MAPP (methylacetylene-propadiene) is an all-purpose industrial fuel having the high-flame temperature of acetylene but has the handling characteristics of propane. Being a liquid, MAPP is sold by the pound, rather than by the cubic foot, as with acetylene. One cylinder containing 70 pounds of MAPP gas can accomplish the work of more than six and one-half 225-cubicfoot acetylene cylinders; therefore, 70 pounds of MAPP gas is equal to 1,500 cubic feet of acetylene.
Total weight for a MAPP cylinder, which has the same physical size as a 225-cubic-foot acetylene cylinder, is 120 pounds (70 pounds which is MAPP gas). MAPP cylinders contain only liquid fuel. There is no cylinder packing or acetone to impair fuel withdrawal; therefore, the entire contents of a MAPP cylinder can be used. For heavy-use situations, a MAPP cylinder delivers more than twice as much gas as an acetylene cylinder for the same time period.
Because of its superior heat transfer characteristics, MAPP produces a flame temperature of 5300°F when burned with oxygen. MAPP equals, or exceeds, the performance of acetylene for cutting, heating, and brazing.
MAPP is not sensitive to shock and is nonflammable in the absence of oxygen. There is no chance of an explosion if a cylinder is bumped, jarred, or dropped. You can store or transport the cylinders in any position with no danger of forming an explosive gas pocket. The characteristic odor, while harmless, gives warnings 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. In jobs requiring higher pressures and gas flows, MAPP can be used safely at the full-cylinder pressure of 95 psig at 70°F. Because of this, MAPP is an excellent gas for underwater work.
Bulk MAPP Gas
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 man about 1 minute and is essentially like pumping water from a large tank to a smaller one.
MAPP Gas Safety
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 or 2.5 percent to 80 percent in oxygen. As shown in
Figure 4-6.-Explosive limits of MAPP and acetylene in air.
figure 4-6, you can see these limits are narrow in comparison with that of acetylene.
MAPP gas has a highly detectable odor. The smell 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 1 1/2 pounds of fuel or more in an 8-hour shift; bulk systems will leak even more. Fuel-gas leaks are often difficult to find and often go unnoticed; however, a MAPP gas leak is easy to detect and can be repaired before it becomes dangerous.
MAPP toxicity is rated "very slight," but high concentrations (5,000 ppm) may have an anesthetic effect. Local eye or skin contact with MAPP gas vapor causes no adverse effect; however, the liquid fuel can cause dangerous frostlike burns due to the cooling caused by the rapid evaporation of the liquid.
The identification markings on a MAPP cylinder are a yellow body with band "B" colored orange and the top yellow.
Oxygen is a colorless, tasteless, and odorless gas and is slightly heavier than air. It is nonflammable but supports combustion with other elements. In its free state, oxygen is one of the more common elements. The atmosphere is made up of about 21 parts of oxygen and 78 parts of nitrogen, the remainder being rare gases. Rusting of ferrous metals, discoloration of copper, and
Figure 4-7.-Typical oxygen cylinder.
corrosion of aluminum are all due to the action of atmospheric oxygen. This action is known as oxidation. Oxygen is obtained commercially either by the liquid-air process or by the electrolytic process. In the liquid-air process, the air is compressed and then cooled to a point where the gases become liquid (approximately -375°F). The temperature is then raised to above -321 `F, at which point the nitrogen in the air becomes gas again and is removed. When the temperature of the remaining liquid is raised to -297°F, the oxygen forms gas and is drawn off. The oxygen is further purified and compressed into cylinders for use. The other process by which oxygen is producedthe electrolytic process-consists of running an electrical current through water to which an acid or an alkali has been added. The oxygen collects at the positive terminal and is drawn off through pipes to a container. Oxygen is supplied for oxyacetylene welding in seamless steel cylinders. A typical oxygen cylinder is shown in figure 4-7. The color of a standard oxygen cylinder used for industrial purposes is solid green. Oxygen cylinders are made in several sizes. The size most often used in welding and cutting is the 244-cubicfoot capacity cylinder. This cylinder is 9 inches in diameter, 51 inches high, and weighs about 145 pounds and is charged to a pressure of 2,200 psi at 70°F.
You can determine the amount of oxygen in a compressed-gas cylinder by reading the volume scale on the high-pressure gauge attached to the regulator.