what is the difference between welding transformer

8/18/2019 What is the Difference Between Welding Transformer

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What is the difference between Welding transformer, generator & rectifier?A welding transformer is a step down transformer. In welding transformer in coming voltage

is three phase, outgoing is 1 phase. {Low voltage high current}

Welding transformer is a high power step-up transformer produce very high temperature

while short-circuited for welding.

A welding transformer is a step down transformer that reduces the voltage from the source

voltage to a lower voltage that is suitable for welding, usually between 15 and 45 volts. The

secondary current is quite high. 200 to 600 amps would be typical, but it could be much

higher.

A welding transformer converts (normally) high voltage low amperage current to low voltage

high amperage current.

For example 220v @ 50a down to 55v @ 50-250ampTransformer means transforming from a input voltage to output voltage. It may be step up or

step down transformers. It will have primary and secondary circuits. Welding indicates the

particular usage.

Generator produce Ac voltage while rotated by a motor and rectifier is used to convert AC

voltage into DC voltage.

Welding transformers are high current source for welding

generator are for generating electrical power

rectifiers are for rectifying ac to dc current

WELDING:Welding is defined as the process of joining of two or more pieces of metal by applying heat

or pressure or both or without the addition of filler metal to produce a localized union through

fusion or recrystallization across the interface.

BRAZING:

In brazing the base metals are heated but not melted. Brazing is frequently used to join

dissimilar metals (e.g. copper to steel etc.) Brazing filler metals melt at temperature above 840°

F

SOLDERING:Filler metal melts at temperature below 840° F (450°C).. Soldering is used primarily where

strength is not important. (E.g. joining wire in electrical circuits, etc.).

In both soldering and brazing, the base metals are not melted

ADHESIVE BONDING:

Adhesive bonding is capable of joining dissimilar materials, for example, metals to plastics,

bonding very thin sections without distortion, very thin sections to thick sections, joining heat

sensitive alloys.

TIG WELDING (GTAW PROCESS):


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TIG welds arc stronger, more ductile and more corrosion resistant than welds made with

ordinary shield metal arc welding. The weld bead has no corrosion because flux entrapment

cannot occur.

POWER SUPPLIES (GTAW):

In the DCSP power supply, the tungsten electrode is negative (cathode) and base metal is positive (anode).

In DCRP power supply, the electron flow is from the base metal to the electrode

AC is a combination of DCRP & DCSP, the current value is essentially zero at the instant

when the current reverses direction. . The arc column that is established with AC is unstable

and erratic.

In the standard AC cycle, one half of the heat is absorbed into the tungsten electrode. The

ACHF can be further modified by lengthening out the DCSP cycle and shortening the DCRP

cycle. The ratio between DCSP & DCRP may be as high as 30:1, which means that the tungsten

electrode would be a cool-running electrode most of the time and work piece would receivetwo thirds of the heat.

PENETRATION CHARACTERISTICS:The penetration of DCSP is narrow and deep because the electron impinges on the base metal.

The electrode is thought of as a cool-running electrode.

In DCRP, on the other hand, the electrons flow from the base metal to the electrode and the

major portion of heat is absorbed by the electrode; therefore the weld bead is relatively shallow

and wide.

The alternating current and the ACHF current are a combination of the DCSP & DCRP.

TUNGSTEN ELECTRODE:Three basic kinds of tungsten or tungsten alloys are used for the electrode in TIG welding

-Pure tungsten

-Zirconated tungsten

-Throated tungsten.

Pure tungsten has a melting point of approximately 6170°F and a boiling point of 10706°F,

which gives tungsten electrode a long life.

Thorium has a melting point of 3182°F and zirconium a melting point of 3366°F

SHIELDING GAS:Argon permits the operation of lower voltages at any amperage setting; it is better suited for

the welding of thin metals

ARGON:Argon is a heavy monoatomic gas an atomic weight of 40. It is obtained from the atmosphere

by liquefaction of air. After argon is refined to purities on the order of 99.99 percent, it may

be stored and transported as a liquid at temperatures below -184°C (-300°F)

HELIUM:Atomic weight of four


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Because of its greater thermal conductivity, helium requires higher arc voltages and energy

inputs than argon.

Helium has a higher ionization potential than argon and hence it is a hotter gas- suitable for

welding thick metals and highly conductive metals such as copper and aluminum alloys.

WELDING TERMINOLOGY:The root opening should be increased as the included angle decreases to allow for electrode

access.

If the root opening is too small, root fusion is more difficult to obtain and smaller electrodes

must be used, thus slowing the welding process.

If the root opening is too large, weld quality does not suffer with use of a backing bar but

more weld metal is required, thus increasing welding cost of weld filler metal required for

single groove preparations by about half

OPEN CIRCUIT VOLTAGE:Open circuit voltage is the voltage at the output terminals of a welding power source when it

is energized but has no current out put

ARC VOLTAGE:ARC voltage (or working voltage) refers to the amount of voltage being used during the arc

welding process.

It usually registers at between 18 and 36 volts on the voltmeter. When the work is not in

progress (but the welding machine is running), the voltage rises on the voltmeter to

approximately, three times that of the arc voltage reading. This is referred to as open circuit

voltage.

CONSTANT CURRENT AND VOLTAGE CLASSIFICATIONThey are the drooping arc voltage (DAV), the constant arc voltage (CAV) and the rising arc

voltage (RAV).

The machine that is designed with the DAV characteristics provides the highest potential

voltage when the welding current circuit is open and no current is flowing. As the arc column

is started, the voltage drops to a minimum which allows the amperage to rise rapidly. WithDAV, when the length of the arc column is increased, the voltage rise and the amperage

decrease

Duty cycle expresses as a percentage, the portion of the time that the power supply must

deliver its rated output in each of a number of successive ten minutes intervals without

exceeding a predetermined temperature limit

Heavy industrial units designed for manual welding arc normally rated at 60 percent duty

cycle. For automatic and semiautomatic processes, the rating is usually 100 percent duty

cycle

WELDING CABLES:


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Exceeding the length without increasing the diameter of the cable results in a serious voltage

drop. This in turn will produce poor weld.

ARC BLOW:Some suggested adjustments for reducing the arc blow are as follows-

1) The arc length should be shortened as much as possible.

2) Reduce the welding current.

3) Change to AC, which may require a change in electrode classification.

4) Place the ground connection as far as possible from the joints to be welded

In straight polarity, the electrode is negative and the work is positive.

In reverse polarity, the electrode is positive and the work is negative

CLASSIFICATION OF STAINLESS STEEL ELECTRODE:

E 310-15 and E310-16.

The number-1 indicates that the electrodes are suitable in all positions.

The number-5 indicates that the electrodes are suitable for use with DCRP.

The number-6 indicates that the electrodes are suitable for either AC or DCRP.

