Cylinders can explode if damaged

Shielding gas cylinders contain gas under high pressure. If damaged, a cylinder can explode. Since gas cylinders are normally part of the welding process, be sure to treat them carefully.

· Protect compressed gas cylinders from excessive heat, mechanical shocks, physical damage, slag, open flames, sparks, and arcs.

· Install cylinders in an upright position by securing to a stationary support or cylinder rack to prevent falling or tipping.

· Keep cylinders away from any welding or other electrical circuits.

· Never drape a welding torch over a gas cylinder.

· Never allow a welding electrode to touch any cylinder.

· Never weld on a pressurized cylinder – explosion will result.

· Use only correct shielding gas cylinders, regulators, hoses, and fittings designed for the specific application; maintain them and associated parts in good condition.

· Turn face away from valve outlet when opening cylinder valve.

· Keep protective cap in place over valve except when cylinder is in use or connected for use.

· Use the right equipment, correct procedures, and sufficient number of persons to lift and move cylinders.

· Read and follow instructions on compressed gas cylinders, associated equipment, and Compressed Gas Association (CGA) publication P-1 listed in Safety Standards.

Quality OF WELDING

Most often, the major metric used for judging the quality of a weld is its strength and the strength of the material around it.

Many distinct factors influence this, including the welding method, the amount and concentration of energy input, the base material, the filler material, the flux material, the design of the joint, and the interactions between all these factors. To test the quality of a weld, either destructive or nondestructive testing methods are commonly used to verify that welds are defect-free, have acceptable levels of residual stresses and distortion, and have acceptable heat-affected zone (HAZ) properties.

Welding codes and specifications exist to guide welders in proper welding technique and in how to judge the quality of welds.

Heat-affected zone

The blue area results from oxidation at a corresponding temperature of 600 °F (316 °С). This is an accurate way to identify temperature, but does not represent the HAZ width. The HAZ is the narrow area that immediately surrounds the welded base metal.

The effects of welding on the material surrounding the weld can be detrimental— depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. The thermal diffusivity of the base material plays a large role—if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Conversely, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process plays an important role as well, as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input. [29] [30] To calculate the heat input for arc welding procedures, the following formula can be used:

where Q = heat input (kJ/mm), V = voltage (V), I = current (A), and S = welding speed (mm/min). The efficiency is dependent on the welding process used, with shielded metal arc welding having a value of 0.75, gas metal arc welding and submerged arc welding, 0.9, and gas tungsten arc welding, 0.8.

Distortion and cracking

Welding methods that involve the melting of metal at the site of the joint necessarily are prone to shrinkage as the heated metal cools. Shrinkage, in turn, can introduce residual stresses and both longitudinal and rotational distortion. Distortion can pose a major problem, since the final product is not the desired shape. To alleviate rotational distortion, the workpieces can be offset, so that the welding results in a correctly shaped piece.[32] Other methods of limiting distortion, such as clamping the workpieces in place, cause the buildup of residual stress in the heat-affected zone of the base material. These stresses can reduce the strength of the base material, and can lead to catastrophic failure through cold cracking, as in the case of several of the Liberty ships. Cold cracking is limited to steels, and is associated with the formation of martensite as the weld cools. The cracking occurs in the heat-affected zone of the base material. To reduce the amount of distortion and residual stresses, the amount of heat input should be limited, and the welding sequence used should not be from one end directly to the other, but rather in segments. The other type of cracking, hot cracking or solidification cracking, can occur with all metals, and happens in the fusion zone of a weld. To diminish the probability of this type of cracking, excess material restraint should be avoided, and a proper filler material should be utilized.

Weldability

The quality of a weld is also dependent on the combination of materials used for the base material and the filler material. Not all metals are suitable for welding, and not all filler metals work well with acceptable base materials.

