ESAB TRAINING & EDUCATION

TIG welding

Content

Introduction ............................................................. 3Historical background ........................................... 4General information on TIG welding ................... 5The principle of TIG welding ................................. 7Why use the TIG method? ...................................... 7Equipment .............................................................. 8Power sources .......................................................... 8TIG torch ................................................................. 8Gas hood .................................................................. 9Electrodes ................................................................ 9Shielding gas ......................................................... 11Argon ..................................................................... 12Helium .................................................................... 12Argon/hydrogen mixtures ...................................... 12Shielding gas flow .................................................. 12Gas lens .................................................................. 13Shielding gases for TIG welding ........................... 14Gas shield when welding titanium......................... 15Environmental aspects ........................................... 16Welding parameters ............................................... 17Weld imperfections ................................................ 18

Weld imperfections in TIG welding ...................... 18Joint preparation in pipe welding ...................... 20Wall thickness ........................................................ 20Consumables ......................................................... 21Unalloyed and low-alloy steel .............................. 22Stainless and acid-resistant steel ......................... 23Aluminium and its alloys ..................................... 24Other material ...................................................... 24Mechanised TIG welding ..................................... 26Historical background .......................................... 26Applications ........................................................... 26Advantages of mechanisation ............................... 27Narrow gap welding ............................................. 28Introduction ........................................................... 28General recommendations .................................... 28Summary ................................................................ 30Welding examples .................................................. 30Aluminium welding .............................................. 31Aluminium welding with direct current ............ 31Examples of aluminium welding ......................... 33Glossary ................................................................ 35

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TIG welding

TIG welding is a fusion-welding method and its name is an acronym of Tungsten Inert Gas. Tungsten is the material from which the electrode is made. The word “inert” re-lates to the gas which is inert, inactive, and does not participate in the welding process in any way apart from protecting the molten pool and the electrode from the harmful effect of the air. The gas also influences the way the ionisation of the atmosphere in the arc functions. Another name is GTAW, which stands for Gas Tungsten Arc Weld-ing. In Germany, the name WIG, Wolfram (tungsten) Inert Gas, is used. TIG welding is primarily characterised by:

• High weld quality• Narrow-gauge metal• Versatile method, suitable for many

different materials• Even, smooth welds• No spatter• Good tolerances• Concentrated, stable arc

• Relatively slow method, especially in thick material

• Can sometimes be used to weld without consumables

• No welding fumes• All welding positions• No slag formation• The heat that is supplied is independent

of the consumable

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Historical background

This welding method was developed in the USA at the beginning of the 1940s for the metals mag-nesium and aluminium, which are both difficult to weld. The trend was triggered by the require-ments of the aircraft industry.

TIG welding was first used with helium as the shielding gas. A change was then made to argon, which is less expensive and in some cases a bet-ter shielding gas. The welding was initially per-formed with direct current and with the electrode connected to the plus pole. Eventually, however, light metals – and, at a later date, other materials were welded with alternating current and with the electrode connected to the minus pole. To begin with, pure graphite or pure tungsten were used as the electrode material, but develop-ments have taken place in this area and alloyed tungsten electrodes, which have better characte-ristics, are now used.

Initially, scratch starting was used as the stan-dard way of striking the arc, but high-frequency (HF) ignition was then developed as a result of the risk of contaminants finding their way into the weld metal. At the beginning of the 1950s, TIG welding had been fully accepted as a welding method. It is currently used very extensively in the USA, but it is somewhat less usual in Europe. As a re-sult of its many positive characteristics, TIG will continue to be an extremely important welding method in the future. During its first 20 years, TIG welding was known as argon welding. Nowadays, argon gas is used for a number of other welding methods, so argon welding can no longer be used exclusively as the name of one welding method. To begin with, TIG was only used for manual welding, but developments have moved continu-ously towards more mechanised equipment. TIG is now used in robots, pipe-cutting tools, tube-welding machines and longitudinal automatic welders, for example. Power sources, automatic welders and periphe-ral equipment are also being developed to enable the process to be used in new applications. New software for controlling the welding process is making more controlled welding possible.

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General information on TIG welding

In TIG welding, an arc is created between a non-consumable electrode and the workpiece. The electrode, arc, molten pool and any additional wire are protected from the effect of the air using an inert (chemically inactive) shielding gas, nor-mally argon. The air contains oxygen, nitrogen and moisture which must not be allowed to enter the process. In most cases, direct current is used, with the electrode connected to the minus pole, but alter-nating current is normally used for welding light metals. The ability to break up oxides when the electrons travel from the workpiece to the elec-trode is the objective when welding with direct current. The torch can also be connected to the plus pole, when welding aluminium, for example (to break up the oxides), but this is not recom-mended (it is necessary to use thick electrodes). When welding with direct current, the heat is distributed in such a way that around 70 per cent of the output is produced at the plus pole. As a result, the electrode is normally connected to the minus pole and the workpiece to the plus pole. When welding with alternating current, the heat distribution is 50%-50%. In connection with normal direct current weld-ing with the electrode connected to the minus pole, DCSP (Direct Current Straight Polarity), the electrons travel from the electrode to the workpiece. This does not produce sufficient

oxide disintegration when welding aluminium, however. So a compromise is reached by nor-mally using alternating current for aluminium. The electrode is made of tungsten, which has

such a high melting point that it does not meltduring welding (melting point around 3,400°C) unless it is overloaded. The welding can be performed by simply melt-ing the weld metal, but it is more common for consumables to be used. The joints are often filled with consumable wire. Alloys can also be supplied to the joints. The wire which does not conduct the current is supplied separately from the side. Unlike MIG welding, for example, it is therefore easy to con-trol the heat/consumable ratio. It is important that the end of the wire is pro-tected the whole time in the gas atmosphere to prevent it oxidising. It is best if the wire is sup-plied at the edge of the molten pool. When the welding has been completed, the oxi-dised end should be cut off before welding begins again, to ensure that unnecessary contaminants

do not enter the molten pool. To start welding, the arc has to be struck. This is normally done using an HF generator that is incorporated in the power source. A high voltage at high frequency (HF) starts the welding. When welding with di-rect current, the machine senses when the arc has been struck and turns off the HF generator. When welding with alternating current, the arc is ex-tinguished every time the current short circuits and for this reason the HF generator needs to be connected the whole time. Another way of starting is to touch the work-piece with the electrode and then lift the elec-trode so that the open-circuit voltage ignites the arc. This is used with power sources that do not have HF (MMA power sources). Lift-arc is a rel-atively new method. The electrode is placed on the workpiece and a very low, harmless current

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flows through it. When the electrode is lifted, the arc ignites. The disadvantage of touch starting is that tung-sten can be transferred to the workpiece. This can be clearly seen on X-ray film. Lift-arc and HF leave no tungsten inclusions. When it comes to HF ignition, the disadvan-tage is that it can disrupt radio communication and electronic equipment, such as computers, if they are not protected sufficiently. Once welding has begun, the current is increased steplessly to the set value during a certain period that can also

Lift-Arc ignition begins by placing the tip of the electrode on the precise point at which you plan to begin welding. You are then in the right position when the arc ignites. The electrode does not conduct electricity, so there is no risk of a short circuit.

Press the button on the torch. The electronic system is connected and controls the entire starting process auto-matically. The welding current is not flowing at this stage and the electrode cannot be damaged.

Now lift the electrode from the workpiece, either straight up or by tilting it above the gas hood. The electronic system senses that this has been done and automatically ignites the arc. The current increases to the set welding current without leaving any trace of tungsten in the molten pool.

When you release the button, the craterfilling function is activated. The current is reduced and the arc is extin-guished. The slope time is adapted to match the set cur-rent value and is therefore higher the higher the welding current becomes. The aim here is to avoid welding defects at the end of the process.

be set. This is known as slope-up and it is used to enable the welder to get into position with his welding torch if he is welding manually Another advantage of slope-up is that there is no shock effect on the electrode if it is cold. This prevents tungsten being “spattered” on the workpiece. Slope-up also extends the service life of the elec-trode. When slope-up has been completed, a molten pool has been created and welding can begin. The welding can be performed with or without pulsing current and this may even need to be changed during the welding process.

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There are many parameters that need to be taken into account during welding. They include:

• Pulsing current• Basic current between pulses• Times for pulsing and basic current• Arc voltage (=arc length)• Welding speed• Welding position• Possible weaving• Wire-feed speed

Their effect on the process varies and they all need to be taken into account to produce a goodresult. When the welding is going to be interrup-ted, the current should be reduced steplessly from the welding current to zero. This is done to avoid a crater forming when the welding stops. Oth-erwise a welding defect known as a pipe could occur. When the arc has been extinguished, the shielding gas should be allowed to continue flo-wing for a while, depending on the current and electrode diameter, to protect the molten pool and the electrode from oxidation.

1. Power source2. HF generator3. Shielding gas4. Gas hood

The principle of TIG welding

Why use the TIG method?

The advantage of TIG compared with other met-hods is the high weld quality. This method can be used for manual welding in short series or site welding, but it is also ideal for mechanisation.

