WE4 Fabrication and Application Engineering 3of3

8/10/2019 WE4 Fabrication and Application Engineering 3of3

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(2) Welding cost i tems and calculationWelding labor, welding equipment, and welding consumables are

n ca e n money as e npu or e we ng process, an e amounof money spent per a unit of weld joint length is often sought for the mostgeneral method of calculation of welding costs.

Ordinarily, a simplified butt joint and fillet joint made of flat plates arechosen as the subject of measurement.

Table 4.15 shows welding cost items and examples of calculationformulas.

At the time of calculation in accordance with the calculation formula after deciding the welding method, it is necessary to determine the priceand total weld length in a year for each cost item.

,material is adopted.



Table 4.15 Welding cost items and calculation formulas

Major categories Detail categories

Depreciation costpera on cos or we ng

equipment(yen/m)

epa r cos or equ pmenCost for consumables

Cps = C d+ C r + C c+C e+C wCost for cooling water

Cost for welding consumables

(yen/m)CCM =C el+C wi+ C fl+C ga +C ba Wire cost

ux cos

Gas costos or ac ng ma er a

Labor cost(yen/m) , C LB

Wage +Indirect cost

Welding cost(yen/m)



The total weld length in a year is expressed by the following formula,which is related to the efficienc and ca acit o eratin rate of each set ofwelding equipment and the arc time ratio.

=L Y

where, WL: weld length in a year (m/year)

E f : capacity of joining speed (m/hr man machine)TY: working hours in a year (hr/year)

: capac y opera ng ra eR: arc time ratio (%) And,Fabrication hours per year (hr/year) = TY× P

Ca acit of oinin s eed E is defined as “the len th of a weld ointthat can be welded by a certain welding process on the face and backsides of the joint within a given time by a given number of personnel and a

” ,

of labor productivity in welding or of equipment productivity (the details areto be described later).



Capacity operating rate ( P ) is the ratio of the annual operable hours of,

downtime of the equipment as for repair, maintenance, and spare from thewhole working hours.

measurement of arc time ratio is mainly done on the welders in the actualproduction line and thus equipment productivity is not assessed.

Arc time ratio ( R ) is the one of the welding equipment in the productionline or the one of the welders engaged in work. Therefore, P × R can be

regarded as the genuine arc time ratio through a year. At the time of examining the productivity of large-scale weldinge ui ment, es eciall in com arin it with shielded metal arc weldin , it isbetter to examine P and R separately for grasping the point of issue moreaccurately.

,cost, durable years, residual value, and method of depreciation. In general,durable years are 15 years and the residual value is 10% of the acquisition

.



As to the method of depreciation, there are the fixed amount method andthe fixed ercenta e method and the amount of de reciation can becalculated as follows:

Amount of depreciation by the fixed amount method=

Amount of depreciation by the fixed percentage method

The values taken into the cost calculation formula are determined by theproce ures a ove.

Fig. 4.12 shows examples of welding cost component ratios forvarious welding methods processes . The ratio of labor cost is about80% in shielded metal arc welding, about 50% in double-sided submergedarc weldin , and about 18% in lar e-scale one-sided submer ed arcwelding.

This clearly indicates that the cost of shielded metal arc welding is

of welding progresses, or, in other words, as labor equipment ratioincreases, the ratio of labor cost in the welding costs diminishes.



Welding cost component ratios (%)

Shielded metal arc wedling (flat ×overhead)

Semi-automatic CO arc welding2

u oma c we ng

Double-sided automatic submerged arc welding

-

EB welding

Electroslag welding

Running cost of Cost of welding

Shielded metal arc welding (Vertical, up)

welding machine consumables

Fig. 4.12 Welding cost component ratios for various welding methods (for 25-mm thick plate) [Ref. 8]



3 Wa s of enhancement of roductivit

There are three main approaches to enhancement of welding productivity.

Welding technology as a specific production technology.

Production system and production management technique.③

In practice, the issue is not approached only from one aspect but tackledrom mu p e aspec s n an n egra e manner.

Furthermore, whatever approach is taken, it is necessary to achieveimprovement by the following methods and to enhance productivity finally.

Increase in deposition rate Improvement in arc time ratio and capacity operating rate③ Reduction of volume of work④ Reduction of workers



The contribution of , and ③ above to productivity can beex ressed b the followin formula .

E f = (60 × Ds× P × R) /(7.9 × S )

where, E f : capacity of joining speed (m/hr man machine)

s P : capacity operating rate (%)R : arc time ratio (%)

: cross sec ona area o e groove mm



For enhancement of welding productivity, deposition rate ( Ds ),

capac y opera ng ra e , an arc me ra o are o e ncrease ,and the cross sectional area of the groove ( S ) is to be decreased.

Concrete measures for these matters are described in the following.① In order to increase deposition rate( D

s ), adoption of such anassembly procedure that welding can be done in the flat position shouldbe given the first priority.② Application of high current and high current density is effective. Fig.

1.44 shows the effects of weldin method wire diameter and weldin

current on deposition rate ( Ds).Furthermore, the use of multiple electrodes is also a positive measure.

,peculiar to the equipment, and furthermore, by the status of work load and

production management of the factory. ,arc time ratios for ordinary welded structures are said to be 35 to 45% inshielded metal arc welding and 35 to 50% in semi-automatic MAGwe ng w a w re e au oma ca y, a e g er an n s e e me aarc welding.



However, in the case of on-site welding , arc time ratio goes down to 15

o norma y. ven n wor s op we ng, arc me ra o s sa o e aslow as that of on-site welding in cases where the structure is big thatrequires a relatively long time for preheating and tack welding.

Generally speaking, for improvement of arc time ratio, it is importance toexamine such matters of production management other than arcgenerating time as the preparatory work, conveying work, and latencyidle time .③ With respect to reduction of work volume , it is important to examine

the number and location of oints first of all at the time of desi nin .

During the actual fabrication work, reduction of mistaken work anddefective ratio of weld quality is especially important , and in this

, ,operation, education and training of welders are significant .④

The cross sectional area of a groove (S

), which is related to,diminish the amount of deposited metal. However, the use of a narrowgroove is likely to give an adverse effect on the weld quality causingwe e ec s. ere ore, ec s on on se ec ng a groove s ape s oupremise the securing of weld quality.



⑤ It is very important to appropriately control a groove shape with high

gap and to appropriately control leg length with correct selection ofwelding parameters .

,bigger in proportion to virtually the second power of the plate thickness.

Therefore, in welding of plates thicker than 50 mm , consideration ofadoption of a narrow groove welding method becomes necessary .

As discussed above, there are many ways and approaches to enhancement

of welding productivity.Though this section does not discuss in details, the mechanization andautomatization of weldin ex lained in Cha ter 1 have ro ressed agreat deal . Therefore, in the future, employment of “unmanned operation”technology by positively transplanting the techniques and skills that welders

equipped with more advanced automatization technology is expected tocontribute to enhancement of productivity even more, in addition to an

,

work volume.



