Gas Welding


1.0.0 OXYGAS Welding Equipment

2.0.0 Operation and Maintenance of OXYGAS Equipment

3.0.0 OXYGAS Welding Techniques

Review Questions

Welding (also called fusion welding) is the process of heating two or more materials (usually metals) to a melting point where they can coalesce, sometimes with additional material (a third metal) called filler. When the heating is provided by gas, naturally, the term used is “gas welding.” Oxyacetylene and oxy-MAPP (methylacetylenepropadiene) welding are two types of gas-welding processes. Both require a gas-fueled torch to raise the temperature of two similar pieces of metal to the fusion point that allows them to flow together. A filler rod is used to deposit additional metal as necessary to merge the two base materials. The gas and oxygen must be mixed to correct proportion and pressure in the torch, and you can adjust the torch to produce the type of flames appropriate for the metal being welded.

This course presents information on the equipment and materials used in gas welding, as well guidance on the operation and maintenance of oxyacetylene and oxy-MAPP equipment. In addition, it will recommend welding techniques for both ferrous and nonferrous metals.

When you have completed this course, you will be able to:



Fundamentally, an oxygas welding outfit is the same as an oxygas cutting outfit; the only exception is the torch, or in some combination torches, only the torch head. An oxygas welding outfit is also called a welding rig (Figure 1). Like the cutting outfit, the minimum welding outfit consists of the following parts:

Figure 1 — Typical oxygas welding rig similar to oxygas cutting rig.

In addition to the basic equipment shown, you also will use much of the same auxiliary equipment as tip cleaners, cylinder trucks, clamps, strikers, gang wrench, and holding jigs. Safety apparel such as goggles, gloves, as well as leather aprons, sleeves, and leggings are essential, and you should wear them as appropriate for the work being performed (Figure 2). 


Figure 2 — Examples of common auxiliary and safety equipment for oxygas welding and oxygas cutting.

Like oxygas cutting equipment, a welding rig may be stationary or portable. Figure 3 shows the setup of a portable oxygas welding or cutting rig. This portable setup is very advantageous when it is necessary to move the equipment, particularly on a project site with rough terrain since the metal wheels will not go flat. To perform your gas welding duties, you must be able to set up and adjust the equipment, so you must understand the purpose and function of the basic pieces.

Figure 3 — Typical setup of a portable welding or cutting rig.

1.1.0 Welding Torches

A properly adjusted oxygas welding torch mixes oxygen and the selected fuel-gas in the proper proportion and delivers a controlled amount of the mixture to burn at the welding tip. An oxygas welding torch has the following basic parts:

Welding tips are made from a special copper alloy available in a wide range of styles, configurations, and sizes to accommodate for various plate thicknesses, and to meet welders’ needs ranging from industrial manufacturers to the individual hobby shop user (Figure 4).

Figure 4 — Examples of the variety of oxygas welding tips available.

Some manufacturers’ models are designed as tubes, silver-brazed to the head with rear-end forgings fitted into the handle. Other manufacturers have welding tips with flexible tubes.

There are two general types of welding torches:

The low-pressure torch is also known as an injector torch. The injector torch uses fuel-gas pressure at about 1 psig (pound per square inch gauge) or less, with oxygen pressure ranges set between 10 to 40 pounds, depending on the size of the torch tip. The flow of relatively high-pressure oxygen produces the suction (venturi effect) necessary to draw the low-pressure fuel-gas into the mixing head. The welding tips may or may not have separate injectors in the tip. Figure 5 shows a typical mixing head for a low-pressure (injector) torch.

Figure 5 — Mixing head for a low-pressure (injector) torch.

Medium-pressure torches are also known as balanced-pressure or equal-pressure torches. While overall operating pressures will vary depending on the size and type of tip necessary for the thickness of the material, these torches operate with the fuel-gas and oxygen pressure relatively equal.

Figure 6 shows a typical equal-pressure (general-purpose) welding torch. A medium-pressure torch is easier to adjust than a low-pressure torch and, since you are using equal oxygen and fuel-gas pressures, you are less likely to get a flashback.

Figure 6 — Typical equal-pressure (general-purpose) welding torch mixing head.


If you use acetylene as the fuel-gas, never allow the pressure to exceed 15 psig; acetylene becomes very dangerous at 15 psig and is self-explosive at 29.4 psi.

Welding mixers and tips are designed in several ways.

Some torch designs have a separate mixing head or mixer for each tip size (Figure 7, View A). Other designs have only one mixer for several tip sizes.

Figure 7 — Examples of fixed and removable tips.

Tips come in various types; some are onepiece hard-copper tips, and others are two-piece tips that include an extension tube to make the connection between the tip and the mixing head (Figure 7, View B).

When used with an extension tube, removable tips are made of hard copper, brass, or bronze.

Each manufacturer assigns its own arrangement for classifying tip sizes, but typically they are designated by a number system which corresponds to the diameter of the hole in the tip.

1.2.0 Filler Rods

The term filler rod refers to the filler metal you use in gas welding, brazing, and certain electric welding processes such as gas tungsten arc welding or TIG, where the filler metal is not a part of the electrical circuit. As its name implies, filler rod supplies the filler metal to the joint. Depending on the characteristics and thickness of the metal, a weld design’s required gaps and bevels may vary widely, so filler rod comes in a variety of sizes and in wire or rod form to accommodate a project’s needs.

Most rods are available in 36-inch lengths and a wide variety of diameters, ranging from 1/32 to 3/8 inch. The thickness of the base metal will determine which diameter you need to use.

