with MAPP gas for optimum results. Table 3-2 is a
good guide to follow when you are using acetylene tips
for MAPP-gas welding.
MAPP is not sensitive to shock, and it is
nonflammable in the absence of oxygen. There is no
chance of an explosion if a cylinder is bumped, jarred,
or dropped. The cylinders can be stored for
transporting in any position without danger of an
explosive air pocket being formed. The characteristic
odor, while harmless, gives warnings of fuel leaks in
the equipment long before danger.
MAPP gas is not restricted to a maximum working
pressure of 15 psig as is acetylene. In jobs requiring
higher pressure and gas flow, MAPP at the full-
cylinder pressure of 95 psig at 70°F (21°C) can be used
WELDING AND BRAZING.With MAPP
gas, this requires some differences in equipment and
Prepare steel to be welded with MAPP the same as
for welding with acetylene. For metals thinner than 1/8
inch (3.1 mm), clean the metal to be welded well, either
with a wire brush or a grinding wheel. When metal is
thicker than 1/8 inch, bevel it first and clean it
Position the steel with a root opening equal to the
material thickness when the work is thinner than 1/8
inch. If the metal is thicker than 1/8 inch, leave a gap
equal to the diameter of the welding rod to be used.
Set the gauge pressure with the torch valves
closed; if the metal to be welded is 3/16 inch (4.2 mm)
or less, set the gas (MAPP) pressure at 2-3 psig and the
oxygen pressure at 10-15 psig. When working with 1/4
Figure 3-49.Portable oxygas welding and cutting outfit.
cutting, heating, and brazing because of its superior
heat transfer characteristics.
Acetylene regulators, hoses, torches, and welding
tips may be used without any significant disparity.
Very often the same-size tip can be used for welding
with MAPP gas as with acetylene. However, it is
recommended that a tip one or two sizes larger be used
Table 3-2.Substituting Acetylene Tips for MAPP Gas Use
SIZE OF TIP
MAPP GAS USE