4.3 Welding performance control



4.3.1 Material control for identification4.3.2 Protection from moisture4.3.3 Type of weld joint

4.3.4 Voluntary inspections (Self checking) for quality control. . on ro an recor s4.3.6 Welding and related work

. .4.3.8 Preparation for welding4.3.9 Welding conditions4.3.10 Back chipping and back (side) gouging4.3.11 Heat treatment before and after welding

. .4.3.13 Weather and environment considerations



4.3.6 Welding and related work

(1) CuttingCutting is performed by thermal cutting or machining.

,finishing method should be determined beforehand .

When press work is done on a gas cut edge, grinding off ofthe hardened surface beforehand.



(2) Bending/Press work

en ng press wor nc u es en ng, sp nn ng, u g ng,upsetting, and extrusion..

Hot working may be performed at both higher and lower thantransformation temperature.

When cold working is applied, special attention should bepa o preven e occurrence o crac s ue o ar en ng anbrittleness by aging.

,of cold working is generally specified up to about 5 % in

order to prevent the deterioration of notch toughness of formedplate.



Beveling may be performed along the entire length of aweld oint to eliminate rou hness notches or harmfullaminations. Any sharp notch should be removed even if the

depth is within allowable limits.



4.3.7 Welding and deposition sequence

When a structure is made up of structural blocks, the sequence of assemblymust be considered. Basic procedures should be determined in the designphase based on the facilities available.

A sequence of assembly should be determined considering transportation ofthe blocks stabilit and safet durin assembl . Outdoor work or site erection works must take into account wind pressure.

a. From the center outwards , and from bottom to top.b. Larger depositions first (to minimize deformation) .

’Butt joint

. - .d. High restraint joints first .

In the figure of flat panel welding,the basic sequence of weldingshould be ④→①→②→③

Fig. 4.3 Welding sequence for aflat panel



Welding sequence at a cross weld joint



Welding sequence for the closing plate of a hole or an

access o e ue o g res ra n s ress



Welding sequence for -

① ② the butt joint of the flange plate(largest welding deposition)

③ the butt joint of the web plate



Deposition sequence;a. De osition se uence alon the weld oint-- ro ressive weldin back-step welding, symmetrical sequence, intermittent welding .b. Deposition sequence for multi-pass welding--progressive welding, block

, .



. .(1) Cleaning of weld joint1 Moisture oil aint rust mill scale dust etc. on weld ointsshould be removed before welding to prevent weld defects such

as pits, blowholes, or cracks.2) A thin coating of shop primer to prevent rust is generallyallowed. A wire brush, paint solvent, gas flame, or grinder may

.3) When galvanized plate is welded, removal of zinc isrecommended for weld ualit and health.



(3) Tack welding

Tack welds should be strong enough to hold structuralmembers together and to maintain the proper groove.

Tack welds which will not be removed should be donecare u y an e re a e n qua y.

may be melted down during welding, use of a low hydrogentype electrode or MAG welding is necessary.

Tack welding of high strength steel should be done with a low.

-

prevent hardening of the HAZ and cracking due to low heatinput



(3) Accuracy of weld joints and repair methods

The required tolerance of a weld joint (root gap, misalignment,etc.) is decided in accordance with the type of structure, jointdesign, welding procedure, etc.

a . Misalignment at the weld joint:



b. Root gap of fillet welding:In case of MMA weldin oint stren th increases when a

small root gap exists, but joint strength decrease with a lagerroot gap.



c. Tolerance for fillet weld and repair standard of the joint

ccor ng o : Japanese Shipbuilding Quality Standard)

Root gap < 2 mm : No repair

2 mm < root gap ≦ 5 mm :size as far as root gap,

5 mm < root gap : Repair as shown in the figure below



d. Tolerance for butt weld and repair standard of the joint

As an excessive root a in a butt weld oint ma cause weld defectsexcessive residual stress, or distortion, when a root gap is over tolerancerepair methods as shown in the figure below are recommended.



Use of backing strip: .

As the backing strip material affects the quality of the weldmetal the ualit should match that of the base metal of thestructure.

When a copper backing is used, strict control so as not toblend the copper into the weld metal is required to preventcracking.



(4) Welding of temporary fittings

Various temporary fittings such as jigs, small pieces, orbrackets may be welded on a structure for assembly work,installation of staging, or transportation.

ese we s requ re no on y s reng , u a so grea care soas not to cause defects such as undercuts, cracks or arc strikes

.

When these welds are done on thick plate, high strength steel,or low alloy steel, the heat input should be sufficient to avoidexcessive hardening or cold cracking at the HAZ.

,and avoiding a short bead (less than 40 mm) should be

Undercuts and arc strikes, if any, must be repaired carefully.



4.3.9 Welding conditions

Welding conditions include many factors such as welding

current, arc voltage, welding speed, preheating temperature,inter-pass temperature, post heating, backing, shielding gas,number of electrodes, type of polarity (AC or DC; electrode

, , .

All factors should be considered based on the base metal,welding process, position, equipment, consumables, etc.

very ng s ou e c ear y escr e n a an worinstruction sheet.



The setting and controlling of welding conditions:

Parameters may be considerably different depending on thewelding process.

Each welding condition usually has its own allowablearameter ran e.

Within this range, the most suitable conditions should beselected according to thickness, size, root face, root gap, etc.



Weldin en ineers or ractitioner su ervisor enerall

decide the most suitable conditions and then advise or trainwelders.

The number of passes or layers is, in some cases,

predetermined in the interest of maintaining the mechanicalproperties of the weld joint.

These requirements should be supported by adequate

welding current and welding speed.Other factors such as heat treatment heat in ut etc. were described in previous sections.

such as welding current, arc voltage, and welding speed alsomeans control of heat input.



4.3.10 Back chi in and back side ou in

Tack welding and first pass welding often results in welde ec s suc as ac o us on, s ag nc us on, ow o es, or

cracks.,

of one- side welding which should result in a perfect back sidebead Uranami .

The most important point of back chipping is that all defects ine roo ayer mus e remove .

Also, the shape of the back-chipped groove should be- - ,

both side walls in the groove V- shaped).The groove should be carefully inspected by a welder, foreman,

or engineer.

Back chipping method:



Back chipping method:(1) Pneumatic chisel or grinder

,low and noise and vibration are hard on the operater.(2) Gas gouging

n oxy-ace y ene or oxy-propane gas ame s use or pre ea ng, an s eecombustion energy is used. The equipment (gas burner) is simple, and noise is

less and efficiency better than pneumatic chisel, but distortion by heat is greaterthan that of other methods, sometimes causing cracks due to thermal stress.(3) Arc air gouging An arc i nited between a carbon electrode and the base metal melts the steel.

The molten steel is then blown away by compressed air . The figure belowdepicts the torch used with a DC welding power source or gouging machine.- ,

be obtained with this method. However, ventilation and use of a mask with adust filter is required due to heavy dust and fumes



4.3.11 Heat treatment before and after welding

(1)Preheating and interpass temperature

Preheating is carried out to prevent hardening and cold cracking atthe HAZ due to rapid cooling and to obtain stable penetration.

intermediate and final layers in order to keep inter-pass temperature.

,

does not require preheating may be heated to about 40 ℃.This is to lower the cooling speed or to prevent dew and is called "warm

up o s ngu s rom pre ea ng.