Steels

The weldability of steels is inversely proportional to a property known as the hardenability of the steel, which measures the probability of forming martensite during welding or heat treatment. The hardenability of steel depends on its chemical composition, with greater quantities of carbon and other alloying elements resulting in a higher hardenability and thus a lower weldability. In order to be able to judge alloys made up of many distinct materials, a measure known as the equivalent carbon content is used to compare the relative weldabilities of different alloys by comparing their properties to a plain carbon steel. The effect on weldability of elements like chromium and vanadium, while not as great as carbon, is more significant than that of copper and nickel, for example. As the equivalent carbon content rises, the weldability of the alloy decreases. [34] The disadvantage to using plain carbon and low-alloy steels is their lower strength—there is a trade-off between material strength and weldability. High strength, low-alloy steels were developed especially for welding applications during the 1970s, and these generally easy to weld materials have good strength, making them ideal for many welding applications.

Stainless steels, because of their high chromium content, tend to behave differently with respect to weldability than other steels. Austenitic grades of stainless steels tend to be the most weldable, but they are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and reduced corrosion resistance as well. Hot cracking is possible if the amount of ferrite in the weld is not controlled—to alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not as easily welded, and must often be preheated and welded with special electrodes.

Aluminum

The weldability of aluminum alloys varies significantly, depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input. Preheating reduces the temperature gradient across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.

WELDING DIFFICULTIES

Many of the welding difficulties in metal-arc welding are the same as in oxygas welding. A few such problems include undercut, cracked welds, poor fusion, and incomplete penetration. Table 7-3 provides an illustration of the most common welding problems encountered during the arc- welding process and methods to correct them. Every welder has the responsibility of making each weld the best one possible. You can produce quality welds by adhering to the rules that follow:

1 Use only high-quality welding machines, electrodes, and welding accessories.

2 Know the base material that you are working on.

3 Select the proper welding process that gives the highest quality welds for the base material used.

4 Select the proper welding procedure that meets the service requirement of the finished weldment.

5 Select the correct electrode for the job in question.

6 When preheating is specified or required make sure you meet the temperature requirements. In any case, do not weld on material that is below 32°F without first preheating.

7 Clean the base metal of all slag, paint, grease, oil, moisture, or any other foreign materials.

8 Remove weld slag and thoroughly clean each bead before making the next bead or pass.

9 Do not weld over cracks or porous tack welds. Remove defective tack welds before welding.

10 Be particularly alert to obtain root fusion on the first pass of fillet and groove welds.

11 When groove weld root gaps are excessive, build up one side of the joint before welding the pieces together.

12 When fillet weld root gaps are excessive, be sure you increase the size of the fillet weld to the size of the root gap to maintain the strength requirement. In some cases, it is advantageous to make a groove weld 1 to avoid extremely large fillet welds.

13 Inspect your work after completion and immediately remove and replace any defective weld.

14 Observe the size requirement for each weld and make sure that you meet or slightly exceed the specified size.

15 Make sure that the finished appearance of the weld is smooth and that overlaps and undercuts have been repaired.

PIPE WELDINGWelding is the simplest and easiest way to join sections of pipe. The need for complicated joint designs and special threading equipment is eliminated. Welded pipe has reduced flow restrictions compared to me­chanical connections and the overall installation costs are less. The most popular method for welding pipe is the shielded metal-arc process; however, gas shielded arc methods have made big inroads as a result of new advances in welding technology. Pipe welding has become recognized as a profession in itself. Even though many of the skills are com- parable to other types of welding, pipe welders develop skills that are unique only to pipe welding. Because of the hazardous materials that most pipelines carry, pipe welders are required to pass specific tests before they can be certified. In the following paragraphs, pipe welding positions, pipe welding procedures, definitions, and related information are discussed.

PIPE WELDING POSITIONSYou may recall from chapter 3 of this manual that there are four positions used in pipe welding (fig. 3-30). They are known as the horizontal rolled position (1G), the horizontal fixed position (5G), pipe inclined fixed (6G), and the vertical position (2G). Remember: these terms refer to the position of the pipe and not to the weld PIPE WELDING PROCEDURES.Welds that you cannot make in a single pass should be made in interlocked multiple layers, not less than one layer for each 1/8 inch of pipe thickness. Deposit each layer with a weaving or oscillating motion. To prevent entrapping slag in the weld metal, you should clean each layer thoroughly before depositing the next layer.

