MAPP gas


MAPP gas
A set of MAPP and oxygen cylinders used for oxy-fuel welding and cutting.

MAPP gas is a trademarked name belonging to Linde Group, previously to Dow, for a fuel gas based on a stabilized mixture of methylacetylene (propyne) and propadiene. The name comes from the original chemical composition: methylacetylene-propadiene propane. MAPP gas is also widely used as a generic name for UN 1060 stabilised methylacetylene-propadiene (unstabilised methylacetylene-propadiene is known as MAPD). MAPP gas is widely regarded as a safer and easier-to-use substitute for acetylene. In the spring of 2008, true MAPP gas production ended when production was discontinued at the only plant making it. Current products labeled ""MAPP" are in fact MAPP substitutes. These versions are stabilized liquefied petroleum gas (LPG) with high levels of propylene.

MAPP gas can be used in combination with oxygen for heating, soldering, brazing and even welding due to its high flame temperature of 2927 °C (5300 °F) in oxygen. Although acetylene has a higher flame 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, and it is much safer in use.

The MAPP/oxygen flame is not entirely appropriate for welding steel, due to the high concentration of hydrogen in the flame - higher than acetylene, but lower than any of the other petroleum fuel gases. The hydrogen infuses into the molten steel and renders the welds brittle. For small-scale welding with MAPP this is not too serious a problem as the hydrogen escapes readily, and MAPP/oxygen can in practice be used for welding small steel parts.

MAPP/oxygen 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 However, underwater oxy/fuel gas cutting of any kind has been replaced by exothermic cutting[1] due to the much faster cut rate and greater safety.

MAPP gas is also used in combustion with air for brazing and soldering, where it has considerable advantages over competing propane fuel due to its high combustion temperature of 2,020 °C (3,670 °F).

The biggest disadvantage of MAPP gas is cost; it is typically one-and-a-half times as expensive as propane at the refinery, and up to four times as expensive to the consumer. It is no longer used much in any large-scale industry - for larger scale users acetylene/oxygen is more economic than MAPP/oxygen when high flame temperatures are needed, and propane/air is more economic when big overall heats are needed.

However, for the small-scale user the MAPP/oxygen flame is still highly desirable, having higher flame temperatures and energy densities than any flame other than acetylene/oxygen, but without the dangers and inconveniences of acetylene/oxygen. Jewellers, glassbead makers, and many others find it very useful. Plumbers, refrigeration and HVAC engineers, and other tradesmen also value the high heat capacity of the MAPP/air flame; MAPP was until recently widely used, supplied in small to medium size containers.

On April 31, 2008, the Petromont Varennes plant closed its methylacetylene/propadiene plant. They were the only North American plant making MAPP gas, and the only legal supplier of trademarked MAPP gas in the world. This caused a widescale shortage, and many substitutes were introduced by the companies who had repackaged the Dow and Varennes product(s). Most of these substitutes were propylene, like MAP//Pro [2] from BernzOmatic. Some were mixtures with higher hydrocarbons or with other ingredients like acetone. Many of these work acceptably in gas/air torches, but none work as well as MAPP in gas/oxygen torches.

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, as for the natural gas commonly used for cooking. MAPP gas is toxic if inhaled at high concentrations.

The composition of the supplied gas has varied widely, with the gases as supplied by different repackagers/resellers at any one time varying, as well as the general composition varying over time, but a typical composition for an early Dow gas might be: methylacetylene (propyne) 48%, propadiene 23%, propane 27%. For a later Dow/Petromont gas propyne 30%, propadiene 14%, propylene 43%, propane 7%, C4H10 (isobutane, butane) 6% might be more typical.

See also

References

  1. ^ "Exothermic cutting" uses the heat of burning steel wire to cut metals and even non-metals (e.g., concrete). Typically, the wire is ignited electrically and combustion is sustained via a flow of compressed oxygen. See: U.S. Navy Underwater Cutting & Welding Manual, NAVSEA S0300-BB-MAN-010 (1 June 2002), Chapter 2, especially sections 2.3 (Exothermic electrodes) and 2.4 (Seeler Enterprises LU-001 Exothermic Cutting Tool (Kerie Cable)), pages 53-74 (pages 2-22 to 2-43 of original document). Available on-line at: http://www.hnsa.org/doc/pdf/cut_weld.pdf .
  2. ^ BernzOmatic - Resources: Gas Types

External links


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