Rods for welding cast iron vary from 12 to 24 inches in length and are frequently square, rather than round.

As a rule, filler rods are uncoated except for a thin film resulting from the manufacturing process.

Filler rods for welding steel are often copper-coated to protect them from corrosion during storage (Figure 8).

Figure 8 — Typical filler rod and packaging.

Many different types of rods are manufactured for welding ferrous and nonferrous metals.

In general, welding shops stock only a few basic types that are suitable for use in all welding positions. These basic types are known as general-purpose rods.

You select the proper filler rod based on the specifications (specs) of the metal being joined, and there are specs for filler rods that identify which filler rod should be used with which metal.

Test Your Knowledge

1. Fundamentally, an oxygas welding outfit is the same as an oxygas cutting outfit.

A. True
B. False


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This section presents the basic procedures involved in setting up oxygas equipment, securing the equipment, lighting it off, and adjusting the flame. It also provides information on the maintenance of oxygas welding equipment.

2.1.0 Operation

A properly made gas weld has a consistent appearance that shows a uniform deposit of weld metal and complete fusion of the sidewalls forming a good joint (Figure 9).

Figure 9 — Example of consistent appearance and uniform deposit.

You must consider some of the following factors when making a gas weld:

In some cases, you need to use fluxes to remove oxides and slag from the molten metal and to protect the puddle from atmospheric contamination.

When you join sections of sheet and thin plate by gas welding, you need to melt the edges uniformly with the heat from the torch. When you weld heavier plate, you need to use filler metals to accommodate the designed gaps and beveled edges required to permit heat and weld penetration to reach the base of the joint. You melt the filler metal along with the base metals, and as they mix and solidify, they form a continuous piece.

Usually, you do not need filler metal for light sheet metal, and the edges of light sheet metal are flanged at the joint so they flow together to form one solid piece when you melt them.

2.1.1 Selecting the Welding Torch Tip Size

The size of a welding tip is designated by a number stamped on the tip, and the tip size is determined by the size of the orifice (Figure 10).

Figure 10 — Welding tip orifices.

The various manufacturers do not use a common system of identifying welding tip sizes; each has its own part number identification system.

This course refers to tip size by using the number drill for the orifice size.

Once you are familiar with a specific manufacturer’s torch and tip numbering system, referring to the tip by the orifice’s number drill size will become unnecessary.

Number drills consist of a series of 80 drills, numbered 1 through 80. The diameter of a number 1 drill is 0.2280 of an inch, and the diameter of a number 80 drill is 0.0135 of an inch. Table 1 shows the full range of number drill sizes.



The higher the number of the drill, the smaller the size the drill.

Table 1 — Number Drill Bit Conversion Table

Orifice size determines the quantity of fuel-gas and oxygen fed to the flame, and by extension, it determines the amount of heat the torch tip can produce: the larger the orifice, the greater the heat.

If you use a torch tip with too small an orifice, you will not be able to generate enough heat to bring the metal to its fusion temperature.

If you use a torch tip with too large an orifice, you are likely to produce poor welds for these reasons:

Therefore, the quality of the weld is unsatisfactory.

For practice purposes, use an equal-pressure torch with the filler welding rod sizes and the tip sizes shown in Table 2; they should give you satisfactory results as you develop your hands-on skills.

Table 2 — Welding Rod Sizes and Tip Sizes Used to Weld Various Thickness of Metal

2.1.2 Equipment Setup

Except for the selection of the torch, or just the welding tip in the case of a combination torch, you set up the oxygas equipment and prepare for welding the same way you set it up for oxygas cutting.

Select the correct tip and mixing head (depending on the torch manufacturer), and connect them to the torch body. Tighten the assembly snugly by hand, adjust the tip to the proper working angle, and then tighten the tip. Depending on the manufacturer and model, you tighten some equipment with a wrench (those with nut ends), while others you only hand tighten (those with knurled ends).

2.1.3 Torch Lighting and Flame Adjustment

Light the torch and adjust the flame by following the manufacturer’s directions for the particular model of torch you are using. Procedures vary with different manufacturers’ torches and, in some cases, even with different models made by the same manufacturer, so always use their guidance for lighting. After lighting, adjust the flame according to the type of metal being welded: carburizing, neutral, or oxidizing. Again, review Chapter 4 Gas Cutting if you need more in-depth coverage of the different types of flames.

2.2.0 Maintaining the Equipment

Like any other equipment, you must perform minor upkeep and proper maintenance for welding equipment to operate at peak efficiency, give useful service, and be readily available when you need it. You are not required (or authorized) to make major repairs; however, when major repairs are indicated, you need to remove the equipment from service and turn it in for repair. This section presents some of the common types of maintenance duties you will need to perform.

2.2.1 Torch Gas Leaks

Occasionally, the torch head’s needle valves may fail to shut off when hand tightened in the normal manner. If this occurs, do not use a wrench to tighten the valve stem. Instead, use the following procedures:

  1. Open the valve and try to blow the foreign matter off the valve seat by using increased working gas pressure in the hose. (Do not exceed 15 psig for acetylene.)
  2. If this fails, remove the stem assembly and wipe the needle valve and seat clean. Reassemble the valve and try closing it tightly by hand several times.
  3. If these measures fail to stop the leak, have the parts replaced or the valve body reseated. Only a qualified person should make this repair.

When there is leakage around the torch valve stem, you can tighten the packing nut or repack it if necessary. For repacking, use only the packing recommended by the torch’s manufacturer. DO NOT USE ANY OIL. While it is disassembled for repacking, observe the valve stem, and if bent or badly worn, replace it.