Unusual conditions

While many welding applications are done in controlled environments such as factories and repair shops, some welding processes are commonly used in a wide variety of conditions, such as open air, underwater, and vacuums (such as space). In open-air applications, such as construction and outdoors repair, shielded metal arc welding is the most common process. Processes that employ inert gases to protect the weld cannot be readily used in such situations, because unpredictable atmospheric movements can result in a faulty weld. Shielded metal arc welding is also often used in underwater welding in the construction and repair of ships, offshore platforms, and pipelines, but others, such as flux cored arc welding and gas tungsten arc welding, are also common. Welding in space is also possible—it was first attempted in 1969 by Russian cosmonauts, when they performed experiments to test shielded metal arc welding, plasma arc welding, and electron beam welding in a depressurized environment. Further testing of these methods was done in the following decades, and today researchers continue to develop methods for using other welding processes in space, such as laser beam welding, resistance welding, and friction welding. Advances in these areas could prove indispensable for projects like the construction of the International Space Station, which will likely rely heavily on welding for joining in space the parts that were manufactured on Earth.

Safety issues

Welding, without the proper precautions, can be a dangerous and unhealthy practice. However, with the use of new technology and proper protection, risks of injury and death associated with welding can be greatly reduced. Because many common welding procedures involve an open electric arc or flame, the risk of burns is significant.

To prevent them, welders wear personal protective equipment in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat and flames. Additionally, the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Goggles and welding helmets with dark face plates are worn to prevent this exposure, and in recent years, new helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light. To protect bystanders, translucent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.

Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides, which in some cases can lead to medical conditions like metal fume fever. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce fumes and various gases, most commonly carbon dioxide, ozone and heavy metals that can prove dangerous without proper ventilation and training. Furthermore, because the use of compressed gases and flames in many welding processes poses an explosion and fire risk, some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.

Costs and trends

As an industrial process, the cost of welding plays a crucial role in manufacturing decisions. Many different variables affect the total cost, including equipment cost, labour cost, material cost, and energy cost. Depending on the process, equipment cost can vary, from inexpensive for methods like shielded metal arc welding and oxyfuel welding, to extremely expensive for methods like laser beam welding and electron beam welding. Because of their high cost, they are only used in high production operations. Similarly, because automation and robots increase equipment costs, they are only implemented when high production is necessary. Labour cost depends on the deposition rate (the rate of welding), the hourly wage, and the total operation time, including both time welding and handling the part. The cost of materials includes the cost of the base and filler material, and the cost of shielding gases. Finally, energy cost depends on arc time and welding power demand.

For manual welding methods, labour costs generally make up the vast majority of the total cost. As a result, man)* cost-savings measures are focused on minimizing the operation time. To do this, welding procedures with high deposition rates can be selected, and weld parameters can be fine-tuned to increase welding speed. Mechanization and automatization are often implemented to reduce labour costs, but this frequently increases the cost of equipment and creates additional setup time. Material costs tend to increase when special properties are necessary, and energy costs normally do not amount to more than several percent of the total welding cost.

In recent years, in order to minimize labour costs in high production manufacturing, industrial welding has become increasingly more automated, most notably with the use of robots in resistance spot welding (especially in the automotive industry) and in arc welding. In robot welding, mechanized devices both hold the material and perform the weld, and at first, spot welding was its most common application. But robotic arc welding has been increasing in popularity as technology has advanced. Other key areas of research and development include the welding of dissimilar materials (such as steel and aluminum, for example) and new welding processes, such as friction stir, magnetic pulse, conductive heat seam, and laser-hybrid welding. Furthermore, progress is desired in making more specialized methods like laser beam welding practical for more applications, such as in the aerospace and automotive industries. Researchers also hope to better understand the often unpredictable properties of welds, especially microstructure, residual stresses, and a weld's tendency to crack or deform.

Welding Glossary

Actual throat thickness - The perpendicular distance between two lines each parallel to a line joining the outer toes one being tangent at the weld face and the other being through the furthermost point of fusion penetration.

Air-arc cutting - Thermal cutting using an arc for melting the metal and a stream of air to remove the molten metal to enable a cut to be made.

