CUTTING TORCH SAFETY The Safe Use and Handling of OXY Fuel Cutting, Welding, and Heating Equipment
Introduction Safe operation for the use of gas cutting, heating and welding requires a clear understanding of oxy fuel cutting torch equipment and the fundamentals of combustion.
Handling Acetylene and Oxygen Cylinders Under normal conditions, the handling and use of oxygen and acetylene cylinders is very safe. It is the improper use and handling of this equipment that can cause serious damage and injury.
Why is it important to keep cutting torch and other gas cylinders secured? Securing cylinders is important to prevent damage to the high pressure valve, in the event the cylinder were knocked over, allowing the high pressure contents to escape in an uncontrolled fashion.
Why is it important to keep cutting torch and other gas cylinders secured? High pressure cylinders, particularly oxygen, with pressures of 2,000 psi or greater have the potential of causing damage or injury. This potential can occur if the valve assembly on the cylinder is damaged. Cylinders should always be secured with the valve cap in place, when not in use.
Cylinders Cutting torch Fuel cylinders, such as acetylene, are filled to a much lower pressure, but fuel cylinders can also be dangerous if the valve assembly is damaged. Another risk to acetylene cylinders would be the creation of voids within the cylinder if it is indented or struck. Voids allow for the acetylene gas to move around more freely. This increases the potential for cylinder explosion, as the gas molecules tend to separate.
If an acetylene cylinder has been laid down, should it be put into immediate service? NO!!... Did you know that acetylene cylinders are filled with liquid acetone? Acetylene cylinders are also filled with a porous concrete like substance. The liquid acetone saturates the porous material and the acetylene gas is compressed into the liquid, kind of like the gas bubbles that are in a soft drink. When the acetylene cylinder is leaned over or stored horizontally, there is possibility of acetone being present in the valve which would then enter the regulator.
Acetylene cylinders are filled with an inert porous material, which is then saturated with acetone. Acetylene gas is then charged into the cylinder. The gas then dissolves with the acetone, which keeps the gas stable at low pressures. Since the acetone is a liquid, acetone will flow into the cylinder valve assembly if the cylinder is on its side. Acetone will flow into the regulator if used, which can damage the regulator.
What is the maximum regulator pressure setting when using acetylene? 15 psi. Acetylene molecules are held in solution with acetone in the cylinder. Pressures above 15 psi allow the molecules to decompose or separate. Smith acetylene regulators are set to prevent pressurizing above this threshold. Separation of the molecule can be explosive.
What are four types of regulator burnouts (RBO s)to be concerned about when using a cutting torch?... A. Dust Always blow out the oxygen cylinder valve assembly before attaching the regulator. If dust has accumulated in the valve, there is potential for a dust explosion if the cylinder is opened rapidly. B. Oil oxygen Oils and grease also could cause a regulator explosion. Oxygen lowers kindling temperatures and accelerates combustion.
C. Dissociative gas Dissociative gas explosions are caused by acetone being withdrawn and entering the regulator. D. Mixed gas The fuel gas and oxygen being combined in one or both regulators cause mixed gas explosions. Since the oxygen cylinder has greater pressure, there is more potential for oxygen to be mixed in the fuel side.
Proper assembly of regulators onto compressed gas cylinders should be as follows:. Blow out oxygen cylinder valve, attach regulator Attach fuel regulator to fuel cylinder Be sure both regulators are pointed up to minimize damage in the event of a regulator explosion Attach hose and torch to regulators Be sure both regulator adjusting screws are in the out and off position
Open oxygen cylinder SLOWLY, to avoid heat of recompression (capable of creating up to 1700 degrees F); open valve completely; standing with cylinder between you and regulator If using acetylene, open fuel cylinder ½ to ¾ turn; standing with cylinder between you and regulator Make sure torch valves are in the off position
Turn in adjusting screw to desired pressure on both regulators Check all points the system for leaks, with approved leak detection solution, or non-oil based soapy water Purge each line by opening the torch valves for a few seconds and close Cutting torch is ready for use
What is the function of the fuel gas in an oxy fuel cutting torch process? The first function of the fuel gas is to provide a medium for ignition. The second function is to combine with oxygen, typically adjusted to a neutral flame setting, and provides the heat to raise the temperature of the material to it s kindling temperature.
