As a welder, the methods you might use in cutting metal are oxygas
flame, air carbon-arc, and plasma-arc. The method you will actually make use
will depend on the type of metal to be cut and the local availability of
Either oxygas flame or air carbon-arc equipment will be the most common type of equipment available, and the former is probably the method you will use most often. This handbook covers oxygas equipment; plasma-arc and carbon-arc cutting are presented in other welding handbooks in this series.
The oxygas cutting torch has many uses in steelwork. It is the most readily available equipment at naval activities, it is accessible from outside resources in most locations, and it is portable enough to be taken to the work site. You will find it an excellent tool for cutting ferrous metals.
This versatile tool is used for a variety of operations such as cutting reinforcing iron, beveling plate, cutting and beveling pipe, piercing holes in steel plate, cutting wire rope, and, when properly adjusted, preheating metal prior to welding. Once you are familiar with the equipment and procedures, you should be able to make a quality cut with oxygas equipment in a safe and professional tradesman-like manner.
When you have completed this work, you will be able to:
For a typical oxygas cutting outfit, also referred to as a cutting rig (Figure 1), you need:
Figure 1 — Typical oxygas cutting outfit (cutting rig).
Numerous types of additional auxiliary equipment are available to improve the overall cutting operation; two of the most important are the spark igniter (commonly called a striker) and an apparatus wrench (commonly called a gang wrench) that fits all the connections on the cutting rig. The gang wrench has a raised opening in the handle that serves as an acetylene tank key (Figure 2).
Figure 2 — Typical apparatus wrench (gang wrench) and spark igniter (striker).
Some other common accessories include tip cleaner, tip drill set, hose connectors, extra striker and refill flints, extra cutting tip, hose repair kit, and a cylinder truck (Figure 3).
Figure 3 — Typical oxygas accessories for cutting rig.
Personal safety apparel, such as goggles, hand shields, gloves, leather aprons, sleeves, and leggings, is essential and should be worn as required for the job at hand (Figure 4).
Figure 4 — Typical personal safety apparel for oxygas cutting operations.
Oxygas cutting equipment can be stationary or portable. A portable oxygas outfit, such as the one shown in Figure 5, is particularly advantageous when you need to move the equipment from one shop cutting project to another. When working on a project field site, though, a cart with a larger set of wheels has a distinct advantage in moving over rough terrain, as in foundation work. In fact, building a cart with spoked metal wheels can be a shop-welding project with excellent field application later.
Figure 5 — Typical portable cutting rig.
Proficient cutting, like proficient welding, cannot be learned from reading text; it takes hands-on practice to be an accomplished Steelworker or Ironworker (civilian term) who can cut a smooth-edged bevel on a pipe to prepare it for welding. However, what text can give you is the foundation of how to set up the equipment and how it functions to best advantage. You must be able to set up the cutting equipment and make the necessary adjustments to be able to perform your cutting tasks. Therefore, you need to know and understand the purpose and function of the basic equipment making up the cutting rig. However, before learning about the equipment, you must be familiar with the gases most often used to fuel the cutting equipment: acetylene, MAPP gas, oxygen.
Acetylene (C2H2) is a fuel gas made up of carbon and hydrogen. It is manufactured by the chemical reaction between calcium carbide, a gray stone-like substance, and water in a generating unit. Acetylene is colorless, but it has a distinctive odor (strong garlic) that can be easily detected. Mixtures of acetylene and air that contain from 2 to 80 percent of acetylene by volume will explode when ignited.
However, with suitable equipment and proper precautions, acetylene can be safely burned with oxygen for welding and cutting purposes. When burned with oxygen, acetylene produces a very hot flame that has a temperature between 5,700°F and 6,300°F. Acetylene is obtained directly from the cylinder when a portable cutting outfit is used, as shown in Figure 5.
For stationary equipment and larger operations as might be found in large shops, however, acetylene can be piped to a number of individual cutting stations from a manifold configuration similar to the acetylene cylinder bank shown in Figure 6.
Figure 6 — Example of a stationary acetylene cylinder bank.
Acetylene stored in a free state under pressure greater than 15 psi can be made to break down by heat or shock and possibly explode. Under pressure of 29.4 psi, acetylene becomes self-explosive, and a slight shock will cause it to explode spontaneously. However, when dissolved in acetone, it can be compressed into cylinders at higher pressures.
Acetylene becomes extremely dangerous if used above 15 pounds pressure.
Acetylene can be safely compressed up to 275 psi when dissolved in acetone and stored in specially designed cylinders filled with porous material such as balsa wood, charcoal, finely shredded asbestos, corn pith, Portland cement, or industrial (in-fyoo-SAWR-ee-uhl), earth. These porous filler materials help prevent high-pressure gas pockets from forming in the cylinder.
Acetone [OC(CH3)2] is a liquid chemical that dissolves large portions of acetylene under pressure without changing the nature of the gas. Since it is a liquid, acetone can be drawn from an acetylene cylinder when it is not upright.
Do not store acetylene cylinders on their sides. However, if they have been, you must let the cylinder stand upright for a minimum of 2 hours before using to allow the acetone to settle to the bottom of the cylinder.
Acetone contaminates the hoses, regulators, and torch, and disrupts the flame.
Acetylene is measured in cubic feet. One of the most common cylinder sizes is 225 cubic feet (Figure 7).
Figure 7 — Example of the variety of acetylene cylinder sizes available.
However, just because a cylinder has a 225-cubic-foot capacity does not necessarily mean it has 225 cubic feet of acetylene in it. Because the acetylene is dissolved in acetone, you cannot judge how much acetylene is left in a cylinder by gauge pressure. The pressure of the acetylene cylinder will remain comparatively constant until most of the gas is consumed.
Figure 8 is an example of an acetylene cylinder. These cylinders are equipped with fusible plugs that relieve excess pressure if the cylinder is exposed to undue heat. A standard acetylene cylinder of 225 cubic feet weighs about 250 pounds.
Figure 8 — Cut detail of an acetylene cylinder.
Compressed-gas cylinders are color-coded for identification, but the color identifications are not standardized among all commercial-owned sources. Typical acetylene cylinder colors, for instance, may be black or red-- unless you use a European supply system where the EEU color is maroon.
As presented in the Introduction to Welding Chapter, MAPP (C3H4 methylacetylenepropadiene) is an all-purpose industrial fuel with the high-flame temperature of acetylene and the handling characteristics of propane. MAPP is sold by the pound as a liquid instead of by the cubic foot, as with acetylene. One 70-pound MAPP cylinder can accomplish the work of more than six and one-half 225-cubic-foot acetylene cylinders, making it equal to 1,500 cubic feet of acetylene.
A full MAPP cylinder (about the same physical size as a 225-cubic-foot acetylene cylinder) is 120 pounds (70 pounds is MAPP gas). MAPP cylinders contain only the liquid fuel with no packing or acetone to impair fuel withdrawal, so the entire contents of a MAPP cylinder is usable. For heavy-use situations, a MAPP cylinder delivers more than twice as much gas as an equivalent acetylene cylinder for the same time period. A typical MAPP cylinder is canary yellow and, as is common to propane-type gas cylinders, it has a protective collar around the valve.
