specified - 1500mV is typical.The coating is assessed after a given period of time, e.g., a few weeks, for the amount of stripping which has occurred from the boundary of the hole.

CATHODIC DISBONDMENT TEST

28 HOLIDAY DETECTION

Holiday detection or pinhole detection is an operation that detects any holes/holidays in a coating or wrapping. The instrument used for this is known as a holiday detector or pinhole detector. Substantial lack of thickness and inclusions in a coating may also be detected in some cases.Visual inspection in addition to holiday detection is still a very important part of inspection.There are various types of holiday detector, some used for thin paint coatings, e.g., the wet sponge type, whilst others may be used for coatings over 25mm thick, e.g., high frequency spark testers. For coatings ranging from approximately 0.5mm to 4mm thick, AC, DCC or pulsed DC holiday detectors, usually powered by a 6volt battery would normally be used.Note Holiday detection must not be carried out on wet surfaces or in the rain.

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Sodium chloride solution

D.C. impressed current

araldite

6mm hole drilled into substrate

Paint system

Plastic ring


28.1 HIGH VOLTAGE HOLIDAY DETECTORS

Voltage selectionPrior to carrying out holiday detection the correct voltage must be selected, because too high a voltage may indicate the presence of holidays that do not exist. Really excessive voltages may even burn a hole in the coating. Not enough voltage can result in holidays not being detected.The voltmeters or voltage settings on holiday detectors should be checked (Note 1) for accuracy by using a method recommended by the holiday detector manufacturer. This may involve using a calibrated volt/multi-meter or proprietary calibration voltmeter supplied by the detector manufacturer.When relatively thin coatings are being tested, e.g., fusion bonded epoxy coatings, it is usually necessary to have a fine scale on the machine, e.g., 0 to 5kV for accurate voltage selection. For thicker coatings 0 to 20kV is normal.Correct holiday detection voltage is governed by the thickness and dielectric strength of the coating. The method to use for selecting voltage should be specified for each type of coating.The correct voltage is ideally determined by detecting the presence of a known pinhole, which has been induced diagonally through the coating to bare metal. However the voltage is normally selected by measuring the coating/wrapping thickness and applying a formula,(Note2) e.g., 125v per 25μm of thickness (same as 5kV per mm), or following other specification requirements.OperationWhen operating a holiday detector on a coated structure, an earth wire from the main unit is either clipped to the structure or trailed along the ground. If the earth lead is to be trailed along the ground, the structure must be earthed, usually via a crocodile clip to a wire with a metal spike attached, which is hammered into the ground.The electrodes (brushes) used, which are attached to the end of an insulated hand stick, are normally for the wire brush type, although carbon impregnated neoprene brushes also exist, but are not as effective. Spring wrap around coils are commonly used on pipes.The maximum travel speed for brushes or coils may be quoted in the specifications, e.g., 300mm/sec.When the brush or coil comes into contact with a holiday, a spark will jump across the gap, which completes the circuit. One or more of the following indications will warn the operator of its presence.

a. The kV dial will drop.b. An alarm will sound.c. A light will come on.d.

When a holiday is detected it should be marked / circled with a waterproof marker, but the marking should be sufficient distance from the holiday so as not to interfere with the adhesion of the repair.

28.2 WET SPONGE PINHOLE DETECTORS

Only low voltages are required for these instruments, because water, sometimes containing a wetting agent, such as washing up liquid, is used as an electrolyte to conduct the current from an electrode (wet sponge) through a pinhole to the conductive substrate.Water is used to wet a sponge that is connected to the positive terminal on the test instrument. When the sponge passes over a pinhole, the water is drawn into it, which allows the d.c. current to pass through to the substrate and back along the return wire to complete the circuit. Some wet sponge pinhole detectors have a variable voltage setting between 9V and 90V, whereas others only have a single setting e.g. 9V.There is no hard and fast rule for which voltage to use with these instruments, but it is generally accepted that up to 300μm the 9V setting is adequate and up to 500μm would require 90V setting. The specification or written instruction should state the voltage to be used.

Note 1 Holiday detectors should be checked throughout the working day to ensure correct set up.Note 2 It is preferable to ensure the coated structure is properly earthed by testing for the presence of a known pinhole. This may not be permitted due to the repair, which will have to be made on the pinhole.