All-position - A gas welding technique in which the flame rightward welding

All-weld test piece - A block of metal consisting of one or more beads or runs fused together for test purposes. It may or may not include portions of parent metal.

All-weld test- specimen - A test specimen that is composed wholly of weld metal over the portion to be tested.

Arc blow - A lengthening or deflection of a DC welding arc caused by the interaction of magnetic fields set up in the work and arc or cables.

Arc fan - The fan-shaped flame associated with the atomic-hydrogen arc.

Arc voltage - The voltage between electrodes or between an electrode and the work, measured at a point as near as practical to the work.

Atomic-hydrogen welding - Arc welding in which molecular hydrogen, passing through an arc between two tungsten or other suitable electrodes, is changed to its atomic form and then re-combines to supply the heat for welding

Back-step sequence - A welding sequence in which short lengths of run are (Back-step sequence)

Backfire - Retrogression of the flame into the blowpipe neck or body with rapid self extinction.

Backing bar - A piece of metal or other material placed at a root (Temporary backing) (These terms are applied only to the welding of pipes or tubes.)

Backing strip - A piece of metal placed at a root and penetrated by (Permanent backing)

Block sequence - A welding sequence in which short lengths of the (Block welding)

Blowhole - A cavity generally over 1.6 mm in diameter, formed by entrapped gas during solidification of molten metal.

Blowpipe - A device for mixing and burning gases to produce a flame for welding, brazing, bronze welding, cutting, heating and similar operations.

Burn back - Fusing of the electrode wire to the current contact tube by sudden lengthening of the arc in any form of automatic or semi-automatic metal-arc welding using a bare electrode.

Burn off rate - The linear rate of consumption of a consumable electrode.

Burn through - A localised collapse of the molten pool due to (Melt through)

Carbon-arc welding - Arc welding using a carbon electrode or electrodes.

Chain intermittent weld - An intermittent weld on each side of a joint (usually fillet welds in T and lap joints) arranged so that the welds lie opposite to one another along the joint.

C02 flux welding - Metal-arc welding in which a flux-coated or flux containing electrode is deposited under a shield of carbon dioxide.

C02 welding - Metal-arc welding in which a bare wire electrode is used the arc and molten pool being shielded with carbon dioxide.

Concave fillet weld - A fillet weld in which the weld face is concave (curved inwards).

Cone - The more luminous part of a flame, which is adjacent to the nozzle orifice.

Continuous weld - A weld extending along the entire length of a joint.

Convex - fillet weld - A fillet weld in which the weld face is convex (bulbous).

Coupon plate - A test piece made by adding plates to the end of a joint to give an extension of the weld for test purposes. (Note: this term is usually used in the shipbuilding industry.)

Crack - A longitudinal discontinuity produced by fracture. Cracks may be longitudinal, transverse, edge, crater, centre line, fusion zone underhead, weld metal or parent metal.

Crater pipe - A depression due to shrinkage at the end of a run where the source of heat was removed.

Cruciform testpiece - A flat plate to which two other flat plates or two bars are welded at right angles and on the same axis.

Cutting electrode - An electrode with a covering that aids the production of such an arc that molten metal is blown away to produce a groove or cut in the work.

Cutting oxygen - Oxygen used at a pressure suitable for cutting.

De-seaming - The removal of the surface defects from ingots, blooms, billets and slabs by means of a manual thermal cutting.

Dip transfer - A method of metal-arc welding in which fused particles of the electrode wire in contact with the molten pool are detached from the electrode in rapid succession by the short circuit current, which develops every time the wire touches the molten pool.

Drag - The projected distance between the two ends of a drag line.

Drag lines - Serrations left on the face of a cut made by thermal cutting.

Electron-beam cutting - Thermal cutting in vacuum by melting and vaporising a narrow section of the metal by the impact of a focused beam of electrons.

Excess penetration bead - Excessive metal protruding through the root of a fusion weld made from one side only.

Face bend test - A bend test in which a specified side of the weld Normal bend test. (The side opposite that containing the root or )

Feather - The carbon-rich zone, visible in a flame, extending around and beyond the cone when there is an excess of carbonaceous gas.

Fillet weld - a fusion weld, other than a butt, edge or fusion spot weld, which is approximately triangular in transverse cross-section.

