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MAPP Gas Cylinder Corrosion

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MAPP™ Gas Cylinder Corrosion

Two pipe fitters were working in a confined area. When one of the plumbers lit a match to ignite a torch connected to a portable welding cylinder, there was a flash fire. Upon the flash fire, the plumber dropped the portable welding cylinder, which was followed by an even stronger flash fire.

The gas used is believed to be a mixture of liquefied petroleum gas and methylacetylene-propadiene, also commonly referred to as MAPP™ gas.

The accompanying photos show the opening that occurred in the fitting-to-cylinder connection along with some metallography of an exemplar fitting-to-cylinder connection.

It is believed that the first flash fire was caused by a slow leak (caused by corrosion) in the fitting-to-cylinder connection. The second, larger flash fire was the result of the leak opening further when the plumber dropped the cylinder.

The exemplar metallography shows a number of features that could lead to accelerated corrosion in the right environment. For example, there is a lack of fusion within the joint that could set up crevice corrosion if it were exposed to the outside environment. There are also fissures in the brazing compound exposed to the outside environment. There were traces of corrosion beginning in the exemplar. There is also the possibility of galvanic corrosion between the brazing alloy and the steel cylinder in the right environment.

  

Dr. Fox is a nationally recognized metallurgy expert, corrosion expert and failure analysis expert who has published numerous peer-reviewed, scientific papers in these fields. He worked for years as a bench scientist and a research manager in the fields of corrosion, metallurgy and failure analysis of materials in nuclear reactors. Dr. Fox is also a Certified Fire and Explosion Investigator.

Dr. Michael Fox, the Founder of Chemical Accident Reconstruction Services (www.chemaxx.com), can be contacted by e-mail or by phone at 800-MIKE-FOX (645-3369).