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29 WEATHER CONDITIONS

The coating specification should always state the weather conditions in which a coating can or cannot be applied. A typical painting specification extract is as follows:‘it is not permissible to apply paints when the following conditions apply.

During rain, snow or high winds. When the air or metal temperature is not at least 3˚C above the dew point temperature. When the air or metal temperature is below 5˚C. When the relative humidity is above 90%.’

29.1 RELATIVE HUMIDITY (R.H.%) & DEW POINT

DefinitionsRelative humidity is the amount of water vapour in the air expressed as a percentage, compared to the amount of water vapour, which could be in the air at the same temperature.The higher the air temperature the greater the amount of water vapour, which can be held in it (Note 1).The dew point is the temperature at which water vapour in the atmosphere would form condensation. Therefore, if the temperature dropped to the dew point temperature the relative humidity would rise to 100% and condensation would be formed on any objects at or below that temperature.

Measuring R.H.% and dew pointBoth relative humidity and dew point are measured using a hygrometer of which there are many types.1.Aspirated hygrometers

a. The screen hygrometer and Masons hygrometer are static types, which rely on a natural airflow over a wet wick.

b. Assman and psychrodyne hygrometers are also static types, which work by a fan driven air supply over a wet wick.

c. Whirling hygrometer is a portable and dynamic type, which operates by physically moving a wet wick through the air.

2. Dial hygrometers come in two main forms: hair and paper. Hair hygrometers operate by expansion and contraction of hair, usually human (treated) and are extremely accurate and fast in operation. Pare hygrometers also work on absorption, but this time on the absorption properties of paper.

3. Digital hygrometers are split into two categories: (1)RH meters which give digital readouts of RH and DP only, (2) thermo-hygrometers, which give digital readout of RH, DP and ambient dry bulb temperatures.

The whirling hygrometer, or psychomotor is the most common type used by coating inspectors, consisting of two mercury-in-glass(Note2) thermometers set side by side in a frame, which is provided with a handle and spindle, so the frame and thermometers can be rotated quickly about a horizontal axis. The bulb of one of the thermometers, called the wet bulb thermometer, is covered with a closely fitted cylindrical cotton wick, the end of which dips into distilled water or clean rainwater contained in a small cylinder attached to the end of the frame.The frame is rotated by hand as fast as possible for at least 90 seconds, or as otherwise specified, so the bulbs pass through the air at least 4 ms-1. this causes the water to evaporate from the wet bulb. The wet bulb cools down to a constant wet bulb temperature due to the evaporation rate of water from the wet wick. Always read the wet bulb temperature before the dry bulb temperature (Note 3) immediately after rotation.Repeat the operation until consecutive readings of each bulb temperature agree to within 0.2˚C.Note 1 The capacity of air to hold water doubles every 11˚c rise in temperature 2 The transport of mercury by air is not permitted, therefore coloured alcohol in glass thermometers may be specified for work, which involves equipment being transported by air. 3 The dry bulb temperature is the air temperature with a wind chill factor

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If it is 100% relative humidity the wet bulb will be the same as the dry bulb, because no evaporation can occur, i.e. the air is saturated. If the wet and dry bulb temperatures are the same, the current temperature is the dew point.

The relative humidity and dew point cannot be read directly from the apparatus; hygrometric tables or special slide rules must be used. Hygrometric tables are more accurate in the 90% RH region and above.

29.2 METAL TEMPERATURE

The metal temperature may be measured with a magnetic temperature gauge, sometimes known as a limpet gauge or with an electrical contact thermometer.

30 HEALTH & SAFETY

30.1 COSHH Regulations 1994 - Scope.The control of Substances Hazardous to Health (COSHH) Regulations 1994 (SI No. 3246) define a substance hazardous to health as:

a. a substance listed in Part 1 of the approved list as dangerous to supply within the meaning of Chemicals (Hazard Information and Packaging) and for which an indication of danger specificed for the substance in Part V of that list is very toxic, toxic, harmful corrosive or irritant.

b. one which has a maximum exposure limit (MEL) in Schedule 1 of COSHH or if the H & S Commission has approved an occupational exposure standard ((OES).

c. a biological agent.d. dust in air – when substantial.e. a substance comparable with the above.