Flame cutting - Oxygen cutting in which the appropriate part of the material to be cut is raised to ignition temperature by an oxy-fuel gas flame.

Flame snap-out - Retrogression of the flame beyond the blowpipe body into the hose, with possible subsequent explosion.

Flame washing - A method of surface shaping and dressing of metal by flame cutting using a nozzle designed to produce a suitably shaped cutting oxygen stream.

Flashback arrestor - A safety device fitted in the oxygen and fuel gas system to prevent any flashback reaching the gas supplies.

Floating head - A blowpipe holder on a flame cutting machine which, through a suitable linkage, is designed to follow the contour of the surface of the plate, thereby enabling the correct nozzle-to-workpiece distance to be maintained.

Free bend test - A bend test made without using a former.

Fusion penetration - In fusion welding. The depth to which the parent metal has been fused.

Fusion zone - The part of the parent metal which is melted into the weld metal.

Gas economiser - An auxiliary device designed for temporarily cutting off the supply of gas to the welding equipment except the supply to a pilot jet where fitted.

Gas envelope - The gas surrounding the inner cone of an oxy-gas flame.

Gas pore - A cavity generally under 1.6 mm in diameter, formed by entrapped gas during solidification of molten metal.

Gas regulator - A device for attachment to a gas cylinder or pipeline for reducing and regulating the gas pressure to the working pressure required.

Guided bend test - A bend test made by bending the specimen round a specified former. Heat affected zone - The part of the parent metal which is metallurgically affected by the heat of welding or thermal cutting but not melted. (Also known as the zone of thermal disturbance).

Hose protector - A small non-return valve fitted to the blow-pipe end of a hose to resist the retrogressive force of a flashback.

Included angle - The angle between the planes of the fusion faces of parts to be welded.

Inclusion - Slag or other foreign matter entrapped during welding. The defect is usually more irregular in shape than a gas pore.

Incomplete root penetration - Failure of weld metal to extend into the root of a joint.

Incompletely filled groove - A continuous or intermittent channel in the surface of a weld, running along its length, due to insufficient weld metal. The channel may be along the centre or along one or both edges of the weld.

Intermittent weld - A series of welds at intervals along a joint.

Kerf -The void left after metal has been removed by thermal cutting.

Tack of fusion -Tack of union in a weld.(Between weld metal and parent metal, parent metal and parent metal or between weld metal and weld metal.)

Leftward welding -A gas welding technique in which the flame is (Forward welding)

Leg -The width of a fusion face in a fillet weld.

Metal-arc cutting -Thermal cutting by melting using the heat of an arc between a metal electrode and the metal to be cut.

Metal-arc welding -Arc welding using a consumable electrode.

Metal transfer -The transfer of metal across the arc from a consumable electrode to the molten pool.

MIG - welding - Inert-gas welding using a consumable electrode (inert-gas metal-arc welding)

Multi-stage regulator - A gas regulator in which the gas pressure is reduced to the working pressure in more than one stage.

Nick-break test - A fracture test in which a specimen is broken from a notch cut at a predetermined position where the interior of the weld is to be examined.

Open arc welding - Arc welding in which the arc is visible.

Open circuit voltage - In a welding plant ready for welding, the voltage between two output terminals which are carrying no current.

Overlap - An imperfection at a toe or a root of a weld caused by metal flowing on to the surface of the parent metal without fusing it.

Oxygen-arc cutting - Thermal cutting in which the ignition temperature is produced by an electric arc, and cutting oxygen is conveyed through the centre of an electrode, which is consumed in the process.

Oxygen lance - A steel tube, consumed during cutting, through which cutting oxygen passes, for the cutting or boring of holes.

Oxygen lancing - Thermal cutting in which an oxygen lance is used.

Packed lance - An oxygen lance with steel rods or wires.

Penetration bead -Weld metal protruding through the root of a fusion weld made from one side only.

Plug weld - A weld made by filling a hole in one component of a workpiece so as to join it to the surface of an overlapping component exposed through the hole.

Porosity - A group of gas pores.

Powder cutting - oxygen cutting in which powder is injected into the cutting oxygen stream to assist the cutting action.