Before you use a new torch for the first time, check the packing nut on the valves to make sure they are tight; some manufacturers ship torches with these nuts loose.

Leaks in a torch’s mixing-head seat will cause the oxygen and fuel-gas to leak between the inlet orifices leading to the mixing head; this causes improper gas mixing and flashbacks. You can correct this problem by sending the equipment to the manufacturer for repair by having the seat in the torch head reamed and the mixing-head seat trued.

2.2.2 Welding Torch Tips

Welding tips are subject to considerable abuse just by the nature of their working environment. The tip may be damaged if you allow it to contact the welding work, bench, or firebricks. This damage roughens the end of the tip and causes the flame to burn with a “fishtail.” In addition, you must avoid dropping a tip because that may damage the seat that seals the joint with the mixing chamber.

For a welding tip to perform satisfactorily, you must:

Exercise care when you clean a welding tip; do not enlarge or scar the orifice.

Special welding/cutting tip cleaners are available to help remove carbon or slag from the tip orifice (Figure 11).

Figure 11 — Typical welding/cutting tip cleaner.

The cleaner set contains a series of broach wires that correspond to the diameter of the tip orifices.

These wires are packaged in a holder, which makes their use safe and convenient. Figure 12, View A shows a tip cleaner in use.

Figure 12 — Typical welding/cutting tip cleaner in use.

Some welders prefer to use a number drill the size of the tip orifice to clean welding tip orifices (Figure 12, View B).

A number drill must be used carefully so the orifice is not enlarged, bell-mouthed, reamed out of round, or otherwise deformed. Refer to Table 1 for number drill sizes.

Recondition the tip face if it becomes rough, pitted, or the orifice is bell-mouthed.

To ensure a properly shaped flame, the face end of the tip must be clean, smooth, and at right angles to the centerline of the tip orifice.

Some tip cleaner sets contain a small file for maintaining the tip face (Figure 13, View A).

Figure 13 — Reconditioning the face of a welding/cutting tip.

As an alternative, you can use a 4-inch mill file (Figure 13, View B) to recondition the surface provided you exercise extreme care not to over-file the surface of the much softer copper.

Another easy method involves a piece of emery cloth. Place it grit side up on a flat surface; hold the tip face perpendicular to the emery cloth and rub the tip back and forth just enough to true the surface and to bring the orifice back to its original diameter.

2.2.3 Regulator Leaks

Regulator creep, that is, gas leakage between the regulator seat and the nozzle, is the most common type of trouble with regulators.

The most obvious indicator of this problem is the gradual rise of working-gauge pressure without having moved the adjusting screw. This trouble can be caused by worn or cracked seats, but it is due more often simply to foreign matter lodged between the seat and the nozzle.

You need to remove leaking regulators from service at once, and then send them for repair to prevent possible injury to personnel or additional equipment damage, particularly with faulty fuel-gas regulators. Fuel-gas under pressure in a hose becomes an explosive hazard, and remember, acetylene is over-pressured and dangerous at just 15 psig. To ensure the safety of personnel and equipment, ensure that regulators with such leaks are removed from service and turned in for repair.

Test Your Knowledge

2. What characteristics indicate a properly made gas weld?

A. Complete fusion of the sidewalls
B. Uniform deposit of weld metal
C. Consistent appearance
D. All of the above


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You can use the forehand or backhand method to weld with oxygas. Each technique has its advantages, particularly in different positions, so you need to become skillful with both; it is the relative position of the torch and rod that determines whether you consider a technique forehand or backhand, not the direction of welding. Under any circumstances, you need to use the method considered best, but the best method will depend upon a combination of factors: type of joint, joint position, joint design, and heat control on the parts.

3.1.0 Forehand

Welding In forehand welding, also called puddle or ripple welding, you point the flame in the direction of travel. You hold the tip at an angle of about 45 degrees to the working surfaces and keep the rod ahead of the flame in the direction in which you are making the weld (Figure 14).

Figure 14 — Example of forehand welding.

This flame position preheats the edges you are welding just ahead of the molten puddle.

While moving with the torch tip, rotate the tip and welding rod back and forth in opposite, semicircular paths to distribute the heat evenly.

As the flame passes the welding rod, it melts a short length of the rod and adds it to the puddle.

The motion of the torch distributes the molten metal evenly to both edges of the joint and to the molten puddle.

Forehand is ideal for thin plate; it permits better control of a small puddle and results in a smoother weld.

You can use the forehand technique in all positions for sheet and light plate up to 1/8 inch thick. However, it is not the recommend method for heavy plate because it lacks sufficient base metal penetration.

3.2.0 Backhand

Welding In backhand welding, you point the flame away from the direction of travel and back at the molten puddle and completed weld (Figure 15).

Figure 15 — Examples of backhand welding.

Hold the welding tip at an angle of about 60 degrees with the plates or joint being welded, and place the welding rod between the torch tip and the molten puddle.

You use less motion in the backhand method than in the forehand method.

If you use a straight welding rod, rotate it so the end rolls from side to side and melts off evenly.

You may, however, need to bend the rod when working in confined spaces.

If you have to bend the rod, it becomes difficult to roll, so to compensate, move the rod and torch back and forth at a rather rapid rate.

When you make a large weld, move the rod so it makes complete circles in the molten puddle, and move back and forth across the weld while advancing slowly and uniformly in the direction of the welding.

Backhand welding is best suited for material more than 1/8 of an inch thick. You can use a narrower vee at the joint than is possible with forehand welding, and an included angle of 60 degrees is sufficient to get good joint penetration. In addition, the backhand method requires less welding rod or puddling than the forehand method.