TIG is used primarily to weld stainless and other high-alloy steel and to weld non-ferrousmetals such as aluminium, copper alloys, inconel and monel. Examples of materials that are idealfor welding with TIG include:

• Low-alloy killed carbon steel• Stainless steel• Acid-proof stainless• Duplex• Inconel• Monel• Titanium• Copper alloys• Aluminium and aluminium alloys• Rare welding metals such as beryllium

The only metal that is actually impossible to weld is zinc. After joint preparation, the TIG method can be used on virtually all metal thicknesses. Its main application is lighter gauge material, approxi-mately 0.3-4 mm, where butt welding is often the chosen welding method. Generally speaking, TIG is a method that provides top-class control of heat supply to the workpiece. In this way, small parts can be

welded that could not be welded using other methods, such as MIG/MAG. If complete penetration of the material is required, in pipe welding, for example, TIG is ideal. This method produces extremely clean weld metal. The welds are often ex-tremely even and beautifully rounded and TIG can be used when the visual ap-pearance is important and when the sur-face smoothness requirements are rigor-

ous, as they are in the food industry. Compared with MIG/MAG welding and sub-merged arc welding, TIG is a slow method, es-pecially on thicker material. The method uses a lower current and lower arc voltage and the output density is therefore lower. As has already been stated, it is used for lighter gauge material, but it can also be used for heavier material after joint preparation. TIG welding can be combined with other weld-ing methods. The root run in a weld joint can be performed using TIG, while the filling passes are

5. Electrode6. Arc7. Workpiece

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performed using MIG/MAG or submerged arc welding, for example. This means that satisfactory complete penetra-tion of the root is obtained and the welding speed is high. This method is used extensively when welding equipment for nuclear power stations, as the demands imposed on weld quality are extremely rigorous, for obvious reasons. Other areas in which TIG is used include the food in-dustry and the petrochemical industry, the air-craft industry and military industries. In connec-

tion with quality work in the offshore industry, the TIG method is also used. Large areas within mechanised TIG welding include the joining of pipes and the welding of pipes to tubular plates, in heat exchangers, for example. Applications in-clude:• Stainless pipes• Duplex pipes• Titanium pipes• Carbon steel pipes• Welding pipes to tubular plates

Equipment

for this purpose. They are in principle TIG power sources based on inverter technology, which are supplemented with a computer unit to control the process.

TIG torches

The electrode is fixed in a collet made of copper, which transfers the current to the electrode. This collet is clamped in a gas lens or electrode nozzle. It is surrounded by a gas hood to direct the flow of gas onto the weld. To fit and change electrodes, there is a backplate which is sealed with an O-ring gasket to prevent any air leaking in. There is a seal between the gas hood and the electrode holder The torch head can be at-tached to a manual TIG torch, a robot arm or automated ma-chines of different kinds, such as a pipe-welding head. A cable for the welding current and a hose for supplying shielding gas are connected to this torch head. Depending on the current that is being used, the electrode holder is cooled with water or air to prevent it becoming too hot or melting. If water is used there are two additional hoses for wa-ter cooling. Water cooling is somewhat more cum-bersome than air cooling, but there are still more advantages and water cooling is therefore more common. Depending on their design, air-cooled torches can accommodate approximately 50-150 A, while the corresponding figure for water-cooled torches is 250-600 A.

Power sources

There are different power sources for TIG weld-ing. The least complex type that can be used for manual welding is an MMA power source that is used for touch starts. It has one characteristic (constant current) that is suitable for TIG weld-ing. The current is set and must not be changed when the arc voltage is changed. On the other hand, MIG/MAG power sources cannot be used, as they have a totally different characteristic (constant voltage). There are also dual power

sources which can accommodate both alternat-ing and direct current. At the present time, no programmable dual power sources are available. If you want to connect pipe-welding or tube-welding tools, the power source needs a suitable control unit. ESAB has PROTIG and MECHTIG

This figure shows the characteristics of a TIG power sour-ce. When the current changes, the change in voltage is very small.

Workpiece

Gas hood

Elektrode mouse

Collet

Elektrode

Arc

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frequently used with alternating current. ESAB has tested different electrodes in terms of star-ting characteristics, slag formation and stability. Lanthane proved to be best, closely followed by cerium. They were both shown to have excel-lent starting characteristics, stable arcs and little collar formation. Yttrium electrodes have good arc stability and little burr formation compared with thorium, but their starting characteristics are slightly poorer. Thorium is the most common electrode and it is used with direct current. The thorium additive is slightly radioactive, however. This is not particularly important in conjunction with welding, but care should be taken with the dust produced by grinding. This is one of the main reasons why people have started to use the alter-natives of lanthane and cerium. With alternating current, pure tungsten or tungsten with zirconium is used.

Recommendations:

Current type Elektrode typeUsed, for example with

AC welding: Pure tungstenZirconiumLanthane

AluminiumMagnesium Electron

DC- welding: ThoriumLanthaneCerium

MonelSteelStainlessCopperCopper nickelBronzeLeadBrassTitanium

Elektroder för TIG-svetsning

ElectrodeContains approxi-mately

Colour marking

Designa-tion

Pure tung-sten

99,8% green WP

Thorium 2% red WT20

Zirconium 0,8% brown (white)

WZ8

Lanthane 1% black WL10

Cerium 2% gray WC20

Every effort should naturally be made to use the right type, but it should nonetheless be pointed out that it does not make that much difference if the ”wrong” electrode is used for AC or DC welding. It is, for example, perfectly all right to use zirco-nium electrodes for DC welding. The most com-

Gas hoods are available in many different sizes and designs. The most common material is alu-minium oxide (Al2O3), a type of ceramic. This material is designed to withstand the temperatures that are generated during welding. As a rule, a gas hood with an inner diameter which should be 4 times the electrode diameter chosen. If a gas hood with a small diameter is used, the gas flow speed is higher. This may be a good thing in a location in which the ambient air circulates at high speed. However, as the gas jet is narrower, the gas shield does not cover such a large area and this can be a disadvantage if the welding is very hot and/or if a sensitive material is involved. Alarger gas hood covers a larger area, but the gas flow setting then has to be higher.

Electrodes

The electrodes that are used for TIG and plasma welding are made of the metal tungsten, as this pre-vents them from melting at the temperatures that are generated during the various processes. The melting point of a tungsten electrode is as high as 3,410°C and these electrodes also have good cur-rent and heat conduction capabilities. Electrodes for TIG welding are available in different kinds and dimensions. The kind that is normally used for TIG welding is made of tungsten alloyed with 2% thorium oxide (ThO2). If alternating current is being used, tungsten is often chosen. Pure tung-

sten is often used with alternating current. Elec-trodes made of tungsten alloyed with zirconium (ZrO2) are also often used with alternating cur-rent. Oxides of other kinds have also started to be tested. They include lanthane, yttrium and cerium. The advantage of adding oxides to tungsten is that the electrode can be subjected to higher current without melting. Additional advantages include:• Improved striking and re-striking• Electron emission is facilitated• Arc stability improves. Pure tungsten in an al-ternating current electrode has the advantage of being inexpensive and making it easy to create a well-rounded tip. Zirconium electrodes are most

Gas hood

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mon electrode length is 175 mm. Only around 140 mm of this length can be used in a torch with a long back plate, while even less can be used in a mechanical torch, as it is not possible to insert the whole electrode. It must instead be divided into shorter pieces. Electrodes are available with di-ameters of 0.5, 1.0, 1.6, 2.4, 3.2, 4.0 and 6.4 mm. The most common diameters are 1.6 mm and 2.4 mm. They cover the current ranges that are most frequently used within TIG. If these dimensions are used, thorium can accommodate around 30-180 A and this is enough for many of the relevant applications. During welding, the electrodes are consumed and they therefore have to be ground or replaced. Burrs form on the tip and the arc be-comes less concentrated. If the tip of the electrode is dipped in the molten pool, the electrode also needs to be replaced. If a poor or rough electrode is used, there is a real risk that the welding will be negatively affected. To extend the service life of the electrode, the following factors should be taken into account. • Use an electrode with the correct dimensions to

match the current. • Grind the tip to give it a good surface finish. A

grinding wheel with a grain size of more than 120 should not be used.

• The tip of the electrode should be ground length-ways so that the grinding welts follow the elec-trode along its length.

• To prevent the electrode cracking, it should be broken off in the correct manner. Grind a notch with the edge of a grinding wheel and break off the electrode at that point using pliers.

• In an emergency, you can break off the electrode using a hammer against a sharp edge.

• The electrodes should be kept dry and clean by storing them in their original packaging.

• Air must not be allowed to make contact with the electrode during welding. The flow of gas should be sufficient. Any leakage from hoses will quick-ly destroy the electrode.

• Pre-flow times and, in particular, after-flow times should be sufficiently long.

• The electrode stick-out outside the gas hood should be kept short, whenever possible.

• Keep the gas hoses as short as possible and make sure they are not cracked.

• Replace the gas cylinder in time (low pressure - more moisture in the gas).

• Use quality rubber (such as butyl), whenever pos-sible (less diffusion of gases).

• If possible, use a gas lens.• Make sure that the gas regulator and hose con-

nections are undamaged, airtight and firmly tightened.

• Before starting to weld after a long break, the gas should be allowed to flow for longer than usual in order to flush the hoses and so on properly.

The pre-flow time is only designed to force away the air under the gas hood and at the point of welding and it can normally be set at around four seconds. The after-flow time must be longer as it is designed to protect the electrode and the mol-ten pool until they cool to the point at which they cannot be affected by the air. If the electrode is blue-annealed or develops a burr, it must immedi-ately be replaced or re-ground.

Grinding electrodes

In connection with AC welding, the electrode should not be ground. It should instead be shaped using the welding current by increasing the current to such a degree that a soft, rounded end is created on the electrode. The current should not be increased to such an extent that a large ball forms at the end of the electrode. In connection with DC welding, the

electrode should be ground to create a sharp tip and a certain angle. The very top of the electrode should be ground to prevent it melting and ending up in the weld. It is in fact so fine that it is not able to withstand any current. A reference value is about 0.5 mm at the tip of the electrode, but this must be determined from case to case. The appearance of the arc and the penetration of the weld is influenced to some degree by the amount that is removed from the tip of the electrode. Good equipment for grinding electrodes is availa-ble to ensure that the same angle is always produced. These grinding machines are also equipped with dia-mond grinding wheels which do not contaminate the electrode. Grinding machines should be equipped

Correct Incorrect Incorrect

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with extraction equipment as thorium is slightly ra-dioactive. The angle of the tip of the electrode should be kept constant whenever welding is performed, to prevent unpleasant surprises. It is important that the angle is the same ”all the way round” to keep the arc stable. In the case of electrodes with a diameter of less than 2.5 mm, the length of the tip can be twice the diam-eter (approx. 45°).