Powder lance - An oxygen lance in which powder is mixed with the oxygen stream.

Preheating oxygen - Oxygen used at a suitable pressure in conjunction with fuel gas for raising to ignition temperature the metal to be cut.

Residual welding stress - Stress remaining in a metal part or structure as a result of welding.

Reverse bend test - A bend test in which the other than that specified for a face bend test is in tension.

Rightward welding - A gas welding technique in which the flame is (Backward welding)

Root (of weld) - The zone on the side of the first run farthest from the welder.

Root face - The portion of a fusion face at the root which is not bevelled or grooved.

Run-off-plate(s) - A piece, or pieces, of metal so placed as to enable the full section of weld to be obtained at the end of the joint.

Run-on-plate(s) - A piece, or pieces, of metal so placed as to enable the full section of weld metal to be obtained at the beginning of a joint.

Scarfing - The removal of the surface defects from ingots, blooms, billets and slabs by means of a flame cutting machine.

Seal weld - A weld, not being a strength weld, used to make a (sealing weld)

Sealing run - The final run deposited on the root side of a fusion (backing run)

Shrinkage groove - A shallow groove caused by contraction of the metal along each side of a penetration bead.

Side bend test - A bend test in which the face of a transverse section of the weld is in tension

Skip sequence - A welding sequence in which short lengths of run are (skip welding )

Slag-trap - A configuration in a joint or joint preparation which may lead to the entrapment of slag.

Slot lap joint - A joint between two overlapping components made by depositing a fillet weld round the periphery of a hole in one component so as to join it to the other component exposed through the hole.

Spray transfer - Metal transfer which takes place as globules of diameter substantially larger than that of the consumable electrode from which they are transferred.

Stack cutting - The thermal cutting of a stack of plates usually clamped together.

Staggered intermittent weld - An intermittent weld on each side of a joint (usually fillet welds in T and lap joints) arranged so that the welds on one side lie opposite the spaces on another side along the joint.

Striking voltage - The minimum voltage at which any specified arc may be initiated.

Submerged-arc welding - Metal-arc welding in which a bare wire electrode or electrodes are used; the arc or arcs are enveloped in a flux, some of which fuses to form a removable covering of slag on the weld.

Surface-fusion welding - Gas welding in which a carburizing flame is used to melt the surface of the parent metal which then unites with the metal from a suitable filler rod.

Sustained backfire - Retrogression of the flame into the blowpipe neck or body the flame remaining alight. Note: This manifests itself either as "popping" or "squealing" with a small pointed flame issuing from the nozzle orifice or as a rapid series of minor explosions inside.

Test piece - Components welded together in accordance with a specified welding procedure, or a portion of a welded joint detached from a structure for test.

Test specimen - A portion detached for a test piece and prepared as (Test coupon)

Thermal cutting - The parting or shaping of materials by the application of heat with or without a stream of cutting oxygen.

TIG - welding - Inert-gas welding using a non-consumable electrode (inert-gas tungsten-arc welding)

Toe - The boundary between a weld face and the parent metal or between weld faces.

Tongue-bend test specimen - A potion so cut in two straight lengths of pipe joined by a butt weld as to produce a tongue containing a portion of the weld. The cuts are made so that the tongue is parallel to the axis of the pipes and the weld is tested by bending the tongue round a

Touch welding - Metal-arc welding using a covered electrode, the covering of which is kept in contact with the parent metal during welding.

Tungsten inclusion - An inclusion of tungsten from the electrode in TIG-welding.

Two-stage regulator - A gas regulator in which the gas pressure is reduced to the working pressure in two stages.

Undercut - An irregular groove at a toe of a run in the parent metal, or in previously deposited weld metal, due to welding.

Weld junction - The boundary between the fusion zone and the heat affected zone.

Welding procedure - A specified course of action followed in welding including the list of materials and, where necessary, tools to be used.

Welding sequence - The order and direction in which joints, welds or runs are made.

Welding technique - The manner is which the operator manipulates an electrode, a blowpipe or a similar appliance.

Worm-hole - An elongated or tubular cavity formed entrapped gas during the solidification of molten metal.