Guide to Optimum Marine Coating Application - Part 1 - Environmental Conditions Testing and...

Guide to Optimum

Marine Coating Application

Part 1

Environmental Conditions

Testing and Monitoring

by Alexandros Michelis

1

Environmental Conditions Testing & Monitoring

2

General

• Environmental conditions are crucial to all stages of

coating process (surface preparation, coating application

and curing).

• Optimal environmental conditions:

o Key to high quality surface preparation.

o Key to high quality coating application.

o Maximize service life and in service performance of

the coating.

• Ensuring optimal environmental conditions should be

continuous throughout the whole coating process.


3

General

• The majority of shipyards and marine construction /

repair facilities carry out most or all construction / repair

work outdoors. Only few have the means to perform

surface preparation and coating application under cover

and under controlled environmental conditions.

• Optimal environmental conditions for the application of a

coating may differ from product to product and relevant

information is provided by the manufacturer.

• Special products exist for application in extreme / severe

environmental conditions.


4

General

• Proper inspection of the coating process should include

testing / monitoring of the environmental conditions.

• Testing / Monitoring of environmental conditions is part of

the job of the coating inspector.

• Environmental conditions should be addressed by the

job specification.


5

Environmental Conditions Affecting Coating

Application

• Substrate temperature

• Ambient conditions:

o Air temperature

o Relative humidity

o Dew point

o Wind

• Contaminants (soluble salts, dust, debris, exhaust

fumes, oil, grease, flame burns, etc)


6

Substrate Temperature

• Substrate: surface to be coated (metal, wood, composite

material, etc)

• Need to follow coating manufacturer’s recommendations

concerning upper and lower limits of substrate

temperature during coating application.

• Relative information should be obtained from coating

technical data sheet or directly from the manufacturer.


7


• Substrate temperature too low → substrate temperature

≤ dew point → condensation of moisture → flash rusting

of blasted steel → poor performance of applied coating /

coating failure.

• Substrate temperature too high → rapid solvent

evaporation → film formation failures and poor wetting of

surface (poor coating flow).


8


Instruments used to measure substrate temperature are:

• Magnetic surface-contact thermometer. Analogue

function. Cheapest and most common type of gauge.

Direct measuring. Need time to stabilize.

• Direct-reading thermocouple / thermistor. Digital

instrument. Direct measuring. Fast reading.

• Infrared thermometer (laser thermometer). Digital

instrument. No need for contact. Fast reading.


9


Remarks:

• Measurements should be made at the actual surface to

be coated, and not to adjacent structures.

• The number of measurements should provide sufficient

temperature mapping of the substrate.

• Need to pay special attention to hotter or colder areas of

the structure, such as areas exposed to direct sunlight.


10

Air Temperature

• Affects directly the coating process.

• Increased air temperature causes acceleration of solvent

evaporation and drying of the coating, which can result in

failures such as poor wetting or film formation defects

(mud cracking, alligatoring).

• Too low air temperature can cause inability of the coating

to dry / cure after application.

• Coating manufacturer’s recommendations concerning

upper and lower limits of air temperature during coating

application and curing must be followed. Relevant

information should be obtained from coating technical

data sheet or directly from the manufacturer.


11

Air Temperature

• Job specifications may also provide limits of air

temperature.

• For example, NATO AEP-611 defines application

temperature to be no less than 5°C, and no greater than

35°C.

1 NATO PUBLICATION AEP-61, EDITION 2, PERFORMANCE REQUIREMENTS FOR UNDERWATER HULL PAINT

SYSTEMS, FEBRUARY 2009.


12

Relative Humidity

• Relative Humidity (RH): measurement of the amount of

moisture in the air compared to saturation level (0-

100%).

• Coating specifications / manufacturers provide upper

and lower limits of RH during coating application,

depending on the coating type and the environment in

which it is applied.

• General rule for most coatings when coating outdoors:

maximum RH = 80-85%.

• According to NATO AEP-591, maximum RH when

coating tanks, voids and vent plenums should be 50%.

1 NATO PUBLICATION AEP-59, EDITION 1, APPLICATION PROCESS FOR OPTIMUM PAINT AND COATING

SYSTEM’S PERFORMANCE, SEPTEMBER 2006


13

Relative Humidity

• Too high RH blocks solvent evaporation and affects

curing. Furthermore, solvent vapors can be entrapped

and cause formation of blisters.