In the case of electrodes with a diameter of more than 2.5 mm, the length should be 1.5 times the di-ameter (approx. 45°). This could be a good starting value, but in some cases it may be necessary to change the angle in or-der to control the welding in the optimal manner. A larger angle produces improved penetration in conjunction with a high current. The width of the weld also changes with the angle. The width is reduced if the angle is increased and this is only natural as the arc becomes more concen-trated. Generally speaking, it would be true to say that a more pointed electrode is used with lower cur-rents, while a less pointed one should be used with higher currents. The electrode should be ground in such a way that the arc is stable. A stable arc is

obtained if the grinding welts follow the electrode along its length and if the electrode is evenly ground. It is also important that it has a good surface finish.

The dimensions of the electrode should be chosen to match the current that is being used. As a rule, the diameter of the electrode should be as small as possible to obtain a concentrated arc and thereby a smaller molten pool and deeper penetration. If the diameter of the electrode is too large for the current that is being used, the arc will be unstable. The fol-lowing table gives some reference values.

Shielding gas

During welding, the electrode, molten pool and surrounding hot metal should be protected from the air. Oxides and nitrides are produced and they result in an inferior weld if the air gains access. In addition, the electrode is quickly destroyed if it is not protected by shielding gas. So it is the task of the shielding gas to force away the air and also to be chemically inactive. These gases are known as inert gases (noble gases). Two inert gases are used in TIG welding, argon (Ar) and helium (He). There are four other inert gases – neon, krypton, xenon and radon – but they are not used. In special cases, the root side should also be protected and either an inert gas or a re-ducing gas mixture is then used for this purpose. One example of a reducing root gas is hydrogen in nitrogen. The hydrogen in the gas reacts with the oxygen, thereby protecting the weld. The hy-drogen content is small, approximately 5-10%. The choice of shielding gas is dependent on many factors, such as the type of material, the thickness of the material, the welding position, energy requirements, welding costs and working environment. The gas should also function as a current and heat conductor and should therefore have the appropriate characteristics. The gas also has a cooling effect on the electrode and moltenpool.

Elektrode diameter mm

Pure tungstenA (AC)

0,8% zirconium A (AC)

2% thoriumA (DC)

0,5 5-15 5-20 5-20

1,0 10-60 15-80 20-80

1,6 50-100 70-150 80-150

2,4 100-160 110-180 120-220

3,2 130-180 150-200 200-300

4,0 180-230 180-250 250-400

Choice of electrode size

The tip hould be ground

Correct Correct

Instable arc Stable arc

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As has already been mentioned, helium and ar-gon are the gases that are used most frequently in TIG welding and their characteristics vary some-what. Argon is about 1.4 times heavier than air, while helium is some eight times lighter. Their ability to transfer current and heat also varies. Pen-etration ability is influenced by the gas that is cho-sen. Argon is easy to ionise and the arc voltage is around 10-15 volts. Helium, on the other hand, is more difficult to ionise, which makes the arc more difficult to strike and the arc voltage is 40% higher at the same arc distance. As a result of the higher arc voltage, the output (heat development) is higher when helium is used for welding. The output P = U x I, where P is the output, U is the voltage and I is the current. So, with the same current and arc length, the out-put is higher when helium is used, because of the higher arc voltage. There are also mixtures in which argon and he-lium are mixed in different proportions, giving the mixed gases characteristics that are somewhere in the middle. The most common mixtures are 30/70% and 70/30%. Argon

Argon is by far the most commonly used gas. It is used to weld low-alloy steel, stainless and nickel alloys, for example. The air contains about 1% ar-gon and it is produced using fractionated distilla-tion, which means that it is relatively inexpensive. Argon has the following characteristics.• It is easy to ignite• It produces a stable arc• It is relatively insensitive to variations

in arc length• It is inexpensive• It is heavier than air

As it is less sensitive to variations in arc length than other gases, it is ideal for manual welding, where it may be difficult to maintain a constant arc length. The argon is delivered in compressed form in containers. They come in four different sizes with volumes of 5, 20, 40 and 50 litres. The gas is com-pressed to a pressure of 150 and 200 kg/cm2 re-spectively, depending on the type of container.

As a result of the rigorous purity requirements that are set for argon, the containers must not be completely emptied. To prevent condensation forming in the container, it must always have some excess pressure. This pressure must not be less than 10 kg/cm2.

Helium

Helium and helium/argon mixtures are ideal for welding materials with high thermal-conduction properties, such as copper and aluminium. They can also be used for heavy materials and mecha-nised welding where higher welding speeds can be utilised. The characteristics of helium or argon/helium mixtures are as follows. • They produce deeper penetration• They enable higher welding speeds• They can be used to weld heavier materials• They are more expensive than argon• They are more difficult to ignite• They require a higher flow of gas• They are lighter than air• They produce better wetting in relation to

the parent metal

Argon/hydrogen mixtures

Adding hydrogen (H2) to argon increases arc volt-age and produces a more concentrated arc. This enables high heat input and a more concentrated welding profile. Argon-hydrogen mixtures are used for welding austenitic stainless steel and nickel-based alloys. The addition of hydrogen produces higher welding speeds and deeper pen-etration, as the weld is narrower. This is associated with the fact that the current transfer is limited to a smaller surface on the anode (workpiece). The normal mixture is 1-10% hydrogen. Because of the metallurgical effects hydrogen produces in the weld metal, these mixtures cannot be used for car-bon steel, aluminium, copper or titanium. This gas is used for the longitudinal welding of pipes, for example.

Shielding gas flow

The effectiveness of the shielding gas in terms of protection is influenced by many factors. The ap-propriate shielding gas flow must be determined

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from case to case, while taking account of all these factors. It goes without saying that the aim should be to use the smallest possible flow, while still pro-viding sufficient protection. In normal welding, the initial starting value could be around 8-10 l/min. In conjunction with hot welding, for example, the flow of gas must be increased slightly, whereas it can be reduced for cold welding. If a large gas hood is being used, the flow must be increased, but a large part of the weld must be covered at the same time. So a certain minimum gas flow is needed to pro-duce a satisfactory effect, but this flow must not be too high. If it is, gas is wasted for no reason and the protection can be reduced. In addition, the weld will be colder. If the flow is too high, the ejector effect can cre-ate turbulence in the gas and enable air to enter. If the angle of the torch exceeds around 30°, this has

the same effect - air can be sucked into the gas at-mosphere. The difference in the density of the gas/gas mixture affects the set gas flow. A light gas re-quires a higher flow than heavier gases, such as ar-gon. If helium or helium-based gases are used, the gas flow should be increased twice or three times. Currents in the ambient air can have a negative ef-fect on the gas shield. Large, draughty factory halls or outdoor welding may necessitate special meas-ures, such as increased gas flow and screening, in order to produce a good result. Gas lens

A long electrode stick-out and large gas hoods make higher flows necessary. If circumstances permit, a gas lens should be used. This is an out-standing accessory. It helps to produce a laminar gas flow which effectively protects the electrode and molten pool.

This means that:• The gas flow can be

reduced by approximately 50%• The electrode stick-out can be increased to

15-20 mm, thereby making it easier to follow the welding process and obtain access in tight spaces

• The risk of welding defects caused by draughts is reduced

Difference with and without a gas lens

With a gas lens Without a gas lens

Checklist for a good gas shield

• Correct flow• Gas leaks• Diffusion of air in gas hoses• Correct torch angle• Absorption of moisture in the hoses during stoppages• Sufficient pressure in the gas container• Electrode stick-out too long• Gas lens• Water leak in the torch• Draughts in the workshop

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Shielding gases for TIG welding

The most frequently used gas is 99.99% argon. The purer (and more expensive) 99.995% argon is used when the requirements for the purity of the gas are extremely rigorous, when welding ti-tanium, for example.

Root gas

When welding with complete penetration, it may also be necessary to use a gas shield on the re-verse side, depending on the material. If the root is exposed to the air, the weld will be uneven and oxidised. Materials that require a root gas shield include stainless, acid-proof steel and titanium. When welding high-alloy steel, aluminium al-loys and copper alloys, root gas should be used. Pure argon or formier gas (90% N2+10% H2) is used as the root gas. Argon is by far the most frequently used root shielding gas. Formier gas is less expensive than argon. The choice between argon and formier gas is determined by the sen-sitivity of the material, as the hydrogen in the formier gas can cause hydrogen embrittlement. Formier gas is used for austenitic stainless steel. The hydrogen reacts with the oxygen, thereby shielding the weld. In pipe welding, the pipe can be filled with gas. If a large pipe system is involved, the cost of the gas is high and filling takes a long time. Anumber of volume exchanges are needed to re-duce the oxygen content to a sufficient level. The number of volume exchanges varies from case to case and needs to be determined by trial and error, but it may be as many as five to ten. Small filling volumes require more exchanges than lar-ger ones.

GAS AGA Alfax

Argon 99.99% Argon S Argon N40

Argon 99.995% Argon SR Argon U

Argon+0,03% NO Mison 12 -

Helium 99.995% Helium Helium U

70% helium+30% argon

Helon 70 Inarc 17

30% helium+70% argon

Helon 30 Inarc 13

95% argon+5% hydrogen

Tyron 5 Noxal 5

90% nitrogen+10% hydrogen

Naton 10 Supporting gas

The flushing time for the gas can be calculated using the following formula:

Where:T = time in minutes,V = volume in litres,A = number of volume exchanges andG = gas flow in litres/minute

If a pipe is going to be welded, the volume can be calculated using the following formula:

Where:π = 3.14d = inner diameter of the pipe in decimetresL = length of the pipe in decimetres

T = V x AG

V = π r2 x L4

Special equipment is available to limit the amount of gas reaching the area where welding is being performed to prevent no more gas than necessary being consumed. This equipment in-cludes expanding rubber seals that can be fitted on the ends of pipes. Plates of various types with rubber seals can also be used.

One very practical solution is a special fixture made of metal, called a centrator, which has ex-panding hoods containing small holes for the gas supply. Another advantage is that this centrator locks the pipe in place, thereby eliminating the need for tack welding. This fixture also conducts the heat away, so that the conditions around the pipe are more or less the same. The pipe not heated to such a high degree when this fixture is used.