The COSHH regulations are not applicable to the control of lead, asbestos, radioactivity, explosive or flammable properties of materials, high or low temperatures, high pressures, medical treatment or below ground working (mining). Other Regulations deal with these.

Responsibilities.The exposure of an employee to substances hazardous to health is under the control of the employer. A training organisation is responsible for exposure by trainees.Employers must prevent exposure to substances hazardous to helsth or control exposure when total prevention is not reasonably practicable. Personal protective equipment, e.g. masks, are a second choice for control.Prior to work commencing, employers must always carry out a risk assessment for all substances hazardous to health to which employees may be exposed.Employees have a duty to report any problems in exposure control procedures or any defects found in protective equipment.Employers must keep records of examinations/monitoring tests carried out. These are kept for 5 years; 40 years for identifiable employees.

30.2 Occupational Exposure Limits (EH40)The Guidance Note EH40 entitled Occupational Exposure Limits, is a document published by the Health and Safety Executive and updated every year, which gives occupational exposure limits for substances hazardous to health.An organic solvent, which is a substance hazardous to health, has its own occupational exposure limit as given in EH40.The toxicity value of a solvent is expressed in parts per million (ppm), e.g. the occupational exposure limit for xylene is 100 ppm, this means to say that if the air contained xylene(Note 1) exceeding 100 ppm the air would be considered to be a significant hazard to health.

Note 1 The occupational exposure limit for xylene is an occupational exposure standard (OES), therefore the OES is 100ppm.

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There are two types of occupational exposure limit:a. maximum exposure limit (MEL): ‘is the maximum exposure limit for that substance set out in

Schedule 1 in relation to the reference period specified (in COSHH) when calculated by a method approved by the Health & Safety Commission.’

b. Occupational exposure standard (OES)(Note 1) ‘the standard approved by the Health & Safety Commission for that substance in relation to the specified reference period when calculated by a method approved by the Health & safety Commission.’

When a MEL is specified, exposures must be kept as low as reasonably practicable, but always below the specified value.An OES should not be exceeded, but an exposure over the limit is acceptable providing that the reason for exceeding the OES has been identified and measures are taken to reduce the exposure below the OES as soon as reasonably practicable.Examples of solvents with their corresponding long term exposure limits (OES’s unless otherwise specified) can be seen in the following table.

Solvent Examples with Corresponding OEL’s

Group Name OEL (ppm)Alcohols Methanol

Ethanol2001000

Ethers Ethyl etherIsopropyl ether

400250

Esters Methyl acetateEthyl acetateIsobutyl acetate

200400150

Ketones AcetoneM.E.K.M.I.B.K.

75020050

Hydrocarbons(Aromatic)

XyleneTolueneBenzene

100505

Hydrocarbons(Aliphatic)

n-OctaneHexaneWhite spirit

300500100

Chlorinated hydrocarbons

1,1,1-TrichloroethaneTrichloroethyleneCarbon tetrachlorideMethyl chloride

350ab

100ac

250

Miscellaneous WaterNitromethaneNitrobenzene

N/a1001

aMELbMaximum short term exposure limit: 450ppmcMaximum short term exposure limit: 150ppm

Note 1 Long term exposure limits are averaged over an 8 hour reference period. Short term exposure limits are taken over a 15 minute reference period.