The BTU value of MAPP gas makes it an excellent fuel gas for preheating and stress relieving metals. MAPP produces a flame temperature of 5300°F when burned with oxygen and equals or exceeds the performance of acetylene for cutting, heating, and brazing. However, like all of the liquefied petroleum gases, MAPP is not appropriate for welding steel due to the high concentration of hydrogen in the flame. The hydrogen infuses into the molten steel and renders the welds brittle.
MAPP is nonflammable in the absence of oxygen and not sensitive to shock, so if a cylinder is bumped, jarred, or dropped, there is no chance of an explosion. You can store or transport MAPP cylinders in any position with no danger of forming an explosive gas pocket. It has a harmless but characteristic odor to give warning of fuel leaks in the equipment long before a dangerous condition can occur.
MAPP gas is not restricted to a maximum working pressure of 15 psig, as is acetylene; it can be used safely at the full-cylinder pressure of 95 psig at 70°F on jobs requiring higher pressures and gas flows. Hence, MAPP is an excellent gas for underwater work.
Bulk MAPP gas facilities, similar to liquid oxygen stations, are installed at some activities where large supplies of the gas are used. In bulk installations, MAPP gas is delivered through a piping system directly to the user points. Maximum pressure is controlled centrally for efficiency and economy. Cylinder-filling facilities are also available from bulk installations that allow users to fill their cylinders on site. Filling a 70- pound MAPP cylinder takes one person about 1 minute and is essentially like pumping water from a large tank to a smaller one.
MAPP gas vapor is stable up to 600°F and 1,100 psig when exposed to an 825°F probe. The explosive limits of MAPP gas are 3.4 percent to 10.8 percent in air, whereas acetylene’s explosive limits are 2.5 percent to 80 percent. As Figure 9 shows, MAPP’s limits are narrow compared to those of acetylene.
Figure 9 — Example of explosive limits of MAPP and acetylene in air.
MAPP’s garlicky odor is detectable at 100 ppm, or at a concentration of 1/340th of its lower explosive limit. Small fuel-gas systems may leak 1 or 1½ pounds of fuel or more in an 8-hour shift, bulk systems even more. Often, fuel-gas leaks are difficult to find and go unnoticed; however, a MAPP gas leak is easily detectable and repairable before becoming dangerous.
MAPP toxicity is rated “very slight,” but high concentrations (5,000 ppm) may have an anesthetic effect. MAPP gas vapor causes no adverse effects in local contact with eyes or skin, but the liquid fuel can cause dangerous frostlike burns due to the liquid’s rapid evaporation.
Oxygen (O) is a colorless, tasteless, and odorless gas slightly heavier than air. It is nonflammable in its pure state, but vigorously supports combustion with other elements. In its free state, oxygen is the third most common element, with the atmosphere made up of about 21 parts of oxygen and 78 parts of nitrogen, the remainder being rare gases.
Working with metals, Steelworkers soon become very familiar with atmospheric oxygen in the form of oxidation, the results of which include rusting ferrous metals, discolored copper, and aluminum corrosion, to name a few. The commercial processes for extracting oxygen are liquid-air and electrolytic.
Figure 10 shows the components of a typical oxygen cylinder. Oxygen is supplied for oxyacetylene welding in seamless steel cylinders.
Figure 10 — Example of a typical oxygen cylinder.
Oxygen cylinders are available in several sizes (Figure 11). A commonly used size for welding and cutting is the 244-cubic-foot capacity cylinder. This cylinder is 9 inches in diameter and 51 inches high, weighs about 145 pounds, and is charged to a pressure of 2,200 psi at 70°F.
Figure 11 — Example of the variety of oxygen cylinder sizes available.
To determine the amount of oxygen remaining in a compressed-gas cylinder, you read the volume scale on the non-adjustable high-pressure gauge attached to the regulator.
Regulators reduce the high-pressure gas in a cylinder to a working pressure you can safely use. That is their one basic job, but in addition, they control the flow (volume of gas per hour).
Regulators come in all sizes and types for use with a wide variety of gases, some for high-pressure oxygen cylinders (2,200 psig), others for low-pressure gases such as natural gas (5 psig). Some gases freeze when their pressure is reduced (nitrous oxide or carbon dioxide), so they require electrically heated regulators.
Most regulators have two gauges: one indicates the cylinder pressure when the valve is open, and the other indicates the pressure of the gas coming out of the regulator.
Figure 12 — Example of the variety of regulators for different gases.
The regulator must be open to get a reading on the second gauge, but before opening the cylinder valve, be sure to lower the regulator setting (back-off counter clockwise) to avoid damage from a sudden rush of pressure from the high pressure cylinder.
The reading on the regulator setting is the delivery pressure of the gas, and you set the pressure for your particular job.
The pressures you read on regulator gauges are called gauge pressures. If you are using pounds per square inch (psi), it should be written as psig (pounds per square inch gauge). A zero reading gauge does not mean the cylinder is empty. To the contrary, the cylinder is still full of gas but the cylinder pressure is equal to the surrounding atmospheric pressure, which at sea level is 14.7 psi.
No gas cylinder is truly empty unless it has been pumped out by a vacuum pump.
Two types of regulators are used to control the flow of gas from a cylinder: single-stage regulators and double-stage regulators.
Single-stage regulators are used on both high- and low-pressure systems. Figure 13 shows two single-stage regulators: one for acetylene and one for oxygen, along with a diagram of their interior functioning.
Figure 13 — Example of single-stage regulator functioning.
The regulator mechanism consists of:
These mechanisms are all enclosed in a suitable housing. Fuel-gas regulators and oxygen regulators are the same basic design.
The difference is in the pressures (high/low) for which they were designed.
In the oxygen regulator, the oxygen enters through the high-pressure inlet connection and passes through a glass wool filter that removes dust and dirt. Turning the adjusting screw IN (clockwise) allows the oxygen to pass from the high-pressure chamber to the low-pressure chamber of the regulator, through the regulator outlet, and through the hose to the torch. Turning the adjusting screw further clockwise increases the working pressure; turning it counterclockwise decreases the working pressure.
The high-pressure gauge on an oxygen regulator is graduated from 0 to 4,000 psig. Gauges are calibrated to read correctly at 70°F. The working pressure gauge may be graduated in “psig” from 0 to 150, 0 to 200, or 0 to 400, depending upon the type of regulator used. For example, on regulators designed for heavy cutting, the working pressure gauge is graduated from 0 to 400.
The single-stage regulator’s major disadvantage is that you must constantly monitor and reset the regulator if you require a fixed pressure and flow rate. With a single-stage regulator, the pressure you set will decrease as the cylinder pressure decreases. Keeping the gas pressure and flow rate constant is too much to expect from a regulator that has to reduce the pressure of a full cylinder from 2,200 psig down to cutting pressures or all the way down to 5 psig for welding. Double-stage regulators solve this problem.
The double-stage regulator is similar in principle to the one-stage regulator. The main difference is that the total pressure drop takes place in two stages instead of one.
Figure 14 shows two double-stage regulators: one for acetylene and one for oxygen, along with a diagram of their interior functioning. In the high-pressure stage, the cylinder pressure is reduced to an intermediate pressure that was predetermined by the manufacturer. In the low-pressure stage, the pressure is again reduced from the intermediate pressure to the working pressure you select.
Figure 14 — Example of double-stage regulator functioning.