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As argon is heavier than air, it has to be supplied in the lower part of the pipe. The argon finds its way to the bottom, while the lighter air positions itself on top of the argon. When additional argon is sup-plied, the air is pushed into the discharge hole.

This discharge hole should therefore be located at the top of the pipe in order to be able to drain all the air from the pipe. A nitrogen/hydrogen mixture is lighter than air, so it should be supplied from above and the discharge hole should be at the bottom. To avoid mixing argon with air, the argon should not be supplied too quickly. This is particularly impor-tant if small volumes are involved. For volumes of less than three litres, the flow of root gas should not exceed five litres a minute. It may be a good idea to install a diffusor inside the pipe at the inlet and allow the gas to be discharged through a large number of small holes, for example. This prevents

turbulence forming inside the pipe. When no air is left and welding has begun, root gas should still be supplied to ensure that no air leaks in. The flow should not, however, be so large that excessive sur-plus pressure is created inside the pipe and presses out the molten pool, thereby creating arches. The flow should normally be around four to six litres a minute. Root gas is not normally used to weld unalloyed and low-alloy steel, but it still offers cer-tain benefits. Oxide scale, which might otherwise have to be ground away, is avoided. The root is even and this has a positive effect on strength. The corrosion characteristics are improved. The molten pool is also less viscous. A root gas shield can also be used when sheet metal is being butt welded. The reference values for the fixture are as follows.

Gas shield when welding titanium

When welding titanium, the gas shield has a to-tally decisive effect. If titanium is heated in air, the layer of oxide on the surface begins to form very rapidly and, above a certain temperature (different refer-ences specify different temperatures from 400 to 650°C), contaminants such as oxygen, nitro-gen, carbon and hydrogen begin to diffuse into the material, which results in a risk of embrittle-ment. The purity of the shielding gas is important when welding titanium. The oxygen content and nitrogen content should not exceed 0.003 per-

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centage by volume (30 ppm) and 0.008 percent-age by volume (80 ppm) respectively. Argon SR or the equivalent complies with these requirements. The purity of argon SR is 99.995% - in other words, the combined content of contaminants must not exceed 50 ppm (ppm = parts per million). Both the root side and the weld side must be shielded. One good indicator of the quality of the weld is to look for possible discoloration. If the weld is shiny, there is no embrittlement. Some kind of collector shoe should be used to protect the weld. There are different models for both pipe welding and longitudinal welding. Collec-tor shoes are also ideal when welding stainless steel.

Environmental aspects

During TIG welding, ozone (O3) is created by the oxygen (O2) molecules in the air. Ozone forms when the ultraviolet radiation from the arc enters the ambient air and makes contact with the oxy-gen molecules. They are split and the free mol-ecules combine with other oxygen molecules. Increasing the distance between the arc and the available oxygen molecules reduces the intensity of the light and ozone formation is reduced. A gas mixture of argon and helium with varying density can be used. Argon is somewhat heavier than air and drops down and protects the molten pool, while the helium rises and forces out the air. This increases the distance to the available oxygen molecules and reduces ozone formation. Argon combined with a little nitrogen monox-ide, NO (0.03%), can also be used. This produces a very rapid reduction in the amount of ozone that forms and what is in practice an insignificant increase in the amount of nitrogen dioxide, NO2. This gas mixture is sold by AGA and is known as Mison 12.

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Welding parameters

To produce a satisfactory appearance and com-ply with the quality requirements that are set for the weld, a range of welding parameters need to be adjusted to obtain the optimal setting. A list of these parameters and the effect they have on the weld now follows.

Welding parameters Effect

Higher pulse current: Increased penetrationIncreased risk of excessive penetration at 6 o'clockReduced risk of incomplete fusion

Longer pulse current: Reduced penetrationIncreased risk of incomplete fusion

Longer pulse time: Increased penetrationIncreased risk of excessive penetration at 6 o'clockReduced risk of incomplete fusion

Shorter pulse time: Reduced penetrationReduced risk of excessive penetration at 6 o'clockIncreased risk of incomplete fusion

Longer pause time: Reduced penetrationIncreased risk of incomplete fusion

Shorter pause time: Increased penetrationIncreased risk of excessive penetration at 6 o'clockReduced risk of incomplete fusion

Higher voltage: Reduced excessive convexity or excess weldReduced risk of incomplete fusion

Lower voltage: Increased excessive convexity or excess weld

Increased wire-feed speed: Increased excessive penetrationHigher deposition rateReduced risk of excessive penetration at 6 o'clock.Increased risk of incomplete fusion

Reduced wire-feed speed: Lower deposition rateIncreased risk of excessive penetration at 6 o'clockReduced risk of incomplete fusion

Higher welding speed: Reduced penetrationReduced excessive penetrationReduced risk of excessive penetration at 6 o'clock.Increased risk of incomplete fusion

Lower welding speed: Increased penetrationIncreased risk of excessive penetration at 6 o'clock

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Welding defects

In principle, weld imperfections can be divided into two groups.• External imperfections and deviations, such as

undercut, excess weld or excessive convexity, root imperfections, root concavity and so on. These imperfections are found during inspec-tions.

• Internal imperfections, such as pores, oxide and slag inclusions, incomplete penetration and so on. These imperfections are found by X-ray or ultrasound tests.

The rules governing permissible weld imper-fections are described below, as specified in the Swedish Standard SS 066101. The quality requi-rements are described in four weld classes. These weld classes are known as WA, WB, WC and WD. The highest class is WA, in which basically no imperfections are permitted. The stress a structure must withstand determines the imperfections that are permitted. Defects and deviations that are identified using X-rays are evaluated on a five-point scale. This scale has been drawn up by the IIW Commission (International Institute of Welding ) and is used all over the world. The scores are shown using different colours, but in Sweden numbers are used instead of co-lours. The highest score is 5 and the lowest is 1.

5 black colour

4 blue colour

3 green colour

2 brown colour

1 red colour

An approved welder’s test should have a lowest X-ray rating of 4.

SS 066101 has now been replaced by SS-ISO 5817 and SS-EN25817 with quality levels, B, C and D.

UndercutWeld class WB: permitted locally if A ≤ 0.05 x t but nomore than t 0.5 mm, L ≤ 25 mm.IIW’s X-ray atlas: not permitted for a score of 5, score of 4 = WB.

Excess weld metal - uniform bevelWeld class WB: A ≤ 1.5 + 0.05 x B.IIW’s X-ray: approved as WB.

Uneven bevel - indication of fractureWeld class WB: not permitted.IIW’s X-ray: like WB, score ≤ 3.

Excessive penetrationWeld class WB: A ≤ 1.5 + 0.1 x C. IIW’sX-rays: approved as WB.

Welding defects in TIG welding

Designations and quality requirements according to SS 066101.

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Welding defects in TIG welding

Excessive weldWeld class WB: not permitted.IIW’s X-ray: like WB, score ≤ 3.

Root concavityWeld class WB: A ≤ 0.05 x t but t max 0.5 mm.IIW’s X-ray: approved as WB.

Incompletely filled grooveWeld class WB: A ≤ 0.05 x t, t but max. 0.5 mm.IIW’s X-ray: approved as WB..

Lack of penetrationWeld class WB: not permitted.IIW’s X-ray: like WB, score ≤ 3.

Linear misaligamentWeld class WB: at t ≤ 5 mm 0.5 xt, but no more than 1 mm. At t = 5-10 mm, 0.2 x t is permit- ted. More than 10 mm 0.1 x t + 1 but no more than 4 mm.IIW’s X-ray: like WB

Lack of fusionWeld class WB: not permittedIIW’s X-ray: like WB

CrackingWeld class WB: not permittedIIW’s X-ray: like WB

PoresWeld class WB: the odd small, rounded pore or groups of pores. Pore distance less than t/3 if the rest of the weld metal is free from imperfections. Long pores are regarded as slag inclusions.IIW’s X-ray: like WB, score 4-5.

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In normal circumstances, it is best to use some kind of U groove. It can be turned in either a sta-tionary lathe or using portable joint-preparation equipment which is available in different vari-ants. The U groove should be produced with a ”nose” which has a certain thickness and a cer-tain radius between it and the groove wall. The wall of the groove should slope at a certain angle. It is very important that the grooves are identical every time, as the welding equipment is unable to compensate for variations in joint preparation.

Wall thickness

Wall thickness plays a major role in the design of joints. If only fusion welding (without filler material) is used, it is possible to weld as long as the molten pool can be controlled and does not become unstable, provided that the material does not require additional wire in order to avoid pores. In the case of austenitic stainless steel and car-bon steel, it is possible to weld wall thicknesses of up to around 2 mm without any major pro-blems and up to around 3 mm with some diffi-culty. Welding wall thicknesses of 4 mm is very difficult and the results are not particularly good, but it is nonetheless possible. The same problems are experienced with titanium in walls that are about 20% less thick. If the pipe can be rotated, it is possible to weld far thicker metal with I joints. When the wall thickness increases, the size of the molten pool also increases and this makes the welding increa-singly unstable and difficult to control. To counteract these problems, the current can be pulsed and, in some cases, even the rotation can be pulsed. This makes the molten pool alter-nate between melting/solidification and this then restricts the size of the pool more effectively. If the molten pool becomes too large, joint

Joint preparation during pipe welding

preparation is essential and the welding must be performed with filler wire. Instead of welding one very hot pass, a number of passes should be welded with filler wire. The welding is then col-der and therefore easier to control. The number of passes depends on the thickness of the pipe and the shape of the joint. As only the ends of the pipe are used as con-sumables in fusion welding without wire, the quality of the weld is largely dependent on the preparations that have been made. The parame-ters that have an impact are: • Variations in wall thickness • The flatness of the pipe ends • The occurrence of burrs • Ovality • Tooling-up and possible tack welding • The cleanness of the pipe ends • The base material

The variation in wall thickness should not exceed 3% at any point, in order to be on the safe side. The flatness of the end of the pipe should not vary by more than 1% of the wall thickness. This should not be difficult, as most joint-preparation tools on the market are able to comply with these requirements. No burrs should be left on either the inside or outside of the pipe. Materials such as stainless have a very abrasive effect on cutting tools and this can then cause burrs. These burrs must be removed. The two ends of the pipes should be in contact with one another without any gap. Any gap should not exceed 5% of the wall thickness of the pipes. The joint should be completely free from cutting fluid, oxides and dirt. The quality of the welding is totally dependent on these factors, as the molten pool can move from wall to wall and cause incomplete penetra-tion. For the same reason, the tungsten electrode should be correctly ground.