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30.3 Volatile organic compoundsVolatile Organic Compounds (VOC’s)(Note 1) are toxic and harmful to the environment. It is estimated that in 1992 in the UK alone, some 1.8 million tons of VOC’s were released into the atmosphere – 35% to 50% which came from paints. As an example the weight volume ratio, each litre of car paint contains 0.5kg (1.25lb) of VOC’s. Each gallon (4.55lts) of industrial coating can contain 4-5lb (1.8 – 2.3kg) of VOC’s.The European Community directives are demanding a reduction of 30% VOC emissions by 1999, with further reductions thereafter. The UK Environmental Protection Act of 1992 goes even further, requiring a reduction of 38% of VOC by 1998. COSHH Regulations also require paint manufacturers to screen all raw material used in the manufacture of their product and eliminate where possible, all materials which may be dangerous to manufacturing operatives and to applicators.The alternatives to standard paints containing organic solvents are solvent free paints (100%VS), high volume solid paints, i.e. over 65% V.S..Most paint manufacturers have chosen their particular product path, some have opted for acrylics and vinyls, some for new formulations of water borne epoxies and some for 100%V.S.. Each of the systems have their advantages and disadvantages, e.g. 100% V.S. urethanes have no VOC’s: they are mainly fast curing; highly resistant to chemical attack; chalking and natural erosion is virtually nil, but the activator chemicals are extremely toxic.High volume solid paints still contain VOC’s and therefore their future use is likely to be restricted.Water borne coatings are environmentally friendly and biodegradable, therefore extra costs are not incurred in disposing of containers and sludges etc, but application areas are significantly reduced because of the slow evaporation rate of the solvent water. Water borne epoxies(Note 2) have been in use for some time now, but when used in high humidity environments their successful application and attainment of intended properties is difficult to achieve.Powder coatings can be applied as thin as 25μm electrostatically with a utilisation yield of 98%. The disadvantage is that costly heat is required for the reaction. The component needs to be heated to a minimum 70ºc (over 200ºC in some cases) to melt the powder in order to form a film and for the reaction to take place. Powders can be formulated to melt at much lower temperatures, but this would create manufacturing problems and storage stability problems.

30.4 Health & Safety data sheetThe information typically present on a health & safety data sheet is as follows:

1. Date of issue.2. Product name/reference and manufacturer.3. Intended use.4. Health hazards:

a. OEL (8hrs & 15mins)b. Respiratory; skin, eye, long term effects

5. Flammability – fore prevention, fire fighting.a. Flash pointb. LEL and UELc. RAQ (to 10% of LEL), e.g. 100m3 of air per litre of paint applied

6. Requirements when handling – barrier creams, masks etc.7. First aid procedure.8. Storage.9. Spillage.10. Environmental.11. Additional information.

Note 1 Depending on the context of the sentence, VOC can mean volatile organic compounds or volatile organic contentNote 2 Water borne epoxies are often referred to as new generation or third generation epoxies

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31 FLAWS ON THE SUBSTRATE

There are many faults which may exist on the surface of the material to be coated. The potential consequences of coating over these faults are (1) premature failure of the coating system and (2) failure of the component.The coating/wrapping inspector is normally expected to evaluate whether sharp contours such as edges are acceptable to coat/wrap, however, it is rarely ever a coating/wrapping inspectors duty to determine what remedial action, if any, needs to be applied to inherent material defects such as laminations or cracks.It is important for the coating/wrapping inspector to be aware that flaws (Note 1) in the material may still exist after inspection and acceptance by other QC personnel. Flaws may also have been induced by secondary processing, e.g. grinding, or may have been induced in service, e.g. fatigue cracking.Substrate faults may only reveal themselves to visual inspection after surface preparation, it is at this stage the inspector should be vigilant.When a surface flaw is revealed, the coating/wrapping inspector should not try to evaluate its type and significance and should not allow the contractor to remove the fault before it has been evaluated by somebody qualified and authorised to do so.(Note 2)

It should be made clear to coating/wrapping inspectors from the outset of work what action they should take if surface breaking defects are found in the material to be coated, e.g. report immediately to the senior inspector or client before carrying out further work on the affected item.The most common defect on the surface of steel that the coating/wrapping inspector is likely to encounter, especially after abrasive blasting has been carried out, is the surface lamination or sliver. Other terms are used to describe this flaw but most of them used are incorrect, when compared to terms used in national and international standards.Surface laminations are not necessarily shallow flaws, they extend deeply into the material. Disc grinding is usually used to remove them and in the case of critical components such as pressure vessels, is followed up with MPI or DPI to confirm removal. UT testing would be usedto determine whether the maximum wall thickness reduction has not been exceeded.Any cracks found on the materials surface may result in complete rejection of the component, or permission for a localised repair using welding may be granted, providing the material tolerates this type of repair.Flaws in metals may be divided into three categories:

a. Primary processing flaws.b. Secondary processing flaws.c. In-service induced flaws.

To give an idea of the scope and complexity of the subject as a whole, the following text is provided. It is not necessary for the coating/wrapping inspector or Senior inspector to know the detail.