The interior workings of regulators are precise pieces of equipment; carelessness usually does more to damage a regulator than any other gas-using equipment. You can damage a regulator by simply forgetting to clean wherever there will be gas flow: the cylinder connection, the regulator inlet, the hose connection threads. When you open a high-pressure cylinder, the gas can rush into the regulator at the speed of sound. Any dirt particles present in the connections will be blasted into the precision-fitted valve seats, causing them to leak and resulting in a condition known as creep.
When you shut the regulator off but not the cylinder, and gas pressure is still being delivered to the low-pressure side because of dirt in a valve--that is creep.
Manufacturers build regulators with a minimum of two relief devices, which are designed to protect you and the equipment in case of a regulator creep or a high-pressure rush of gas into the regulator. All regulator gauges have blowout backs to release the pressure from the back of the gauge before the gauge face (usually made of plastic) explodes.
The body of the regulator is also protected by safety devices. Blowout disks or spring-loaded relief valves are the two most common types of devices used. When they function for safety, the blowout disk sounds like a cannon, and the spring-loaded relief valves make howling or shrieking noises.
In either case, after you recover from your initial surprise, your first action is to close the cylinder valve, followed by removing the regulator and tagging it for repair or disposal.
Before connecting a regulator, you should always “crack” and close the valve a little. This helps protect the regulator by blowing out any dirt or other foreign material that might be in the cylinder nozzle. Then, back-off the regulator a little, connect the regulator to the cylinder, slowly crack open the cylinder valve, adjust the regulator to the desired setting, and go to work.
Never use oil or other petroleum products around oxygen regulators. These products will cause either a regulator explosion or fire.
The connection between the torch and the regulators is made with hoses that must be strong, nonporous, light, and flexible enough to make torch movements easy yet able to withstand internal pressures as high as 100 psig. The rubber used is specially treated to remove sulfur that could cause spontaneous combustion. Welding hose is available in single- and double-hose design. The proper size to use will depend on the type of work for which it is intended.
Hose intended for light work has a 3/16-in. or 1/4-in. inside diameter and one or two plies of fabric (Figure 15).
Figure 15 — Example of hose diameters.
For heavy-duty welding and cutting operations, use a hose with an inside diameter of 5/16-in. or 3/8-in. and three to five plies of fabric. Single hose is available in the standard sizes as well as in 1/2-, 3/4-, and 1-in. sizes for heavy-duty heating and use on large cutting machines.
The most common type of cutting and welding hose is the double hose with the fuel hose and the oxygen hose joined side by side by a slight melding together of the hoses in the manufacturing process (Figure 16). This can be augmented by clamps, particularly at the split when separated to connect to the regulators. Because they are joined together, the hoses are less likely to become tangled and are easier to move.
Figure 16 — Example of hose design.
The length of hose for a particular task is also important. Delivery pressure at the torch will vary with the length of the hose. A 3/16-inch hose that is adequate for one job at a 20-foot length may not be appropriate for another if it is extended to 50 feet; the pressure drop would result in insufficient gas flow to the torch. Longer hoses require larger inside diameters to ensure the correct flow of gas to the torch. If you are having volume flow problems when welding or cutting, this is one area to check
The fuel gas and oxygen hoses are identical in construction but differ in color; oxygen is green and fuel-gas is red to help prevent mishaps that could lead to dangerous accidents.
The Compressed Gas Association (CGA) has standardized connections for welding and cutting hose fittings. Connections on the regulators must correspond to identifying letter grades A, B, C, D, and E, plus the type of gas. A, B, and C are the most common size connections: A- for low-flow rates; B- for medium-flow rates; and C- for heavy-flow rates. D and E sizes are for large cutting and heating torches.
When ordering connections, you must specify the type of gas the hose will carry because connections are threaded differently for different types of gases. The threadings for fuel gases and oxygen fittings are not compatible (fuel uses left-hand threads, oxygen uses right-hand threads) to prevent the accidental hookup of a fuel gas to a life-support oxygen system or vice versa.
The basic hose connection consists of a nut and gland (Figure 17 View A). The nut has threads on the inside that match up with the male inlet and outlet on the torch and regulator. The left-hand threaded nuts have a distinguishing mark on the exterior as well. The gland slides inside the hose and is held in place by a ferrule that is crimped over the hose. The nut remains loose so it can be turned by hand and gently tightened with a wrench.
Figure 17 — Examples of nut and gland
and check valves (B).
Two often-overlooked but important items are the check valves (Figure 17 View B). These inexpensive valves prevent personal injuries and save valuable equipment from flashbacks. The check valves should be installed between the torch connection and the hose. When ordering, you must specify the type of gas, connection size, and thread design.
The basic equipment and accessories for oxygas cutting are the same you would use for oxygas welding. The singular difference is you use a cutting torch, or cutting attachment, instead of a welding torch. The most characteristic difference between the cutting torch and the welding torch is the additional oxygen tube the cutting torch has for high-pressure cutting. You control the high-pressure oxygen flow with a levered valve on the handle of the cutting torch. In the standard cutting torch, the valve may be in the form of a trigger assembly like one of those shown in Figure 18.
Figure 18 — Examples of cutting torches with different trigger locations.
On most torches, the cutting oxygen mechanism is designed so you can turn on the cutting oxygen gradually. This is particularly helpful in close operations, such as hole piercing and rivet cutting.
While cutting torches are designed for singular purpose, most welding torches are designed so the body can accept a welding tip, heating tip (rosebud), or cutting attachment. This type of torch is called a combination torch. The advantage of this type of torch is the ease in changing from one mode to another (Figure 19).
Figure 19 — Example of a combination torch.
With a combination torch, you do not need to disconnect the hoses; you just unscrew the welding tip and screw on the heating tip or cutting attachment, which has the high-pressure oxygen-cutting lever on the now-attached torch handle.
To do quality work and produce a clean cut, in cutting, as in welding, you must use the proper size tip for the appropriate fuel gas. The preheat flames must furnish the right amount of heat, and the oxygen jet orifice must deliver the correct amount of oxygen at the right pressure and velocity.
To add to this, you must also operate with a minimum consumption of oxygen and fuel gas. Inattentive workers or workers unfamiliar with correct procedures can waste both oxygen and fuel gas. This may not seem important in homeport working in a shop, but on deployment with long supply lead times, it can become critical to a project.
Manufacturers make many different types of cutting tips to serve multiple purposes and service the use of different gases. While orifice arrangements are relatively common based on the best configuration for a particular gas, and tip material is much the same among the manufacturers, the part of the tip that fits into the torch head often differs in design.
Although some tip designs may appear similar to others, there are two distinct areas to watch for if a manufacture’s name is not apparent. Be sure the tip fits snugly into the torch head nut. The tip should fit smoothly into the nut without any undue movement. Secondly, be sure the tip “seats” correctly into the bevels of the torch head, again without any undue movement. Do not try to insert the tip and tighten the nut to see it will “seat”; this will damage the torch head beyond repair.
Because of the way the Navy supply system purchases cutting and welding equipment, there is a distinct possibility you may have two or three different manufacturers’ brands of cutting torches in your kits. Make sure that the cutting tips match the cutting attachment and the cutting attachment matches the torch body. Again, this is particularly critical in deployment scenarios. See Figure 20 for an example of different manufacturers’ cutting tips.
Figure 20 — Example of manufacturers’ differing cutting torch seating designs.