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A wide range of consumables is available for TIG welding and they are usually known as ”welding wire”, as they are ”non-conductive consumables in the form of wire”. Consumables are available for: • Unalloyed and low-alloy steel • Stainless steel • Aluminium and its alloys • Magnesium and its alloys • Copper and its alloys • Nickel and its alloys • Special steel containing titanium, zirconium and

molybdenum, for example

In the case of special materials for which the cor-responding consumable is not available for TIG welding, strips can be cut from the parent metal and used as welding wire. It is also possible, if this is feasible, to create joint types such as edge- or double-flanged seams, in which the parent metal is melted and a joint weld is performed. The same wire range, wound on drums, as that used in MIG/MAG welding is used in automated TIG welding. The increased silicon content that is used in these wires to compensate for melting loss and as deoxidants is an additional advantage, as these characteristics can be utilised to the full in the arc and molten pool in the TIG method. From an alloying angle, these wires are com-posed to match the TIG-welding process and they can therefore also be used, with some reservations, for gas welding. In the reverse situation when it comes to unalloyed welding wire, a wire of this kind, which is designed for gas welding, should not be used for TIG welding. Consumables are normally used in TIG weld-ing. It is generally only normal when welding stain-less steel grades for the material to be allowed to melt without consumables. If carbon steel is weld-ed without a consumable, for example, there is a very real risk of pores. This can be avoided by us-ing a wire containing silicon (Si). Silicon reduces the surface tension of the molten pool so that dis-solved gases can ”bubble” to the surface. What is known as killed material should be used in TIG welding to avoid pores.

Consumables

The composition of the consumable should be such that no pores are produced. In gas welding, the welding flame protects the molten pool from the effects of oxides, but, in TIG welding, there is no effect of this kind. This explains why con-sumables designed for gas welding should not be used for TIG welding. The shielding gas only pro-tects the molten pool from the effect of the atmos-phere. Oxides on the surface of the metal must be absorbed by elements in the consumable, in this case silicon (Si) and manganese (Mn). Traces of the purifying effects of these elements can be seen in the form of small islands of slag on the surface of the weld. Generally speaking, consumables with the same analysis as the parent metal should be chosen. The consumable should be as like the parent metal as possible or more alloyed, as the metals mix to-gether. It is better to use overalloyed than underalloyed consumables. The thicker the material that is going to be welded, the thicker the consumable in order to fill the joint rapidly. It is, however, important to make sure that the material does not come in contact with the tungsten electrode. It is difficult to specify a suitable diameter; this must be tested and chosen to match each individual case. When performing pipe welding with ESAB’s PRB/PRC tool, the di-ameter of the wire should not exceed 0.8 mm. The wire must be kept clean. It should be stored in sealed packaging, in a dry, dust-free place, and should be clearly labelled. Oil, grease, dust and moisture must be kept away from the wire, in or-der to avoid weld defects. Before welding begins, an inspection should be made to ensure that the wire is evenly wound on the drum and can run freely. Before the wire is inserted in the wire conduit, the tip should be ground, if it is sharp, to prevent it penetrating the wire conduit. Any unevenness on the surface could have a very abrasive effect on the wire conduit and wire nozzle. In automatic welding, the wire should be ad-justed so that it enters the front edge of the molten pool. A check should also be made to ensure that

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the wire does not touch the tungsten electrode. When the welding has been completed, the end of the wire should be cut off to prevent oxides in the molten pool. The angle at which the wire is inserted in the molten pool influences the process. The larger the angle, the larger the penetration bead when weld-ing the root run. At the same time, it will be more difficult to set the angle exactly. To begin with, an angle of around 15-30° can be set. This angle may need to be changed during welding and it sometimes needs to be checked so that it does not enter outside the molten pool. TIGROD is a range of rods for manual welding, while AUTROD is wire designed for auto¬matic welding. TIGROD is supplied in 5 kg plastic packages. The rods are 1,000 mm long. Rods are used for manual welding. If no rods are available, a piece can be cut off a reel in emergen-cies. If the MTC 20 feed unit or the more modern MEI 20 and MEI 21 feed units are used for au-tomatic welding, spool type 46-0 should be used. The diameter of the wire is 0.8 mm, but 0.6 mm can also be used. MTC 20, MEI 20 and MEI 21 should be used with PRB, PRC, PRF and PRG welding tools. A smaller 1 kg reel with a diameter of 100 mm should be used with PRD, PRI, POA and POB. These spools are not normally sold by ESAB but must be purchased from another supplier or taken from a larger reel. Consumables with a diameter of up to 1.2 mm can be used with PRD and A25. Fifteen kilogram spools can also be used with A25.

Unalloyed and low-alloy steel

OK AUTROD 12.51 Silicon-manganese-alloyed, copper-coated elec-trode. Designed for the automatic welding of unal-loyed and fine-grain-treated steel.

OK AUTROD 12.51 is recommended for SS steels: 1306, 1311, 1312, 1330, 1332, 1330, 1332, 1350, 1411, 1412, 1414, 1432, 1434, 1435, 2101, 2103, 2172, 2174, 2106, 2107, 2116, 2132, 2133, 2134, 2142, 2143, 2144, 2145, Domex 300, 360, 400, OX 520, 525, 525, 540 and 542.

OK AUTROD 12.64, OK TIGROD 12.64 Copper-plated Si-Mn-alloyed welding wire for unalloyed or low-alloy steel with a nominal ten-sile strength of 510-570 N/mm2. For welding un-alloyed and low-alloy steel types. It is used when a high silicon and manganese content is required compared with OK AUTROD 12.51. The yield stress also increases. The weld metal analysis is basically the same as that of OK AUTROD 12.51. The higher silicon content of the electrode helps to reduce the risk of pores in the weld, with better ”wetting” against the parent metal. It is, however, important to be on the look-out for hot cracking as a result of the silicon content.

OK AUTROD 13.09, OK TIGROD 13.09 Molybdenum-alloyed welding wire for welding lowalloy, heat-resistant steel, containing 0.5% Mo, and high-strength steel such as OX 602 and similar grades. OK AUTROD 13.09 is recommended for welding high-strength steel, when higher tensile strength and impact strength than that provided by OK AUTROD 12.51 are required.

OK AUTROD 13.12, OK TIGROD 13.12 Chromium-molybdenum-alloyed welding wire for the manual TIG welding of heat-resistant steel and some low-alloy, high-strength and heat-resistant steels. Can be used for welding Cr-Mo-alloyed steels of the SS steel 2216, 2223 and 2225 type, as well as other types of high-strength, low-alloy steel, such as OX600, OX800 and USST1 steel. For plate thicknesses of more than 8-10 mm, a working temperature of around 150-200°C should be maintained to reduce the risk of cracking.

OK AUTROD 13.13, OK TIGROD 13.13 Low-alloy solid wire for welding high-strength steel, where good impact strength at low tempera-tures is required. Working and pre-heating tem-peratures of around 150-200°C are recommended to reduce the risk of cracking, especially in plate thicknesses of more than 8-10 mm.

OK TIGROD 13.22 Cr-Mo-alloyed wire for the manual TIG welding of heat-resistant steel of the SS 2218 and 2224 steel types, such as UHB Stato 28, Bofors RO 211 and Sandvik HT8. HB Stato 28, Bofors RO 211 och Sandvik HT8.

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Welding wire composition

Stainless and acid-proof steel

OK TIGROD 16.10Stainless wire with an extra-low carbon content for the manual TIG welding of stainless steel con-taining approximately 19% Cr and 10% Ni. OK

AUTROD 16.11, OK TIGROD 16.11 Niobium-alloyed stainless wire for the manual TIG welding of stainless steel of the 19 Cr 8 Ni Nb and 19 Cr 9 Ni Ti type.

OK AUTROD 16.12 Stainless electrode with an extra-low carbon con-tent for the mechanical TIG welding of austenitic stainless steel of the 19 Cr 10 Ni type. For weld-ing SS 2352, 2333, 2332, 2337, 2338 or their equivalent.

OK TIGROD 16.30 Stainless wire with an extra-low carbon content for the manual TIG welding of stainless and acid-proof steel of the 19 Cr 10 Ni Mo type.

OK AUTROD 16.31, OK TIGROD 16.31 is a niobium-alloyed electrode for welding Ti- and Nbstabilised, so-called acid-proof steel of the 18 Cr 12 Ni 3 Mo type. The Mo content im-proves corrosion resistance and heat resistance.

OK AUTROD 16.32Stainless electrode with an extra-low carbon con-tent for the mechanised TIG welding of austenit-ic stainless and acid-proof steel corresponding to SS 2353 and 2343 and similar or lower alloyed steel (and corresponding steel according to other standards).

OK AUTROD 16.52Overalloyed stainless wire for welding stainless to other steel types and for buffer layers in com-pound steel. It is ideal for welding root passes in the transition between the stainless cladding of the compound plate and the unalloyed basic metal. The resulting dilution of the weld metal means that the composition of the weld metal is a fairly good match for the analysis of a stainless cladding corresponding to SS 2333.

OK AUTROD 16.53, OK TIGROD 16.53 Overalloyed stainless wire with an extra-low car-bon content for welding similar alloys in rolled or cast form. This wire is particularly suitable in demanding corrosion situations which call for a higher alloyed weld metal. It is specially recom-mended for joining different types of steel such as ”18/8” to unalloyed or low-alloy steel and for surfacing unalloyed steel with stainless.

OK AUTROD 16.86, OK TIGROD 16.86 16.86 is a stainless wire designed for welding austenitic-ferritic steel, so-called ”Duplex”, such as Werkstoff no 1.4462, SAF 2205, Avesta 2205 and SS 2377. The weld metal is extremely resist-ant to different types of corrosion.