By using the backhand technique on heavier material, you can increase your welding speed, exercise better control of the larger puddle, and have more complete fusion at the weld root. Also, if you use a slightly reducing flame (carburizing), you melt a smaller amount of base metal while still welding the joint.

When you weld steel with a backhand technique and a slightly reducing flame, a thin surface layer of metal absorbs carbon and reduces the melting point of the steel, thus speeding up the welding operation. You can also use this technique in surfacing with chromium-cobalt alloys.

3.3.0 Multilayer Welding

You use multilayer welding with gas welding for the same reason you do with arc welding: to avoid carrying large, difficult-to-control puddles when working on thick plate and pipe (Figure 16).

Figure 16 — Example of multilayer welding sequence.

Instead, concentrate on getting a good weld at the bottom of the vee in the first pass.

Then, in the next layers, concentrate on getting good fusion with the sides of the vee and the previous layer.

Generally, you can easily control the final layer to get a smooth surface.

Multilayer welding has an added advantage: you are refining the previous layer as you make the succeeding layer. In effect, you heat-treat the weld metal by allowing one layer to cool to a black heat before you reheat it, thus improving the ductility of the weld metal. If you need to develop this added ductility in the last layer, you can deposit an additional or succeeding layer and then machine it off.

3.4.0 Joint Edge Preparation

You can easily melt sheet metal and it does not require special edge preparation. However, for a welding operation involving plate, you must prepare the joint edges and provide for proper spacing. The plate’s thickness will determine the required amount of edge preparation.

You can weld plate 3/8 to ½ inch thick from one side only, but you should prepare and weld thicker sections on both sides. Generally, butt joints prepared on both sides permit easier welding, produce less distortion, and ensure better weld qualities.

Only use oxygas welding for heavy steel plate when all other types of welding equipment are unavailable. It is not cost effective due to the quantity of gases and the **18 amount time needed to complete a weld. Instead, use a form of electric arc welding; you can weld the joint faster and cheaper, with less heat distortion.

3.5.0 Ferrous Metals

The oxygas process easily welds low-carbon steel, low-alloy steel, cast steel, and wrought iron. These metals have oxides that melt at a lower temperature than the base metal, so you do not need to use flux.

During the welding process, enclose the molten puddle with the flame envelope. This is to ensure the molten metal does not contact the air and begin to oxidize rapidly. However, you need to reach a balance and avoid overheating the metal as well.

To make a good weld, you need a properly adjusted flame.

  1. Adjust to neutral or slightly reducing (carburizing) flame. o Do not use oxidizing flame.
  2. Manipulate torch and rod with tip of oxygas cone about 1/16 to 1/8 inch from the work surface.
  3. Melt filler rod in the puddle, not with the flame.

There are no special problems involved in welding low-carbon steels and cast steels other than selecting the proper filler rod.

Low-alloy steels usually require both pre- and post-welding heat treatment. This relieves the stresses developed during welding and produces the desired physical properties of the metal.

With steels, as carbon content increases, welding difficulty increases. Use a slightly carburizing flame to weld steels with carbon content in the 0.3-percent to 0.5-percent range, and these low-carbon steels require post-welding heat treatment to develop their best physical properties.

High-carbon steel and tool steel require a slightly different technique.

After welding, you must heat-treat high-carbon steels and tool steels to develop the physical properties required.

You use the same procedure for oxygas welding WROUGHT IRON as you do for low-carbon or mild steel; however, you need to keep several points in mind (Figure 17).

Figure 17 — Example of wrought iron oxygas weld.

You obtain the best results with wrought iron when you mix the filler metal (usually mild steel) and base metal in the molten puddle with a minimum of agitation.

Oxygas welding CAST IRON is not difficult, but it does require a modification of the procedure used with steel. Figure 18 shows some cast iron welding opportunities.

Figure 18 — Examples of potential oxygas cast iron welding projects.

For metal:

After you complete a cast iron weld, you must stress relieve the weldment by heating it to between 1100°F and 1150°F and cooling it slowly.

Oxygas welding cast iron will provide a good color match and good machinability, but if color match is not essential, you can use braze welding to make an easier and more economical cast iron repair.

You can use oxygas welding for some CHROMIUM- NICKEL STEELS (STAINLESS STEELS), but usually only for light sheet; typically, you join heavier pieces with one of the electric arc welding processes. On material 20 gauge (0.040 of an inch) or less thick, you can make the weld on a turned up flange (equal to the metal’s thickness) without filler metal using the following steps.

  1. Clean joint surfaces with sandpaper or other abrasives.
  2. Apply stainless steel flux.
  3. Use torch tip one or two sizes smaller than used for mild steel of same thickness.
  4. Use carburizing flame, as seen through goggles, with excess fuel-gas feather extending about 1/16 inch beyond tip of inner cone.
  5. Angle flame at an 80° angle to surface with cone tip almost, but not quite, touching molten metal.
  6. Weld in one pass using forehand technique. Do not puddle or retrace.

For welding light-gauge stainless steel, you need to use a uniform speed; if you find it necessary to stop welding or reweld a section, wait until the entire weld has cooled.

3.6.0 Nonferrous Metals

Brazing and braze welding are the more common methods of joining nonferrous metals, but oxygas welding is just as suitable in many situations. In most cases, joint designs are the same for nonferrous metals as for ferrous metals, but welding nonferrous metals usually requires you to clean the surfaces mechanically and also to use flux. Of course, you must use filler metals suitable for the base metal as well.