"Interpass temperature" is the temperature between two passes .When quenched and tempered high strength steel is welded, anexcessive interpass temperature can reduce the joint strength andmake i t bri tt le. An u er l imit for such a tem erature is necessarto prevent this.



High heat input,Excessive interpass temperature,Thin plate

Embrittlement of,Softening of QTmaterial joint

Low e r a t u r e

Slow coolingheat input,Withoutpreheat,Thick plate

T e m

Proper procedure rangeHardening offusion line zone,

Cold crack

Time

g. . oun ness o we o n versus coo ng ra e

P h ti g d i t t t d t i d b th t f t l



Preheating and interpass temperatures are determined by the type of steel,size of structure, thickness of plate, welding method, and welding conditions.

The hardness at the HAZ and the quantity of hydrogen in a weld joint differde endin on the chemical com osition of the base metal the uantit ofhydrogen introduced from welding materials, the cooling rate (decided bythe preheating temperature), and heat input.

,above .

hydrogen because it accelerates the diffusion of hydrogen outside from thewelds resulting decrease of susceptibility of cold cracking.

Table 4.4 shows preheating temperatures for high strength steel.

Table 4.5 shows the same for low alloy steel. Although mild steel less than 25 mm thick generally does not requirepreheating, in cold weather (such as lower than 10 ℃, warm up or

reheatin is desirable.Preheating is not applied to austenitic stainless steel except in special

cases.



Preheating Method:



Preheating Method:

Various methods are used for preheating such as a gas flame,electric resistance, electric inductance, fire furnace, andinfrared ray.

,control (to obtain a uniform temperature during welding) is

. ,

is beneficial to control temperature.

Electric resistance heating is more expensive than the gasflame method, but fine control of temperature can be obtained

.

type, or otherwise heating in the furnace etc. are available.

Preheating Area:



Preheating Area:

As shown in the figure below , preheating should be applied toenough of the area around a weld joint (at least 100 mm fromthe weld joint or three times plate thickness), to make thepreheating most effective.

-chalk, a thermometer with bimetal, thermo- couple, etc. for 50

.



Weldin with reheatin should be erformed continuousl .

② Preheating and interpass temperatures should bemaintained until the whole length of the welding iscompleted .

③ The preheating temperature for small-scale welding (suchas tack weldin weldin of tem orar fittin s etc. shouldbe about 50 ℃ higher than that for the actual welding toavoid a high cooling rate at the HAZ.

④ The preheating temperature for repair welding should also.

(2) Heat treatment after welding



(2) Heat treatment after welding

① post heating,② post weld heat treatment (PWHT),

also called stress relief annealing.

os ea ngPost Heating is applied just immediately after welding to

.

Post heating using a high temperature for a short period oftime can soften a hardened zone and also discharge diffusedhydrogen.

Post heating using relatively low temperature (250-350 )

HAZ.

are used as they affect the hardness of the HAZ and thehydrogen content in different ways.

② Post weld heat treatment (PWHT):



PWHT is applied for the following objectives:

a. Residual stress is eliminated.b. Elongation and notch toughness are improved.. .

d. Stress corrosion cracking may be prevented.

PWHT conditions are shown in Tables 4.6 and 4.7.

easurement, contro , an ata recor ng are necessary ur ngPWHT. When local PWHT is applied instead of heat treatment in

, .

PWHT is usually not applied to austenitic stainless steel.However, when a structure is used under very severecircumstances and carbide or a brittle phase result from hardening

ue o co wor ng, so so u on ea rea men , s a z ng

treatment, or stress relief heat treatment may be applied.



4.3.12 Weld finishing and repair



g p

The surface condition of a weld bead imparts great influenceon the fatigue strength of a joint.The surface of a weld bead should be as smooth as possible

and be free from a harmful degree of surface defects such as, , , ,

bead, flank angle at the toe of weld bead, etc .,

requirement for optimum surface conditions will be mostsevere.When non-destructive testing such as UT, MT, or PT is applied,

a smooth surface is required to carry out an effective.

Grinding, machining, welding with a small diameter electrode

dressing is sometime applied to improve fatigue strength.



(3) Prevention and repair of deformation



( ) p

welding are as follows;

a. Select a welding process requiring low heat input .

. ,deposited metal amount as small as possible.

c. Maximize the accuracy of the groove and avoid anexcessive root gap.

d. The work area should be flat to avoid initial deformation.

desirable.

e. Apply an appropriate welding and deposition sequence .



1. Transverse shrinkage As transverse shrinkage force in a butt joint can be very large,it may be impossible to prevent. If so, this shrinkage should

e a owe o occur ree y.

.

However, to prevent angular distortion due to butt welding, arestraint using a strong back as shown in Fig. 4.8 , or aweight may be effective.To prevent angular distortion due to fillet welding, a pre-strainor pre- en ng ec n que as s own n g. . s a soeffective



orrec on me o s or we e orma on:a. Local heating with a gas flame (air or water cooling)

.c. Application of peening to elongate a weld joint

As methods b. and c. may cause deterioration of materialquality due to cold working, application to thick plate or to acruc a s reng mem er s no recommen e .Method a. with water cooling is the most efficient. When this

,temperature should be below 650 ℃ to avoid quenching,hardening, or brittleness at the weld joint. As temperature control is generally difficult, local heating withair cooling (instead of water cooling) is recommended forma er a s w g ar ena y suc as g s reng s ee .

4.3.13 Weather and environment considerations



4.3.13 Weather and environment considerations ea er

Site welding under the following conditions should not be

a. Wet conditions (dew, rain or snow)

b. In the rain or snowc. Strong windsd. Low material temperaturee. g um y(2) Confined or high locations

confined or high locations due to safety, quality, andefficiency considerations.

Staging, lights, work clothing, safety devices, voltage reducingdevices, access ways, etc. should be well arranged ina vance. e or s o mo va e wor ers an o nsp re sa e y

consciousness should be made.



4.5 Semi-automatic and automatic welding



4.5.1 Precautions for semi-automatic weldin

4.5.2 Precautions for automatic weldin

4.5.3 Treatment and maintenance of weldin e ui ment

4.5 Semi-automatic and automatic welding4.5.1 Precautions for semi-automatic welding



g gas s e e arc we ng an we ng are requen y use

for semi-automatic welding. Precautions to be taken with these weldingprocesses are as follows;a. Protection from wind is necessary during welding. Below 1.5-2m/sec ofwind, it is preferable to keep shielding gas atmosphere at the weld arc over

the molten ool. A wind screen or shelter is usuall used in a worksho . Anawning or box-shaped frame is recommended outdoors.b. The welding groove should be cleaned carefully. Oil, paint, water, and

.c. Welding conditions should be appropriate. The welding torch should beoperated smoothly and kept at an adequate height (15-25 mm of wire

,good penetration, and good appearance of weld bead .d. Abrupt bending of the conduit cable should be avoided to maintain asmoo w re ee ng. e a owa e m o en ng s approx ma e y urnof 500 mm diameter.e. A good match between the contact tip's opening and wire diameter isimportant for smooth wire feeding and ensuring good electric contact.

f. Proper training and qualifications (JIS Z 3841) of all welders involved arenecessary.