The -15 coverings usually contain a large proportion limestone. This ingredient provides CO

and CO2 that are used to shield the arc. The slag solidifies relatively rapidly, so that these

electrodes often are preferred for out of position work, such as pipe welding.

The-16 covering also contains lime stone for arc shielding. In addition it usually contains

considerable Titania (Titanium dioxide) for arc stability. The -16 coverings produce a smoother

arc, less spatter. The slag is however more fluid and the electrode usually is more difficult to

handle in out of position work.

ELECTORDE CONDITIONING

The temperature of the holding oven should be within the range of 65°C to 150°C (150° to

300°F).

WELDING SPEED (TRAVEL SPEED):

When the electrode is pointed in the direction of welding, the forehand technique is being used.

The backhand technique involves pointing the electrode in the direction opposite that of

welding.

CRACKS:Hot cracking is a function of chemical composition

Cold cracking is the result of inadequate ductility (or by martensite formation resulting from

rapid cooling) or the presence of hydrogen in hardenable steels.

MICROFISSURING:


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Micro fissuring can be detected only by the use of a microscope. It is associated with either

hot or cold cracking.

OXIDATION:It occurs when the weld metal has been inadequately protected from the atmosphere.

PREHEATING:

CE < 0.45 %---> Optional preheating

CE > 4.45% or < 0.60% --- > 200 to 400 ° F

CE > 0.60% - 400 to 700 °F.

%Mn %Ni %Mo %Cr %Cu

CE=%C+ ------------- + ----------------- + --------------- + --------------- + --------------

6 15 4 4 13

WELDING DISTORTION:

SKIP WELDING:

Fig: Skip welding Technique (Any sequence of welds may be employed provided that each

short run has time to cool before another is joined to its).

This is a very effective procedure for preventing distortion and reducing locked-up stresses and

consists in distributing the welding heat as widely as possible, thus avoiding excessive heating

of any area.

This is done by making a short weld, then “skipping” some distance ahead and making another

short weld and then returning to the first weld and making another weld adjacent to its; this is

continued until the whole joint is completed.

Sufficient time should elapse between making adjacent welds to ensure that the first weld is

sufficiently cool and is in contraction.

There is no hard and fast rule as to the sequence of the welds; each job must be considered

separately.STEP-BACK WELDING:

4 2 5 3 1 6


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Fig: Step-back welding technique.

This also is a procedure for distributing the heat of welding in order to prevent the accumulation

of stresses and consequent distortion.It comprises making a series of short runs in the opposite direction to the general run of

welding.

If desired, the welds could be made in any sequence by combining the procedure with the skip

technique e.g. 1, 3, 5, 2, 4, 6 etc i.e. “skip-step –back” welding.

E6010 This electrode is used for all position welding using DCRP. It produces a deep

penetrating weld and works well on dirty,rusted, or painted metals

E6013 This electrode can be used with AC and DC currents. It produces a medium

penetrating weld with a superior weld bead appearance.

E7018 This electrode is known as a low hydrogen electrode and can be used with AC or DC.

The coating on the electrode has a low moisture content that reduces the introduction of

hydrogen into the weld. The electrode can produce welds of x-ray quality with medium

penetration. (Note, this electrode must be kept dry. If it gets wet, it must be dried in a rod

oven before use.)

6010

All positions

Deep penetration

DC reverse polarity

Rod is mild steel

Application – use medium arc, whipping or weaving on vertical and overhead to control

bead sag.

7018

All positions

7 6 5 4 3 2 1


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AC or DC reverse polarity

Iron in coating good with AC and allows high current settings

Application – use highest current practical in range, use straightforward progression and

short arc, weld puddle very fluid.

316ELC16

Stainless, NiCr – for welding 316EL & 317 Stainless steels

Use for high heat applications – i.e. Exhaust bellows

AC or DC reverse polarity

Application – any position, vertical – weld up.

1851

For brass, bronze, copper and joining dissimilar metals

Material must be clean

Copper alloys must be pre-heated

Application – all positions, vertical – weld up.

ASME has adopted their own designation for welding processes, which are very differentfrom the ISO definitions adopted by EN24063.

Straight polarity = Electrode -ve

Reverse polarity = Electrode +ve

The next to last digit indicates the position the electrode can be used in.

1. EXX1X is for use in all positions

2. EXX2X is for use in flat and horizontal positions

3. EXX3X is for flat welding

ELECTRODES AND CURRENTS USED

• EXX10 DC+ (DC reverse or DCRP) electrode positive.

• EXX13 AC, DC- or DC+

• EXX18 AC, DC- or DC+

ASME F Numbers


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F

NumberGeneral Description

1 Heavy rutile coated iron powder electrodes :- A5.1 : E7024

2 Most Rutile consumables such as :- A5.1 : E6013

3 Cellulosic electrodes such as :- A5.1 : E6011

4 Basic coated electrodes such as : A5.1 : E7016 and E7018

5 High alloy austenitic stainless steel and duplex :- A5.4 : E316L-16

6 Any steel solid or cored wire (with flux or metal)

2X Aluminium and its alloys

3X Copper and its alloys

4X Nickel alloys

5X Titanium

6X Zirconium

7X Hard Facing Overlay

Note:- X represents any number 0 to 9

ASME A Numbers

A1 Plain unalloyed carbon manganese steels.

A2 to A4 Low alloy steels containing Moly and Chrome Moly

A8 Austenitic stainless steels such as type 316.

ASME Welding Positions

Welding Positions For Groove welds:-

Welding Position Test

Position

ISO

and EN

Flat 1G PA

Horizontal 2G PC


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Vertical Upwards Progression 3G PF

Vertical Downwards Progression 3G PG

Overhead 4G PE

Pipe Fixed Horizontal 5G PF

Pipe Fixed @ 45 degrees Upwards 6G HL045

Pipe Fixed @ 45 degrees Downwards 6G JL045

Welding Positions For Fillet welds:-

Welding Position Test Position ISO and EN

Flat (Weld flat joint at 45

degrees)1F PA

Horizontal 2F PB

Horizontal Rotated 2FR PB

Vertical Upwards Progression 3F PF

Vertical Downwards

Progression

3F PG

Overhead 4F PD

Pipe Fixed Horizontal 5F PF

ASME P Material Numbers

This is a general guide ASME P numbers and their equivalent EN288 groupings.

P No. EN288 Base Metal

1 1

Carbon Manganese Steels, 4 Sub Groups

Group 1 up to approx 65 ksi

Group 2 Approx 70ksi

Group 3 Approx 80ksi

Group 4 ?