• Coatings exposed to high RH after application often

display coating defects such as blushing (amine

sweating).

• Waterborne coatings, which use water as solvent, are

more likely to be affected by high RH.


14

Dew Point

• Dew Point (DP): temperature below which water vapor in

air condenses into liquid water, leaving dew on a solid

surface.

• Dew will cause rapid rusting of freshly blasted steel

(flash rust).

• Moisture trapped between two coating films can cause

failure (delamination, peeling) due to loss of adhesion.

• High RH indicates that DP is also high and close to the

current air temperature.


15

Dew Point

• Newly blasted surfaces should receive the first protective

coat (primer, self-primed epoxy, etc) as soon as possible,

and before nightfall, especially if surface preparation is

performed outdoors.

• General rule: blast cleaning and coating application

should not take place unless surface temperature is at

least 3°C (5°F) higher than the dew point.


16

DP & RH Measurement

• Instruments used to measure dew point / relative humidity

are analogue or digital psychrometers / hygrometers.

• Operating principle: measurement of the air temperature

(dry-bulb temperature) and of the so-called wet-bulb

temperature. This information is used to calculate dew

point and RH.


17

DP & RH Measurement – Analogue (Sling) Psychrometer

• Instrument enclosing two identical thermometers.

• The bulb of one of the thermometers is covered with a

sock / wick. This bulb is called “wet bulb”, because it is wet

/ saturated in water prior to the measuring process.

• The second bulb is called “dry bulb”.


18

Operation of Sling Psychrometer

Steps (1):

• Saturate the sock / wick of the wet bulb with distilled

water.

• Spin the instrument fast for about 40 seconds, and

then read the wet-bulb temperature. Spinning causes

the evaporation of moisture on the wet-bulb, thus

having a cooling effect.

(source: ABS)


19

Operation of Sling Psychrometer

Steps (2):

• Repeat the spinning process without additional wetting

until the temperature reading of the wet-bulb is stable.

• Record the wet-bulb temperature.

• Record the dry-bulb temperature.

• Calculate the wet-bulb depression (difference between

dry and wet-bulb temperature).

(source: ABS)


20

Determination of DP & RH by Psychometric Tables

• Use of psychrometric table: Enter the table with the dry-bulb

temperature (vertical axis) and the wet-bulb temperature /

depression (horizontal axis), and read the intersection of the

their values. The reading corresponds to the relevant value of

dew point (or relative humidity, depending on the table).


21

Determination of DP & RH by Psychometric Tables

• Remark: DP and RH vary with atmospheric pressure. The

atmospheric pressure is not constant, but changes with

altitude and weather.

• Series of psychrometric tables are provided for different

values of atmospheric pressure. Typically, one should first

measure the atmospheric pressure by using a barometer,

and then refer to the respective psychrometric table.

• The table referring to an atmospheric pressure equivalent to

the average sea-level pressure (101.325 kPa or 1013.25

mbar or 29.92 inches of mercury (inHg) or 760 millimeters of

mercury (mmHg)) may be used with small error.

• Psychrometric charts and calculators use the same principle

with the psychrometric tables.


22

Determination of DP & RH by Psychometric Charts


23

Determination of DP & RH by Psychometric Calculators


24

Control of RH

• By using heat to increase temperature.

• By dehumidification (by circulating air through a

refrigeration unit or desiccants).


25

Wind

• Wind effects must be taken into consideration during all

stages of coating application.

• Wind can have an unfavorable and even detrimental effect

by carrying contaminants (dust, debris, abrasives, salts,

etc) on the substrate before / during / after surface

preparation and coating application. These surface

contaminants may cause cosmetic problems, but most

importantly, may become inclusions and cause coating

defects / failure.

• Wind can cause dry spray during application (coating

defect). It appears like sand / dust on the coating surface.


26

Wind

• Can accelerate solvent evaporation during curing, causing

film formation defects and poor wetting of surface.

• Can cause overspray during coating application (loss of

coating, cosmetic problems, collateral damage).


27

Contaminants – Soluble Salts

• The significance of contamination by soluble salts and their

impact on marine structures has been recognized by the

marine industry for long time.

• The most common salts in marine industry are chloride

compounds (sodium chloride) due to the proximity to

seawater (direct contact, spray carried by the wind, etc).