Types of Fuel Gases There are several basic types of fuel gases. What are they and what are their respective temperatures (approximate), when mixed with oxygen to a neutral flame setting using a cutting torch?
Types of Fuel Gases Acetylene - 6000 degrees F MAPP -5400 degrees F Propylene -5200 degrees F Propane -5000 degrees F Natural gas- 4800 degrees F The temperatures quoted here are only approximate.
Types of Fuel Gases Flame temperatures do not tell the whole story regarding differences between fuel gases. There are also different BTU delivery; oxygen mixing ratios; rate of burn; and, differences in the temperature and BTU on different parts of the flame. Acetylene is still one of the most commonly used fuel gases for a cutting torch as well as for heating.
Types of Fuel Gases Soldering, brazing and welding are also done with acetylene. Acetylene contains the greatest amount of hydrocarbons. Acetylene produces the highest temperature of the commonly used fuel gases. It requires one part of oxygen mixed with one part of acetylene to achieve complete combustion of the fuel. The inner cone of the acetylene flame is where the greatest amount of heat and BTU delivery will be obtained. The amount of heat delivery of the acetylene flame is 1,450 BTU/CF.
Types of Fuel Gases Acetylene will burn at the rate of 29 feet per second. One reason why knowing the burn rate, is in the design of cutting torch tips and heating tips. Acetylene tips are typically straight or slightly concave at the tip face. Alternate fuel tips are recessed at the tip face an increasing amount depending on the gas.
Types of Fuel Gases MAPP, propylene, propane and Natural gas are all considered alternate fuels. There are several variations of these, depending on manufacturer. MAPP contains less hydrocarbon than acetylene, but more than the other alternate fuels. When lit, it will produce a sooty flame, similar to acetylene. For complete combustion, 2.5 parts of oxygen are required with one part MAPP. The greatest amount of heat is delivered in the secondary flame cone, of 1900 BTU/s. The MAPP flame produces a total of 2400 BTU s/cf. Its burning rate is 15 feet per second. Cutting tips typically have a 1/32 recess in the tip face to provide for an efficient flame.
Types of Fuel Gases Propylene is the third class of fuel gas. It contains less hydrocarbon, so is a fairly clean gas. It requires 3.5 parts of oxygen mixed with one part propylene to obtain complete combustion. It produces 2400 BTU s/cf, with 2000 BTU s delivered from the outer cone of the flame. It burns at a rate of 13.5 feet per second. Cutting tips designed for propylene have a 1/16 recess in the tip face.
Types of Fuel Gases Propane is a clean burning gas. It requires 4 parts of oxygen, mixed with one part of propane to provide complete combustion of the fuel. It produces 2600 BTU s CF, which is the most of the fuel gases, making it a popular choice for heating. Again, the outer or secondary cone of the flame is where most of the BTU s are delivered. Propane burns at the rate of 11.5 feet per second. Cutting tips designed for propane use will typically be recessed 3/32 in the tip face.
Types of Fuel Gases Natural gas is the cleanest burning gas of the common fuel gases (Hydrogen is cleaner). For complete combustion, 2.5 parts of oxygen are required, with one part Natural gas. It delivers a total of 1,050 BTU s, with 1,000 delivered through the outer or secondary cone of the flame. The burning rate is 10 feet per second. Cutting tips designed for Natural gas are recessed the same as for propane, of 3/32.
The Burning Process Technically speaking, when using an oxy fuel cutting torch to separate metal, are you cutting or burning the metal? Burning. Although commonly referred as cutting, the actual chemical process is burning.
When BURNING metal, why can t an oxy fuel cutting torch be used on aluminum or stainless steel successfully? Lack of iron content in the metal. The combustion process of burning steel is actually oxidation. Aluminum and stainless will not rust due to a lack iron content.