OK AUTROD 16.95, OK TIGROD 16.95 An austenitic stainless welding wire with a high manganese content. Specially designed for join-ing steel that is difficult to weld and for steel of different types. It is primarily used to join 18/8 steel and carbon steel and low-alloy steel.

Wire C Si Mn Cr Mo Ni

12.51 0,1 0,85 1,5

12.64 0,1 1,0 1,7

13.09 0,1 0,6 1,1 0,5

13.12 0,1 0,6 1,0 1,1 0,5

13.13 0,08 0,5 1,1 0,6 0,3 0,5

13.22 0,1 0,5 1,7 0,8 2,5 1,0

Welding wire composition

Aluminium and its alloys

OK AUTROD 18.01,18.11. OK TIGROD 18.01, 18.11 Pure aluminium wire, 99.5 Al, for the TIG and oxygen-acetylene welding of aluminium and its alloys. (Flux is required for oxy-acetylene wel-ding.) The difference between 18.01 and 18.11 is that 18.11 has a small addition of titanium which improves weldability. (The weld metal is more fine grained and therefore more resistant to cracking.) For welding aluminium grades SS 4005, 4007, 4008 and 4010.

OK AUTROD 18.04, OK TIGROD 18.04 Silicon-alloyed aluminium wire of the Al Si 5 type for the manual TIG welding of Al-Si alloys and Al-Mg-Si alloys with a silicon content of up to approximately 10%. Recommended for SS 4104, 4212, 4224, 4230, 4231, 4244, 4251 and 4253.

OK AUTROD 18.15 OK TIGROD 18.15 Magnesium-alloyed aluminium wire of the Al Mg 5 type for the TIG welding of saltwater-resis-tant Al-Mg alloys containing up to 5% Mg. More crack-resistant than Al-Mg alloys with a lower Mg content.

OK AUTROD 18.16, OK TIGROD 18.16 Magnesium-manganese-alloyed welding wire for TIG welding. This alloy type corresponds to material grades according to Swedish standard 4140.

In 18.11 wire, there is an addition of 0.20% titanium.

Wire Al Zn Fe Si Mn Mg

18.01 99.5 <0.07 <0.40

18.04 rest. <0.1 <0.4 5 <0.05

18.11 99.5 <0.07 <0.40

18.15 rest. <0.4 <0.25 <0.2 5

18.16 rest. <0.4 <0.25 0.7 4.8

Other materials

OK AUTROD 19.12A copper wire designed for the mechanised TIG welding of pure and low-alloy copper. Recom-mended for SS 5010, 5011, 5013 and 5015 Drum: Packaging 12 kg. Ø 1.2, 1.6 mm Contents: Mn 0.25%, Si 0.25%, Sn 0.7%, Cu min. 98%

OK AUTROD 19.40 An aluminium-bronze wire for mechanised TIG welding. For welding and hard-facing rolled and cast aluminium-bronze alloys. This alloy type is characterised by high strength, good wear resistance and excellent corrosion resistance, particularly in saltwater.

Drum: Packaging 12 kg. Ø 1.0, 1.2, 1.6 mm. Contents: Al 8%, Mn <1.8%, Fe <0.5%, Cu rest. (??)

Wire C Si Mn Cr Ni Mo Nb N

16.10 ≤ 0,025 0,4 1,8 20 10

16.11 ≤ 0.07 0,8 1,8 20 10 0,7

16.12 ≤ 0.025 0,85 1,8 20 10

16.30 ≤ 0.025 0,4 1,8 18,5 12 2,7

16.31 ≤ 0,07 0,8 1,8 19 12 2,6 0,7

16.32 ≤ 0,025 0,85 1,8 18,5 12 2,7

16.52 ≤ 0,08 0,8 1,8 23,5 13,5

16.53 ≤ 0,025 0,4 1,8 24 13

16.86 ≤ 0,020 0,5 1,5 23 9 38 0,15

16.95 ≤ 0,20 0,4 7 18

Welding wire composition

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OK AUTROD 19.49 A copper-nickel wire for welding similar mate-rial such as 90 Cu 10 Ni , 80 Cu 20 Ni and 70 Cu 30 Ni alloys. Excellent corrosion resistance, particularly in saltwater.

OK AUTROD 19.82, OK TIGROD 19.82OK AUTROD 19.82 is used to weld high-alloy corrosion- and heat-resistant material, 9%-Ni steel and similar steel with high impact strength at low temperatures and for joining materials of different types of the above kind. The weld metal has good mechanical properties at both high and low temperatures. Good resistance to pitting and fatigue corrosion. Drum: Packaging 12 kg. Ø 0.8, 1.0, 1.2, 1.6 mmRods: Packaging 5 kg. Ø 1.6, 2.0, 2.4, 3.2 mmContents: Ni min. 60%, Cr 22%, Mo 9%, Nb 3.5%

OK AUTROD 19.85, OK TIGROD 19.85Type Inconel 82. For welding high-alloy heat- and corrosion-resistant material.

Drum: Packaging 12 kg. Ø 0.8, 1.0, 1.2, 1.6 mmRods: Packaging 5 kg. Ø 1.6, 2.0, 2.4, 3.2 mmContents: Ni min. 67%, Cr 20%, Nb 2.5%, Mn 3%

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Mechanised TIG welding

Historical background

Mechanised pipe welding was developed at the be-ginning of the 1950s. It began in southern Califor-nia, at which point the aerospace industry was in its infancy. The first welding heads to use the TIG process were developed here. When they proved successful, more and more companies began developing increasingly sophis-ticated equipment, first and foremost when it came to the mechanical design of the welding head. To begin with, the power sources were sourced standard units. The necessary modifications were then made to suit the new tools. The first generation of welding heads were only able to weld without wire. Functions for wire feed were subsequently developed and this enabled thicker material to be welded. The use of wire also make it possible to permit some degree of linear misalignment displacement in the pipes, something that was not advisable if only fusion welding was used. It was easier to deal with the occurrence of gaps using wire. At approximately the same time, automatic volt-age control, AVC, was also discovered. This func-tion meant that it was possible during welding automatically to control the distance between the electrode and the workpiece. This was particularly valuable when filling the joints required several passes with wire. The final function to be added was weaving the torch over the joint. Nowadays, the welding heads are light, easy to install and able to perform precision welding using all the above-mentioned functions. Greater precision was now required of the elec-tronic systems that controlled the current and all the functions on the welding head, so the manufacturers started to develop automatic power sources. To be-gin with, these power sources were relaycontrolled analogue machines. They were limited by the fact that only a few parameters could be controlled and that the operators had to be extremely active during the welding process. When microprocessors were invented, additional opportunities to control the process were created and it was only now that the equipment could be called fully automated. The serious production and

sale of this equipment started at the beginning of the 1980s. Since then, equipment including infrared sensors and cameras has been added for monitoring pur-poses. Automatic positioners and robots have also been incorporated in the mechanised TIG welding process.

Applications

As some applications are not suitable for automat-ed welding and in order to utilise the new allround welding tools correctly, a number of factors must be taken into consideration. The most important points to consider are the following.

Opportunity to weld Is the welding joint straightforward? Can it be performed using a straight all-round weld or are more complicated movements necessary? Does the thickness of the pipe enable only fusion welding to be used or is welding wire needed? Is wire needed to avoid pores?

Production tolerances Have the parts been produced with sufficiently nar-row tolerances so that the welding procedure can be repeated and produce similar welds every time?

Metallurgical considerations Is it actually possible to weld the parts that need to be welded? Are the materials in the parts known or, even better, are they certified? Is the chemical composition of all the parts the same and is it the same from batch to batch?

Customer/quality requirements Has the used of automated machinery been speci-fied by the customer or does the quality of the weld make mechanised welding necessary?

Size of assignment Is it realistic to install a machine for a limited number of welds? If you are planning to acquire a machine, is the welding assignment sufficiently large to pay for the machine and, if not, will there be more assignments of this kind in the future?

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Attitude of operators Even the most skilled welders become tired and lose concentration, but the same cannot be said of mechanised equipment. However, are the produc-tion staff prepared to learn and use the new tech-nology? When they first make contact with auto-mated equipment, can the operators abandon their old established way of working and assimilate new knowledge without being negative? Every time a contractor or customer uses or considers purchas-ing all-round welding equipment for an applica-tion, the above mentioned points should be taken into account. If this is not done, it could result in a technically inferior solution which could prove economically unsatisfactory.

Weldability with automated equipment Mechanised pipe-welding equipment is best suit-ed to applications in which there are many simi-lar welds. It is best with circular, straightforward welds. The machine does the welding and the operator does not become tired. The machine per-forms the programmed weld every time, provided that the joint has been well prepared and the op-erator sets up the pipes and fixes the welding head in place in the same way every time. Two factors have to be taken into account - the design of the weld joint and access to the joint.

Advantages of mechanisation

The equipment can maintain the parameters, such as arc distance, more effectively than a manual welder. Thin-walled pipes in particular are easy to weld and operating the equipment is virtually a question of ”simply pressing the button”, even if pipes in which the joints have been prepared have to be monitored during welding. In this case, it is necessary to have a remote control, so that pa-rameters such as the current can be changed dur-ing welding. The parameters for standard pipes or pipes which the customer often welds can be saved in a library and retrieved the next time the same type of pipe is going to be welded. Other advan-tages include the following. • Less robust pipes with heat problems can be

welded • Underbeads and overbeads can be minimised

through programming • All the equipment produces the same welding re-

sult at every point

• More reliable welding of materials that are dif-ficult to weld

• Pulsing rotation and wire feed makes it even eas-ier to control the molten pool

• Higher productivity • Same result every time, identical welds • Fewer defects • More welders can be licensed • Better working environment for the welder

Profitability As long as the customer does not demand automat-ed equipment, a careful analysis should be made of the number of welds and a specification of the project should be made. If the contractor/ custom-er already has equipment and the welding can be performed, there is no reason not to mechanise the equipment. Setting up mechanised equipment is not that much more difficult than setting up man-ual equipment. When a customer is thinking about purchasing equipment, it is important not simply to base calculations on the next job. Economic calculations should also be based on unspecified future jobs and the quality improvements mecha-nised TIG welding produces. Depending on the number of welds and the length of the welding, the machine should pay for itself in 12 months. If the equipment is not going to make a profit on the job in question, the machine could perhaps be leased. It is important that the staff have a positive attitude and that they are given enough training, as this is essential if an installation is to be successful.