The tips and seats are designed to produce an even flow of gas and keep themselves as cool as possible. The seats must seal tightly to develop leak-proof joints. If the joints leak, the preheat gases could mix with the cutting oxygen or escape to the atmosphere, resulting in poor quality cuts or the possibility of flashbacks.
To make clean and economical cuts, you must keep the tip orifices and passages clean and free of burrs and slag. If tips become dirty or misshapen, put them aside for restoration. Since it is extremely important that the sealing surfaces be kept clean and free of scratches or burrs, store the tips in a container that cannot scratch the seats.
Aluminum racks, plastic racks, or wooden racks and boxes make ideal storage containers.
When you are cutting, sometimes the stream of cutting oxygen blows slag and molten metal into the tip orifices instead of away from the workpiece. When this happens, it can clog one or more of the tip orifices and you need to clean it before you use the tip again. A small amount of slag or metal in an orifice will seriously interfere with the cutting operation. Figure 21 shows four tips: one is repairable, two need replacing, and one is in good condition.
Figure 21 — Examples of repairable and non-repairable acetylene tips.
Follow the torch manufacturer’s recommendations for the size of the tip drill or tip cleaner to use for cleaning the orifices. If you do not have a tip drill or cleaner, you may use a piece of soft copper wire. Do not use twist drills, nails, or welding rods for cleaning tips; these are likely to enlarge and distort the orifices.
Figure 22 shows a typical set of tip cleaners. Clean the orifices of the cutting torch tip in the same manner as the single orifice of the welding torch tip; push the cleaner straight in and out of the orifice. Be careful not to turn or twist the cleaning wire.
Figure 22 — Typical tip cleaner.
Occasionally, even when you use the proper tip cleaners, the orifices become enlarged and/or distorted. When this happens, you will get shorter and thicker preheating flames and the jet of cutting oxygen can spread, instead of leaving the torch in a long, thin stream.
If the orifices become slightly belled, sometimes you can correct this by rubbing the tip back and forth against emery cloth placed on a flat surface. This action wears down the end of the tip where the orifices have been belled, thus bringing the orifices back to their original size.
The action serves the same purpose as the file provided with some tip cleaning tools, but if you use this file, exercise caution: the file is typically a much harder metal than the tip. These procedures, of course, will not work if the damage is great or if the belling is extensive.
After reconditioning a tip, test it by lighting the torch and observing the preheating flames. If the flames are too short, the orifices are still partially blocked. If the flames snap out when you close the valves, the orifices are still distorted.
If the tip seat is dirty or scaled and does not properly fit into the torch head, heat the tip to a dull red and quench it in water. This will loosen the scale and dirt enough so you can rub it off with a soft cloth.
MAPP gas cutting tips are available in four basic types: two for use with standard pressures and normal cutting speeds; two for use with high pressures and high cutting speeds.
Only standard pressure tips, types SP and FS, will be presented, as they are the ones that Steelworkers are likely use. SP stands for standard pressure and FS stands for fine standard.
The SP tip (Figure 23 View A) is a one-piece standard pressure tip used for cutting by hand, especially by welders who are accustomed to one-piece tips.
SP tips are more likely to be used in situations where MAPP gas is replacing acetylene as the fuel gas. Notice the MAPP tip has 8 fuel orifices versus acetylene’s typical 4 or 6.
The FS tip (Figure 23 View B) is a two-piece, splined, standard pressure tip used for cutting by hand as well as by machine. Welders accustomed to two-piece cutting tips will use them in hand cutting, especially when MAPP gas is replacing natural gas or propane as the fuel gas.
Figure 23 — Examples of MAPP cutting tips.
FS two-piece tips produce heavier preheating flames and faster starts than the SP tips, but they will not take as much thermal or physical abuse as SP one-piece tips. However, in the hands of skilled steelworkers and in a shop atmosphere where cleaning slag from the splines is more available, they can last as long as one-piece tips. Table 1 provides recommended tip sizes and gas pressures when using MAPP to cut different steel thicknesses.
Table 1 — Recommended MAPP Tip Sizes and Oxyfuel Pressures
|Cutting Tip Number||
Oxygen Cutting Pressure
MAPP Gas Pressure
|1 1/4 (31.8)||54||50-60|
|1 1/2 (38)|
|2 1/2 (63.5)||48||6-10|
|Test Your Knowledge
1. As a welder, what method are you most likely to use for cutting metal plate?
- To Table of Contents -
Before you begin any cutting operation, make a thorough inspection of the area for any combustible materials that could be ignited by sparks or slag. If you are burning into a wall, inspect the opposite side and post a fire watch as required.
When you use the oxygas cutting process, proceed as follows:
This rapid oxidation is called combustion or burning. Slow oxidation is known as rusting.
When you use an oxygas torch to cut metal, the oxidation of the metal is extremely rapid and part of the metal actually burns. Heat, liberated by the burning of the iron or steel, melts the iron oxide formed by the chemical reaction and accelerates the preheating of the object. The molten material runs off as slag, exposing more iron or steel to the oxygen jet.
In oxygas cutting, only the metal in the direct path of the oxygen jet is oxidized, and the narrow slit formed as the cutting progresses is called the kerf. Most of the material removed from the kerf is in the form of oxides (products of the oxidation reaction); the remainder is molten metal blown out of the kerf by the force of the oxygen jet.
A quality cut leaves the kerf walls fairly smooth and parallel with no excess of slag (Figure 24). When you develop your torch handling skills, you should be able to keep the cut within close tolerances; guide the cut along straight, curved, or irregular lines, and cut bevels or other shapes that require holding the torch at an angle.
Figure 24 — Example of a quality oxygas cut.
Partial oxidation is a vital part of the oxygas cutting process. Hence, metals that do not oxidize readily are not suitable for oxygas cutting.
Carbon steels are easily cut by the oxygas process, but special techniques are required for cutting many other metals.
To avoid costly mistakes and avoid injury to yourself and others, set up the oxygas equipment and prepare for cutting in a careful and systematic manner.
Take the following steps before attempting to light the torch:
Some fuel-gas cylinders have a hand wheel for opening the fuel-gas valve; others require using a gang wrench or T-handle wrench. Leave any wrench in place while the cylinder is in use so the fuel-gas bottle can be turned off quickly in an emergency.
To light the torch and adjust the flame, always follow the manufacturer’s directions for that particular model of torch. Procedures vary somewhat with different types and, in some cases, even with different models of torches made by the same manufacturer.
In general, the procedure is to open the torch oxygen needle valve a small amount, followed by opening the torch fuel-gas needle valve slightly more. Then use a spark igniter or stationary pilot flame to light the mixture.
NEVER use matches to light the torch; their length requires bringing the hand too close to the tip. Upon igniting, accumulated gas may envelop the hand and result in a severe burn. Also, never light the torch from hot metal.
After checking the fuel-gas adjustment, you can adjust the oxygas flame to obtain the desired characteristics for the work at hand by further manipulating the oxygen and fuel-gas needle valves according to the torch manufacturer’s direction.
A pure fuel-gas flame is long and bushy with a yellowish color. It takes the oxygen it needs for combustion from the surrounding air and there is not enough oxygen available to burn the fuel gas completely. Consequently, the flame is smoky, sooty, and unsuitable for use.