What is the kindling temperature of steel? 1600 degrees F. (approximately) Mild carbon steel needs to be a minimum of 1600 degrees before the burning process will begin.
Why are cylinders of oxygen required, rather than using oxygen in the atmosphere, to operate a cutting torch? Cutting or burning of steel, requires an oxygen purity content of 99%. When steel is brought to its kindling temperature, the combustion process will initiate when oxygen purity of 99% is added directly to the steel.
If when cutting or burning steel using a oxy fuel cutting torch, the cut is lost, why does this happen? One of two things happened. Either the kindling temperature was not maintained, or the oxygen purity was compromised over the full profile of the metal profile. To initiate a cut or burn, the metal must be preheated to its kindling temperature. At that point, pure pressurized oxygen is introduced in the flame, causing the metal to oxidize and the velocity of the oxygen blows the burned metal away.
If impurity in the metal is present, a different kindling temperature may be required. Speed of travel may vary from dirty to clean metals. If traveling too fast, the kindling temperature will not be maintained and the cut will be lost. The amount of oxygen pressure set at the regulator influences the volume of oxygen that passes through the cutting tip. The greater the thickness of metal to be cut, the greater the amount of oxygen volume required.
Oxygen purity must be maintained over the full profile of the cut. The reason that difficulty is commonly found when cutting thick steel, is that oxygen purity is compromised. Insufficient pressure (volume of oxygen) causes the cutting jet oxygen stream to lose concentricity before exiting the bottom of the cut. If the kindling temperature is maintained, and sufficient oxygen is flowing through the full cut profile, virtually any thickness of steel can be cut.
Cutting tips are designed to cut a certain thickness of material, with a certain amount of oxygen and fuel gas. The operator should refer to the manufacturer's suggestion for pressure settings for any given cutting tip. Oxygen is used in the preheat flame and in the cutting jet. If a machine torch is to be used, as in a motorized carriage, pressure settings for both pre-heat and cutting oxygen need to be followed. The speed of oxygen through the orifice of the cutting jet is approximately Mach 1 or approximately the speed of sound.
A center oxygen orifice of a cutting tip needs to be extremely smooth. Any roughness will cause the oxygen stream to be turbulent, which in turn causes the oxygen stream to lose concentricity prematurely. Excess oxygen will also cause excessive slag at the bottom of the cut, and the slag may be difficult to remove. Slowing the cutting speeds may also produce excess slag. Torch designs that use two versus three tubes to supply gases to the cutting tip, provide a large difference in performance, if cutting thick material.
Three tube designs allow for a separate tube for the fuel gas and the pre-heat oxygen, with a third tube for the cutting oxygen. Two-tube designs combine the pre-heat oxygen with cutting jet oxygen. On thicker materials, when large volumes of oxygen are required, engaging the cutting lever may change the pre-heat flame settings, and cause the kindling temperature to be lost.
How do you set a neutral flame on a cutting torch? What is the difference between an oxidizing flame and a carburizing or reducing flame? A neutral flame is a flame that consumes all of the fuel gas and oxygen. An oxidizing flame has excess oxygen. A carburizing flame contains excess fuel gas. The correct procedure to follow when lighting an oxy-fuel torch, with acetylene, consists of the following steps:
After all connections are made and no leaks are detected, set regulators to correct pressures for the tip to be used. Open the fuel valve at the butt of the torch a 1/8 to 1/4 turn. Let the fuel flow through the hose for 2 to 3 seconds, to purge the line. With a cutting torch striker (not an open flame), light the fuel gas. No oxygen should be flowing yet.
The fuel gas will ignite, producing a yellow to orange flame, with soot. Increase the flow of fuel until the flame is bushy at the end, with little or no soot. Now, open the oxygen valve, slowly increasing the volume of oxygen being added to the fuel flame. Add oxygen until the visible secondary cone is reduced, exactly matching the primary cone of flame. This is a neutral flame setting.
An oxidizing flame is set by continuing to add oxygen, producing a flame that has a primary cone with very sharp flame points. A carburizing flame is the opposite, where the secondary cone has not yet matched the primary cone. All three flame settings are determined by the amount of oxygen being added to the fuel flame.
