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
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 70F (21C) can be used safely.
WELDING AND BRAZING. - With MAPP gas, this requires some differences in equipment and technique.
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 thoroughly.
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.
Table 3-2. - Substituting Acetylene Tips for MAPP Gas Use