To set the flame appropriately, you need to increase the amount of oxygen by opening the oxygen needle valve until the flame takes on a bluish white color with a bright inner cone surrounded by a flame envelope of a darker hue. The inner cone is the portion of the flame that develops the required operating temperature.
All oxygas processes commonly use one of three types of preheat flames: carburizing, neutral, or oxidizing.
You need to know their characteristics to ensure proper flame adjustment.
Figure 25 shows how the three different flames look.
Figure 25 — Example of carburizing, neutral, and oxidizing flames.
The temperature of a carburizing flame is about 5400°F. It always shows distinct colors; the inner cone is bluish white, the intermediate cone is white, the outer envelope flame is light blue, and the feather at the tip of the inner cone is greenish.
The length of the feather can be used as a basis for judging the degree of carburization. The highly carburizing flame is longer with yellow or white feathers on the inner cone; the slightly carburizing flame has a shorter feather on the inner cone and becomes whiter.
Strongly carburizing flames are not used in cutting low-carbon steels because the additional carbon they add causes brittleness and hardness. However, these flames are ideal for cutting cast iron; the additional carbon poses no problem, and the flame adds more heat to the metal because of its size
Slightly carburizing flames are ideal for cutting steels and other ferrous metals that produce a large amount of slag. Although a neutral flame is best for most cutting, a slightly carburizing flame is ideal for producing a lot of heat down inside the kerf. It makes reasonably smooth cuts and reduces the amount of slag clinging to the bottom of the cut.
The temperature of a neutral flame is about 5600°F. It is the most common preheat flame for oxygas cutting. The carburizing flame becomes neutral when you add additional oxygen. The feather will disappear from the inner flame cone, and all that will be left is the dark blue inner flame and the lighter blue outer cone.
The neutral flame will not oxidize or add carbon to the metal you are cutting. In actuality, a neutral flame acts like the inert gases that are used in TIG and MIG welding to protect the weld from the atmosphere. When you focus a neutral preheat flame on a single spot on the metal until it melts, it forms a clear-looking molten puddle that lies very quietly under the flame.
The temperature of an oxidizing flame is about 6000°F. When you add a little more oxygen to the preheat flame, it will quickly become shorter. The flame will start to neck down at the base next to the flame port, and the inner flame cone changes from dark blue to light blue. Oxidizing flames are much easier to look at because they are less radiant than neutral flames.
The oxidizing flame is rarely used for conventional cutting since it produces excessive slag and does not leave square-cut edges. Oxidizing flames are used in conjunction with cutting machines that have a high-low oxygen valve. The machine starts the cut with an oxidizing flame then automatically reverts to a neutral flame.
The oxidizing flame gives you fast starts when using high-speed cutting machines and is ideal for piercing holes in plate. They are used also in cutting metal underwater where the only source of oxygen for the torch is supplied from the surface.
To cut mild-carbon steel with the oxygas cutting torch, adjust the preheating flames to neutral.
Hold the torch perpendicular to the work, with the inner cones of the preheating flames about 1/16 inch above the end of the line to be cut (Figure 26).
Figure 26 — Typical position to start a cut.
Hold the torch in this position until the spot you are heating is a bright red. Open the cutting oxygen valve slowly but steadily by pressing down on the cutting valve lever. When the cut is started correctly, a shower of sparks will fall from the opposite side of the work, indicating that the flame has pierced the metal.
Move the cutting torch forward along your proposed cut line just fast enough for the cutting oxygen flame to continue to penetrate the work completely. If you make the cut properly, you will get a clean, narrow cut that looks almost like it was made by a saw.
When cutting round bar or heavy sections, you can save preheating time by raising a small burr with a chisel where you will begin the cut. This small raised portion will heat quickly, allowing you to start cutting immediately.
Once you start the cut, move the torch slowly along the cutting mark or guide; watch the cut to observe progress and adjust as necessary. You need to move the torch at the correct speed.
Too slow — the preheating flame melts the top edges along the cut and they may weld back together again behind the cut.
Too fast — the oxidizing flame will not penetrate completely, as shown in Figure 27. When this happens, sparks and slag will blow back towards you. Make sure there is no slag on the opposite side if you have to restart the cut.
Figure 27 — Example of moving too rapidly across the work.
When you cut steel 1/8-inch thick or less, use the smallest cutting tip available and angle the tip in the direction of travel to give the preheating flames a chance to heat the metal ahead of the oxygen jet (Figure 28).
Figure 28 — Example of method for cutting thin metal.
For thin metals, holding the tip perpendicular decreases the amount of preheated metal and the adjacent metal cools the cut enough to prevent smooth cutting action.
You can actually rest the edge of the tip on the metal during this process. If you do so, be sure to keep the end of the preheating flame inner cone just above the metal.
For steel thicker than 1/8-inch, hold the torch so the tip is almost vertical to the surface. One method, if you are right-handed, is to start at the right edge and move to left. Left-handed people tend to cut left to right but either direction is correct, and if conditions permit, cut in the direction that is most comfortable for you. Figure 29 shows the progress of a cut in thick steel.
Figure 29 — Example of progress cutting mild steel thicker than 1/8-inch.
- Hold the preheat flame 1/16 to 1/8 inch from surface until the metal becomes cherry red.
- Press the cutting oxygen valve and move the torch at an even rate to maintain rapid oxidation even though the cut is only partially through the metal.
- The cutting oxygen cuts through the entire thickness as the bottom of the kerf lags slightly behind the top edge.
Avoid unsteady movement of the torch; a smooth movement helps prevent irregular cuts and premature stopping of the cutting action. There are three methods to starting a cut quicker in thick plate.
Table 2 provides recommended tip sizes and gas pressures when using Acetylene to cut different steel thicknesses.
Table 2 Acetylene cutting tip chart.
The iron oxides in cast iron melt at a higher temperature than the cast iron itself. This makes cutting cast iron more difficult than cutting steel. Before you cut cast iron, preheat the whole casting to prevent stress fractures, but do not heat it to too high a temperature; that will oxidize the surface and make cutting more difficult. A preheat temperature of about 500°F is normally satisfactory.
Use a carburizing flame when you cut cast iron. This prevents the formation of oxides on the surface and provides better preheat.
A cast-iron kerf is always wider than a steel kerf due to the presence of oxides and the torch movement.
Use a torch movement similar to scribing semicircles along the cutting line (Figure 30).
Figure 30 — Example of torch movement for cast iron.
As the metal becomes molten, trigger the cutting oxygen and use its force to jet the molten metal out of the kerf.
The difficulty in cutting cast iron with the usual oxygas cutting torch has led to the development of other processes such as the oxygen lance, carbon-arc powder, inert-gas cutting, and plasma-arc methods.
A cutting torch can also be used to cut curved grooves on the edge or surface of a plate or to remove faulty welds for rewelding. Typically, for gouging you use an angled tip with a large orifice and a low-velocity jet of oxygen instead of a high-velocity jet. The low-velocity jet oxidizes only the surface of the metal and gives you better control for more accurate gouging. By varying travel speed, oxygen pressure, and tip to plate angle, you can make a variety of gouge contours.
A gouging tip usually has five or six preheat orifices that provide a more even preheat distribution. Figure 31 shows the variety of gouging tips available and an example of a typical gouging operation. Note the large cutting oxygen orifice typical of gouging tips.
