What is Oxy Acetylene Welding? | Oxy Fuel Welding

What Is Oxy Acetylene Welding?

Oxyacetylene welding is a process that utilizes heat from a flame created by gas that burns at a high temperature to melt base materials and create fusion at the welding joint.

Then type of welding is best described as autogenous welding whereby metal is joined together without additional filler metal. However, the more common method of welding involves the use of filler metal.

It is to be noted that you may also hear this type of welding referred to as “gas welding.” The flame is produced by burning a combustible gas mixture – in a precise ratio or ratio of oxygen and acetylene.

Other fuel gases can be used, including propane, hydrogen, natural gas, and methylacetylene propadiene (MPS, formerly MAPP gas) although the most common fuel gas to be used in welding in acetylene.

Acetylene has been chosen as the type of fuel gas in welding because oxygen and acetylene will burn in a neutral flame at between 5,600 and 6,300 degrees Fahrenheit, which is the hottest of all flame gas combustibles, and is a temperature capable of melting and welding most metals.

Other oxygen-fuel gas combinations do not create the necessary BTUs to effectively weld two pieces of metal together, but they still can be used for soldering or brazing metals in place.

Oxyacetylene welding as a process or technique is versatile because it can be used for welding, cutting, AND heating, soldering and brazing.

Oxyacetylene welding can also be much more cost-effective than arc welding. Furthermore, oxyacetylene welding is highly portable because it has no electrical power source.

Oxyacetylene is capable of welding metals of many thicknesses, although sections greater than 1⁄4 inch can lead to welding challenges.

The unfortunate aspect of oxyacetylene welding is that the art of oxyacetylene welding can be skillfully hard to master, and there is the real danger of using and working with an extremely flammable material, acetylene.

Oxyacetylene welding equipment will consist of an oxygen cylinder, acetylene cylinder, pressure regulators, hoses, a torch and a welding tip.

Related: What is Gas Welding?

Oxy-Acetylene Welding Equipment

1. Cylinders.

Oxygen is contained in a high pressure cylinder (sometimes referred to as a bottle or tank) at 2,200 pounds per square inch (psi) when full. Additionally, the cylinder valve should be covered with the supplied safety cap whenever it is stored or transported. Never lift the cylinder by the safety cap.

You should always store and transport the cylinders in an upright position. Acetylene is an extremely unstable gas. It must never be above 15 psi in its free state. To safely pressurize acetylene to 225 psi in the cylinder, the acetylene cylinder is filled with a porous substance and acetone.

When the acetylene is pressurized, the acetylene is absorbed by the acetone, which lends itself a stable medium for the gas.

Upon release of the pressure (opening the valve), the acetylene “bubbles” out of the acetone solution. Acetylene cylinders have fusible safety plugs that will melt in the event of a fire, allowing the gas to harmlessly release, rather than exploding.

Acetylene cylinders should always be stored upright. If an acetylene cylinder is used at an angle, it would allow acetone through the regulator and hose, which would damage these components.

Cylinders should always be upright and secured with a chain or strap to lessen the chance of falling over. Cylinders should never be used as rollers to move heavy equipment or used for any purpose other than its specified usage.

2. Cylinder Valves.

Every type of cylinder has its own valve that regulates the flow of gas from the cylinder to the user. The valve is opened and closed via a hand wheel or valve wrench.

A high-pressure cylinder, such as an oxygen cylinder or an argon cylinder, should always be opened fully (to backseat the valve); when the valve is completely closed or completely open, it is leak-proof (not so when partially opened).

Cylinder valves are also designed for specific gases. Each cylinder valve is threaded with a different size thread for a specific regulator, as a safety feature to protect from using the wrong gas. The valve on an acetylene cylinder should never be opened more than 3⁄4 to 1 1⁄2 turns.

Anything less may not allow adequate gas flow, resulting in a backflash; anything more would make it more difficult to close the cylinder quickly in the event of an emergency.

If the acetylene valve is opened all the way or opened too quickly, acetone may escape from the cylinder and could destroy the hoses and regulator diaphragms.

3. Pressure Regulators and gauges.

Pressure regulators decrease the pressure of the gas leaving the cylinder. A single stage regulator will decrease the cylinder pressure to a working pressure in one step. A two stage regulator reduces the pressure in two steps.

A two-stage regulator allows for a more precise gas flow. It will typically be much more expensive compared to a single stage regulator but is not necessary in activities like welding. A single stage regulator should be good enough in most welding situations.

