Английский для сварщиков. Гричин С.В. - 72 стр.

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72
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,
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
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
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 produced— the
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. 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-cubic-foot 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

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