3.6.1 Copper

You can oxygas weld pure copper, but where high-joint strength is a requirement, use DEOXIDIZED copper (copper that contains no oxygen). Use the following guidance.

Other than the extra volume of heat required, the technique for welding deoxidized copper is the same as for steel.

3.6.2 Copper-Zinc Alloy (Brasses)

You can weld copper-zinc alloys (brasses) using the same methods as for deoxidized copper. However, for welding brasses you use a silicon-copper rod, which is usually already flux-coated so you do not need additional flux. The preheat temperature for brass is 200°F to 300°F.

3.6.3 Copper-Silicon Alloy (Silicon Bronze)

Welding copper-silicon alloy (silicon bronze) requires a different technique than for pure copper and brass. Use the following guidance:



Safeguard against zinc poisoning by doing welding outdoors or by wearing a respirator, or by both, depending on the situation.

3.6.4 Copper-Nickel Alloy

To oxygas weld copper-nickel alloys, you must prepare the surface and preheat the material. Use the following guidance:

3.6.5 Nickel and High-Nickel Alloys

You can oxygas weld nickel and high-nickel alloys similar to the methods you use for copper-nickel alloys.

  1. Mechanically clean joint surfaces.
  2. Use joint designs similar to steel thickness. (For V-butt welds, use included angle of 75°).
  3. Apply flux (a thin paste) with a brush to both sides of seam, top and bottom, and to filler rod. (Plain nickel does not require flux; high-nickel alloys require special boron-free and borax-free flux).
  4. Use very slightly carburizing flame.
  5. Use same size or one size larger tip as used for steel of same thickness.
  6. Keep flame soft and cone’s tip in contact with molten pool.
  7. Use suitable rod and keep it well within protective envelope of flame.
  8. After completion, postheat and cool slowly.
  9. Remove flux with warm water.

3.6.6 Lead

To oxygas weld lead, you need to use special tools and special techniques. When you weld lead or lead alloys, wear a respirator approved for protection against lead fumes.



Lead fumes are poisonous.

Flux is not required, but you must ensure the metal in the joint area is scrupulously clean by shaving the joint surfaces with a scraper and wire brushing them to remove all oxides and foreign matter.

You can use a square butt joint if you are welding in the flat position, but for all other positions, you need to use a lap joint with edges overlapping from ½ to 2 inches, depending upon the thickness.

3.6.7 Aluminum and Aluminum Alloys

If you are assigned to work with nonferrous metals, you can expect to do projects that involve welding aluminum and aluminum alloys. Pure aluminum has a specific gravity of 2.70 and a melting point of 1210°F, but pure aluminum is seldom used; it is soft, not hard enough or strong enough for structural purposes. However, manufactured aluminum is strengthened significantly with the addition of other elements to form aluminum alloys.

Pure aluminum has only about ¼ the strength of steel, and the alloys are usually about 90 percent pure. Yet, when elements such as silicon, magnesium, copper, nickel, and/or manganese are added to aluminum, the aluminum alloy is stronger than mild steel.

A considerable number of aluminum alloys are available and used to manufacture many everyday items (Figure 19).

Figure 19 — Examples of potential oxygas aluminum alloy welding projects.

You may need to use some aluminum alloys in sheet form to make and/or repair lockers, shelves, boxes, trays, and other containers, or you may need to repair chairs, tables, and other items of furniture.

Typically, oxygas welding aluminum alloy is confined to materials from 0.031 to 0.125 inch thick, but you can weld thicker material if necessary.

On the other hand, thinner material is usually spot or seam welded. Melting Characteristics

Before you attempt to weld aluminum alloy for the first time, you need to be familiar with how it reacts under the welding flame. You can practice using the following guidance.

Observe — almost without warning, the metal suddenly melts and runs away, leaving a hole.

Observe —the puddle quickly solidifies when you remove the flame.

Continue this practice until you are able to control the melting. With a little practice, you will be able to melt the surface metal without forming a hole.

When you have mastered this, proceed by practicing actual welding. Start with simple flanged and notched butt joints that do not require a welding rod, then try using a welding rod with thin sheet, and then with castings. Welding Rods

There are two types of welding rods available for gas welding aluminum alloys.


  • For welding 1100 and 3003 type aluminum alloys only.
  • Provides maximum resistance to corrosion.
  • Offers high ductility.


  •  For all other wrought aluminum alloys and castings.
  • Provides greater strength.
  • Minimizes tendency for cracking. Welding Fluxes

It is extremely important to use the proper flux when welding aluminum. Aluminum welding flux is designed to remove the aluminum oxide by combining with it chemically. In gas welding, oxide forms rapidly in the molten metal and must be removed or your weld will be defective. To ensure proper flux distribution and minimize the oxide, paint the flux on the welding rod as well as the surface to be welded.

Aluminum flux usually comes in powder form and you mix it with water to form a paste. Keep the prepared paste in an aluminum, glass, or earthenware container; steel or copper containers will contaminate the mixture.

For flanged joints where you do not use filler rod, it is essential that you apply plenty of flux to the edges of both the bottom and top sides in the area of the weld.

On the other hand, after you finish welding, you must remove all traces of flux with a brush and hot water; if you leave aluminum flux on the weld, it will corrode the metal. Welding Preparation

The thickness of the aluminum will determine how you need to prepare edges.

On material up to 0.062 inch thick, form a 90° flange with the height of the flange about the same height, or a little higher, as the thickness of the material (Figure 20).

Figure 20 — Example of aluminum alloy flanged edge preparation.

The flange edges must be straight and square.

You can use flange joints for material up to 0.125 (1/8) inch thick.