To adjust the regulator, turn the adjustment screw clockwise to increase pressure, and counter clockwise to decrease the pressure.

The regulator is completely off when the adjustment screw is loose or “backed out”. Be sure to back out the adjustment screws for your regulators as part of your post-welding routines.

WARNING: Never use oil or any other type of lubricant on regulators or other welding equipment. The combination of oil and oxygen in a spark-filled environment can lead to a fire in the regulator, which could cause a cylinder explosion.

4. Hoses.

The flexible rubber hoses that transfer the gas from the regulator to the torch are built to be leak proof and withstand high pressure. The oxygen hose is green and the acetylene or fuel hose is red.

Hoses are offered as a single hose, or dual hose (twin) where the fuel and oxygen hoses are together, at the same time. Twin houses are the most common and most commonly used.

Always protect hoses from damage by moving them off of the floor when not used, keeping them behind the welding area so it does not come into contact with sparks, and keeping them out of traffic lanes or areas so that they are not stepped on or run over by the vehicles.

Hoses should not be exposed to oily surfaces, and should be protected from sunlight and chemical fumes to keep them in good condition. Always drain hoses after a welding session to release the pressure, as this will extend the life of the hoses.

5. Fittings.

The fittings connect hoses to the regulator on one side and the torch on the other side. For safety reasons, the fuel hose nut (red color) on the end of the fuel hose uses left handed threads, and there is a groove machined into the entire surface of the nut to identify it is for fuel use.

The oxygen (green color) hose nut on the oxygen hose uses right hand threads and there is no groove. You must never switch the oxygen and acetylene hoses or fittings; they are color coded, and they also have different threads for consistency and safety.

Do not force a fitting: brass is a soft metal and fittings can be damaged very easily. Always hand thread and hand tighten fittings prior to using a wrench, and be careful not to overtighten them. Never use pliers to tighten fittings as you will damage the brass fittings.

6. Check Valves and flashback Arrestors.

Check valves and flashback arrestors are both safety devices that are intended to prevent reverse gas flow or flashbacks. The check valve will ONLY allow gas to flow from the cylinder to the torch.

If the gas pressure builds in the torch beyond the hose pressure, the valve is held shut by a spring to prevent back flow. The check valve must be replaced if ever experiencing a flashback. A flashback arrestor will be located between the hose and torch, which has more protection than a check valve.

A flashback arrestor prevents burning oxygen from flashing back into the hoses and regulator that could explode. Flashback arrestors also will have a check valve, pressure sensitive valve, stainless steel filter, and heat sensitive check valve.

If there is a flashback, the flashback arrestor does NOT need to be changed. When these valves are used, it creates a restriction and may require the gas supply pressure to be increased to eliminate (or minimize) fuel starvation, which could create overheating in the torch.

7. Torch.

The torch is used to blend and control the flow of the fuel gas and oxygen. A torch comprises valves, torch body, mixing chamber, and tip. A combination torch contains mixing chamber and adjustment valve which will be part of the cutting attachment.

8. Welding Tips.

The welding tips couple to the torch body and come in a wide range of sizes to make different sized flames. The tip size refers to the size of the opening orifice: the larger the tip size, the larger the fuel gas mixture, and hotter the flame.

It is critical that you match the correct size tip to the thickness of the metal being welded. In order to create quality welds, you should match the tip size, the welding material, and gas pressure.

How To Set Up An Oxyacetylene Welding Outfit

1. Position the cylinders in an upright manner, chained to a cart or strapped to a wall or post. Remove the caps protecting the cylinder. Wipe the cylinder valve seats, regulator connections, and hoses with a clean cloth.

Crack each cylinder valve open briefly, to purge any dirt stuck in the valve opening. “Flat top” acetylene cylinders (inset) may also have antifreeze in the recessed valve seat. Use a clean rag and wipe it off and dry the valve seat. A cylinder wrench is also required to open the valve on a flat top acetylene cylinder.

2. Next, attach the regulators to the cylinders. (The acetylene connectors have left hand threads.) Always hand tighten them first, and then tighten them with a fixed wrench, not pliers or an adjustable wrench. Do not over-tighten. Firm seating is adequate.

Next, attach the hoses to the regulators. The acetylene hose is red and has left hand threads. The oxygen hose is green. Do not use grease, oil, or pipe dope to lube fittings. Grease and oil can spontaneously ignite upon contact with oxygen even without a spark or flame.

3. Turn the adjustment screws on the oxygen and acetylene regulators counterclockwise until they are loose. (Some regulators have a knob to loosen.)