Service induced and secondary processing cracksService induced cracks are attributable to some external influence during service, such as vibration or cyclic thermal stress.There are many ways to categorise or term cracks which have occurred in service or during secondary processing. The following list identifies the main types:

a. heat treatment cracks.b. Grinding cracks.c. Hydrogen cracking.d. Brittle fracture.e. Ductile fracture.f. Fatigue fracture.g. Stress corrosion cracking.

Note 1 Terms such as defects, flaws, discontinuities or imperfections may be used to describe faults on the subtrateNote 2 Inspectors are sometimes used to carry out dual inspection roles, e.g. welding and painting/coating . in this situation the inspector

used should be qualified for both activities. These dual approved inspectors are often authorised to evaluate substrate faults ad to request remedial action.

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Heat treatment cracksThere are three common causes for cracking during heat treatment process:

a. During heating – cracking due to thermal shock.b. During quenching – cracking due to rapid contraction.c. After a hardening process – when the component is not tempered soon enough.

Grinding cracksGrinding cracks usually occur in groups at right angles to the direction of grinding or as a network of cracks when rotary grinding wheels are used. They are commonly caused by using the incorrect grade of grinding wheel, by applying to much force or by loss of grinding fluid (if used) and only occur in materials which can be hardened.

Hydrogen crackingHydrogen cracking may not only occur during welding, but may occur in service or due to secondary processing. A sufficient quantity of hydrogen has to be available to enter the material or the inherent hydrogen content has to be high enough. The material must also have a grain structure which is susceptible to cracking.The following list shows common sources of hydrogen which may lead to hydrogen cracks:

a. Chemicals used during etching – etching cracksb. Chemicals used during the plating process – plating cracksc. Acids used during pickling – pickling cracksd. Hydrogen contained within chemicals being transported via pipework or contained within

vessels, e.g. sour gas.Fatigue cracksFatigue cracking is a service failure which occurs under cyclic stress conditions. It normally occurs at a change in section, e.g. groove, radius, step, weld toe, etc. therefore design and workmanship are important to minimise failure by fatigue.There are two main sources or stress cycles:

a. Mechanical stress cycles – caused by vibration or movement.b. Thermal stress cycles – repeated heating and cooling creates repeated expansion and contraction.

All metals are susceptible to fatigue failure. Since design and workmanship play a major part, ferrous based materials have an endurance limit applied to one grade of steel in a specific heat treated condition, operating within specific parameters, below this limit fatigue is unlikely to occur. Other metals will all have the potential to fail by fatigue given the required conditions.Fatigue failures start at a specific point and propagate with each stress cycle at a rate that depends on the applied stress. Fatigue failure is easily identified by beach markings on the fractured face. Final failure can be any other mode of fracture, e.g. brittle or ductile failure.

Stress corrosion crackingThis type of cracking sometimes occurs in materials in a state of tensile stress and in contact with a corrosive medium. The level of stress which can cause cracking may be well below the yield point of the material. Stress corrosion cracks are surface breaking and are usually found at any sharp change in section, notch or crevice, especially in structures which have not been stress relieved.Both ferrous and non-ferrous materials are susceptible to corrosion cracking.

32 CATHODIC PROTECTION (INTRODUCTION)Basic principles and methods.The first line of defence against corrosion on a buried or immersed iron or steel structure is usually the coating. If the coating totally isolates the structure from the environment, which causes corrosion, the structure will not corrode. However, coatings are not totally impermeable( Note 1) and they are also likely toNote 1 All coatings are permeable to water, to a greater or lesser extent.

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contain some defects, therefore corrosion would take place unless a secondary system protected these areas. Cathodic protection prevents the structure corroding at areas where coating defects exist. the coating defects must be of the type which allow an electrical path to exist from the soil/water to the metal surface. Therefore, cathodic protection is usually a back-up to the coating for anti-corrosion purposes, although it should be noted that cathodic protection can also be applied to uncoated structures.Both anodic and cathodic areas would be present on the surface of a structure without cathodic protection. Anodic areas on the structure corrode, current flows from anodic areas through the electrolyte to cathodic areas.When any exposed metal on the structures surface receives current, the area becomes cathodic; this prevents corrosion.Cathodic protection is defined in British Standard BS 7361 : Part 1 : 1991 – Cathodic protection (Code of practice for land and marine applications)as: ‘A means of rendering a metal immune from corrosive attack by causing a direct current to flow from its electrolytic environment into the entire metal surface.’