No filler rod is necessary for welding flange joints.

On material 0.062 to 0.188 inch thick, you can make unbeveled butt welds, but notch the edges with a saw or cold chisel similar to that shown in Figure 21.

Figure 21 — Example of aluminum alloy notched edge preparation.

When you edge notch aluminum welding, it aids in getting full penetration and preventing local distortion. All butt welds made in material over 0.125-inch thick are usually notched in some manner.

To weld aluminum alloy more than 0.188 inch thick, both bevel the edges and notch them as shown in Figure 22, with the included angle of bevel from 90° to 120°.

Figure 22 — Example of aluminum alloy notched and beveled edge preparation.

After you properly prepare the edges, clean the surfaces you will be welding. Use a stainless steel wire brush to remove any heavy oxide, or a solvent-soaked rag to wipe off any dirt, grease, or oil.

If you are welding aluminum plate 0.250-inch thick or greater, preheat it to 500°F to 700°F; this aids in avoiding heat stresses. Preheating also reduces fuel and oxygen requirements for the actual welding.

Do not exceed 700°F during your preheating operation or you may severely weaken the alloy; high temperatures can cause large aluminum parts to collapse under their own weight. Also, warm thin material with the torch before welding; this slight preheat helps prevent cracking. Welding Techniques

After preparing and fluxing the aluminum alloy pieces for welding, use the following guidance to weld.

With practice, you can easily master the rod and flame movement. Generally, you should use the forehand method for welding aluminum alloys; the flame points away from the completed weld, preheating the edges to be welded, which helps prevent too rapid a melting as you progress.

hen you weld aluminum alloys up to 0.188-inch thick, you do not need to add any motion to the torch other than forward, but on flanged material, you must break the oxide film as the flange melts down. You can do this by stirring the melted flange with a puddling rod, which is essentially a paddle flattened and shaped from a ¼- inch stainless steel welding rod.

When you weld aluminum alloys above 0.188 inch thick, give the torch a uniform lateral motion to distribute the weld metal over the entire width of the weld. Also, use a slight back-and-forth motion to assist the flux in removing oxides. Dip the filler rod in the weld puddle with a forward motion.

Your welding speed will be directly related to the torch’s angle; instead of having to lift the flame to avoid melting holes, hold the torch at a flatter angle to the work. Never let the flame’s inner cone contact the molten metal; keep it about 1/8-inch away from the metal, and as you approach the end of the sheet, increase your welding speed.

If you are welding in the vertical position, give the torch an up-and down motion, rather than a rotating one. If you are in the overhead position, give the torch a light back-and-forth motion as in flat welding.

Whenever possible, hold heat-treatable alloys in a jig for welding to help eliminate cracking. You can also reduce the likelihood of cracking by using the 4043 filler rod. 4043 rod has a lower melting range than the alloy being joined, thus permitting the base metal to solidify before the weld puddle freezes.

The weld is the last area to solidify, so all of the contraction strains are in the weld bead rather than throughout the base metal. To reduce cracking further, tack weld parts while in the jig and then loosen the clamps and complete the work

As soon as the weld is complete and the work has cooled, thoroughly wash the weld by scrubbing it vigorously with a stiff brush as hot water runs over it. Continue until you have removed all traces of flux; if any flux is left on the weld, it can corrode the metal. If hot water is unavailable, use a diluted solution of 10 percent sulfuric acid, then wash the acid solution off with cold, fresh water.

3.7.0 Welding Pipe

In considering oxygas welding for pipe, many tests have proven that properly made fusion-welded pipe joints are as strong as the pipe itself. There are three essential requirements to meet for successful oxygas welding of pipe.

  1. You must have a convenient source of controlled heat available to produce rapid, localized melting of the metal.
  2. You must remove the oxides present on the surface or edges of the joints.
  3. You must make a metal-to-metal union between the edges or surfaces by means of molten metal.

Refer to Figure 23. It shows a welding operation at the top of a joint on a (assumed) horizontal pipe. For certification welding test purposes, if the pipe is rolled, the test would be to qualify the welder in the 1G position; if stationary, the test would be in the 5G position.

Figure 23 — Example of a pipe welding operation using the backhand technique.

Now refer to Figure 24.

This figure shows a detail of the flame and rod motions used to weld the pipe with the backhand technique. The rod and flame are moved alternately toward and away from each other in an accordion motion.

Figure 24 — Example of the flame and rod motion performed on a pipe with the backhand technique.

An experienced welder can make full-strength oxygas welds in any physical welding position, and on a stationary pipe, most positions will be used.

The cohesiveness of the molten metal, the pressure of the flame, the support of the weld metal already deposited, and the manipulation of the rod all combine to keep the molten metal in the puddle from running or falling.

The soundness and strength of your welds will depend heavily on the quality of the welding rod you use. If you have any doubt about the quality of the rods available, or you are unsure of which type to use, contact the rod manufacturer or one of the distributors. If your rod was supplied through the federal stock system, supply personnel should be able to look up the information you need based on the federal stock number.

The Linde Company has a method of fusion welding that is remarkably fast and produces high quality welds. Anyone can use this process for welding pipe if they adhere to the following conditions:

The following is a brief explanation:

One of the most valuable tools you can use when welding pipe is the pipe clamp. Pipe clamps hold the pipe in perfect alignment until tack welds are placed. They are quickopening, and you can move or attach a clamp quickly. Figure 25 shows four different variations of using chain clamps for pipe welding setup.

Figure 25 — Examples of typical chain clamps aligning various pipefittings.