2 - Not Used

3 4 3 Sub Groups:- Typically half moly and half chrome half moly


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4 5 2 Sub Groups:- Typically one and a quarter chrome half moly

5A 5 Typically two and a quarter chrome one moly

5B 5

2 Sub Groups:- Typically five chrome half moly and nine chrome one

moly

5C 6 5 Sub Groups:- Chrome moly vanadium

6 8 6 Sub Groups:- Martensitic Stainless Steels Typically Grade 410

7 8 Ferritic Stainless Steels Typically Grade 409

8 9

Austenitic Stainless Steels, 4 Sub groups

Group1 Typically Grades 304, 316, 347

Group 2 Typically Grades 309, 310

Group 3 High manganese grades

Group 4 Typically 254 SMO type steels

9A, B, C 7 Typically two to four percent Nickel Steels

10A,B,C,F,G ? Mixed bag of low alloy steels, 10G 36 Nickel Steel

10 H 10 Duplex and Super Duplex Grades 31803, 32750

10J ? Typically 26 Chrome one moly

11A Group 1 7 9 Nickel Steels

11 A Groups 2

to 5? Mixed bag of high strength low alloy steels.

11B ? 10 Sub Groups:- Mixed bag of high strength low alloy steels.

12 to 20 - Not Used

21 21 Pure Aluminium

22 22a Aluminium Magnesium Grade 5000

23 23 Aluminium Magnesium Silicone Grade 6000

24 - Not Used

25 22b Aluminium Magnesium Manganese Typically 5083, 5086

26 to 30 Not used


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47 to 50 Not Used

51, 52, 53 Titanium Alloys

61, 62 Zirconium Alloys

WELDING IS A METALLURGICAL PROCESS:

WELDING is the joining of two or more pieces of metal by applying heat or pressure or both,

with or without the addition of filler metal, to produce a localised union through fusion or re-

crystallisation across the interface.

WELDABILITY OF METALS & ALLOYS:

Weldability, as the name suggests, is a specific or relative measure of the ability of the

material to be welded under a given set of conditions.

1.

Oxy-fuel welding, in which a combustible gas is burned with additions of oxygen to

produce a high temperature flame;

2. Resistance welding in which high current density is introduced to create a high metal

temperature and pressure is applied to produce a weld;

3. Flash Welding in which an arc is created and followed by instantaneous force to bring the

parts being welded together;

4.

Diffusion welding, in which clean metallic parts are brought together with high force tocreate bonding through diffusion,

31 Pure Copper

32 Brass

33 Copper Silicone

34 Copper Nickel

35 Copper Aluminium

36 to 40 Not Used

41 Pure Nickel

42 Nickel Copper:- Monel 500

43 Nickel Chrome Ferrite:- Inconel

44 Nickel Moly:- Hastelloy C22, C276

45 Nickel Chrome :- Incoloy 800, 825

46 Nickel Chrome Silicone

47 Nickel Chrome Tungstone


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5. Friction welding in which two parts to be welded are brought together with force and

movement at high speed to create high temperature and bonding;

6. Electron beam welding, in which a focused stream of electrons produce melting and

joining:

7. Laser beam welding, in which a coherent light beam is focused on the work-piece to create

melting for welding or cutting: 8. Ultrasonic welding, in which a concentrated beam of sound waves is used: and

9. Explosion welding, in which a high energy explosive is used to create very high forces

between two workpieces, thus bonding them together .

The SAW or submerged arc process (See Figure 8 & 9) is a high-production process and that

can be used for shop, field and semi-automated applications. However, this process has certain

limitation for weld-position requirements.

Plasma arc welding (See Figure 7) is a high-energy source application that is particularly

adaptable to automated welding techniques. It has been used advantageously for hard facingwith special metal alloys for wear and abrasion applications.

The EBW, LBW, DFW, EXW, FRW, USW and flash welding processes are rather

Figure 1: Metallurgical Zones developed in a typical weld

The industrial usage of a welding process depends to a great extent on the following

considerations:

The material and its weldability

Production requirements

Design specifications and intended service

Size and complexity of weldments

Fabrication site – shop or field

Cost of welding equipment

Welder skill and training required

WELDING & DILUTION:

Ideally, welding a particular alloy with filler metal that matches exactly provides severaladvantages:


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Uniform composition throughout the weld joint

Excellent match of physical properties such as colour, density and electrical and thermal

conductivities, and,

Uniform mechanical properties throughout the weld joint and the base metal after post weld

heat treatment

In commercial arc welding practice, however, s steel plate of one composition, such as IS

2062, ASTM A 441 or API-5LX is most likely to be welded with a steel electrodes of a

different chemical composition, such as E7018 or ER70-S3 electrodes. Similarly,

non-ferrous metals including aluminium alloys such as 3004, 5005, 6061 and A357.0 are all

ordinarily welded with ER4043 filler metal for general-purpose gas metal arc or Gas tungsten

arc welding applications.

the weld joint is usually a chemically heterogeneous composite consisting of as many as

metallurgically six distinct regions, (refer to figure 1) namely;

1.

the composite zone2. the unmixed zone

3. the weld interface

4. the partially melted zone

5. the heat affected zone (HAZ)

6.

the unaffected base metal

Composite Zone: The admixture of filler metal and melted base metal comprises a completely

melted and homogenous weld fusion zone in this composite zone or region. For instance, when

a grey cast iron is welded with Nickel electrode, this region would contain a homogeneous

welded pool of nickel filler metal diluted with melted grey iron base metal. The chemical

composition of the composite zone would be the weighted average of the elements (i.e. carbon,

nickel, iron, manganese etc.) from both the filler metal and the melted base metal. Even

completely dissimilar metals such as copper and Nickel, for instance, can be welded

autogenously to each other, without filler metal, using GTAW, and the bulk composition of

this zone would be surprisingly uniform.

Unmixed zone: The narrow region surrounding the bulk composite zone is the unmixed zone,

which consists of a boundary layer of melted base metal that froze (solidified) before

undergoing any mixing in the molten composite zone. This is usually visible when the filler

metal composition is different from the base metal (for example, pure nickel filler metal andgrey cast iron base metal)

Obviously, if the filler metal matches the composition of the base metal, the unmixed zone will

not be visible since the composition and the cooling conditions of the base metal would match

those of the filler metal. (For example, welding of pure nickel base material with pure Nickel

filler using GTAW)

Weld Interface: The third region defined in a weldment is weld interface. This surface clearly

delineates the boundary between the un-melted base metal and the solidified base metal.

Partially melted zone: In the base metal immediately adjacent to the weld interface, wheresome localised melting may occur, the partially melted zone is observed.


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In many alloys that contain low-melting inclusions and impurity or alloy segregation at grain

boundaries, liquation of those low-melting microscopic regions may occur and extend from the

weld interface into the partially melted zone. The classic example is HY 80 where liquation of

Manganese sulphide inclusion results in hot cracking or micro-fissures, which extend from the

unmixed zone into the partially melted zone.

