MAPP gas is liquefied petroleum gas (LPG) mixed with methylacetylene-propadiene. MAPP is the tradename for a product of the Dow Chemical Company. In Australia it is known as RazorGas and is a trademark of ELGAS.
The gas is used in combination with oxygen for heating, soldering, and brazing due to its high combustion temperature of 2927 °C (5300 °F) in oxygen. Although acetylene has a higher combustion temperature (3160 °C, 5720 °F), MAPP has the advantage that it requires neither dilution nor special container fillers during transport, allowing a greater volume of fuel gas to be transported at the same given weight. MAPP was advantageously used in underwater cutting, which requires high gas pressures (under such pressures acetylene polymerizes explosively, making it dangerous to use). However underwater oxy/fuel gas cutting of any kind has been replaced by exothermic cutting due to the much faster cut rate and greater safety.
MAPP like all of the Liquified Petroleum gasses is not appropriate for welding of steel, due to the high concentration of hydrogen in the flame. The hydrogen infuses into the molten steel and renders the welds brittle.
The gas is also used for brazing and soldering, under combustion in ambient air, where it has considerable advantage over competing propane fuel due to its higher combustion temperature. A typical MAPP gas brazing operation would involve metals such as aluminum, copper, et al braze (sometimes colloquially and inaccurately called silver solder) steel parts together.
Plumbers use both MAPP gas and propane for pipe soldering and brazing, but MAPP gas's higher combustion temperature makes such jobs quicker. MAPP gas is also popular among glass lampworkers, for instance glass bead makers.
The biggest disadvantage of MAPP gas is cost; it is between two and four times as expensive as propane (depending on quantity, supplier, and bottle size). While nine kilogram propane cylinders are common, the largest MAPP cylinder available in Australia is three kilograms. Additionally, MAPP gas torches often cost more than propane torches, around 3 times as much.
MAPP is colorless in both liquid and gas form. The gas has a pronounced garlic or fishy odor at concentrations above 100 ppm, due to the addition of Mercaptans for safety, and is toxic if inhaled at high concentrations.
MAPP gas is being replaced in industry by other LP gas mixes, because one of the constituent gasses, Propadiene, is becoming more valuable to the plastics industry than the welding industry. Flamal and Chemtane are two of the newer LP gas mixes on the market.