Figure 31 — Typical gouging tips and the gouging process.
You must start the gouging operation properly (not too deep) or you can unintentionally cut through the entire thickness of the plate. Alternately, if you cut too shallow, you can cause the operation to stop.
The travel speed of the torch along the gouge line is important as well; moving too fast creates a narrow, shallow gouge, and moving too slow creates the opposite, a deep, wide gouge.
Steelworkers must cut plate or pipe on a bevel to meet a joint design for welding. To make a 45° bevel cut on a 2-inch steel plate, you will actually have to cut through 2.8 inches of metal and need to consider this when you select a tip and adjust the pressures. You must use more pressure and less speed for a bevel cut than for a straight cut.
When you make a bevel cut, adjust the tip so the preheating orifices straddle the cut. To help maintain the proper angle and travel speed, use a piece of 1-inch angle iron with the angle up as a guide for beveling straight edges.
You can keep the angle iron in place by using a heavy piece of scrap angle, clamping a lighter angle down, or tack welding the angle to the plate being cut. Then move the torch along your guide, as shown in Figure 32.
Figure 32 — Example of using angle iron to assist in a bevel cut.
One improvement over a mechanical guide is an electric motor-driven cutting torch carriage. With this tool, you can vary the speed of the motor to cut to dimensions at a specific speed. A typical motor-driven carriage has four wheels: one driven by a reduction gear, two on swivels (castor style), and one freewheeling.
The torch is mounted on the side of the carriage and adjusted up and down by a gear and rack. This machine comes with a radial bar for use in cutting circles and arcs (Figure 33). The carriage is equipped with an off-and-on switch, a reversing switch, a clutch, and a speed-adjusting dial calibrated in feet per minute.
Figure 33 — Example of using a cutting torch carriage to cut a circle.
This machine comes with a straight two-groove rack. The rack is a part of the special torch. The torch also can be tilted for bevel cuts. Figure 34 shows an electric drive carriage on a straight track being used for cutting a plate straight edge to size. Figure 33).
4-34 — Example of using a cutting torch carriage on track to cut a straight edge.
Still other specialty carriages are used in commercial and industrial projects to prepare pipe for welding
Figure 35 shows a cutting torch carriage being used to bevel a large diameter pipe.
Figure 35 — Example of using a cutting torch carriage to bevel a pipe.
Regardless of which automatic carriage is available, the operator must ensure that the electric cord and gas hoses do not become entangled on anything during the cutting operation.
The best way to check for hose, electric cord, and torch clearance is to free-wheel the carriage the full length of the track by hand.
On the worksite, you may find the torch carriage a valuable asset, especially if your shop is tasked with producing a quantity of identical parts, such as handhole covers for runway fixtures or thick base plates for vertical columns. When you use the torch carriage, perform the following steps in order.
The machine will begin to move along the track and continue to cut automatically until it reaches the end of the track. The cutting speed will depend on the thickness of the steel you are cutting.
When the cut is complete, perform these steps in order:
You need practice, experience, and a steady hand to cut pipe in a smooth, true bevel. Do not attempt to cut and bevel a heavy pipe in one operation until you have developed that considerable skill.
Instead, until you develop the single step skills, cut the pipe off square, remove all the slag from the inside of the pipe, then bevel the pipe.
For the inexperienced steelworker, this procedure will produce a cleaner and better job.
When you cut pipe, keep the torch pointed toward the centerline of the pipe.
Start at the top and cut down one side; then begin at the top again and cut down the other side, finishing at the bottom, as shown in Figure 36.
Figure 36 — Example of cutting pipe.
The cutting torch is a valuable tool when you need to make T and Y fittings from pipe. The usual procedure for fabricating pipefittings is to develop patterns like those shown in Figure 37 Views A-1 and B-1. Be sure to leave enough material so the ends overlap.
After you develop the patterns, wrap them around the pipe, as shown in Figure 37 Views A-2 and B-2, and trace around the pattern with soapstone or a scribe.
It is also a good idea to mark the outline with a prick punch at 1/4-inch intervals. Place the punch marks so the cutting action will remove them. If you leave them on the pipe, they could provide notches where cracking could start. During the cutting procedure, as the metal is heated, the punch marks stand out and make it easier to follow the line of cut.
As already mentioned, an experienced Steelworker can cut and bevel pipe at a 45° angle in a single operation, but a person with little cutting experience should cut the pipe at a 90° angle then bevel the edge of the cut to a 45° angle.
Figure 37 — Example of fabricating a pipe “T” section.
With the two-step procedure, you need to mark an additional line on the pipe. Draw the second line parallel to the line traced around the pattern, but draw it on the waste area away from the original pattern line at a distance equal to the thickness of the pipe wall. Make your first (90°) cut along the second line in the waste area. Make your second (45°) cut along the original pattern line.
The disadvantages of the two-step procedure are the time expended and the consumption of oxygen and gas, but it is better than a wasted attempt if the single cut effort damages the pipe. When deployed at the end of a long resupply, you will need to weigh the risks.
The one-step method, while not particularly difficult, does require a steady hand and a great deal of experience to turn out a first-class job.
Refer again to Figure 37 for an example of the one-step method for fabricating a T.
View A, Step 3 shows the procedure for cutting the miter on the branch. Begin the cut at the end of the pipe and work around until the one-half of one side is cut. Keep the torch at a 45-degree angle to the surface of the pipe along the punched cut line. While the tip is at a 45-degree angle, move the torch steadily forward, and at the same time, keep swinging the butt of the torch upward through an arc, always angling the tip towards the centerline of the pipe. This torch manipulation is necessary to keep the cut progressing in the proper direction with a bevel of 45 degrees at all points on the miter. Cut the second portion of the miter in the same manner as the first.
View B, Steps 3 and 4 show the torch manipulation necessary to cut the run in the main branch of the T. Step 3 shows the torch angle for the starting cut, and Step 4 shows the cut at the lowest point on the pipe. Here you change the angle to get around the sharp curve and start the cut in an upward direction.
View B, Step 5 shows the completed cut for the run. The bevels must be smooth and obtain complete fusion when you weld the joint. Of course you will check the fit of your cut pieces, but before you do your final assembly and tack weld for a fabricated fitting, you must clean all the slag from the inner pipe wall.
The cutting torch is also valuable for piercing holes in steel plate. Figure 38 shows the steps to use.
Figure 38 — Typical steps in piercing a hole with a cutting torch.
The molten slag will blow out of the hole and fly around, so BE SURE your goggles are tightly fitted to your face, and avoid placing your head directly above the cut.
If you need a larger hole, outline the edge of the hole with a piece of soapstone, and follow the procedure indicated above. Begin the cut from the hole you pierced by moving the preheating flames to the normal distance from the plate and follow the line drawn on the plate. You can make round holes easily by using a radius bar attachment with the cutting torch.
The cutting torch is a proven and excellent tool for removing rivets from structures to be disassembled. The basic method is to heat the head of the rivet to cutting temperature with the preheating flames and turn on the cutting oxygen to wash it off. The remaining portion of the rivet can then be punched out with light hammer blows. The key is to avoid gouging the surface metal. Figure 39 shows the rivet cutting procedures.
Figure 39 — Example of rivet cutting steps.
