A 13% Chromium stainless steel welded compressor failed by sulfide-stress cracking (SSC) even though it had been heat treated and tested to the requirements of NACE MR0175 and contained no evidence
of prior defects. The impeller was in the first stage of a hydrogen recycle compressor in a gas oil hydrocracker and failed under normal operating conditions. The failure was attributed to a combination of the high operating stresses inherent in the design of centrifugal compressors, a highly aggressive environment containing ammonium chloride salts and the heat treatment used by the fabricator, which produced a
coarse-grained microstructure.