4.5.2 Precautions for automatic weldingSubmerged arc welding has been representative of all automatic welding



Submerged arc welding has been representative of all automatic weldinguntil recently, but automatic types of CO2 gas shielded metal arc weldingincluding MAG/MIG are now also routine.Due to dee enetration a ver accurate weld roove is re uired for

submerged arc welding. The weld groove should be cleaned verythoroughly. Oil, water, or rust in or near a weld groove will often cause

.Precautions for gas shielded metal arc welding are the same as described

in sec.4.5.1.

Precautions for unmanned automatic welding , such as a robot welding, areas follows;a. ccura e par s an accura e assem y wor s as we as we ng grooveaccuracy are required.b. Use of an adequate combination of shielding gas and wire to reducespatter is necessary. The choice of welding equipment is also important.c. A seam tracking device is necessary for welding equipment for largescale structures.d. Automatic nozzle cleaners, automatic wire end cutter and automatic tip

changers are desirable.



. Accordingly, consideration for the prevention of lack of

fusion and sla removal are re uired.

The required skill of operators of automatic equipment isnot as great as that required for semi- automatic welding,but substantial training and skill to operate the equipment,

, ,materials, welding consumables, welding conditions, etc.

are still re uired.

4.5.3 Treatment and maintenance of welding equipment



-

well maintained electronically and mechanically.ISO 9000 and ISO 3834 also require periodic maintenance for

the equipment and calibration for the instruments . Wire feedingdevices are the main recipients of daily maintenance. Otherma n cons era ons are s e e ow;a. Greasing of wire- feeding gears and bearings.

.

pressure rollers.c. Cleaning and check for wear of conduit cables and wirepassages.d. Cleaning and periodical checks of contact tips and torch

.e. Check of shield gas passages and electric cables.

easily deterioration. Periodical cleaning with an air blower isnecessary.



4.7 Prevention of weld defects

4.4 Prevention and repair methods of weld defect



4.7.1 Weld defects and their influences A weld joint must possess various qualities according to therequ re oa , type o o nt, or mportance o t e structure.Poor workmanship or defects affect those qualities. Harmful

manner, according to repair procedure specification.The location to be re aired and details of the re airprocedure must be well studied and decided in advance.When serious defects such as cracks are located, the cause

o e e ec s mus e nves ga e an coun ermeasuresimplemented to prevent recurrence.

required to study and decide how to repair defects. Also, ofcourse, a high degree of skill is required to repair them.Remember that many cases of trouble or damage are due to

incorrect repair.

Significance of defects and repair welding:



A considerable degree of insufficient weld size, hardening, softening, andbrittleness also affect the quality of a weld joint.Weld defects generally have greater influence on fatigue, brittle fracture,

elongation, and corrosion than on static strength .

Re air weldin often lowers the total ualit of the weld oint. In articular repair welding of QT steel, low alloy steel, and stainless steel should beperformed very carefully.

,

it difficult to guarantee weld the quality.

Chapter 1, repetition of repair welding is not desirable.

e orts s ou e ma e to o we ng correct t e rst t me.

Important repair work should be planned and performed under thesupervision of a responsible welding engineer and it is desirable to prepare

the repair procedure specification.

Residual tensile stress zone



(Heterogeneous zone

Shape of toe (stress concentration)

Welding distortion (e.g. angular distortion)

Initial irregularity (e.g. misalignment)

Heat-affected zone Weld metal Blowholes

Weld defects

Degradation of material

ag nc us onsLack of fusion

Cracks

Weld defectsLack of penetration

. . ,hot strain embrittlement )

Softening or hardening of HAZDegradation of material(decrease in strength or toughness)

Fig. 3.17 Main features viewed from the mechanical point which affectthe strength of welded joint of steel



4.7.2 Prevention of weld defects



enera emsa. Choose a suitable base metal and welding process consideringweldability of base metal.b. Suitable welding consumables (type, diameter, etc.).

Use proper treatment such as storage and drying.

c. Choose a suitable weldin osition and t e of roove . d. Use operation techniques , such as the retract start technique, to preventdefects which may occur at the start and end of an arc. Finish welding

, .e. Confirm adequate height and width of weld bead .f. Consider tack welding and location.

. .h. Training and manning of welders and related operators .i. Consideration of work circumstances such as high location, narrow space,

g or ow temperature, ar ness, ra n, w n , etc. j. Motivation to maintain quality and confirmation of quality. Treatment toensure that a trouble does not occur at the next work stage. Maintain goodcommunication with related work stages.

2 Prevention of cold cracks



Cold cracks can be prevented by controlling a) chemicalcomposition, b) cooling time (cooling rate), c) hydrogencon en , pos - ea ng, an e n ens y o res ra n .

.(carbon equivalent) and low P CM (index of steel plate coldcrack sensitivity) should be used.b. Cooling rate : As previously described in Chapter 2, thecooling time from 800 ℃-500 ℃ governs micro structure, whiche ec e onga on an e oug ness o e . e amounof diffusible hydrogen is also determined by the cooling time

.preheating can be used to lengthen cooling time (i.e., slow thecooling rate). Attention should be paid to the welding of thickplate and short welding such as tack welding or jig weldingdue to the short cooling time generally involved.



Longitudinal crack



Transverse crack



Toe crack



High heat input,Excessive interpass temperature,Thin plate

Embrittlement of,Softening of QT

material joint

Low e r a t u r e

Slow coolingheat input,Withoutpreheat,Thick plate

T

e m

Proper procedure rangeHardening offusion line zone,Cold crack

Time

g. . oun ness o we o n versus coo ng ra e

c. n a amoun o us e y rogen : e amoun o us e y rogen



y g y g

in weld metal changes depending upon the type of electrode, electrode re-drying, moisture in the weld groove, rust, oil, and atmospheric humidity.

Accordingly, use of a low hydrogen type electrode, cleaning and drying ofweld groove, consideration to the weather, and preheating or warming of

the weld groove can help to prevent cold cracks.Use of TIG, or MAG welding is also effective to reduce the amount ofdiffusible hydrogen. Also, a lower preheating temperature than that forMMA weldin with an ordinar covered electrode ma be a lied.

.discharge of diffusible hydrogen and can help to prevent cold cracking.Post heating at 500-650 ℃ requires only a short time, while lower

. , -should be done for 30 minutes to 1 hour. Welding of successive passesprior to the occurrence of a crack at the root pass is effective in preventingroo crac s ecause per orms e same e ec as pos ea ng.

e. Intensity of restraint : The intensity of restraint must, ,



and welding sequence, and affects cold cracking. Effortsshould be made to kee the intensit of restraint small bgood design and work performance. The influence of a weldgroove to the intensity of restraint is large, and the degree ofinfluence, from large to small, is T joint (single bevel), Kgroove, single bevel, single V (partial penetration) and X

.

restraint, special considerations for electrodes, weldingconditions reheatin and ost-heatin are re uired.

f. Others: The use of extra low hydrogen type electrode,ncrease eat nput, or m stee e ectro e may e e ect ve.Root cracks in fillet welding are not as common compared

,welding can be lower than those for butt welding.

