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The Case of the Exploding MAPP Gas Cylinder

Burner Assembly for MAPP CylinderThe Problem:

The home-owner’s insurance adjuster claimed that there was a defective weld on MAPP gas cylinders after exposure to a residential fire. The insured reportedly used the MAPP gas burner flame to heat and solder a copper pipe in the basement of the house. The MAPP gas cylinder, torch and flame were inadvertently dropped onto the concrete floor.  The MAPP gas escaped uncontrollably from the damaged cylinder. The burner flame ignited nearby materials, which ultimately burned down the entire house.

Failed Weld on MAPP Gas CylinderMy Assessment: 

The subject cylinder and an exemplar cylinder were photographed, examined and sectioned in the metallurgical laboratory.  The brazed filler material from the threaded connector to the cylinder head was melted-away for access to the brazed joint design.  The fracture occurred adjacent to the braze joint in the HAZ of the cylinder base metal.   The outside appearance of the brazed joint was inconsistent with the exemplar joint design.  There were regions of the brazed joint on the subject cylinder that exhibited non-fusion, micro-fissures and corrosion.

MAPP Cylinder with Burner AttachedThe Consequences: 

There are several 49 CFR OSHA references to performance standards for the MAPP cylinder valve assemblies. These connections must be of sufficient strength to not leak when dropped 6 feet onto a non-yielding floor, impacting the valve assembly or protection device at an orientation most likely to cause damage.   The flash fire was ignited by the torch flame and a leak at the connector-to-cylinder braze joint.

The Lessons Learned:

The MAPP cylinder and attached burner torch failed structurally when dropped head-long onto the concrete floor. The design of the burner assembly connection to the cylinder is unprotected and fractured in the brazed joint.  Closely examine and test all propane cylinders and threaded connections before each use.  Be extremely cautious with portable MAPP gas cylinders and burners to avoid damage and injuries.

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Welding Failures I Have Known, Interesting cautionary tales from Metals & Welding  expert, Dr Jesse A Grantham, PE