• It has been reported that a small increase in the chloride

salt content (+1μg/cm2) can lead to a 200% decrease in

the lifetime of an epoxy resin coating1.

• Other salts are sulfurous compounds (generated in

industrial environments) and nitrogenous compounds

(generated in urban environments). 1 A.W. MOMBER AND W.D. GREVERATH, SURFACE PREPARATION STANDARDS FOR STEEL SUBSTRATES

- A CRITICAL REVIEW, JPCL, THE JOURNAL OF PROTECTIVE COATINGS & LININGS, FEBRUARY 2004


28


• Soluble salts form deposits on the substrate, which can

cause coating failure:

o By inducing corrosion under the coating film. Their

chemical reaction with the substrate creates new

compounds, which are electrochemically bound to the

surface and form active corrosion cells.

o By promoting osmotic blistering, which is one of the

most common coating defects in marine environment.

o By causing loss of adhesion (delamination, peeling).

• Soluble salts boost corrosion (galvanic, pitting, crevice,

etc) by increasing the efficiency of the electrolyte (humid

air, dew, water) and the ion concentration.


29


Osmotic blistering: Formation of a hemispherical projection

(blister) by drawing water through the coating, from an area of

low ionic concentration to an area of high ionic concentration.

Schematic osmotic blister formation (source: ABS1)

1 ABS,GUIDANCE NOTES ON THE INSPECTION, MAINTENANCE AND APPLICATION OF MARINE COATING

SYSTEMS, 3RD EDITION, 2007


30

Testing for Soluble Salts

• Proper inspection during the coating process should include

testing for soluble salts.

• Usually, testing for soluble salts takes place after the stage

of surface preparation and prior to coating application.

• Optimally, testing for soluble salts should be performed

before the stage of surface preparation.

• Abrasive blasting or power tool cleaning might not remove

soluble salts effectively or even cause “pinning” / spreading

of the salt compounds on the substrate.

• If soluble salts are detected on the substrate, corrective

measures may be required, depending on the acceptable

level of contamination by the applied standard /

specification.


31


Two methods:

• Chloride testing

o Measures chloride ions concentration.

o Units:

Surface concentration: μg/cm2, mg/m2

Volumetric concentration: μg/cm3 (ppm)

o Sulfates and nitrates concentrations can also be measured.

• Conductivity testing

o Measures conductivity of a sample (ability to conduct

electricity).

o Measures more than just chlorides (total ionic content).

o Units: μS/cm (microsiemens/cm)


32


According to NAVSEA Standard Item 009-321:

• One surface conductivity or chloride reading for every 200

ft2 for the first 1,000 ft2. One determination for every

additional 500 ft2 or less.

• Limits:

1 NAVSEA STANDARD ITEM 009-32 FY 13, 31 JANUARY 2011.

Application Maximum allowable

chloride measurement Maximum allowable

conductivity measurement Immersed 3 μg/cm2 (30 mg/m2) 30 μS/cm

Non-immersed 5 μg/cm2 (50 mg/m2) 70 μS/cm


33


• According to NATO AEP-591, “for immersed applications,

concentration due to soluble salts (total ionic) shall not

exceed 5μg/cm2. For non-immersed applications,

concentration due to soluble salts (total ionic) shall not

exceed 10μg/cm2”.

• According to IMO PSPC2, the water soluble salt limit

(equivalent to NaCl) of dedicated seawater ballast tanks is ≤

50mg/m2 (5μg/cm2) of sodium chloride.

1 NATO PUBLICATION AEP-59 EDITION 1, APPLICATION PROCESS FOR OPTIMUM PAINT AND COATING

SYSTEM’S PERFORMANCE, SEPTEMBER 2006 2 IMO RESOLUTION MSC.215(82), PERFORMANCE STANDARD FOR PROTECTIVE COATINGS FRO

DEDICATED SEAWATER BALLAST TANKS IN ALL TYPES OF SHIPS AND DOUBLE-SIDE SKIN SPACES OF

BULK CARRIERS, ADOPTED ON 8 DECEMBER 2006


34

Testing for Soluble Salts – Sample Collection

• Washing / Swabbing of substrate:

o Most common method.

o Applicable standard: ISO 8502-1:2001, “Preparation

of steel substrates before application of paints and

related products. Tests for the assessment of

surface cleanliness. Field test for soluble iron

corrosion products”.