Heat affected zone (HAZ): The true HAZ is the portion of the weld joint which has been

subjected to peak temperatures high enough to produce solid-state micro-structural changes but

too low to cause any melting. For example, in high carbon steels, solid-state carbon diffusion

at low temperatures (from 250 to 100 deg. C. during cooling of the weldment) may result in

the formation of hard martensite in the HAZ. In a single-phase alloy, such as say pure Copper

or pure Nickel, this is evident by the increasing grain size from the outer extremity of the HAZ

to a maximum grain size at the weld interface.

Unaffected base metal: Finally, the part of the work-piece that has not undergone any

metallurgical change is the unaffected base metal. Although metallurgically unchanged, the

unaffected base metal and the entire weld joint is likely to be in a state of high residualshrinkage stress, depending on the degree of restrain imposed on the weld.

ARC WELDING OF PLAIN AND HARDENABLE CARBON STEELS AND ALLOYSTEELS:

Steels are alloys of iron and carbon with carbon content of maximum of 2%.

Plain carbon steels contain less than 1.65Mn, 0.6Si and 0.60Cu.

content in hundredth of a percent)

-Manganese steels

13xx Mn 1.75

-Nickel steels

23xx 3.50% Ni

25xx 5.00% Ni

-Molybdenum steels

40xx Mo 0.20 - 0.25

41xx Mo 0.40 - 0.52

-Chromium-Molybdenum steels

41xx Cr 0- 0.50, -0.80 & 0.95Mo 0.12, 0.20 & 0.30

In general, the weldability of steel decreases as the hardenability increases; because higher

hardenability promotes formation of microstructures, which are more sensitive to cold

cracking.

Steels having CE of less than 0.35% usually require no preheating or post heating. Steels with

CE values of 0.35 –0.55 usually require preheating and those with CE of >0.55 require both

preheating and post weld heat treatment.

The carbon equivalent is calculated only from the chemical composition and includes no othervariable; it is at best only an approximate measure of weldability or susceptibility to cold


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cracking. Section thickness and weldment restraints are of equal or greater importance than the

carbon equivalent. Figure 2 shows the relationship between the carbon content and section

thickness as they affect weldability.

Low carbon steels (Carbon -0.50%) are difficult to weld because of their susceptibility to

cracking. Low hydrogen consumables are mandatory for welding medium and high carbon

steels. Austenitic stainless steels are sometimes used for welding high carbon steels to obtain

greater notch toughness in the joint. However, the HAZ may still be hard and brittle and preheating and post weld stress relieving ma

High strength Quenched and tempered steels (QT Steels) of carbon less than 0.25% and the

total alloy content (without Mn and Si) of 0.85 – 16% can be successfully welded using

SMAW, SAW, GMAW and FCAW processes. Many QT steels are produces with

sulphur content of less than 0.025% or more importantly, Mn to S ratio of greater than

30:1, so that with carbon content of about 0.20% or less, the susceptibility to hot

cracking is negligible. The cooling rates in welding are so high that the mechanical

properties of the HAZ approach those of the steel in quench-hardened condition.

Therefore, PWHT such as quenching and tempering is unnecessary unless stresscorrosion is factor.

ARC WELDING OF STAINLESS STEELS:

Most stainless steels that do not contain more than 0.03% Sulphur are considered weldable.

Austenitic stainless steels, usually designated as AISI 300-series stainless steels, are classified

with respect to the chemical composition and the differences in chemical composition among

these steels affect weldability and performance in service.

For example, types 302, 304 and 304L differ primarily in carbon content and consequently

there is a difference in the amount of carbide precipitation that can occur in the heat-affected

zone (HAZ) after the heating and cooling cycle encountered in welding.

Types 316 and 317 contain Molybdenum for increased corrosion resistance and higher creep-

strength at elevated temperatures. However , unless controlled by extra low carbon content, as

in 316L, carbide precipitation occurs in the HAZ during welding.

Types 347, 321, 318 and 348 are stabilised with titanium, or niobium + tantalum, to prevent

inter-granular precipitation of Chromium carbides when the steels are heated to a temperature

in the sensitising range, as during welding.

The austenitic stainless steels are easiest to weld and produce welded joints that are

characterised by a high degree of toughness, even in the as-welded condition


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The precipitation of inter-granular chromium carbides is accelerated by an increase in the

temperature within the sensitising range and by an increase in time at the temperature. When

carbides are precipitated at the welded joints, the resistance to inter-granular corrosion and the

stress corrosion markedly decreases. Sensitisation is restricted generally to a narrow range –

between 625 to 875oC, however, this range varies with time and composition.

Extra low carbon steels: Although solution annealing, a heat treatment that puts carbides back

into solution and restores normal corrosion resistance is a solution to this problem, it is

generally inconvenient. This problem is overcome by using extra low carbon steels and filler

metals of similar composition, e.g. 304L, 316L. However, when these steels are used for

extended period at elevated temperatures, significant carbide precipitation occurs. The extra

low carbon steels are therefore recommended for use below 400oC.

Stabilised steels exhibit higher strength at elevated temperatures in comparison with the extra

low carbon steels. For service in a corrosive environment in the sensitising temperature range

of 625 to 875oC, austenitic steel stabilised with Nb + Ta or Ti is needed.

Micro-fissuring in welded joints: Inter-dendritic cracking in the weld area that occurs before

the weld cools to room temperature is known as hot cracking or micro-fissuring. The

occurrence of micro fissuring is related to:

The microstructure of the weld metal as solidified

Composition of the weld metal, especially the content of residual or trace elements

Amount of stress developed in the weld as it cools

Ductility of the weld metal at high temperatures and

Presence of notches

This can be prevented or minimised by proper control of ferrite in the weld metal. Wide use of

the modified Schaffler diagrams have been made to determine the approximate amount of

ferrite that will be obtained in the austenitic weld metal of a given composition.

Selection of filler metals:The compositions of most filler metals are adjusted by the manufacturers to produce weld

deposits that have.

ferrite containing microstructures. Thus ferrite-forming elements, such as Chromium and

Molybdenum are maintained on the higher side of their allowable ranges and austenite-forming

elements are kept low.

The amount of ferrite in the structure of the weld metal depends upon the ratio or balance ofthese elements. At least 3 or 4 FN delta ferrite is needed in the as-deposited weld metal for

effective suppression of hot cracking.

Other families of stainless steels are:

Nitrogen strengthened austenitic steels (Duplex stainless steels), which have superior pitting

corrosion resistance and higher elevated temperature strength. These are welded with balanced

consumables of similar composition to maintain the ferrite to austenite ratio in the weld metal.

Ferritic stainless steels – (400 series stainless steels such as 446, 405, 430 and 430Se) – these

are welded with fillers of equivalent compositions, and are frequently welded with austenitic

filler metals to provide ductile weld joints.