Customer’s quality requirements On many occasions, the customer specifies that automated pipe-welding equipment is to be used. This is sometimes due to the quality requirements that are set for the weld. They can relate to penetra-tion, the heat affected zone, concavity, the colour of the weld, purity and porosity. Checks conducted on the weld can be divided into an ocular inspec-tion and checks using different test methods. Visu-al factors include: • Surface concavity • Full penetration • Excessive penetration on the inside of the pipe • Centring the pipes • Width of the molten pool • Surface colour • Surface cracking

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Introduction

TIG welding is a well-established method when welds of very high quality are required. As a result of the relatively low productivity offered by the TIG method, the root run is often welded with TIG, while the filling passes are welded with MMA. Using TIG for the whole welded joint produces a number of quality benefits. One of them is the opportunity to reduce the large angles and thereby the large volumes that are created in the joint when welding thick-walled material. This is achieved in narrow gap welding with TIG, with an extremely narrow groove and a small volume. Welding is possible in all positions. Stain-less and carbon steel can be welded. This method increases productivity with wall thicknesses of more than 7 mm. The advantages of narrow gap welding include: • Shorter welding times - greater productivity • Less welding tension and deformation • Lower use of consumables

Narrow gap welding is performed with ESAB’s PRD pipe-welding tools which should be connec-ted to the programmable PROTIG 250 or PROTIG 315 Inverter power sources.

General recommendations

This description includes the most common in-structions and reasons for care when performing narrow gap TIG with the PRD pipe-welding tool.

Parent metal All types of stainless and unalloyed material can be welded. Dimensions It is possible to weld ma-terials with a maximum thickness of 80 mm using the PRD tool.

Joint preparation n Joint preparation varies somewhat depending on the material. The following figures show the joint preparation for carbon steel and stainless steel. When stainless is welded, the joint angle in-creases to 6º and the thickness of the “nose” is re-

Narrow gap welding

duced to 2-3 mm. The joint preparation should be performed by a rotating machine and even the in-side should be turned to compensate for deviations in the thickness of the metal in the pipe. The surfa-ces of the joint should be cleaned prior to welding. Acetone or some kind of alcohol can be used for cleaning.

Connection to workpiece In narrow gap welding, it is essential that there is a good earth connection between the workpiece and the power source. If the connection is not suf-ficiently good, it can cause a magnetic blister ef-fect. The best way to avoid this problem is to fit a copper braid around the pipe and connect it to the power source.

Tack welding Tack welding has to be used for several applica-tions. Tack welding can be performed with a hand torch or the PRD tool. We recommend that the PRD tool should be used to improve the gas shield. Another disadvantage is that it may be difficult to access narrow joints with a torch. It is very im-portant that the pipes are correctly centred during tack welding. This centring can be performed with a special fixture to join the pipes together. ESAB is able to recommend the type of fixture than can be used for each application. After tacking, the tacks should be ground to avoid weld defects in the root pass.

Welding tools When the railtrack is installed, it is important to maintain the same distance between the edges of the rail and the weld joint all round the pipe. Other-wise the distance must be corrected during the ac-tual welding process using the programming unit.

Pre-heating material It is possible to weld material that has been pre-heated up to 200°C. At high temperatures, a rail-track that is larger than that recommended in the instruction book should be used. This means that the clamping bolts must be longer. If welding is performed with long bolts, a distance plate should

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be used for the torch. This plate is supplied with the narrow gap gas nozzle.

Electrodes Tungsten containing 2% thorium oxide should be used as the electrode. The end should be ground so that the top angle is a total of 45°. The standard electrode diameter for narrow gap is Ø 3.2 mm. It is also possible to use an electrode with a diameter of 4.0 mm. The position of the electro-de should be such that the top of the electrode is angled towards the centre of the joint. To adjust the position of the centre line during welding, the +/- function on the programming box can be used.

Wire feed The PRD tool has wire feed fitted on the wel-ding head. To maintain problem-free wire feed, the wire conduits should be blown clean and checked at regularly intervals. There is also a section straightening mill for wire which must be used when welding with PRD. This mill should be twisted in such a way that, when the wire has passed through it, it is straight.

Consumable wire The diameter of consumable wire should be Ø 0.8-1.2 mm. The angle between the workpiece and the wire should be adjusted so that it is around 25°-30°.

Shielding gas To increase the welding speed and improve wet-ting against the sides of the joint, it is best to use a gas mix which contains 70% He + 30% Ar. A hy-drogen-argon mixture can also be used for austeni-tic stainless steel. The gas flow should be around 15-20 litres/minute.

Root gas Root gas is always used for stainless steel to avoid oxidation in the root pass. This root gas is argon or formier gas. When root gas is used for pre-flushing, seven to nine times the volume of the root gas cham-ber should normally be used. The root gas flow is normally six litres/minute. Root gas is normally not needed for unalloyed steel or low-alloy steel.

Welding processes Welding is normally performed using pulsed cur-rent to guarantee good wetting against the sides of the joint. The last layer is normally welded using weaving. The welding speed is 0.8 mm/ second for the root run and 1-2.5 mm/second for the filling passes. The deposition rate varies, but it is usually between 0.5-0.7 kg/hour.

Root run When welding the root run, the wire should always come from the front of the electrode. To avoid un-der beads “at 6 o-clock” when welding the root run, the amount of wire should be adjusted during

the actual welding. This adjustment can be pre-programmed.

Filling passesThe first layer after the root run should be welded with the wire from the front of the electrode. For the other filling passes, the wire can be fed alternately from the front and back. The direction should be changed for each pass. This procedure can be pre-programmed. When the wire is fed behind the electrode, it is important that the wire in the exact position, otherwise it can touch the molten pool and stick. This can be avoi-ded by making manual adjustments during the ac-tual welding procedure. It is also possible to take this into account when programming the welding process. The arc voltage should normally be increased by 0.4 volts. The final filling pass is normally welded with weaving to obtain a low. smooth transition be-tween the pipes.

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Welding examples

Specifications:

Equipment: A21 - PROTIG Tool: PRD Pipe material: SIS 2132 Pipe diameter: Y.D. Ø 350 mm Pipe thickness: T = 17.5 mm Pipe position: G5 Consumable wire: OK AUTROD 12.64 Diameter: 1.2 mm Electrode type: Tungsten-thorium 2% Electrode diameter: Ø 3.2 mm Electrode angle: 45° Shielding gas: He 70% Ar 30% Starting position: First: 2 o’clock, welding counter-

clockwise Third: 12 o’clock, welding

counter-clockwise Arc time: 90 min Welding time: Total 120 min Welding speed: 1.22 mm/second

ManagementThe welding process for narrow gap TIG using the PRD tool must be supervised by a trained operator. This operator should have a basic knowledge of TIG welding and he/she requires about one week of training on narrow gap TIG welding.

Summary

The most important requirements when it comes to narrow-gap TIG welding with PRD are as follows:

Earth: A copper braid fitted round the pipe Electrode: Tungsten 2% thorium oxide Diameter: Ø 3.2 mm or Ø 4.0 mm. Tip angle: 45º Consumable wire: Diameter: Ø 0.8-1.2 mm. Angle: Ø 25-30°. Shielding gas: 70% He + 30% Ar Gas flow: 15-20 litres/minute Root gas: Argon or formier gas Pre-flushing: 7-9 times the volume of the root

gas chamber Welding speed: Root run normally 0.8 mm/second Filling passes 1-2.5 mm/second Deposition rate: Between 0.5 and 0.7 kg/hour for

the filling passes

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The two dominant welding methods for alumini-um are the MIG and TIG processes with plas¬ma, resistance welding and standard electrodes are also used. The TIG method is better for narrow-gauge material, situations in which a fine surface finish is required and welding from one side, when the root side cannot be accessed, such as pipe welding. Aluminium is normally welded with alternating current. Pulsed MIG is an interesting technique for alu-minium and is rapidly gaining in popularity. The main advantage of pulsing is that it enables weld-ing with a stable spray arc, even at low current, which results in effective control of the molten pool and less welding spatter. The risk of weld de-fects is also reduced. The following points must be taken into account during the mechanised welding of aluminium pipes, particularly if the welding is performed in the 5G position. To obtain the best results from all-round welding, the welding must be performed with a programma-ble power source which enables the complete con-trol of the molten pool and the process. One of the characteristics of aluminium is the high melting point of the oxide film that forms on the surface. This oxide causes weld defects if it is mixed in the molten pool. The advantage of welding with alternating cur-rent in connection with TIG is that AC produces effective oxide disintegration and AC/DC power sources are normally not programmable. Good ox-ide disintegration can also be obtained with direct current with reverse polarity (+pole on the elec-trode). The disadvantage of this method, however, is that the electrode can overheat and melt, thereby reducing current capacity.

Aluminium welding with direct current

In recent years, processes for the aluminium weld-ing of pipes using ESAB’s A21 PROTIG and a new welding tool, PRI, have been developed. In this case, the welding is performed with DC and

Aluminium welding

the electrode is connected to the minus pole. Spe-cial measures have to be implemented to obtain a good weld result. They are as follows. • Pure helium must be used • Consumables must be used • Electrode grinding, 30º total angle • Degreasing and steel brushing should be per-

formed just before welding begins • Axial pressure on the ends of the pipe to elimi-

nate possible gaps

Using helium as a shielding gas imposes demands on the power source and welding tool. Helium is difficult to ionise. Some power sources are equipped with a start-gas function which enables the arc to be struck in pure argon, after which the power source automatically changes to helium. The use of thorium- or lanthane-alloyed electrodes makes it easier to strike the arc. Another phenomenon that has to be taken into account is that the arc voltage of helium is about 40% higher than that of argon. It is therefore a good thing if the tool is equipped with AVC. Other- wise a slight change in arc distance could have a major effect on arc voltage and thereby heat input. As has already been mentioned, consumables are necessary. In order to feed soft aluminium wire at a uniform, constant speed, the tool must be equipped with a wire-feed unit. ESAB has introduced all-round tools for the alu-minium welding of pipes. They are known as PRI and come in the following sizes: 36-80 mm, 71-160 mm and 140-220 mm. These tools are equipped with arc voltage controlled (AVC) arc length and an integrated feed unit. These functions are also included on the PRD tool for large diameters and this tool can therefore also be used for aluminium welding.