(3) Prevention of hot cracking



prevention method is different for each. Prevention methodsfor typical cracks are as follows;

a. Solidification cracks : Crater cracks and center linecrac ng ea s ape n uce crac ng, e.g., pear s apecracking) belong in this category. Prevention methods

metallurgical structure of the material,②

welding parameters,and ③ size and type of welding groove. Use of adequatewelding conditions so as not to make a pear-shaped beadand large craters are most important.

Cracking in weld metal may also occur because of the

deterioration of elongation . Relaxation of restraint iseffective in preventing this.



Weld crack

Growing direction of dendrite

Fig. 4.36 Pear-shape crack



Propagation of crater cracks in aluminum weld

. e ea crac or crac



The crack usually occurs at weld toe in the high strength.

The following precautions are required for the material andwelding procedure which may experience a reheat crack;

on ro o mpur es suc as an o er race e emen s

(refer to Chapter 2).

When PWHT is applied,① smooth the finishing of the toe area,② avoid residual stress and stress concentration, and③minimize thermal stress during heating and cooling.

(4) Prevention of lamellar tear - -



with heavy plate thickness under the high restraint condition .Elon ated inclusion such as MnS and throu h-thickness Z direction property in the material are strongly affected in the

tendency of lamellar tear.

The best way to prevent lamellar tear is to use an anti- - , - - .

second best way is to minimize the restraint forceer endicular to the direction of the main structural member . Application of proper welding and deposition sequence willreduce residual stress where a lamellar tear may occur.Local use of a mild weld bead is also a useful preventionmethod. Reduce of diffusible hydrogen is effective to prevent

.

Lower hull



-

(b) Box structure weld joint(c) Lap fillet weld joint with large leg length

Section A-A

(d) Various cruciform fillet weld joints (e) Weld joint with large amount deposition

(f) Various T-shape weld joints

Fig. 4.37 Weld joints that tend to have lamellar tears

(Original plan) (Improved plan)



Fig. 4.38 Improvements on joint design to avoid lamellar tears

Buttering



First layer Under-matchingGrindin toe

Second layer

. .

5 Prevention of orositGasses caught in deposited metal may cause porosities such



g p y pas blowholes, wormholes, piping, or pits . The followingac ons are e ec ve n preven ng poros y;a. Remove all dust, rust, moisture, oil, and paint from welding

.b. Control drying and storing of welding consumables .c. Keep arc length short and maintain the proper operationand manipulation of the electrode.d. Don't use an excessive welding current .e. en gas s e e arc we ng s per orme , poros y ueto lack of shield gas, dirt on wire or base metal, excessive arc

, , .should be avoided.Cleaning inside of the nozzle should be carried outoccasionally.



Isolated surface porosity



Radiograph of scattered porosity

Nozzle

Streamline flow zone



Turbulent flow zone

Shielding gas flow rate(17 litter/min.)



Nozzle

Shielding zone for

4% air

25% air50% air

4% air

25% air50% air

4% air

25% air

50% air

75% air75% air a r

WindWind

(a) With no wind (b) With a wind at 1.0 m/sec. (c) With a wind at 1.0 m/sec. +increased gas flow

. .

(6) Prevention of slag inclusion



Slag may be caught in the weld metal or between passesue o poor opera on on e par o e we er, or nsu c en

cleaning of the groove or removal of slag.

. .b. Prevent a preceding slag (especially in the case of verticaldownward welding).c. When a previous pass makes a sharp V-shape, so-calledvalley at the bottom of the groove, grinding must be appliedo ma e e groove -s ape .

d. Correct and steady operation of electrode (angle, weaving,

. .e. In the case of MAG welding with short arc technique, slagfrom the previous pass must be removed completely.



Sla inclusion in the surface



Radiograph Image of Elongated Slag Inclusions

(7) P i f l k f f i



(7) Prevention of lack of fusionThe side walls of a groove or previous weld bead may notfuse together due to improper preparation of the weld groove,insufficient heat input, or poor operation or manipulation of

.a. Heat input should be sufficient.

c. The shape of the groove should not be too narrow.d. In the case of gas shielded arc welding, remove slag onthe bead surface, avoid excessive weaving, avoid too smalla bevel angle, and maintain good arc position .

.subsequent pass welding.



Locations of lack of fusion (incomplete fusion)



Radiograph of side-wall lack of fusion

(8) Prevention of incomplete penetration



(8) Prevention of incomplete penetrationDue to an insufficient heat input or poor operation, thebottom of a groove or root face may not fuse together.a. Heat input should be sufficient.

. .face, too small a root gap, or too small a bevel angle should

c. Back gouging should be properly and sufficientlyperformed.d. The arc should trace a proper position in the grooveduring welding.



Examples of incomplete penetration

(9) Prevention of undercuts

strength of a weld joint the following actions should be taken



strength of a weld joint, the following actions should be taken.a. Proper welding current should be used (an excessivewelding current must be avoided ).b. Correct and steady operation of electrode ( arc position,

e ec ro e ang e, arc eng s ou e ma n a ne .c. Proper welding speed should be maintained.

. position (especially for the final layer of multi-pass welding)must be made.e. Weaving operation should be proper (frequency, width, dwelltime, etc.)

.considered.-. ,

and the welding condition of the root pass should be carefullycontrolled.



(10) Defects in austenitic stainless steel



(10) Defects in austenitic stainless steel

a. Hot crack

,may occur in addition to cracks in the weld metal (such ascrater crack, longitudinal or transverse cracks, or microcrack ).5-10% ferrite in weld metal is said to be effective in

preven ng crac s n we me a . owever, excess ve err ecauses deterioration of anti-corrosive properties and may

.

.

The HAZ of austenitic stainless steel when heated to 550-℃



The HAZ of austenitic stainless steel, when heated to 550850 ℃ ma reci itate chromium carbide at the rainboundary, so called “Sentisizing”.When this material is exposed to a corrosive atmosphere,

intergranular corrosion called "weld decay" may occur . A solid solution heat treatment after welding, use of low

,can prevent weld decay.

When the HAZ of stabilized austenitic stainless steel isheated to more than 1000 ℃ and used at high temperatures,

etween an an n a corros ve atmosp ere, a“ knife line attack ” may occur. Stabilizing heat treatment in

prevent this.



4.8 Repair Welding

4.8.1 Basic cosideration for repair welding

A high degree of knowledge and experience is required to



A high degree of knowledge and experience is required to.

Generally speaking, repair welding is performed locally,restraint is large, cooling rate is high, and the work area andwelding positions are generally limited. Accordingly, repair welding generally requires a higher

,

ordinary welding.

The repair welding should surely and properly be conductedin accordance with the following procedures to repair a crack

and/or failure caused by a breakage accident of productsand structures during service. The repair welding records

.

① Figure out and record the circumstances (such as situation of occurrence,range of occurrence, and results of inspection) of nonconformance (such ascracks and failure).