By the time you cut the slot, the rest of the rivet head is at cutting temperature. Just before you get through the slot, draw the torch tip back the 1½ inches to allow the cutting oxygen to scatter slightly. This keeps the torch from breaking through the ever present layer of scale between rivet head and plate and allows you to cut the rivet head off without damaging the surface of the plate. If you do not draw the tip away, you could cut through the scale and into the plate.
Figure 40 shows a typical rivet cutting tip. Use this type whenever it is available.
Figure 40 — Example of a rivet cutting tip.
For buttonhead and countersunk rivets, a low-velocity cutting tip is better. This tip has a large diameter cutting oxygen orifice similar to the gouging tip shown in Figure 31. It has three preheating orifices above the oxygen orifice. Always place a low-velocity rivet cutting tip in the torch so the heating orifices are above the cutting orifice when it is in the cutting position.
You can use a cutting torch to cut wire rope. Wire rope is constructed by wrapping multiple strands around a core, and since these strands do not form one solid piece of metal, you could have trouble in making the cut. When you cut wire rope, you need to focus the torch on one strand at a time working your way through the layers. Figure 41 is an example of wire rope construction.
Figure 41 — Typical wire rope construction.
To prevent the wire rope strands from unlaying during cutting, seize the wire rope on each side of the place where you intend to cut.
Adjust the torch to a neutral flame and cut the strands one at a time between the seizings.
If the wire rope is going to go through sheaves, you should fuse the strand wires together and point the end.
This makes reeving the block much easier, particularly when you are working with a large-diameter wire rope and when reeving blocks are close together.
To fuse and point wire rope, adjust the torch to a neutral flame; then close the oxygen needle valve until you get a carburizing flame.
Manipulate the torch in an in-and-out and oscillating manner to fuse the wires together and point the wire rope at the same time.
Wire rope is lubricated during fabrication and lubricated routinely during its service life. Some lubrication burning is likely to occur, so ensure that excess lubricant is wiped off before you begin to cut it with the oxygas torch.
Never cut or weld on containers that have held a flammable substance until they have been cleaned thoroughly and safeguarded. Cutting, welding, or other work involving heat or sparks on used barrels, drums, tanks, or other containers is extremely dangerous and can lead to property damage or loss of life.
Whenever available, use steam to remove volatile materials. Washing the containers with a strong solution of caustic soda or a similar chemical will remove heavier oils.
Even after thorough cleansing, the container should be further safeguarded by filling it with water before doing any cutting, welding, or other hot work. In almost every situation, it is possible to position the container so it can be kept filled with water during these operations.
Always ensure there is a vent or opening in the container to release the heated vapor that builds inside. You can do this by opening the bung, handhole, or other fitting above the water level.
When it is practical to fill the container with water, you also should use carbon dioxide (CO2) or nitrogen (N) in the vessel for added protection, and examine the gas content of the container periodically to ensure the concentration of carbon dioxide or nitrogen is high enough to prevent a flammable or explosive mixture. You can test the air-gas mixture inside any container with a suitable gas detector.
The carbon dioxide concentration should be at least 50 percent of the air space inside the container, and 80 percent or more when you detect the presence of hydrogen (H) or carbon monoxide (CO). If you use nitrogen, ensure the concentration is at least 10 percent higher than that specified for carbon dioxide. (
Even in apparently clean containers, you should use carbon dioxide or nitrogen because there may still be traces of oil or grease under the seams. Although the vessel was cleaned and flushed with a caustic soda solution, heat from the cutting or welding operation could cause the trapped oil or grease to release enough flammable vapors to form an explosive mixture inside the container.
A suspiciously light metal part may be hollow inside; therefore, you should vent the part by drilling a hole in it before heating. Remember: air or any other gases confined inside a hollow part will expand when heated and the internal pressure created may be enough to cause the part to burst.
Before you do any hot work, take every possible precaution to vent any air confined in jacketed vessels, tanks, or containers.
|Test Your Knowledge
2. What is the kindling temperature for steels?
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How good a cutting job are you doing? See Figure 42. To know how good a cut you are making, you need to know what constitutes a good oxygas cut. The quality of an oxygas cut is judged generally by four characteristics:
Figure 42 — Typical effects of correct and incorrect cutting procedures.
Drag lines show on the face of the cut. Good drag lines are almost straight up and down (Figure 42 View A). Poor drag lines are long and irregular or excessively curved (Figure 42 View B). Poor drag lines indicate you are using a poor cutting procedure, which could result in the loss of the cut (Figure 42 Views B and C).
A satisfactory oxygas cut will show smooth sides. A grooved, fluted, or ragged cut surface is a sign of poor quality.
The top edges should be sharp and square (Figure 42 View D). Rounded top edges (Figure 42 View E) are unsatisfactory. The top edges melting may be a result of incorrect preheating procedures or of moving the torch too slowly.
An oxygas cut is not satisfactory when slag adheres so tightly to the metal that it is difficult to remove. Overall, draglines are the best single indication of the quality of your cut with an oxygas torch. When the draglines you make are short and almost vertical, the sides smooth, and the top edges sharp, you can be assured that the slag conditions are satisfactory.
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In all cutting operations, you must ensure that hot slag is not exposed to combustible material. Globules of hot slag can roll along the deck for long distances, so do not cut within 30 to 40 feet of unprotected combustible materials. If you cannot remove combustible materials, cover them with sheet metal or some other flameproof guards.
Keep the fuel gas and oxygen cylinders far enough away from the work so hot slag does not fall on the cylinders or hoses.
Many of the safety precautions discussed in the welding series of handbooks apply to cutting as well as to welding. Be sure you are completely familiar with all the appropriate safety precautions before attempting oxygas cutting operations.
Backfire is the result of improperly operating the oxygas torch and the flame goes out with a loud snap or pop. If this happens, close the torch valves, check the connections, and review your operational techniques before relighting the torch. You may have caused the backfire by touching the tip against the work, by overheating the tip, or by operating the torch with incorrect gas pressures. It may also be caused by a loose tip or head, or by dirt on the seat.
Flashback occurs when the flame burns back inside the torch, typically with a shrill hissing or squealing noise. If this happens, close the torch oxygen valve at once to stop the flashback; then close the gas valve and the oxygen and gas regulators.
Flashbacks may extend back into the hose or regulators. They indicate that something is wrong either with the torch or with the way you are using it. Investigate every flashback to determine the cause before you relight the torch. Allow the torch to cool before relighting it and blow oxygen through the cutting tip for a few seconds to clear out soot that may have accumulated in the passages.
A clogged orifice or incorrect oxygen and gas pressures are often responsible for flashbacks. Avoid using gas pressures higher than manufacturers’ recommendations.
Gas cylinders are made of high-quality steel. High-pressure gases, such as oxygen, hydrogen, nitrogen, and compressed air, are stored in cylinders of seamless construction. Only non-shatterable, high-pressure gas cylinders may be used by ships or activities operating outside the continental United States. Cylinders for low-pressure gases, such as acetylene, may be welded or brazed. Cylinders are carefully tested, either by the factory or by a designated processing station, at pressures above the maximum permissible charging pressure.
Color warnings provide an effective means for marking physical hazards and for indicating the location of safety equipment. Five classes of material have been selected to represent the general hazards for dangerous materials, while a sixth class has been reserved for fire protection equipment. Table 3 shows the colors that represent the six classes.