Instructions The following instructions include a description of all the measurements and steps that have to be tak-en in connection with the splice welding of pipes made of weldable aluminium alloys. PRD and PRI welding tools and PROTIG 250 or PROTIG 315 Inverter power sources should be used.

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Parent metal The pipe material that is used is a weldable alloy complying with DIN 1746.

Joint preparation I joints can be used up to around 3 mm. The root faces must be machined to make them square and the inside edge should be rounded to r = 0.5 mm. The pipe tolerances should be such that the wall thickness around the pipe should not exceed 0.05 mm, while the tolerance between the largest and smallest diameter must not exceed 0.2 mm after machining.

Cleaning pipes If necessary, the ends of the pipe should be de-greased and pickled 100 mm inside the pipe so that any contamination that is left after joint prepara-tion is removed. Degreasing agents: acetone, alco-hol or alkaline cleaning agents Pickling agents: 65 g chromic acid CrO/litre of water 15 ml 85% H3 phosphoric acid PO/litre of water, 2-10 minutes. Steel brushing with a rotating stainless steel brush is also effective.

Root preparation Immediately prior to welding, the layers of oxide, on both the inside and outside of the pipe, must be removed, at least 10 mm inside the pipes. This can be done using a rotating stainless steel brush. The oxide layer on the side of the pipe must be removed with a file.

Electrode Thorium-alloyed tungsten containing 2% thorium must be used. The tip of the electrode should be ground to an angle of 20° and the end should be ground down to 0.3 ± 0.1 mm. The position of the electrode should be adjusted so that the top is aimed at the centre of the pipe. The distance be-tween the electrode and the workpiece should be 2.5 mm. The diameter of the electrode should be chosen to match the selected current Ø 1.6 mm: up to 150 A Ø 2.4 mm: 120-220 A Ø 3.2 mm: 200-300 A The electrode should be changed before each new weld.

Fixing the pipes The pipes must be carefully centred and joined to-

gether before welding to obtain the optimal result. If possible, a fixture should be used. It should be possible to use the fixture to exert axial pressure on the pipes during welding. The fixture can be the kind that sits inside the pipe, but it can also have an exterior design.

Earth connection Connecting current to the workpiece calls for careful attention in order to ensure that arc con-trol functions correctly. For this reason, a special earth clamp should be prepared and attached to the outside of the pipe to ensure the optimal electri-cal contact around the pipe. At the point at which this device is attached, the oxide layer should be brushed or blasted away.

Tack welding Instead of using a fixture, the pipes can be tack welded. They must be firmly pushed together prior to tack welding. Normally, three tacks evenly po-sitioned around the pipe are sufficient. The tacks must be brushed clean before welding begins.

Wire feed Experience indicates that the use of aluminium wire together with separate wire-feed units is not advisable, as the wire-feed speed is not constant. For this reason, PRI and PRD tools have feed units fitted on the actual tool so that the part of the wire that is fed is as short as possible. To ensure prob-lem-free wire feed, the wire conduits should be flushed and inspected at regular intervals.

Consumables Wire is absolutely essential when welding alumini-um with direct current. The wire should be dry and clean and free from oxide layers. The wire should never be touched with the fingers. When the PRI tool is used, the wire should have a diameter of 1.0 mm. With PRD, wire with a diameter of 1.0 or 1.2 mm can be used.

Positioning the wire nozzle The wire nozzle should be positioned in such a way that the extension of the wire touches the surface of the pipe immediately before the molten pool. The electrode should be at the correct height under this. If droplets form at the end of the wire, the wire nozzle is not in the correct position or the wire stick-out from the nozzle is too long.

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Equipment settings When setting the arc voltage (AVC), it is impor-tant to remember that the arc voltage is 40% higher when helium is used as the shielding gas compared with argon.

Shielding gasOne hundred per cent (100%) pure helium should be used as the shielding gas. After a long break (more than two hours), it is necessary to ensure sufficient pre-flow of the shielding gas before the start of welding. Hoses and hose connections should be regularly inspected. The maximum flow of shielding gas should be related to the inner di-ameter of the gas hood. A good rule of thumb is approximately one (1) litre/minute as a flow of shielding gas per mm of inner diameter. The gas flow should not exceed 10 litres/minute for a 10 mm gas hood, for example.

Root gas It is not necessary to use a root gas shield when welding aluminium with direct current. If a root-gas is used, the surface on the back side will be slightly lighter. Pure argon is recommended as the root gas.

Other comments An aluminium molten pool absorbs moisture from the air. Welding aluminium when the relative hu-midity is high should therefore be avoided.

SummaryThe most important points when TIG welding alu-minium pipes with direct current and PRD andPRI tools are as follows.

Joint preparation tolerances: Wall thickness: 0.05 mm High-low: 0.2 mm max. Electrode: Thorium-alloyed tungsten 2% Diameter: Ø 1.6 mm up to 150 A Ø 2.4 mm 120-220 A Ø 3.2 mm 200-300 A Top angle: 20º Ground top: 0.3 ± 0.1 mm Distance between electrode and workpiece: 2.5 mm Wire diameter: PRI Ø 1.0 mm PRD Ø 1.0 or 1.2 mm Shielding gas: 100% helium Gas flow: 1 0 litres/min per 10 mm

gas hood diameter

Job descriptionA description of welding an aluminium pipe meas-uring Ø 57 x 3 mm now follows.The welding is performed with the PRI tool.The different steps described below are given in chronological order and should be performed toguarantee effective splice welding.• Remove the oxide layer at least 10 mm inside

the end of the pipe using a rotating brush.• Fit the specially-made clamp around the pipe

(brush or blast the pipe before).• Fit the welding tool.• Attach the tool in the first tack-welding posi-

tion.• Place the torch over the joint and set the correct

height.• Load the tack-welding program.• Press the joint together, preferably using a

special clamping device.• Perform the tack weld-

ing.• Lift the torch and turn

it to the second tack-welding position.

• Set the correct arc dis-tance.

• Perform the second tack weld.

• Lift the torch and turn it to the third tack-welding position.

• Perform the second tack weld.

• Lift the torch and turn it one revolution to the starting position.

• Load the welding pro-gram.

• Set the correct arc distance and feed the wire to the surface of the pipe.

• Perform the welding.• After welding, the torch

should be lifted up and the welding head should be removed. The end of the wire should be cut off and the weld should be brushed.

Examples of aluminium welding

Specifications Equipment: A21-PROTIG 315 Tool: PRI 36-80 Pipe material: Aluminium Pipe dimensions: Ø 57 mm t=3 mm Tack welding Position: 5G Wire: Al Mg 5 Wire: Ø =1.0 mm Electrode: Ø =2.4 mm Grinding angle: 30º Top: 0.3 ± 0.1 mm Electrode distance: 2.5 mm Welding gas: He 100% Root gas: - Welding positions: First tack 0º Second tack 90º Third tack 240º Welding parameters: see appendix

Root run: Pipe position: 5G Wire: Al Mg 5 Wire: Ø =1.0 mm Electrode material: Tungsten - thorium 2% Electrode: Ø =2.4 mm Grinding angle: 30° Top: 0.3 ± 0.1 mm Electrode distance: 2.5 mm Welding gas: He 100 % Root gas: - Starting position: 150° Welding parameters: see appendix

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Notes

Glossary

Aluminium ...................................................................... 24Argon ............................................................................. 12Cracking ........................................................................ 19DCSP ............................................................................... 5Earth connection ........................................................... 32Electrode ......................................................................... 9Excessive penetration ................................................... 19Excess weld metal ......................................................... 19Gas hood ......................................................................... 9Gas lens ......................................................................... 13GTAW ............................................................................... 3Helium ........................................................................... 12HF generator ................................................................... 5Hydrogen ....................................................................... 12Lack of fusion ................................................................ 18Mechanisation ............................................................... 26Narrow gap .................................................................... 28Quality requirements ..................................................... 27Root concavity .............................................................. 18Root gas ............................................................ 14, 29, 33Root run ......................................................................... 29Shielding gas ..................................................... 11, 14, 29Shielding gas flow ......................................................... 12Tack welding .................................................................. 28Titanium ......................................................................... 15Tungsten .......................................................................... 5Undercut ........................................................................ 18Wall thickness ................................................................ 20Water cooling .................................................................. 8Welding class ................................................................ 18Weld imperfections ........................................................ 18Welding environment ..................................................... 16Welding parameters ...................................................... 17Wire feed ....................................................................... 32

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ESAB AB

Box 8004, SE-402 77 Göteborg

Phone+46 31-50 90 00, Fax +46 31-50 93 90

info@esab.se www.esab.com

Content• Introduction• Historicalbackground• GeneralinformationonTIGwelding• TheprincipleofTIGwelding• WhyusetheTIGmethod?• Equipment• Powersources• TIGtorch• Gashood• Electrodes• Shieldinggas• Weldingparameters• Weldimperfections• WeldimperfectionsinTIGwelding• Jointpreparationinpipewelding• Wallthickness• Consumables• Unalloyedandlow-alloysteel• Stainlessandacid-resistantsteel• Aluminiumanditsalloys• Othermaterial• MechanisedTIGwelding• Historicalbackground• Applications

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• Advantagesofmechanisation• Narrowgapwelding• Introduction• Generalrecommendations• Summary• Weldingexamples• Aluminiumwelding• Aluminiumweldingwithdirectcurrent• Examplesofaluminiumwelding• Glossary