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Martensitic stainless steels (such as 410, 414, 416, 420 431) are the most difficult stainless

steels to weld because they are chemically balanced to become harder, stronger and less ductile

through thermal treatment. These same metallurgical changes occur during welding. As a result

these changes are restricted to the weld area only and are not uniform over the entire section.

This non-uniform metallurgical condition of the part makes it susceptible to cracking.

Precipitation hardened stainless steels (PH steels) are welded using similar arc welding

processes as the austenitic stainless steels, and using fillers of equivalent composition.

However, they are usually heat-treated after welding to achieve the required mechanical

properties. There are a wide variety of hardenable filler materials available for these PH steels.

ARC WELDING OF HEAT-RESISTANT ALLOYS:

Heat resistant alloys can be welded by most arc-welding processes. GTAW and SAMW are

widely used; GMAW and SAW are used for welding thick sections.

The weldability of heat resistant alloys is markedly affected by the cleanliness of the base metal

and the filler metal. Sulphur and lead can diffuse through into the base metal when heated and

can result in severe cracking.

Nickel Base Alloys: The commercial alloys in this family are Incoloys and Inconels, Hastelloy

C, C276, B and X, Waspaloy etc. These are solid-solution alloys and are not age-hardenable.

These are welded in both the annealed and cold-worked conditions. Weldments can be used as

welded or after stress relieving, depending on the alloy and application. Filler metals are

usually of the same composition as the alloy being welded. Compositions are frequently

modified to resist porosity and hot cracking of the weld metal.

Cobalt base alloys: These alloys are available in both cast and wrought forms. Generally, castalloys are more difficult to weld than the wrought alloys. GTAW and GMAW are used where

the applications require high reliability welds, otherwise SMAW is used. Some of the

commercial alloys are Stellite® (trademark of Stellite Corporation, USA) grade 1, 6, 12, 21

206 etc. These fillers are used more for hard-surfacing of shear blades, augurs, screw flights

where high temperature hardness is required to be retained in service and in addition to the

hardness, where corrosion resistance is required.

Welding Process

SMAW - shielded metal arc welding

OFW - oxyfuel gas weldingSAW - submerged arc welding

PAW - plasma arc welding

ESW - electroslag welding

EGW - electrogas welding

EBW - electrobeam welding

LBW - laser beam welding

FCAW - flux-cord arc welding

Heat input = voltage x amperage x 60

Travel speed (in/min ; mm/min.)

Types and purposes of test and examinations


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Mechanical test: used in procedure or performance qualification as follows:

Tension test: used to determine the ultimate strength of the groove weld joints.

Guided bend test: used to determine the degree of soundness and ductility of groove weld joints.

Fillet weld test : used to determine the size, contour, and degree of soundness of fillet welds.

Notch-toughness test : used to determine the notch toughness of the weldment.

Stud-weld test: used to determine the acceptability of the stud welds.

Mechanical properties of metals:

Strength

Ductility Hardness

Toughness

Fatigue strength

Stainless steels:

Having at least 12% chromium

Five main classes of stainless steels:

Ferritic

Martensitic

Austenitic

Precipitation Hardening (ph)

Duplex Grade- half ferrite/half austenite

Austenitic grades- “200” and “300” grades

304 and 316 grades

Martensitic grades – 416 steels

Ferritic grades – 430 steels

Ph grades – 17.4 h

Duplex grade – AL-6XN

Six different types of penetrants:

visible / water washable

visible / solvent removable

visible / post-emulsifiable fluorescent / water washable


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fluorescent / solvent removable

fluorescent / post- emulsifiable

Maximum interpass temperature:

P1-315* c ( 600*f) carbon steelP8 – 177*c ( 350 *f) stainless steel

Ferrite number of Austenitic Stainless Steels:

Steel except type 310 = 3 and 10 FN

HAZ = the portion of the base metal whose mechanical properties or microstructure have been

altered by the heat of welding, brazing, soldering of thermal cutting.

The following grain structures starting from the area immediately adjacent to the weld are

typically present on a 0.15% carbon steel.

1. coarse grained region : ( heated bet. 1100*c and melting point)

2. refined region : 900*c to 1100*c

3. partial transformation: 750*c to 900*c

4. spheroidization (just below 750*c)

Welding procedure qualification is performed to show the compatibility of:

Base metals

Weld or base filler metals

Process

Techniques

P- Number of Materials:

P1 - Carbon steel

P2 - Low temp./ impact tested carbon steel

P3/ P4 – 1 ¼ Chrome - ½ MoSteel

P5 – 2 ¼ chrome-1 MoSteel

9 Cr – 1 MoSteel

5 Cr – ½ MoSteel

P6 /P7 – 12 CrSteel

P8 – Stainless steelP11 – 1 ½ chrome – ½ Mo

P22 – 2 ½ Chrome – 1 Mo

P41 – Nickel

P42 – Monel

P44 – Hasteloy C 276

P45 – Incoloy 800 H

P51 – Titanium

Commonly Used Filler Wire / Electrode

Carbon steel ( A 106-B,API 5L, A53 B )Fillerwire: ER 70S2 / E 6010


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Electrodes: E 7018

Low temp. Carbon steels :( A 533 Grd. A671 CC class 22)

TGS 1 N / LB-52 NS

Low Alloy Steel Pipe : P11- 1 ½ Cr- ½ Mo ( A335 A691 cl.42)TGS 1 CML CMB-98 or ER 80-SG, E 8018-B2

P22- 2 ½ Cr-1 Mo ( A335 / A 691 Grd. 22 cl. 42)

TGS-2CML/ CMB-108 or ER 80S-G, E-9018-B3

Stainless steels pipes:

A312-TP 304/304 L}

A 358-TP 304/304L} ER 308 L, ER 308L-16

A312-TP 304L}

A358-TP 304L} ER 308 L, E 308L-1G

A312 TP-316 – ER 308 L / E 308 L -16

Carbon steel / Monel – ERNiCu- 7

Carbon Steel / Nickel – ERNi-1

Carbon steel / Stainless steel

ER 309L-GTAW, ER 309L-1G – SMAW

Monel Titanium

ERNiCu-7 ERTi2

Nickel Hasteloy C276

ERNi-1 ERNiCrmo-4

Incoloy 800 H

ERNiCromo-3

Welding Defect Code:

IP - inadequate penetrationIF - incomplete fusion

IC - internal cavity

BT - burn through

SI - slag inclusions

WT - wagon track

SI - slag line

PO - porosity

CR - crack

RUC – root under cut

H/L - high low

EP - excess penetrationTI - tungsten inclusion


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HB - hollow bead

Non- Destructive Examinations (NDE)RT - radiographic test

UT - ultrasonic test

MPT – magnetic particle testPT - liquid penetrant test

VT - visual

AET – acoustic emission test

ET - eddy current test

LT - leak test

NRT – neutron radiographic

PRT – proof test

Destructive Examinations:Impact test

Bend testTensile test

Reasons for the occurrence of the tungsten inclusions include:

1.

contact of filler metal with hot tip of electrode

2. contamination of the electrode tip spatter

3.

extension of electrodes beyond their normal distances from the collet, resulting in

overheating of the electrodes

4. inadequate tightening of the collet

5. inadequate shielding gas flow rates or excessive wind drafts resulting in oxidation

of the weld tip

6. use of improper shielding

7. defects such as splits or cracks in the electrode

8.

use of excessive current for a given size electrode

9. improper grinding of the electrode or

10.

use of too small electrode.