② Investigate and analyze nonconformance (such as cracks and failure) tol if th t d th di d k l f i ldi



g yclarif the causes , stud the remedies, and make a lan for re air weldinprocedure.③ Prepare a repair welding procedure specification (including an inspection

light of standards, technical books, and technical reports and request aresponsible person to examine and judge the adequacy of the specification and

.④ For repairing heavy-duty welded structures (such as pressure vessels, ships,and bridges), get the approvals of the designer, owner, and inspectionorgan za ons suc as e sa e y an secur y nves ga on assoc a on an eship classification society.⑤ Remove cracks and ruptured portion completely and confirm that no crack

remains by means of visual test (VT), liquid penetrant test (PT), and/ormagnetic particle test (MT). Also, the neighboring area and joints welded by thesame procedure should be confirmed that they contain no nonconformance bymeans of nondestructive tests of radiographic test (RT) or ultrasonic test (UT).

⑥ Execute repair welding and check it in accordance with theapproved procedure and record details for traceability . The detailsshould include qualification of repair welders, humidity and

temperature, welding procedure, welding consumables, welding



p , g p , g , g, ,

results.⑦ Re uest an ins ection or anization to witness the re air workand inspection.⑧ Submit the report of repair details and inspection results to therespons e person or s er approva an sen t em to t e

owner and the inspection organization. welded by the same WPS should be investigated and inspectedfor confirmation.⑩ In the light of the nonconformance occurrence report, theoriginal WPS should be examined and amended if necessary, and

e ac on s ou e a en o preven e reoccurrence o enonconformance.

4.8.2 Removal and repair of weld defects(1) Removal of weld defectsFirst, the weld defect to be removed is confirmed by non-



, y .

using a grinder, arc air gouging, or chipping. Removal of a

PT) . As weld defects such as cracks often propagate during repair,stop holes should be made on both ends of the defect before

beginning the repair. After the defect is removed, the groove, ,

successive welding may be performed.

may enlarge. The groove surface should be well inspectedvisually or using non-destructive inspection .

(2) Repair weldingse o ow y rogen e ec ro es or we ng s

recommended for repair welding except in the case of thin



p g p.

Preheating at a higher temperature than that for ordinarywelding is recommended.Post-heating is also often applied to remove diffused

hydrogen and to prevent cracking.

In the case of repair welding for high strength steel , the

a. The length of the weld bead should be more than 50 mm .b. The number of layers should be more than two .

c. After welding is made to the groove surface, one more layerof temper bead is laid and finishing of the bead is performedus ng a gr n er. e er o g .

(3) Repair welding inspection



.necessary, non-destructive inspection should follow.

In the case of high strength steel, magnetic particle testing(MT), or liquid penetrant testing (PT) should be applied afterwe ng.

,or ultrasonic testing (UT) is applied 24-48 hours after weldingto the repaired and adjacent area.

(4) Examples of repair weldingRepair welding is performed as described in the previous sec.4.4. Surface

flaws of the base metal may be repaired by build up welding according toWES 2803



WES 2803.

Fig. 4.22 shows repair of a transverse crack. First, the length of the crack

② the crack is completely chipped or gouged out and a proper weld grooveis made, and ③ repair welding is performed. Finally, the bead surface is

,maintained.

Fig. 4.23 shows repair of at longitudinal crack.The sequence of repair is the same as that of repair of a

transverse crack ① -③ .



en a crac passes roug a c ase p a e e wegroove may be gouged out from both sides of the base plate.

Fig. 4.24 shows a repair procedure to a plate surface which cannot applyPWHT after repair.The welding is performed using dried, low hydrogen electrodes and a

well-planned repair procedure.Pre-heatin inter- ass tem erature and ost-heatin are a lied exactl



Pre heatin inter ass tem erature and ost heatin are a lied exactl as prescribed in the repair procedure.Temper bead method (buttering) is applied to the first pass in the groove,

, . A tempering bead is welded to the surface of the weld bead and removedlater. Finally, a careful non-destructive inspection is performed.

.

Chipped or gouged area for various weld defects.



4.9 Safet and Health

4.9.1 Protection from heat, light,fl b d f



flying objects, and fumes

. . ro ec on rom umes an arm u gasses

. . ec r c s oc

. . xp os on an re

. . enera sa e y an ea

. . , ,

flying objects, and fumes



Welding arcs and gas flames radiate a great amount

ultraviolet rays).

High voltage electron beam welding radiates X-rays .

Arc welding scatters hot spatter , and gas cutting

.

,skin from heat, light, flying spatter, and slag .

(1) Eye and face protectionVery strong visible light due to welding can cause

temporarily blindness and ophthalmia .



painful ophthalmia and burns on the skin .

,time can cause an incurable reduction in eyesight .

When welding or cutting using an arc, welding helmets or

hand-shields (prescribed in JIS T 8142:2003) containing.

When welding or cutting using a gas flame, safety goggles

worn by operators.*JIS T 8142:2003 Personal face protectors for welding*JIS T 8141:2003 Personal eye protections for optical

radiations



Suitable filter plates and lenses must be selected and used depending onthe work conditions as shown in Table 4.22 . If a suitable shade number is more than 10, two plates of smaller shade

numbers can be combined. When two filter plates (shade number n1 and-

, . ,



two filter plates with shade numbers 7 and 4 are used, the total shadenumber used will be 10.]

Welding arc lights may be strong and potentially dangerous over a widearea. The use of protective screens around a welding space may benecessary.

(2) Body protectionFor protection from radiation and heat burns (due to spatter and slag),

leather loves JIS T 8113 sleeves le in s shoes etc. of durable

material must be worn .These protective articles are also effective against electric shock .

*JIS T 8113:1976 Protective leather gloves for welders

4.9.2 Protection from fumes and harmful gassesWelding fumes and gasses are generated in varying degrees from

different welding operations and arc with a product of vaporization,

oxidization, and condensation of components in the consumables and, to ade ree the base metal .



The amount of welding fumes can be measured by methods prescribed in. .

welding methods.*JIS Z 3930:2001 Determination of emission rate of particulate fume in arc

.

The effects of welding fumes on the human body.

3920:1991 (Methods for chemical analysis of



chemical analysis.

When welding is performed with a zinc or cadmium-

copper alloy, harmful fumes caused by the.

Therefore, welding or cutting should be performed.

Fumes from low hydrogen-type electrodes contain

such as fever .

When a welder or other workers are exposed towelding fumes over a period of many years, there is adanger of pneumoconiosis even if acute toxicsymp oms o no appear



symp oms o no appear.

ccor ng y, regu a ons o preven pneumocon os sspecify that arc welding, cutting, or gouging in a narrowspace suc as wor s op, p , an , s p, p pe, ro ng

stock, etc. should be performed with total or localven a on sys ems or w an a r-ven a e e me .

so, prepara on o a res space an c ean ng o ework space are necessary. Every welder and relatedwor er mus a so ave a per o c pneumocon os s

check.

Fume density can be reduced by ventilation . The

JIS Z 3950:2005(Methods of measurement for.



Filter type respirators are widely used for protection

.JIS T 8151:1991 (Dust respirators) prescribes. .

When certain fume generating machines are used, such as a thermals ra er a fume collectin s stem should be established . As a volume of treated air decreases with time, filters should be changed

regularly.

h f h f b b d l h



The notice from the Ministry of Labor prescribes guidelines as shown inTable 4.25



In the case of arc welding, the no-load voltage of thewelding power source must be maintained at a

certain level to maintain arc stability .oug : rc we ng power



oug : rc we ng powersource) prescribes the upper limit of a no-load

vo age as - , ese vo ages can s cause aserious electric shock.