If these clamps are unavailable, you can fabricate your own by welding two C-clamps to a piece of heavy angle iron; a piece of 4” x 4” x 3/8-inch angle iron about 12 inches long is usually suitable. When you are butt-welding a small-diameter pipe, you can lay it in a piece of channel iron to obtain true alignment, or when you are working on a large diameter pipe, you can use a wide flange beam for alignment.


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Gas welding is just one of many skills you need to practice and become proficient in as a Steelworker. Depending on the characteristics and thickness of the material you have for an assigned task, you may determine that gas welding is the preferred method for either repair or fabrication. This chapter presented information about the necessary equipment and identified how similar it is to gas cutting equipment in setup, use, and the gases utilized. It also provided instructions on how to operate and maintain the equipment in good working order with proper tip cleaning tools. Lastly, it offered gas welding techniques with recommendations about when to use the forehand or backhand technique relative to type of weld and specific metal. With this guidance, you should be able to set up the equipment, adjust the pressures, select the appropriate filler metal to match the base metal, and practice/practice/practice until you can demonstrate your capabilities and proficiencies in gas welding to yourself and your supervisors.

Review Questions 

1. Which factor should you consider when considering gas welding?

A. Edge prep, spacing, and joint alignment
B. Flame adjustment and rod and torch manipulation
C. Temperature control, before, during, and after the welding process
D. All of the above

2. From what special type of alloy(s) are welding tips made?

A. Carbon and zinc
B. Tin and iron
C. Titanium
D. Copper

3. In a low-pressure torch, the fuel pressure in pounds per square inch (psig) is _____.

A. 1 psig or less
B. 2 to 3 psig
C. a constant 5 psig
D. greater than 7 psig

4. What device(s) control(s) the volume of oxygen and fuel-gas burned at the torch tip?

A. One needle valve at the torch mixing head
B. Two needle valves at the torch mixing head
C. One separate mixing head for each gas
D. Two different size tips

5. In a low-pressure welding torch, the fuel-gas enters as a result of suction created in the torch by a jet of higher-pressure _____.

A. nitrogen
B. gasoline
C. oxygen
D. helium

6.  In a medium-pressure welding torch, the working pressure of oxygen and fuel-gas is equal.

A. True
B. False

7. What primary function do filler rods serve in oxygas welding?

A. As an electrical connection between the torch and the workpiece
B. As a source of metal to fill the weld joint
C. As a surface for braze welding
D. As a heat conductor

8. The copper coating on steel filler rods enables the rods to _____.

A. melt at a higher temperature
B. melt at a lower temperature
C. clean the weld joint of impurities
D. resist corrosion during storage

9. Which factor determines the proper diameter of filler rod to use for gas welding two steel plates?

A. Type of steel that the plates are made of
B. Thickness of the metal
C. Job specifications
D. Type of welding torch

10. Which factor determines the type of filler rods to use in oxygas welding?

A. Specifications of the metal being joined
B. Composition of the rod coatings
C. Length and shape of available rods
D. Type of welding position required

11.  Welding tip sizes are standardized among manufacturers.

A. True
B. False

12. What mistake have you most likely made when you have difficulty controlling the melting of the welding rod, the welds are being made too fast, and their appearance and quality are unsatisfactory?

A. Used a welding rod that is too small
B. Used incorrect polarity
C. Used an incorrect “dragging” technique
D. Used a welding tip that is too large

13. What factor dictates the adjustment you must make to the flame after igniting a welding torch?

A. Thickness of the metal
B. Type of filler rod used
C. Type of metal being welded
D. Polarity being used

14. What type of flame is best used for welding high-carbon steels, nonferrous metals, and hardfacing?

A. Neutral
B. Carburizing
C. Oxidizing
D. Normalizing

15. What type of flame is correct for use on most metals?

A. Neutral
B. Carburizing
C. Oxidizing
D. Normalizing

16. What flame is limited in use and harmful to many metals?

A. Neutral
B. Carburizing
C. Oxidizing
D. Normalizing

17. What is the first corrective step you should take when needle valves fail to shut off when hand tightened in the usual manner?

A. Use a wrench to tighten it.
B. Open the valve and using the working gas pressure blow out any foreign matter.
C. Remove the stem assembly and wipe the seat clean.
D. Have the parts replaced by qualified personnel.

18. When there is a leak around the torch valve stem, you should tighten the packing nut or repack it if necessary. For repacking, NEVER use oil. Instead, you should use only _____.

A. dry packing
B. the packing recommended by the manufacturer
C. heavy-weight packing
D. granulated packing

19. You must remove deposits of _____ regularly to ensure good performance of welding tips.

A. copper and zinc oxide
B. sodium carbide and phosphorus
C. ferrous oxide and sodium phosphate
D. slag and carbon

20. What procedure should you follow to recondition the end of a torch tip that has become rough and pitted?

A. Insert a drill one size larger than the orifice opening into the tip end.
B. Insert a tip drill into the seat opening and twist until penetration can be made at the tip-end opening.
C. Place emery cloth, grit side up, on a flat surface and rub the tip end over it until the tip is back to its original condition.
D. Use a bench grinder to square off the end of the tip, then drill out the orifice.

21. What type of file is commonly used to recondition a welding tip?

A. Mill
B. Pillar
C. Square
D. Taper

22. When forehand welding, you point the flame in the direction of travel and hold the tip at about a _____ angle.

A. 15°
B. 30°
C. 45°
D. 60°

23. The forehand method is best for welding _____.

A. heavy plate that is between 1 to 3 inches thick
B. sheet and light plate up to 1/8 of an inch thick
C. sheet plate that is between 1 to 2 inches thick
D. any type of metal

24. When backhand welding, you point the flame away from the direction of travel and hold the tip at about a _____ angle.