Eight Major Groups of Alloys of Copper

1.

copper2. high copper alloys

3.

brasses ( Cu-Zn )

4. bronzes ( Cu-Sn)

5.

copper – nickels ( Cu-Ni )

6. copper – nickel-zinc alloys ( nickel silver )

7.

lead copper

8. special alloys

Properties that can determine as the result of the tensile test include:

ultimate tensile strength yield strength


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ductility

percent elongation

percent reduction area

modulus of elasticity

proportional limit

elastic limit toughness

Ventilation:

The bulk of fumes generated during welding and cutting consists of small particles that

remain suspended in the atmosphere for a considerable time.

Example of ventilation includes:

natural

general area mechanical ventilation

portable local exhaust devices

downdraft tables cross draft tables

extractors built into the welding equipment

air ventilated helmets

Highly Toxic Materials:

Certain materials which are sometimes present in consumables, base metals, coatings or

atmospheres for welding or cutting operations, have permissible expose limits of 1.0

mg/m3 or less.

Toxic Metals :

antimony

arsenic

barium

beryllium

cadmium

chromium

cobalt

copper lead

manganese

mercury

nickel

selenium

silver

vanadium

Effects of Chemical Elements in Steels

carbon - the key element in steels, has a major influence on strength, toughness,ductility and hardness


23/33


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horizontal position 2F – plates so placed that the weld is deposited with its axis

horizontal on the upper side of the surface and against the vertical surface

vertical position 3F – plates so placed that the weld is deposited with its axis vertical

Overhead position 4F – plates so placed that the weld is deposited with its axishorizontal on the underside of the horizontal surface and against the vertical surface.

Pipe Positions:

flat positions 1F – pipe with its axis inclined at 45* deg to horizontal and rotated during

welding so that the weld metal is deposited from above and at the point of deposition

the axis of the weld is horizontal and the throat vertical

Horizontal Positions 2F and 2FR

Position 2F – pipe with its axis vertical so that the weld is deposited on the upper side of the

horizontal surface and against vertical surface. The axis of the weld will be horizontal and the pipe is not to be rotated during welding.

Position 2FR – pipe with its axis horizontal and the axis of the deposited weld in the vertical

plane. The pipe is rotated during welding.

Overhead positions 4F – pipe with its axis vertical so that the weld is deposited on the

underside of the horizontal surface and against the vertical surface. The axis of the weld

will be horizontal and the pipe is not rotated during welding.

Multiple positions 5F – pipe with its axis horizontal and the axis of the deposited weld

in the vertical plane. The pipe is not to be rotated during welding.

SMAW

“ Stick welding” more often called in this process. This process operates by heating the metal

with an electric arc between covered metal electrode and the metals to be joined. The primary

element of the SMAW process is the electrode itself. It is made of solid metal core wire covered

with a layer of granular flux held in place by some type of bonding agent. All carbon and low

alloy steel electrodes use essentially the same type of steel core wire, a low carbon, rimmed

steel.

Ex. E-7018

Where: E= stands for electrode

70= tensile strength of the deposited weld metal is at least 70,000 psi

1= “position” indicates the electrode is suitable for use in any position

2= molten metal is so fluid that the electrode can be only be used in the flat or horizontal

filler positions

3= no designation

4= means the electrode is suitable for welding in “downhill progression”

Electrode ending in “5”,”6”, or “8” are classified as “low hydrogen types”.

Oven should be heated electrically and have a temperature control capability in the range of

150* to 350* F. Low hydrogen electrodes be held at a minimum oven temperature of 250*F (120* C) after removal from their sealed container. Advantage of the SMAW process is the


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“speed”. Disadvantage which also affects productivity is the layer of solidified slag which must

be removed.

Discontinuities in the SMAW process :

Porosity- presence of moisture or contamination in the weld region. Arc length too long ( lowhydrogen electrode)

Arc blow- can cause spatter, undercut, improper weld contour and decreased penetration.

Slag inclusions- can also occur simply because it relies on a flux system for weld protection.

Since SMAW process is primarily accomplished manually, numerous discontinuities can result

from improper manipulation of the electrode. Some of these are incomplete joint penetration,

cracking, undercut, overlap, incorrect weld size and improper weld profile.

Suffix Major Alloy Element ( s )A1 = 0.5% molybdenum

B1 = 0.5% molybdenum – 0.5% chromium

B2 = 0.5% molybdenum -1.25% chromium



C1 = 2.5% nickel

C2 = 3.5% nickel

C3 = 1.0% nickel

D1 = 0.3% molybdenum – 1.5% manganese

D2 = 0.3% molybdenum – 1.75% manganese

G* = 0.2% molybdenum; 0.3% chromium; .5% nickel; 1.0% manganese; 0.1%

vanadium

The electrode coating is the feature which classifies the various types of electrodes. It actually

serve five separate functions:

1.

shielding – the coating decomposes to form a gaseous shield for the molten metal

2. deoxidation – the coating provides a fluxing action to remove oxygen and other

atmospheric gases

3. alloying – the coating provides additional alloying elements for the weld deposit

4. ionizing – the coating improves electrical characteristics to increase arc stability

5.

insulating – the solidified slag provides an insulating blanket to slow down the weldmetal cooling rate. ( minor effect ).

GTAW- Gas Tungsten Arc Welding ( TIG )

Electrode is not intended to be consumed during the welding operation. It is made of pure or

alloyed tungsten which has the ability to withstand very high temperatures, even those of the

welding arc. All of the arc and metal shielding is achieved through the use of an inert gas which

flows out of the nozzle surrounding the tungsten electrode. The deposited weld bead has no

slag requiring removal because no flux used.

Class Alloy ColorEWP pure tungsten green


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EWCe-2 1.8-2.2% ceria orange

EWLa-1 1% lanthanum oxide black

EWTh-1 0.8-1.2% thoria yellow

EWTh-2 1.7-2.2% thoria red

EWZr 0.15-0.40% zirconia brown

EWTh-2 type, is most commonly used for joining of ferrous materials. GTAW can be

performed using DCEP, DCEN, AC.

