Metallurgical failure analysis was requested on a failed section of steel pipe from a low vacuum ammonia piping system in a meat processing plant. The 35-inch long, 8-inch diameter, 0.34 inch thick steel pipe contained a 33 inch long bifurcated fracture. Fracture of the ammonia pipe resulted in property loss. The fractured section of the failed pipe is shown in Photograph A. Metallurgical testing included macro and microscopic evaluation, tensile strength testing, and stereomicroscopy.
Photograph A Failed ammonia pipe.
From the examination and testing performed, it appeared as if the subject failure was not a one time, recent event. Numerous other sections of piping were identified with cracking which could initiate catastrophic brittle fracture at any instant. The failure mode was determined to be brittle fracture, probably as a result of stress corrosion cracking and/or hydrogen embrittlement.