A MAPP gas flame, with its characteristically longer
inner cone, differs in appearance from an oxygen
flame, so welders must accustom themselves to adjust
the MAPP gas flame correctly. Although standard
acetylene welding equipment is used to make a MAPP
gas flame, a slightly larger tip is still required because
of a greater gas density and a slower flame propagation
rate. For welding steel, a triple deoxidized rod
analyzed at 0.06-0.12 C, 1.75-2.10 Mn, 0.50-0.80 Si,
0.025 max P, and 0.4-0.6 Mo is best.
Most MAPP gas welding requires a neutral flame.
Laboratory studies have shown neutral flames have a
fuel-to-oxygen ratio of 1:2.3. Investigations of 1/4
in.-thick mild steel plate butt welds have shown that
flame adjustment has a great effect on weld strength.
Neutral flame welds had an average tensile strength of
66,000 psig, while oxidizing flame welds were as low
as 35,000 psig. Welds made with a reducing flame
averaged 52,000 psig.
FIGURE 4-1. MAPP Gas Torch Tip Design