The DCEP will result more heating of the electrode, while the DCEN will tend to heat the base

metal more.

AC alternatively heats the electrodes and base metal. AC is typically used for the welding of

aluminum because the alternating current will increase the cleaning action to improve weld

quality.

DCEN, is commonly used for the welding of steels. GTAW uses inert gas for shielding. Argon

and Helium are commonly used inert gas based on their relative cost and availability compared

to other types of inert gases.

Principal advantage of GTAW is it can produce welds of high quality and excellent visualappearance, no slug to remove after welding, low tolerance for contamination.

AC – alternating current

DCEP – direct current, electrode positive

DCEN – direct current, electrode negative.

GMAW- Gas Metal Arc Welding ( MIG )

The electrodes used for this process are solid wires which are supplied on spools or reels of

various sizes. They are detonated by the letters “ER” designates the wire as being both an

electrode and a rod, meaning that it may conduct electricity ( electrode ) or simply be applied

as a filler metal ( rod ) when used with other welding process.

Ex. ER-70S-2

Where : ER = designates both electrode and rod

70 = tensile strength at least 70,000 psi

S = solid wire

2

= chemistry of the electrode

GTAW electrodes typically have increased amounts of deoxidizers such as manganese.

Silicon. And aluminum to help avoid the formation of porosity. It is normally accomplished

using DCEP .

Useful notes on welding:

approximate welding point of carbon steel is 2780*F

crater cracks are most often the result of improper technique

during tempering, as the temperature increases, hardness decreases ultraviolet light maybe used in PT and MT method


27/33

used of preheat will result a slower cooling rate and wider heat affected zone

for plain carbon steels increase of hardness, is also increase of tensile strength

voltage, current, and travel speed are welding variables that affect heat input

as the temp. increases , tensile strength decreases also ductility increases

the best protection from radiation is to maximize the distance from the radiation

piezoelectricity is a material property used in UT tempering is a thermal treatment that follows quenching and restores some of the metals

ductility

post heat treatment is the method used most often to reduce the high residual stress

created by welding

capillary action is the physical principle that permits the migration of liquid penetrants

in to a very fine surface discontinuities

braze welding is the process where by a large gap is filled with braze material without

the help of capillary action

an increase in the carbon equivalent of a carbon steel will result in an increase of its

hardness and strength

hydrogen in the molten weld can cause cracking and porosity martensite is the rapid quenching of high carbon steel from the austenitizing range

normalizing is the heat treatment in which the metals temperature is raised to the

austenitizing range, held for a prescribed time and then allowed to cool to room

temperature in still air

stess relieving is the heat treatment for carbon steels in which the metals temperature is

raised to just below the lower transformation temperature and held for a prescribed time

before allowing it to cool at a controlled rate

the used of preheat on a medium carbon steel will reduce distortion; reduce the

possibility of hydrogen cracking.

Fluid Service - a general term concerning the application of a piping system, considering the

combination of fluid properties, operating conditions, and other factors which establish

the basis for design of the piping system.

Category “D” Fluid Service – a fluid service in which all the following apply:

1.

the fluid handled is non-flammable, nontoxic, and not damaging to human tissues .

2. the design gage pressures does not exceed 1035 kPa ( 150 psi ) and

3. the design temperature is from -29*C ( -20*f ) through 186 * C ( 366* F ).

Category “ M “ Fluid Service – a fluid service in which the potential for personnel exposure

is judged to be significant and in which a single exposure to a very small quantity of atoxic fluid, caused by leakage, can produce serious irreversible harm to persons on

breathing or bodily contact, even when prompt restorative measures are taken.

High Pressure Fluid Service – a fluid service for which the owner specifies the cause of

Chapter IX for piping design and construction:

Normal Fluid Service – a fluid service pertaining to most piping covered by this code, i.e. not

subject to the rules for Category D, and M or High Pressure Fluid Service, and not

subject to severe cyclic conditions.

100 % examination- complete examination of all of a specified kind of item in a designated

lot of piping.

Random examination – complete examination of a percentage of a specified kind of item ina designated lot of piping.


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Spot examination – a specified partial examination of each of a specified kind of item in a

designated lot of piping e.g. of part of the length of all shop- fabricated welds in a lot

of jacketed piping.

Random spot examination – a specified partial examination of a percentage of a specified

kind of item in a designated lot of piping.

API 651 – cathodic protection of Aboveground storage tanks

API 652 - lining of above ground Petroleum Storage Tanks Bottoms

API 650 - welded steel tanks for oil storage

API 620 - design and construction of large storage tanks

API 653 - tank inspection, repair, alternation and reconstruction

Shall/must – mandatory

Should – recommended

Maybe/ might be - optional

Technique And Workmanship

The maximum allowable SMAW electrode sizes that can be used are given below. The ability

of each welder to use the maximum sizes listed in the table shall be checked by the Inspector

as early as possible during fabrication.

a)Low hydrogen electrodes

5 mm for the 1G/1F position.

4 mm for all other positions.

b) Non-low hydrogen electrodes

5 mm for all positions.

Conditioning, Storage, And Exposure Of SMAW Electrodes (Notes 1, 2, 3, 4)

Low Hydrogen Electrodes To A5.1

Drying

Prior to use all electrodes shall be dried at 260-430 °C for 2 hours minimum. The drying step

may be deleted if the electrodes are supplied in the dried condition in a hermetically sealed

metal can with a positive indication of seal integrity. Electrodes may be re-dried only once.

Storage

After drying, the electrodes shall be stored continuously in ovens at 120 °C minimum.

Exposure

Upon removal from the drying or storage oven or hermetically sealed containers, the electrodes

may not be exposed to the atmosphere for more than 4 hours. The exposure may be extended

to 8 hours if the electrodes are continuously stored in a portable electrode oven heated to 65 °C

minimum. Electrodes exposed to the atmosphere for less than the permitted time period may

be re-conditioned. Electrodes exposed in excess of the permitted time period must be re-dried.

Electrodes that have become wet or moist shall not be used and shall be discarded.

Re-conditioning


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Electrodes exposed to the atmosphere for less than the permitted time period may be returned

to a holding oven maintained at 120 °C minimum; after a minimum holding period of four

hours at 120 °C minimum the electrodes may be reissued.

Low Hydrogen Electrodes To A5.5

DryingPrior to use all electrodes shall be dried at 370-430 °C for 2 hours minimum. For E70xx and

E80xx electrodes, the drying step may be deleted if the electrodes are supplied in the dried

condition in a hermetically sealed metal can with a positive indication of seal integrity.

Electrodes may be re-dried only once.

Storage

After drying, the electrodes shall be stored continuously in ovens at 120 °C minimum.