4. Open the oxygen valve slowly all the way while standing to the side in case the glass reading gauge shatters. Turn the adjustment screw on the oxygen regulator until you have a flow through the hose, then turn the adjustment screw until you stop the oxygen flow. Slowly turn the acetylene cylinder valve 3⁄4 to 11⁄2 turns.

5. Adjust the acetylene regulator valve until gas comes out, then loosen the adjustment screw. Attach the torch to the hoses and make sure you pressurize the system and check for any leaks before lighting.

How To Pressurize (Turn On) An Oxyacetylene Welding Outfit

Verify that both torch valves are off position. Next, turn both regulator adjustment screws counter clockwise (loosen all the way). After this, gently turn on the oxygen cylinder valve.

When the cylinder valve is open, then turn the valve to the full open position to ensure that the valve is sitting properly and will not leak when turned on.

Now turn the adjust screw on the oxygen regulator in a clockwise direction until the gauge reads the desired pressure. (Follow the instructions manual for operating pressures specific to the manufacture.)

Next, open the oxygen valve on torch and read flowing oxygen pressure, at this point, if required, adjusting is permissible and then close the valve on the torch.

Opening the acetylene cylinder valve should be done slowly, 3⁄4 to 1 1⁄2 turns. (If it is a wrench type valve, you can leave the wrench on the valve.)

Once torque has been setup adjust the pressure adjustment screw on the acetylene regulator until the desired cylinders flows pressure is reached as reflected on the regulator gauge.

At this point and using the acetylene valve on the torch check that flowing pressure is the same as desired working pressure, if not, you can adjust the regulator and reach the proper acetylene pressure.

Checking For Leaks

With a small brush, apply leak detecting solution to all connections. (You may use soap and water as long as the soap is not petroleum based.) If any of the connections creates bubbles in the solution, tighten the connections and check again.

WARNING: Backfire and flashback are hazardous situations that can occur if the gas pressures are not set properly. Backfire is when the acetylene and oxygen pre ignites inside the tip which causes a popping sound.

This could damage the tip or spray molten metal from the weld area. Flashback is when the flame burns backward into the torch or hoses causing a popping or squealing noise. Flashback can also cause an explosion in the hoses.

You can avoid both hazards by ensuring that you are using the appropriate tip size for the material, and using the correct pressure settings. Using pressures lower than those recommended can create backfire and possibly flashback.

Lighting The Torch

Prelighting Checklist:

• Ensure the torch valves are all in closed position.
• Turn the regulators adjusting screws counterclockwise until loose.
• Slowly open the oxygen cylinder valve all the way until fully open. Slowly adjust the regulator adjusting screw to the proper pressure.
• Slowly open the acetylene cylinder valve approximately 3/4 to 1 1/2 turns. Adjust the regulator adjusting valve to the proper pressure.

Some welders have been trained to open both the acetylene and oxygen valves before lighting the torch to avoid the smoky acetylene flame. This practice is no longer advised. Also, never light a torch using a match or butane lighter.

Lighting The Torch:

1. Using your dominant hand, hold the torch being sure to keep your thumb and forefinger on the acetylene torch valve. In your other hand, hold the striker out front (3-6 inches from the torch) and at an angle. Use the acetylene torch valve to turn the torch on (1⁄4 to 1⁄2 turn); at the same time, ignite the torch recommend using the spark lighter.
2. The flame will be yellow and smoky.
3. Place the striker down and using your torch hand, turn the acetylene torch valve until the flame is burning without soot. The flame should extinguish the yellow acetylene feather (inset). Flow the oxygen taper with your torch valve while going slowly. You need to adjust the flow of the oxygen until you have a bright white inner flame and a bluish outer flame. Turn down the acetylene flow until the excess acetylene feather is eliminated. When you are finished welding, turn off the oxygen torch valve first and then turn off the acetylene torch valve.

Flame & Flame States

The oxyacetylene torch flame is made up of two flame components: the inner or primary flame and the outer or secondary flame. The flame can have different temperatures at different points in the flame. The outer edges are cooler, as they are burning with ambient air, which is only 21% oxygen.

The tip of the torch is cooler because it has not achieved complete combustion. The hottest point of the flame is at the tip of the primary or inner flame cone. At this point, the gases are completely combusted and are being insulated from the ambient air by the secondary flame.

Within the oxyacetylene flame, there are three flame states: carburizing, neutral, and oxidizing.

