What Is The Difference Between Welding Transformer

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 @ 50-250amp Transformer 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):

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 receive two 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

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 CLASSIFICATION They 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. With DAV, 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:

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 follows1) 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:

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:

4

2

5

3

1

6

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:

7

6

5

4

3

2

1

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

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 different from 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

F Number

General 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:Test Position

ISO and EN

Flat

1G

PA

Horizontal

2G

PC

Welding Position

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

2FR

PB

Vertical Upwards Progression

3F

PF

Vertical Downwards Progression

3F

PG

Overhead

4F

PD

Pipe Fixed Horizontal

5F

PF

Horizontal Rotated

ASME P Material Numbers This is a general guide ASME P numbers and their equivalent EN288 groupings. P No.

EN288

Base Metal Carbon Manganese Steels, 4 Sub Groups

1

1

   

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

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 Austenitic Stainless Steels, 4 Sub groups 

8

9

9A, B, C

7

10A,B,C,F,G

  

Group1 Typically Grades 304, 316, 347 Group 2 Typically Grades 309, 310 Group 3 High manganese grades Group 4 Typically 254 SMO type steels

Typically two to four percent Nickel Steels

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

-

25

22b

26 to 30

Not Used Aluminium Magnesium Manganese Typically 5083, 5086 Not used

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

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 recrystallisation 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 to create bonding through diffusion,

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 facing with 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 several advantages:

  

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 zone 2. 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 and grey 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, where some localised melting may occur, the partially melted zone is observed.

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 residual shrinkage stress, depending on the degree of restrain imposed on the weld.

ARC WELDING OF PLAIN AND HARDENABLE CARBON STEELS AND ALLOY STEELS: 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 & 0.95 Mo 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 other variable; it is at best only an approximate measure of weldability or susceptibility to cold

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 <0.25%) are generally easy to join by any arc welding process. Welds of acceptable quality can be produced without the need for any preheating, post-heating or any special welding techniques. Medium carbon steels (Carbon 0.25%-0. 50%) can also be satisfactorily welded by all arc welding processes. Because of the formation of greater amounts of martensite in the weld zone and the higher hardness of the martensite, preheating or post-heating or both are often necessary. High 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 stress corrosion 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 creepstrength 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

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 of these 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.

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, cast alloys 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 welding SAW - 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

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

 

fluorescent / solvent removable fluorescent / post- emulsifiable

Maximum interpass temperature: P1-315* c ( 600*f) carbon steel P8 – 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. 2. 3. 4.

coarse grained region : ( heated bet. 1100*c and refined region : 900*c to 1100*c partial transformation: 750*c to 900*c spheroidization (just below 750*c)

melting point)

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 steel P11 – 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

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 ERNiCu-7

Titanium ERTi2

Nickel ERNi-1

Hasteloy C276 ERNiCrmo-4

Incoloy 800 H ERNiCromo-3 Welding Defect Code: IP - inadequate penetration IF - 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 penetration TI - tungsten inclusion

HB - hollow bead Non- Destructive Examinations (NDE) RT - radiographic test UT - ultrasonic test MPT – magnetic particle test PT - 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 test Tensile 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. 2. 3. 4. 5. 6. 7. 8.

copper high copper alloys brasses ( Cu-Zn ) bronzes ( Cu-Sn) copper – nickels ( Cu-Ni ) copper – nickel-zinc alloys ( nickel silver ) lead copper special alloys

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

ultimate tensile strength yield strength

      

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



manganese - primary desulphuriser and secondary deoxidizer, often added in order to enable the carbon content to be reduced



silicon



aluminum - grain refiner and tertiary deoxidizer



molybdenum – improves creep resistance and reduces temper embrittlement



chromium - improves hardness and resistance to wear ,in stainless steel it added for corrosion resistance



Nickel - improves ductility, strength and toughness. In austenitic stainless steel it improves resistance to corrosion from acids



Sulfur - exceeds 0.05 % tends to cause brittleness and reduce weld ability. 0.10 to 0.30 % to improve the machinability of steel



Phosphorus – 0.04 % hardened steels, it may tend to cause embrittlement. In low alloy steels may added up to 0.010 % to improve both strength and corrosion resistance.

- primary deoxidizer, reduced toughness if too much exists

Plate Positions (Groove Welds )    

flat position 6G – plate in a horizontal plane with the weld metal deposited from above horizontal position 2G – plate in the vertical plane with axis of the weld horizontal vertical position 3G – plate in the vertical plane with the axis of the weld vertical Overhead position 4G – plate in a horizontal plane with the weld metal deposited from underneath.

Pipe Positions 

flat positions 1G – pipe with its axis horizontal and rolled during welding so that weld metal is deposited from above



horizontal position 2G – pipe with its axis vertical and the axis of the weld in a horizontal plane



Multiple position 5G – pipe with its axis horizontal and with the welding groove in a vertical plane. Welding shall be done without rotating the pipe



Multiple position 6G – pipe with its axis inclined at 45* deg to horizontal. Welding shall be done without rotating the pipe.

Plate Positions (Fillet Welds) 

flat position 1F – plates so placed that the weld is deposited with its axis horizontal and its throat vertical



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 axis horizontal 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

“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 ( low hydrogen 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 B3 = 1.0% molybdenum – 2.25% chromium B4 = 0.5% molybdenum – 2.0% 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% G* = 0.2% molybdenum; 0.3% chromium; vanadium

manganese .5% nickel; 1.0% manganese; 0.1%

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 weld metal 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 Color EWP pure tungsten green

EWCe-2 EWLa-1 EWTh-1 EWTh-2 EWZr

1.8-2.2% ceria 1% lanthanum oxide 0.8-1.2% thoria 1.7-2.2% thoria 0.15-0.40% zirconia

orange black yellow red 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 visual appearance, 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 70 S

= solid wire

2

= chemistry of the electrode

rod

= tensile strength at least 70,000 psi

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

               

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 a toxic 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 in a designated lot of piping.

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

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 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 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 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. 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 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 120-200 °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

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 moist or 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 Requirements For 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

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 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 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 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 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 120-200 °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. 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.

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

Diffusion Brazing

DFB

Dip Brazing

DB

Furnace Brazing

FB

Induction Brazing

IB

Infrared Brazing

IRB

Resistance Brazing

RB

Torch Brazing

TB

Oxyacetylene Welding

OAW

Oxyhydrogen Welding

OHW

Pressure Gas Welding

PGW

Flash Welding

FW

Brazing

Oxyfuel Gas Welding

Resistance Welding

High Frequency Resistance HFRW

Solid State Welding

Soldering

Percussion Welding

PEW

Projection Welding

RPW

Resistance-Seam Welding

RSEW

Resistance-Spot Welding

RSW

Upset Welding

UW

Cold Welding

CW

Diffusion Welding

DFW

Explosion Welding

EXW

Forge Welding

FOW

Friction Welding

FRW

Hot Pressure Welding

HPW

Roll Welding

ROW

Ultrasonic Welding

USW

Dip Soldering

DS

Furnace Soldering

FS

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