The value of the pre-heat flame is important to raise the temperature of the steel to its kindling temperature. Plugging of the pre-heats, by allowing the tip to contact molten steel, will damage the tip. Plugged cutting torch pre-heats slow the time required to heat the material to be cut, and will contribute to flashback. A flashback is created when gases are ignited before they leave the tip. The quality of the oxygen cutting jet orifice is more important to cut quality than the pre-heat flames.
Setup and Use of Rosebud Heating Tips Of all gas operated equipment, which causes the most difficulty for the operator? Multi-Flame (Rosebud) heating tips. What are the causes for oxy fuel multi-flame (rosebud) heating tip problems or failures like overheating, flashbacks, popping etc.? Tip starvation of insufficient gas flow is the usual reason.
A rosebud is designed to use a lot of oxygen and acetylene gas flow. A cutting torch tip uses a lot of oxygen sometimes but a rosebud needs a lot of both gases flowing to keep it cool and to keep from popping back. Another cause is operation in a confined space. (like poking the rosebud up inside an intake manifold )In this situation, reflected heat is not able to escape, and it raises the temperature of the tip.
If the velocity of gas flow outward through the tip is slower than the rate of burn of the gas, the flame will attempt to burn inside the tip. As the tip heats, more inner tip ignition of gases will occur. This will produce a banging or popping sound, and can lead to a flashback. A flashback is defined as the burning of mixed gases inside the tip and/or torch, backward, to the point where the gases mix.
Various torch manufacturers design for the placement of the mixer in different locations in the torch. In modern torches, the mixer will be located in one of three locations the tubes; the head; or, the tip. Mixers can be fuel gas specific or universal. A gas mixer, is that part of the torch that allows the combining of oxygen and a fuel gas. Oxygen and fuel gas are flowing separately within the torch until this point.
A mixer that is fuel gas specific has openings, or a number of orifices, designed for the size of the gas molecule of the specific fuel gas, to flow into the mixer and on through the tip. Each fuel gas molecule is of a specific size. (For commonly used fuel gases, acetylene has the smallest mixer orifice.) It is designed to provide for the unique oxygen/fuel gas mixing ratio, for the particular fuel gas being used. A universal mixer has large enough openings to allow any fuel gas to pass through. A universal mixer has advantages, but is not the best mixer for any one fuel gas.
What is the withdrawal rate of an acetylene cylinder? 1/7 of the cylinder contents per hour. Each manufacturer has a tip chart that lists how much gas a particular rosebud tip uses per hour. Multiply that number by 7 and that is the minimum size tank you need to use.
Acetylene gas vaporizes out of the acetone suspension. The withdrawal rate has a maximum threshold of 1/7 of the contents per hour. Exceeding this rate will cause acetone to be withdrawn from the cylinder. Each heating tip requires a certain consumption of gas. The consumption chart needs to be used to calculate for sufficient fuel gas supply.
For example, if using an ST 610 heating tip, the fuel gas consumption is 136 cubic feet per hour. If using one 330 cubic foot acetylene cylinder, only 47 cubic feet of gas is available per hour. It will require manifolding of three cylinders in this case, to provide sufficient fuel to correctly operate this heating tip. Most people completely ignore this. You just can't run a big rosebud with a little acetylene tank. Big Tip.Big Tank!
What is the correct process for setting flow when using a heating tip? Maximum flow or wide open. that's right! wide open.. It uses a lot of gas, but it is the safe way to use a rosebud. A common mistake in setting gas flow when using heating tips, is to starve the tip. The flame dimension may appear to be maximized, when less than maximum flow is passing through the tip. With the regulator pressures set at the recommended level, proper flow is to open the fuel valve to maximum flow, then neutralize with oxygen addition.
Equipment Inspection Section Inspect your Cutting torch and oxy fuel welding equipment before using. Each operator has the right and responsibility to be safe in the workplace. It is each operator s responsibility to give, at least a brief, inspection to the equipment that is to be used. All components of the system should be checked before operation. "All components" refers to all equipment between the compressed gas source and the cutting torch/heating/welding tip.