There are two methods of applying cathodic protection:a. Using sacrificial anodesb. Using impressed current

Both methods achieve cathodic protection by passing small d.c. currents trough the electrolyte from the anodes which are installed close to the metallic structure. The anodes will corrode and are manufactured in materials which provide a long service life and consistency of corrosion characteristics.The natural potential of steel or cast/ductile iron in soil is approximately – 550 millivolts (mV) when measured at ambient temperatures against a standard known as a saturated copper/copper sulphate Note 1 All coatings are permeable to water to greater or lesser extent.reference electrode. Cathodic protection is considered to have achieved to a level where corrosion activity is arrested – when the potential has been shifted in a negative direction by the application of cathodic protection current by 300mV or to a minimum level of –850mV when referred to a saturated copper/copper sulphate reference electrode.Detailed and further information with respect to cathodic protection levels are shown in BS 7361 : Part 1 : section 2.Considerations for protection of coated structuresIt is essential to obtain a sound, holiday free, coating on the structure, because this minimises the current required for protection. Current has to be substantially increased if there are many bare steel areas on the surface of the structure – this is also the case if other metallic items come into contact with the protected structure. Coating damage also increases the chance of electrical interaction (interference) with other buried /immersed metallic structures.On buried structures it is especially important to have coatings that are uniform in thickness and homogeneity so the coating damage or coating deterioration will be more easily detected.It is possible for the cathodic protection to be too great, i.e. the structure can be over negative. This causes excessive amounts of hydrogen gas to be given off from the metal substrate, resulting in coating disbondment, known as cathodic disbondment; the more negative the structure, the more hydrogen gas is evolved.It is not usually an easy task to attain uniform protection over the full surface area of a structure. Non-uniformity in protection tends to be increased in the following situations:

1. high current density needed for protection2. electrolyte resistivity too high3. the anodes are too close to the structure4. non-uniform coating quality

Determination of adequate protectionTo determine whether a structure is receiving the required protection a device known as a half-cell reference electrode is used – this measures the structure-to-electrode half-cell potential. From the readings taken from a voltmeter attached to the reference electrode, the cathodic protection technician or

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engineer can determine whether or not the structure is being adequately protected. There are various types of reference electrode – see unit CP9.

33 QUALITY ASSURANCEAim of quality assurance.The aim of quality assurance is to improve quality whilst keeping costa to an acceptable level.The object of a system used to implement quality assurance, i.e. a quality system, is to prevent the occurrence of problems which result in remedial action. If problems do occur the objective is to determine and rectify the root causes, thereby reducing faults and wastage in the future. This will in turn, improve quality and reduce costs.The emphasis ic on prevention rather than detection and cure.

Benefits of adopting quality assurance.A properly implemented and managed quality system should:

a. help to ensure that the company focuses on market needs and requirements.b. Make the company more competitive in the market place due to an increased customer

confidence in the company’s output, i.e. a product or service that a customer wants – this includes timing.

c. Lead to a reduction of costs due to a reduced number of faults and wastage.d. Give a measure of performance, which will enable any areas for improvement to be identified.e. Induce a more organised way of thinking which makes management more organised and

effective.f. Provide motivation: motivated employees provide a better working environment in addition to the

product or service output benefits.

What is quality assurance.The definition for quality assurance given in ISO 8402 : 1986 (BS4778 : Part 1) entitled Quality vocabulary:‘All those planned or systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality.’The quality of a product or service is attained only by working in a controlled manner, following formalised procedures, which are designed to eliminate the occurrence of problems.Quality assurance provides the objective evidence needed to give maximum confidence for quality.Quality assurance may be considered as a management tool when used within an organisation.. A supplier that implements and maintains a system for assuring quality, is providing maximum confidence to a purchaser, or potential purchaser, that the supplied product or service attains, or is going to attain, its fitness for purpose.Different people have different concepts for what is meant by a quality product or service, therefore it is very important to be aware of the customers requirements and/or expectations.Contract documents or purchasing specifications should clearly define a company’s requirements for a product or service. The quality of the product or service is deemed to have been achieved when the exact requirements have been met completely and consistently – assuming correct specification!