Electric resistance is usually reduced in thepresence o wa er or o er mo s ure.

When arc welding or cutting is to be done under

amp or we con ons nc u ng eavy persp ra on ,the welder must wear dry gloves and clothing in goodcon on o preven e ec r c s oc .

(2) Protection from electric shock

1) Use of an insulated electrode holder

Electrode holders shall be insulated with heat resistant



holders for arc welding), and Safety and Health Regulations.

The use of a broken electrode holder with the conducting partexposed is strictly prohibited.

2) Use of a voltage reducing device ,voltage reducing device is necessary, as both ends of a

Safety and Health Regulations require the use of a voltagereducing device for AC arc welding power source in a narrowspace enclosed by electric conductive walls, or at a locationmore than two meters high.

3) GroundingThe frame or chassis of welding power sources must be connected to a

good electrical ground.

14mm2

cables are used for grounding the chassis of welding powersources.

An output terminal connected to the base metal must be grounded as well



An output terminal connected to the base metal must be grounded as well,or it will be dangerous as the voltage at base metal and worktable rises.

4) Cables and connections : e ng ca es prescr es we ng ca es or ea s an

electrode holders.For both oil-resistance and durability, chloroprene is superior to natural

rubber or insulation o welding cables.Cables and cable connectors must be used within their current rating and

duty cycle limitations.

Use of an excessive current rating or duty cycle will result in overheatingand rapid deterioration of the insulation and connectors .Excess len th of weldin cables also results in heat ener loss.Cable connectors should be totally insulated.

5) Protective leather gloves for welderse ers mus wear ry ea er g oves o preven e ec r c

shock and bums. and prevent the deterioration of electrical insulation



and prevent the deterioration of electrical insulation .

6) First aid ,

electricity source immediately.

If there is no time to cut off the power source, separate theperson from the electrifying object using dry gloves, a piece of

wood, or any other well-insulating material.While waiting for medical help, loosen clothes, give treatment,

breathing.

4.9.4 Explosion and fire

When welding or cutting is performed, combustible andex losive materials oils aints solvents insulation materials

wood textiles flammable gasses powder dust etc ) must be



wood, textiles, flammable gasses, powder dust, etc.), must beremoved from the work area to prevent ignition or explosion

from open flame, electric arcs, hot metal, sparks, or spatters.

,dangerous items must be confirmed.

Fire-screens and fire extinguishers must also be readilyavailable.

When welding work is suspended, electrical switches must be

circuit between the electrode and the base metal.

Gas welding and cutting use fuel gas and oxygen .

All gasses for these purposes are explosive as



All gasses for these purposes are explosive asshown in Table 4.26 .

Accordingly, special attention must be paid to theirstorage, transportation, and usage.

Gas flames must be carefully watched and shouldsomething be observed amiss (see Table 4.27 ),

necessary countermeasures must be takenimmediately.



4.9.5 General safety and health

(1) Work at high locations

Preparations and precautions for work at high



Preparations and precautions for work at highlocations are shown in Table 4.28 .

In addition, non- flammable seats or screens shouldbe prepared to prevent scattering and falling of spatterand slag.

Remaining electrodes and cut pieces should be

collected in boxes or bags to prevent them from falling



space special attention must be paid to prevent



space, special attention must be paid to prevent, , .

In addition, existing fumes in a confined space can,

gasses evolved or used in the welding process. .

and gasses in a welding environment.

,assigned.

require ventilation to assure adequate oxygen for life

use of an air line mask, when gas shielded arc



use of an air line mask, when gas shielded arc

enclosed area.

JIS T 8151 prescribes air line masks .

regardless of the condition of the work location.

gasses without impairing respiration



(4) Noise Arc air gouging and plasma arc cutting are process that tends

to have high noise levels. , ,causes stress, headaches, etc. and may cause temporary or



, , y p yermanent hearin loss .

Ear plugs or other head gear must be worn to preventear ng oss.JIS T 8 161 (Ear protection equipment) prescribes class 1 ear

,(for protection from high frequency noise).

High frequency noise is generally more harmful than middle

or low frequency noise ;therefore, use of class 2 ear plugs (which cut off harmful highrequency no se ye s perm norma conversa on s

recommended .



. on es ruc ve es ng

4.10.1 Purpose and types of testing and inspection. .

4.10.3 Qualification tests



4.10.5 Visual inspection of weld joint

4.10.7 Radiographic testing of weld joints

4.10.9 Magnetic particle testing

4.10.12 Testing methods for structures

4.10.1 Pur ose and t es of testin and ins ection

Various tests and ins ections are erformed to confirmthe quality of weld joints.



An inspection includes a judgment of whether or notthe test results of satisf the s ecification standards ,while testing does not includes a judgment .

The main purpose of an inspection is to confirm if astructure satisfies quality standards (shape, size,

accuracy, facility, etc.) as prescribed in specificationsand drawings .

Based on a well considered lan the most suitableinspection methods should be chosen to economizetime and cost.



Table 4.8 lists items of weldin erformance controland inspections required for a butt joint withreinforcement of a weldin structure usin hi hstrength steel, affected by alternative loads, and

requiring quality of grade 1 or 2 of JIS Z3104 ”Methods of radiographic examination for weldedoints in steel”.



4.10.2 Destructivean non es ruc ve es ng



Welding is always accompanied by hightem erature meltin and solidif in whichresults in material change and residual stress,

.

,to determine the best welding methods.

(1) Destructive testing

Strength, elongation, and notch toughness of



confirmed.

Destructive tests check these properties in amanner which destroys the test specimens .

(2) Nondestructive testing

A number of defects which occur during the weldingof a structure can be tested or ins ected withoutactual destruction of the structure . These test

th d ll d d t ti t ti



methods are called non-destructive testin .Radiographic testing(RT) and ultrasonic testing(UT)

are used to detect internal defects .Magnetic particle testing (MT) and liquid penetrant

testing(PT) are used to detect surface (or nearsurface) defects .

The appearance and size of welds can be

inspected visually(VT) and are important part ofnondestructive testing.

Various destructive and nondestructive testing

methods are listed in Table 4.9



of nondestructive testing

Prior to actual application on a structure, details oft t ifi ti h ld b h k d d th



test s ecifications should be checked and the appropriateness confirmed.

It is necessary to confirm that possible weld defectscan actuall be detected under both test conditionsand in actual structures with the same test equipment,test materials test method and conditions.

The main points of WES 2005 (qualification of methods of

1) Type of internal weld defects detected by qualification testsa. Cracks and similar defectsb. Lack of penetration or incomplete penetration



p p p

c. ac o us on or ncomp e e us ond. Elongated slag inclusion and similar defects.

The above defects should be found by both radiographic andultrasonic testing, or if not, at least by one method.

The allowable limit of a defect size depends on the inspectionproce ure spec ca on.

When test results satisfy the test specification, the results are

accepted.