• Rubber sample holders (proprietary products):

o “Bresle” patch (uses distilled water)

o “Chlor Test” (uses proprietary test solution)


35

Testing for Soluble Salts – Testing Liquid Samples

• Indicator papers

• Kitagawa tubes

• Lab tests

• Conductivity measurement


36

Testing for Soluble Salts – Bresle Method

• Most common and widely accepted method to extract

soluble salts from steel substrates.

• Applicable standard: ISO 8502-6:20061.

• Method approved / implemented by the US NAVY. Also

approved by the Greek Navy.

1 ISO 8502-6:2006, PREPARATION OF STEEL SUBSTRATES BEFORE APPLICATION OF PAINTS AND RELATED

PRODUCTS -- TESTS FOR THE ASSESSMENT OF SURFACE CLEANLINESS -- PART 6: EXTRACTION OF

SOLUBLE CONTAMINANTS FOR ANALYSIS -- THE BRESLE METHOD


37

Testing for Soluble Salts – Chlor Method

• Measures chlorides.

• Applicable standard: ISO 8502-5:19981.

1 ISO 8502-5:1998, PREPARATION OF STEEL SUBSTRATES BEFORE APPLICATION OF PAINTS AND RELATED

PRODUCTS -- TESTS FOR THE ASSESSMENT OF SURFACE CLEANLINESS -- PART 5: MEASUREMENT OF

CHLORIDE ON STEEL SURFACES PREPARED FOR PAINTING (ION DETECTION TUBE METHOD)


38

• Replicates the Bresle process (ISO

8502-6).

• Automated.

• According to manufacturer, 8x faster

compared to the Bresle Patch method.

Total process time: 1 min.

• Equivalent to ISO 8502-9 (the field

method for the conductometric

determination of soluble salts).

• Approved / Implemented by the US Navy1.

Testing for Soluble Salts – Soluble Salt Meter

by HedoN Electronic Developments

(ARP Soluble Salt Meter model RPCT-07-001)

1 NAVSEA STANDARD ITEM 009-32 FY-13


39

Testing for Soluble Salts – Soluble Salt Meter

by HedoN Electronic Developments

(ARP Soluble Salt Meter model RPCT-07-001)


40

Testing for Soluble Salts – SaltSmart

by Innovative Productivity, Inc.

• Developed over a 5 year

program with funding from the

US Navy1.

• One-time-use disposable

sensor. Multiple tests can be

run in parallel.

• According to manufacturer,

sample time: 8 min for strip

development, 15 sec for meter

analysis .

• Equivalent to ISO 8502-9.

1 NAVSEA STANDARD ITEM 009-32 FY-13


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Comparison of methods (source: SaltSmart)


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Removal of Soluble Salts

• Soluble salts should be removed (dissolved) by clean fresh

water washing. Pressure (< 70 MPa) may be used1.

• Most specifications call for a 3000 psi ≈ 20.7 MPa wash

down.

1 According to ISO 12944-4:1998, PAINTS AND VARNISHES. CORROSION PROTECTION OF STEEL

STRUCTURES BY PROTECTIVE PAINT SYSTEMS. TYPES OF SURFACE AND SURFACE PREPARATION.


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• Removal of soluble salts should take place before the

stage of surface preparation by abrasive blasting or hand /

power tool cleaning.

• According to NSTM 6311, “for all types of substrate

materials, before surface preparation to the specified

cleanliness level using any method other than waterjetting

or wet abrasive blasting, the area to be cleaned shall be

washed with low pressure freshwater to remove any

residual soluble salts”. For best efficiency, the freshwater

used should have a maximum conductivity of 200 μS/cm.

1 NAVAL SHIPS’ TECHNICAL MANUAL CHAPTER 631, REVISION 3, PRESERVATION OF SHIPS IN SERVICE –

GENERAL, 1 NOVEMBER 2008


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1 ISO 12944-4:1998, PAINTS AND VARNISHES. CORROSION PROTECTION OF STEEL STRUCTURES BY

PROTECTIVE PAINT SYSTEMS. TYPES OF SURFACE AND SURFACE PREPARATION.


• Repeat water wash and retest until satisfactory levels of salt

contamination are obtained.

• The presence of pitting corrosion on the substrate makes the

removal of soluble salt contamination more difficult and time

consuming.

• Other options (according to ISO 12944-4:19981): steam

cleaning and alkaline cleaning.

Residual contamination in pits (source: ABS)

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