Exposure


may not be exposed to the atmosphere for more than 2 hours for E70xx or E80xx electrodesand 30 minutes for any higher strength electrodes. The exposure times may be doubled (to 4

hours and 1 hour, respectively) if the electrodes are continuously stored in a portable electrode

oven heated to 65 °C minimum. E70xx and E80xx electrodes exposed to the atmosphere for

less than the permitted time period may be re-conditioned. E70xx and E80xx electrodes

exposed in excess of the permitted time period must be re-dried. Higher strength electrodes

(above E80xx) must be re-dried after any atmospheric exposure. Electrodes that have become

wet or moist shall not be used and shall be discarded.

Re-conditioning

E70xx and E80xx electrodes exposed to the atmosphere for less than the permitted time period

may be returned to a holding oven maintained at 120 °C minimum; after a minimum holding period of four hours at 120 °C minimum the electrodes may be reissued.

Stainless Steel And Non-Ferrous Electrodes

Drying

Prior to use all electrodes shall be dried at 120-250 °C for 2 hours minimum. The drying step



Storage

After drying, the electrodes shall be stored continuously in ovens at 120-200 °C minimum.Exposure


may not be exposed to the atmosphere for more than 4 hours. The exposure may be extended

to 8 hours if the electrodes are continuously stored in a portable electrode oven heated to 65 °C

minimum. Electrodes exposed to the atmosphere for less than the permitted time period may

be re-conditioned. Electrodes exposed in excess of the permitted time period must be re-dried.

Electrodes that have become wet or moist shall not be used and shall be discarded.

Re-conditioning


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Electrodes exposed to the atmosphere for less than the permitted time period may be returned

to a holding oven maintained at 120 °C minimum; after a minimum holding period of four

hours at 120 °C minimum the electrodes may be reissued.

Non-Low Hydrogen Electrodes To A5.1 Or A5.5

The electrodes shall be stored in a dry environment. Any electrodes that have become moistor wet shall not be used and shall be discarded.

Notes:

1) Storage and rebake ovens shall have a calibrated temperature gauge to continuously

monitor the temperature.

2) Portable electrode storage ovens with a minimum temperature of 120 °C are considered

equivalent to storage ovens. Proper use of the oven (e.g. closed lid, continuously on

while in use) and periodic checks of the temperature achieved with each portable oven

are required.

3) Some applications may require higher drying temperatures and shorter atmospheric

exposure times.

4) Electrode types are listed in accordance with ASME SEC IIC.

SAW fluxes:

All fluxes shall be stored in sealed containers in a dry environment. Opened SAW flux

containers shall be stored continuously in ovens at 65 °C minimum or the manufacturer's

recommendation, whichever is greater. Any flux that has become moist or wet shall not be

used and shall be discarded.

SAW, GTAW, GMAW, and FCAW electrodes and wires:

All electrodes and wires shall be stored in sealed containers in a dry environment. Any wires

that have visible rusting or contamination shall not be used and shall be discarded

General

AWS A2.4 "Standard Welding Symbols" shall be used for all welding details on all drawings.

AWS A3.0 "Standard Terms and Definitions" shall be used for all specifications and

documents.

Miscellaneous RequirementsFor field welding, remote current controls shall be used if the welding is more than 30 m

from the welding power source or when the welders are working in "remote" locations (e.g.,

inside a vessel)

Welding power supplies shall be calibrated in accordance with BS 7570 or an approved

equivalent.

Low Hydrogen Electrodes to A5.1

Drying


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Prior to use all electrodes shall be dried at 260-430°C for 2 hours minimum. The drying step



Storage

After drying, the electrodes shall be stored continuously in ovens at 120°C minimum.Exposure

Upon removal from the drying or storage oven or hermetically sealed containers, the

electrodes may not be exposed to the atmosphere for more than 4 hours. The exposure may

be extended to 8 hours if the electrodes are continuously stored in a portable electrode oven

heated to 65°C minimum

Low Hydrogen Electrodes to A5.5

Drying

Prior to use all electrodes shall be dried at 370-430°C for 2 hours minimum. For E70xx and

E80xx electrodes, the drying step may be deleted if the electrodes are supplied in the driedcondition in a hermetically sealed metal can with a positive indication of seal integrity.

Electrodes may be re-dried only once.

Storage

After drying, the electrodes shall be stored continuously in ovens at 120°C minimum.

Exposure


electrodes may not be exposed to the atmosphere for more than 2 hours for E70xx or E80xx

electrodes and 30 minutes for any higher strength electrodes. The exposure times may be

doubled (to 4 hours and 1 hour, respectively) if the electrodes are continuously stored in a portable electrode oven heated to 65°C minimum.

Stainless Steel and Non-Ferrous Electrodes

Drying

Prior to use all electrodes shall be dried at 120-250°C for 2 hours minimum. The drying step


metal can with a positive indication of seal integrity.Electrodes may be re-dried only once.

Storage

After drying, the electrodes shall be stored continuously in ovens at 120-200 °C minimum.Exposure


electrodes may not be exposed to the atmosphere for more than 4 hours. The exposure may

be extended to 8 hours if the electrodes are continuously stored in a portable electrode oven

heated to 65°C minimum.

SAW Fluxes

All fluxes shall be stored in sealed containers in a dry environment. Opened SAW flux

containers shall be stored continuously in ovens at 65°C minimum or the manufacturer'srecommendation, whichever is greater.


32/33

Welding processes and letter designation.

Group Welding Process Letter Designation

Arc welding Carbon Arc CAW

Flux Cored Arc FCAW

Gas Metal Arc GMAW

Gas Tungsten Arc GTAW

Plasma Arc PAW

Shielded Metal Arc SMAW

Stud Arc SW

Submerged Arc SAW

Brazing Diffusion Brazing DFB

Dip Brazing DB

Furnace Brazing FB

Induction Brazing IB

Infrared Brazing IRB

Resistance Brazing RB

Torch Brazing TB

Oxyfuel Gas Welding Oxyacetylene Welding OAW

Oxyhydrogen Welding OHW

Pressure Gas Welding PGWResistance Welding Flash Welding FW

High Frequency Resistance HFRW

Percussion Welding PEW

Projection Welding RPW

Resistance-Seam Welding RSEW

Resistance-Spot Welding RSW

Upset Welding UW

Solid State Welding Cold Welding CWDiffusion Welding DFW

Explosion Welding EXW

Forge Welding FOW

Friction Welding FRW

Hot Pressure Welding HPW

Roll Welding ROW

Ultrasonic Welding USW

Soldering Dip Soldering DSFurnace Soldering FS


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Induction Soldering IS

Infrared Soldering IRS

Iron Soldering INS

Resistance Soldering RS

Torch Soldering TS

Wave Soldering WS

Other Welding Processes Electron Beam EBW

Electroslag ESW

Induction IW

Laser Beam LBW

Thermit TW

what is the difference between welding transformer

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