(1) Dimensional defects and their measurement

a. Misalignment :sa gnmen s ou e c ec e ur ng assem y

work. Fig. 4.26 shows an example of measurement .



g p



2 Weld defects to be confirmed visuall

be checked visually regardless of the



a. Crack

b. Overlapc. Pit

.e. Spatter .

(3) Standards for VT

Acceptance standards for appearance inspections differ, , ,and other circumstances.

The re uired de ree should be reasonable and clearl



The re uired de ree should be reasonable and clearl

understood so that skilled and qualified welders may proceed inthe appropriate manner.

Acceptance standards should also be determined considering, ,

capabilities. Table 4.11 shows an example.

An abstract of ISO 5817:2003 “Welding -- Fusion-welded joints in steel, nickel, titanium and their alloys (beam weldingexc u e -- ua y eve s or mper ec ons s n ro uce nTable 4.12



. . a ograp c es ng o we o n s

A radial ray such as X-rays or γ rays can penetrate a

substance to a considerable depth. The degree of



penetration depends on the kind of material and its thickness .

s p enomenon can e use o e ec e ec s n a we joint. Fig. 4.32 shows the principle of a radiographic test.

- ,on the reverse sides of A and B. This difference is anindication of a defect .

As shown in Fig. 4.32 (b) , an increase in radiation can beseen from the increase of density on a radio logicallysens ve m .



2 Detection of weld defectsBlow holes, lack of penetration, lack of fusion, slag inclusion,

cracks, undercut, etc. can be detected by radiographic testing.

The tungsten inclusion of TIG welding can also be detected,- ,



,is detected as a decreased density on the expected film .

Fig. 4.33 shows examples of defects as they appear in

developed photographs.e oca on, s r u on, s ape, an e s ze o e ec s canbe seen and the type can also be estimated.

Though this method has difficulty detecting a defect with aflat surface, the radiographic picture is a good record for futurereference, and is a useful tool of quality assurance.



(5) Grading classification

1) Confirmation of radiograph qualityRadio ra h ualit should be uniform and sufficient to

evaluate weld joint quality.Confirmation of quality is accomplished using radiograph



density, the density difference of a contrast-meter, anddiscrimination of the number of I.Q.I. wires .

2) Method for classification of image flaw

JIS Z 3104 "Methods of radio ra hic examination for weld joint in steel" classifies the image flaw on a radiograph into fourtypes as shown in Table 4.15 .

Where it is difficult to classify the flaws into type 1 or type 2,classify respective flaws into type 1 or type 2, and then the

.



(7) Safety controlWith proper safety controls, radiation is a very useful tool.

However it is very dangerous if misused. ",Health Law", establishment of comprehensive control system,and the reatest ossible care are re uired.



Operators who deal with radiation must be properly qualified.When X-rays are used, a qualified X-ray handling leader

should be posted at any area where the amount of radiation is.

When - ra s are used a - ra radio ra h handlin leader

should be engaged under the guidance of a radiation handlingsupervisor.Instruction and training are important for all operators who

engage in radiographing to ensure safety.



An ultrasonic pulse is directed at the test material.

material can be calculated by measuring the elapsed time ofecho Fi . 4.44a .

An ultrasonic wave deflected at a flaw is received and



analyzed to define the presence and location of defects ( Fig.4.44 b ).

shown in Fig. 4.44c which displays transmission time on the

horizontal axis distance from material surface to obstacleand the echo strength on the vertical axis . A probe transmits an ultrasonic wave into the material andreceives the echo . The probe includes an oscillator (made ofcrystallized quartz or barium titanate) which converts an

flaw detector by a cable.



Normal beam and Angle beam technique :

When an ultrasonic wave is generated perpendicular to the

surface of the test material, it is called the normal beamtec n que . s s common y use to nspect t c stee p ate,cast steel, or measure material thickness .



When inspecting a weld joint with reinforcement or an inclineddefect , the normal beam method cannot be a lied. Theultrasonic wave must be introduced at an angle to the materialsurface as shown in Fig. 4.45 . This is called the angle beamec n que .In a solid material such as a metal, both longitudinal and

.

normal beam technique, and transverse waves are used for theangle beam technique.

When the angle beam technique is used, however, no echofrom the bottom surface of a metal can be obtained



(2) Information from ultrasonic testingThe echo image displayed on the CRT of an ultrasonic flaw detector shows

the location of an echo (transmission time) on the horizontal axis , and theecho am litude echo hei ht on the vertical axis .

The horizontal axis shows the distance between the surface of the test



ultrasonic wave). This is called the beam path distance.

. ,obstacle is determined as follows;

ep o re ec ve o s ac e : = cos ……… .

Horizontal distance from incident point to reflective obstacle:YF =WF sin θ… (4.3)

WF :beam path distance θ : Angle of refraction



(3) Detection of weld defects by ultrasonic testing1) Kinds of defect and characteristicsWeld defects are generally classified as cracks, lack of penetration, lack of

fusion, slag inclusion, and blowholes. Each weld defect has its owncharacteristics such as sha e cause of occurrence etc. When ultrasonictesting is performed, the following characteristics must be noted;a. Location of defects (groove, root area, toe area, heat affected zone, etc.)

. , , .



c. Defect orientation (perpendicular to ultrasonic beam, parallel orperpendicular to weld line, etc.)

. , , , .

2) Selection of frequency

Ultrasonic frequency is determined by the type of probe used.

Accordingly, prior to choice of probe, the suitable frequency foraw e ec on mus e e erm ne .

b h ) d



becomes shorter), wave expansion decreases . As a wave is most directed with shorter ex ansion, it becomeseasier to reflect, even by small obstacles .

ccor ng y, w en a sma e ec s suspec e a gfrequency wave is preferable .

If a wave frequency is too high, however, the ultrasonic waveis easily dispersed at a metal's crystal grain boundary andbecomes difficult to transmit in test material.



3) Ultrasonic wave directionTo detect weld defects, the ultrasonic beam should be directed as

perpendicular as possible to the defect surface. As shown in Fig. 4.49 , the angle beam method is applied to a butt weldoint with reinforcement. Both the normal beam method and the an lebeam method are applied to a T-joint or corner joint.



(2) Method of magnetic particle testingThe yoke and prod methods shown in Fig. 4.52 are widely used. Table 4.18

shows the characteristics of each method.



(2) Strain measurementThe stress condition of a structure can be determined b measurin strain

at crucial points. In the case of pressure vessels, the fitting location ofnozzles, manholes, and reinforcements are such crucial measurement

.Strain measurement with an electric resistance strain gauge is common. In

addition, the brittle coating method and X-ray stress measuring methods are.

(3) A i i i i



(3) Acoustic emission testingcoust c em ss on test ng cons sts o t e etect on o acoust c s gna s

produced by plastic deformation of crack formations during loading or

thermal stressing. This testing is used mainly for monitoring of equipmentduring operation or welded structures during proof testing . For weld joints,acoustic emission testing is applied to welding condition monitoring and theoccurrence of hot crackin or dela ed crackin .

(4) Thermograph

distribution of infrared radiation. This method can be used to check thecondition of a chemical plant.

WE4 Fabrication and Application Engineering 3of3

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