The cutting torch oxy fuel welding equipment safety inspection checklist: Compressed gas cylinders (oxygen acetylene tank and others) Before use, have all cylinders been handled properly. Are there any physical signs of damage? Check valve assembly on each cylinder? Inspect the chains or other device used to secure the acetylene oxygen tanks.
Attach regulators Be sure that each regulator is correct for the cylinder it is to be attached to. Be sure that the regulator is designed for the pressure of the cylinder. Blow out the oxygen valve assembly before attaching the oxygen regulator, to eliminate the potential for a dust explosion. Inspect the regulator and cylinder valve for presence of any oils or grease. If present, DO NOT USE. Make sure the adjusting screw has not been damaged. Check the pressure relief port.
Cutting Torch or oxy acetylene torch Inspect the torch. Are inlet connections unsatisfactory for threading a tight connection? Is there obvious physical damage on the torch? If using a combination torch, are the O-rings at the base of the cutting attachment in place and free of cracks? Is there any evidence of soot buildup on the torch body? Are the threads satisfactory on the head of the torch, to correctly tighten in the tip? If any of these conditions are present, DO NOT USE THE TORCH.
Safety devices Safety devices normally consist of check valves and flashback arrestors. These devices will be placed at the outlet of the regulator or the inlet of the torch, or both. note: flashback arrestors at both places could restrict the flow and starve the tip when using a rosebud tip. Check valves may be used, flashback arrestors, or both. these days check valves are usually made right into flashback arrestors. By definition, a check valve stops the reverse flow of gas. This prevents mixed gas in the system. A flashback arrestor stops flame.
Safety devices should be replaced periodically. A check valve contains a rubber diaphragm that will stop the reverse flow of gas and operates at 2 psi. If a flashback has occurred, the check valve will be damaged, but will show no evidence of this. To check, remove the check valve and apply clean, dry, oil-free air pressure, in a reverse direction, of 2 psi. If air moves through the device, IT IS NOT WORKING, and should be removed from the system, and replaced.
A flashback arrestor contains a stainless steel screen. This screen will snuff out a fire, but will allow gases to flow through. There is a restrictive property to flashback arrestors, and regulator pressures need to be set to compensate for this. Refer to the manufacturer for the amount of compensation. Flashback arrestors may also contain a check valve.
If the flashback arrestor is torch mounted, there is potential for foreign material to enter the system and plug the device. This will further restrict gas flow and starve the tip. Like check valves, flashback arrestors need to be checked periodically. In similar fashion, remove the device, applying clean, dry, oilfree air pressure of at least 2 psi, in reverse flow through the device. If air goes through, IT IS NOT WORKING, and should be removed, and replaced.
Oxy Fuel Safety Torch Tips Never cut on or apply heat directly to a concrete surface. Concrete contains water that is trapped within the material. Heat will cause the water to expand. This expansion will cause pieces of the concrete to explode. Clean cutting torch tip orifices carefully. Pre-heat holes are the small holes in a cutting tip that are located all around the center hole. To prevent tip overheating and minimize the time it takes to bring steel to kindling temperature, it is important they be kept clean. It is also critical that the cutting oxygen orifice is kept clean and smooth. Any roughness will dramatically affect cut quality.
Be aware of sparks use the Good Neighbor Policy. Cutting may produce sparks that can fly a considerable distance. Protective screens may be advisable, especially if working in a confined area. Be aware of the heat zone when using heating tips like a rosebud tip. A multi-flame (rosebud) heating tip produces a large amount of heat. If large heating tips are used, the heat zone may extend several inches to several feet out from the tip face. Be aware of combustibles and coworkers when using heating tips.
Where are your hoses? Before heating or cutting, be sure to check for the location of the hoses that supply gases to your torch. Double check to insure that no slag, or work piece will fall directly onto the hoses. No oxy fuel safety information would be complete without mentioning that you should never ever cut into a tank or container without knowing what was in it. even if it has been empty for a long time... even if you know what was in it, you should not cut or heat without first washing it out and then purging with argon.