• There is too much fuel in the carburizing or reducing flame. This flame is valuable as it works to break metal oxides down to get at the oxygen and clean the weld area to a minor extent. It adds carbon to the weld, thus making it harder. The carburizing flame consists of a bright white primary flame cone, an acetylene “feather” around the primary flame, and a secondary flame is light bluish-white with orange edges.
• A neutral flame is ‘just right’ in that it represents the juncture of the feather and inner cone with the presence of precisely as much oxygen as is needed for the complete combustion of the fuel gas. A neutral flame is also the flame most welding and cutting processes utilize. The neutral flame has a bright white primary flame with a colorless to bluish secondary flame.
• An oxidizing flame has too much oxygen. The white cone of this flame is small and pointed, and somewhat paler than the neutral flame. This flame usually has a hissing sound. This flame does not have very much utility because it will hasten oxidizing, which is conflicting in welding. It can still be used for removing carbon from molten metal and thus softening the metal while welding.

How To Weld with Oxyacetylene?

Pre-weld Checklist:

• Check for damaged hoses before pressurizing the system.
• When preparing metal for welding, wire brush or sand off any mill scale or rust. When there is oil or other chemical residues, use acetone or denatured alcohol to remove these residues.
• Use fire bricks to reduce excess heat loss and to eliminate welding to the welding table.
• See manufacturer’s recommendation for proper tip sizes and gas pressures.
• Prepare materials and clamp if necessary.

NOTE: The directions for oxyacetylene welding are for righthanded welding. Reverse the directions for left-handed welding, or if you find it easier to manipulate the filler rod with your right hand.

Step by Step:

1. Gather an appropriate filler rod and place it on the table near the bricks. Light the torch and adjust it to a neutral flame. Pull down the face shield. Place small fusion tack welds at each end of the joint and at the center if the joint is long. (A fusion weld uses no filler rod).

Turn the torch off oxygen first and acetylene last. Check that your tacked piece is still in the desired location. If not, either use a hammer to move the piece into position or break the tack weld and reposition.

2. With the torch at a 45° angle to the right side of the workpiece, oscillating the torch in a 1⁄4 to 1⁄2″ radius over both steel pieces, melt a puddle at the right end of your work piece.

3. After you have melted a puddle, take the filler rod and bring it close to (but not in) the puddle and flame. Slowly move to the left while oscillating, keeping the puddle molten. Dip the filler rod into the middle of the molten puddle and remove it; keep it in the heat zone.

4. Continue dipping, oscillating, then moving left. If you move to the left, by the time you get to the end of your weld, due to the cumulative heat and the ability to obtain more heat, you may need to adjust to a shallower angle to deflect heat away from the puddle to avoid burning through it. When completed, turn off the oxygen torch valve first then the acetylene torch valve. Be sure your weld penetrated to the back side. There should not be any burn-through.

Depressurizing An Oxyacetylene Welding Outfit

At the end of your welding operation, or if you will stop welding for more than about 10 or 15 minutes, depressurize your welding setup.

All hoses and regulators will allow for small amounts of fuel and oxygen to leak if they are pressurized and not being used, so depressurizing them is both safer and saves fuel costs.

Before long you will be so accustomed to the depressurizing and pressurizing steps that it won’t feel like an inconvenience at all. Make sure you do fuel gas, then oxygen in separate steps, to avoid having mixed, unburned oxyacetylene mix in the torch.

1. Close the fuel gas cylinder valve.
2. Open the fuel gas torch valve until both gauges read zero.
3. Loosen (counterclockwise) the fuel gas regulator adjustment screw.
4. Close the fuel gas torch valve.
5. Close the oxygen cylinder valve.
6. Open the oxygen torch valve until both gauges read zero.
7. Loosen (counterclockwise) the oxygen regulator adjustment screw.
8. Close the oxygen torch valve.

Why Use Acetylene For Welding?

Welding is a prominent fabrication process in a range of manufacturing and industrial processes. There are many different types of welding processes.

One type of welding is known as gas welding. In gas welding, the heat needed for the welding process is developed through the combustion of a fuel such as acetylene with oxygen. Sometimes, hydrogen, butane, and propane are used as substitutes to acetylene.

Since 1906, operators have been using the combination of oxygen and acetylene to cut metals. Acetylene has grown to be accepted over the years as one of the safest ways to work with a welding gas but also one of the strongest gases.

At this point, it is rapidly becoming a misconception that propane should be accepted as an equal or better welding gas than acetylene. In this post, we will examine the systems and differences between the two gases, and discuss the benefits of using acetylene gas in detail.

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