Scope of quality assuranceQuality assurance should encompass all parts of an organisation and all phases of an activity, i.e. planning, design, production, maintenance, administration etc. in order to give a purchaser, or potential purchaser, maximum confidence that the clients expectations for quality have been met. Collaboration with suppliers and purchasers should also be part of an organisations quality system.

QA, QC and inspection compared.Quality assurance is not inspection. Inspection is one of the important elements within a system for quality assurance. inspection requires continuing evaluation in the same way as other elements, e.g. planning, design/specifications, production etc..

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Inspection is defined in BS 4778 : Part 1 as ‘activities such as measuring, examining, testing, gauging one or more characteristics of a product or service and comparing these with specified requirements to determine conformity.’Inspection is also defined in EN 45020 : 1993 : Glossary of terms for standardisation and related activities: ‘Evaluation for conformity by measuring, observing, testing or gauging the relevant characteristics.’ Evaluation for conformity is defined in the same standard as ‘’systematic examination of the extent to which a product, process or service fulfils specified requirements’.Quality control is defined in BS 4778 : Part 1 as ‘the operational techniques and activities tat are used to fulfil requirements for quality.’ This definition can be vague, so modifying the term to be more specific is advantageous, e.g. manufacturing quality control.Quality control is involved with the monitoring of a process and eliminating the causes of any deficient output of a process, or any phase during a contract, which has an effect on quality. The information obtained from inspection, as defined above, is used for quality control.Quality control deals with the actual measurement of quality performance which is compared against what is required and action is taken on the difference. Quality control is asking the question, ”is the work/action being performed correctly”?Quality control does not reach all elements which effect quality, e.g. quality control will rarely do anything to correct problems relating to management, traceability, training and staff motivation.Quality assurance applies to all areas which have an effect on quality and asks the question, “has the work/action been performed correctly”? This question can only be asked after information has been obtained from quality control and all other departments/areas which affect quality.

QA standardsBS EN ISO 9000 series – Quality systems.BS 4778 – Quality vocabulary.[EN 28402; ISO 8402]BS EN 30011 – Guidelines for auditing quality systems.

34 NORMATIVE DOCUMENTS

a. Normative document: document that provides rules, guidelines or characteristics for activities or their results.

Note: The term normative document is a generic term that covers such documents as standards, technical specifications, codes of practice and regulations.[ISO Guide 2 & EN 45020]b. Standard: Document, established by consensus and approved by a recognised body, that provides for common and repeated use, rules, guidelines or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given context. [ISO Guide 2 & EN 45020]c. Code of practice: Document that recommends practices or procedures for the design, manufacture, installation, maintenance or utilisation of equipment, structures or products. Note A code of practice may be a standard a part of a standard or independent of a standard. [ISO Guide 2 & EN 45020]d. Specification: The document that prescribes the requirements with which the product or service has to conform. Note: A specification should refer to or include drawings, patterns or other relevant documents and should indicate the means and the criteria where by conformity can be checked. [BS 4778 : Part 1]e. Technical specification: Document that prescribes technical requirements to be fulfilled by a

product, process or service,

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Note: A technical specification should indicate, wherever appropriate, the procedure(s) by means of which it may be determined whether the requirements given are fulfilled.A technical specification may be a standard a part of a standard or independent of a standard. [ISO Guide 2 & EN 45020]

f. Regulation: Document providing legislative rules, that is adopted by an authority. An authority is a body that has legal powers and rights. [ISO Guide 2 & EN 45020]g. Procedure 1: Specified way to perform an activity.

[ISO 8402 & ISO 10005]h. Procedure 2: A written description of all essential parameters and precautions to be observed when applying inspection or a test method to a specific item or quantity of items, following an established standard, code or specification.i. Instruction: Provision that conveys an action to be performed.

[ISO Guide 2 & EN 45020]j. Written instruction: A detailed written description of the inspection(s) or test(s) to be performed. [ICorr REQ Doc]

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4. Pipeline Coatings Notes

Documents

Transcript of 4. Pipeline Coatings Notes