There is no universally accepted color coding for gas cylinders. The examples of color codes shown in Table 3 are U.S. military only; the commercial industry does not comply with these color codes.
Table 3 — Standard Colors for General Hazards
Each compressed-gas cylinder carries markings indicating compliance with Interstate Commerce Commission (ICC) requirements. Cylinders at your work site are your responsibility, and when handling and storing compressed-gas cylinders there are several things you should not do.
This is illegal as well as stupid. Cylinder owners and suppliers are the only personnel permitted to work on cylinder safety devices.
Figure 43 — Typical cylinder identifying color patterns.
When cylinders have been stored outside in freezing weather, they sometimes become frozen to the ground or to each other. This is true particularly in the Antarctic and Arctic areas. To free the cylinders, you can pour warm water (not boiling) over the frozen or icy areas. As a last resort, you can pry them loose with a pry bar. If you use a pry bar, never pry or lift under the valve cap or valve.
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This handbook has presented information on the different types of gases and equipment available and necessary to perform quality oxygas cutting on metals. It has also identified the operational steps you should take to prepare the material and adjust the equipment to the characteristics of the metal. However, it takes hands–on practice and experience to develop the skills and steady hand to make good quality cuts. Your tasking is to practice your cutting techniques, judge your work by the criteria presented here, and do so in a manner that is safe for you and those around you in both the shop and field working environments.
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1. What portion, if any, of a ferrous metal becomes oxidized during the oxygas cutting process?
2. Metals that oxidize readily are best suited for oxygas cutting.
3. The principal difference between a standard cutting torch and an oxygas welding torch is that the cutting torch has an extra tube for high-pressure oxygen.
4. What type of problem(s) can occur during their use if the cutting torch tips and seats are not properly matched and assembled?
5. What action should you take to keep cutting tips in proper working order when they are not in use?
6. Which of these basic types of MAPP tips do Steelworkers often use?
Refer to the figure below when answering questions 7-9.
7. Which cutting torch tip is a low-velocity tip?
8. What cutting torch tip is a MAPP gas two-piece tip?
9. Which cutting torch tip is specially designed for cutting rivets?
10. The FS type of MAPP gas-cutting tip can be used for machine cutting.
11. What can you use as a tool to clean torch tip orifices when a tip cleaner is not available?
12. When cleaning the orifices of a tip with a cleaner, you should push the cleaner straight into the orifices and pull it straight out without twisting.
13. With which of these tools can you correct slightly belled orifices by wearing down the end of the tip?
14. Before starting to cut with a torch, you should inspect the working area and adjacent areas for combustibles that must be removed or covered to keep sparks or slag from igniting them.
Refer to the table below when answering question 15.
|Cutting Tip Number||
Oxygen Cutting Pressure
MAPP Gas Pressure
|1 1/4 (31.8)||54||50-60|
|1 1/2 (38)|
|2 1/2 (63.5)||48||6-10|
15. What thickness material can you cut when using a Number 54 tip and setting the oxygen cutting pressure between 50 to 60 psig?
16. What device is used to ignite a cutting torch?
17. What type of flame should you use to cut steels that produce a lot of slag?
18. What distance in inches should you maintain between the preheating flame and the surface of the metal when using the cutting torch to preheat a mild-carbon steel plate?
19. How should the shower of sparks fall when you have started a cut properly and the cut is going all the way through the material?
20. Which of the following actions can save time when you need to cut a round piece of metal stock with a cutting torch?
21. What type of flame is best for piercing holes in plate?
22. One 70-pound MAPP cylinder can accomplish the work of more than _____ 225- cubic-foot acetylene cylinders.
23. What error are you making when cutting metal plate with an oxygas torch and you cause the top surfaces of the kerf to fuse?
24. What effect does moving the cutting torch too fast have on the material during the cutting process?
25. What results when you cut thin steel by holding the torch vertical to the metal surfaces?
26. When, if ever, can you place your cutting torch almost vertical to the surface for cutting?
27. When cutting steel greater than 1/8 inch thick, you position the torch so the preheat flames are from 1/16 to 1/8 inch from the plate. You then hold the flame at this position until the steel becomes _____ red.
28. To start a cut quickly in thick plate, you should hold the cutting torch so it slants toward the direction of travel.
29. One way you can commence a starting cut is to place an iron filler rod at the edge of a thick metal plate and begin preheating it.
30. When cast iron is being cut, what is the preheating temperature?
31. Which of these tasks are you accomplishing by varying the speed of travel, the oxygen pressure, and the angle of a large orifice, and by using a low-velocity-jet cutting tip on the surface of a metal plate?
32. Which of these actions using a cutting torch can result in a deep, wide gouge on a metal plate?
33. When cutting bevels on a plate instead of cutting straight through on the same plate, you must use (a)_____ oxygen pressure and (b)______ cutting spee
34. By what component(s) do you adjust a motor-driven cutting torch up and down?
35. By performing which of the following actions can you check the clearance of the torch before cutting when using an electric drive carriage on a straight track?
36. In what sequence should you secure the machine after the desired cut with the motor-driven cutting torch is completed?
37. Which of the following actions should an inexperienced operator perform to obtain a smooth bevel on heavy pipe with an oxygas cutting torch?
38. When cutting pipe, you should always keep the torch pointed toward the centerline of the pipe.
39. What condition can develop if you do not cut out the punch marks used to mark an outline when fabricating a T-fitting from pipe?
Refer to the figure below when answering questions 40-41.
40. What step shows the procedure for cutting the miter on the branch of the pipe?
41. What step shows the completed cut for the run?
42. What is the desired distance relative to the preheating cones and the metal surfaces when you use the cutting torch to pierce holes in a steel plate?
43. What procedural step should you take just before slicing off a portion of the head when removing a rivet from a plate with a cutting torch?
44. What type of cutting tip with a large diameter cutting oxygen orifice is considered best suited for cutting buttonhead rivets and removing countersunk rivets?
45. How can you prevent the strands of rope from unlaying when cutting wire rope with a torch?
46. What action should you take before cutting a wire rope with an oxygas cutting torch?
47. Acetylene is extremely dangerous if used above _____ pounds pressure.
48. What element in an acetylene cylinder can contaminate cutting torch equipment if the cylinder is not upright when in use?
49. Under what conditions, if any, can you actually rest the cutting tip on the metal you are cutting?
50. A cast iron kerf is always _____ than a steel kerf due to the presence of oxides and the torch movement.
51. On which metal do you use a reciprocating torch movement to cut?
52. A single-stage regulator’s pressure will decrease as the cylinder pressure decreases.
53. Which characteristic indicates a good cutting job with an oxygas torch?
54. Which characteristics of a drag line indicates proper cutting procedures were followed?
55. What minimum distance in feet is permitted between unprotected combustibles and oxygas cutting equipment that is being used?
56. Under which of these circumstances can a backfire occur during the operation of an oxygas cutting torch?
57. What action, if any, should you take to stop a flashback safely with an oxygas cutting torch?
58. What component(s) of an oxygas cutting torch unit is/are usually responsible for a flashback?
59. When, if ever, should you weld or cut a container that once held a flammable substance?
60. What percentage of air space inside a water-filled container should carbon dioxide occupy when it is used in a vessel for additional protection?
61. What additional safety precaution should you take when doing any hot work on water-filled tanks or containers?
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