A. 15°
B. 30°
C. 45°
D. 60°

25. For which of the following reasons should you use the backhand method instead of the forehand method when welding plates thicker than 1/8 inch?

A. It uses less welding rod and results in less puddling of molten metal.
B. It requires less motion of the rod and torch tip and increases welding speed.
C. It results in better control of large puddles of molten metal and achieves more complete fusion at the root of the weld.
D. All of the above

26. For which reason is it possible to weld steel plates faster by using the backhand technique and a reducing flame rather than the forehand technique and a neutral flame?

A. More of the base metal is melted during the welding operation.
B. It is not necessary to control the heat on the plate.
C. A thin surface layer of steel absorbs carbon and reduces the melting point of steel.
D. All of the above

27. Which factor is an advantage of using multilayer welding instead of single layer when welding thick plate and pipe?

A. The final layer is easier to control to get a smooth surface.
B. Ductility of the weld metal is improved since one layer cools before being reheated when an additional layer is made.
C. There is better control over each layer since carrying large puddles of molten metal is avoided.
D. All of the above

28.  Sheet metal melts easily and does not require special edge preparation.

A. True
B. False

29. On what thickness of plate do you begin to make a slight root opening between the parts to get complete penetration?

A. 1/16 to 1/8 inch
B. 3/16 to 1/4 inch
C. 1/4 to 3/8 inch
D. 3/8 to ½ inch

30. What size plate requires beveled edges 30 degrees to 45 degrees and a root opening of 1/16 inch?

A. 1/8 inch and greater
B. 3/16 inch and greater
C. 1/4 inch and greater
D. ½ inch and greater

31. What action must you take to relieve stresses developed when oxygas welding low-alloy steels?

A. Chip and peen after welding
B. Quench after welding
C. Heat-treat before and after welding
D. Use special flux in the welding process

32. What causes the surface of the molten puddle to appear greasy when welding wrought iron?

A. High carbon content of the wrought iron
B. Slag used in manufacturing the wrought iron
C. Use of mild steel as a filler metal
D. Failure to use a special flux

33.  When you oxygas weld cast iron, you must preheat the entire weldment to between 750°F and 900°F. After completing the weld, you must postheat the weldment to between 1100°F to 1150°F to relieve stresses.

A. True
B. False

34. Which characteristics apply to the method of joining a light stainless steel sheet by oxygas welding?

A. No flux, a carburizing flame, no puddle, and a relatively small torch tip
B. No flux, an oxidizing flame, puddle, and a relatively large torch tip
C. Flux, an oxidizing flame, no puddle, and a relatively small torch tip
D. Flux, a carburizing flame, no puddle, and a relatively small torch tip

35. To what temperature range should you preheat the joint area when you oxygas weld deoxidized copper?

A. 100°F to 300°F
B. 300°F to 500°F
C. 500°F to 800°F
D. 800°F to 900°F

36. Assuming the same welding process and same part thickness, compared with the technique for joining steel parts, the technique for joining deoxidized copper calls for the use of a/an _____.

A. smaller torch tip and no preheating
B. larger torch tip and more preheating
C. oxidizing flame and no flux
D. carburizing flame and oxygas brass flux

37. What type of rod is used for welding brass by the oxygas process?

A. Lead
B. Steel
C. Silicon-copper
D. Silicon-bronze

38. Which action should you take when oxygas welding copper-nickel alloys?

A. Adjust the flame to a slightly oxidizing flame.
B. Agitate the molten puddle when adding filler metal.
C. Keep the welding rod end outside the protective envelope of the flame.
D. Remove all traces of flux with warm water after welding is completed and the part has been cooled slowly.

39. You must wear a respirator to guard against poisonous fumes when you weld _____.

A. silver
B. aluminum
C. lead
D. brass

40. What type of welding rod should you use to minimize cracking when gas welding wrought aluminum alloys?

A. 1100
B. 3003
C. 4043
D. 5511

41. Pure aluminum is one fourth as strong as _____.

A. steel
B. iron
C. copper
D. titanium

42. For which reason do you use a flux when welding aluminum alloy?

A. To preserve the luster of the metal
B. To reduce the tendency of the metal to crack
C. To remove the aluminum oxide formed during the welding process
D. To lower the melting point of aluminum

43. Edge notching is a recommended procedure for oxygas butt welding aluminum plate because it _____.

A. gives a clear view of the weld area
B. aids in getting full penetration and prevents distortion
C. allows the torch flame to cover a greater area
D. allows the welder to use either the forehand or backhand method

44. What temperature should you not exceed when preheating aluminum alloys?

A. 300°F
B. 500°F
C. 700°F
D. 900°F

45.  The forehand method of welding is preferred for aluminum alloys.

A. True
B. False

46. What action should you take to reduce the possibility of heat-treatable aluminum alloys cracking during the welding process?

A. Secure them in a jig.
B. Use 4043 filler rod.
C. Tack the work while clamped in a jig, then loosen before completing the seam.
D. All of the above

47. Which requirement must be met to complete a successful weld when oxygas welding pipe?

A. A controlled heat source localized to produce rapid melting
B. Elimination of surface oxides
C. Union of edges or surfaces by means of molten metal
D. All of the above

48.  For welding pipe, the backhand technique is preferred because it produces faster melting of the base metal surfaces, allows a smaller bevel to be used, and results in a savings of 20% to 30% in welding time, rods, and gases.

A. True
B. False



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