The stainless steel cladding plate of a Gas Scrubber unit in a gas processing facility (called
a Booster Station), belonging to the Kuwait Oil Company developed cracking on the shell after
about 10 years in service. The carbon steel base material was unaffected. Since the cracking
was somewhat unusual for the type of cladding material under normal operating conditions of a
Gas Scrubber, a Root Cause Analysis (RCA) exercise was undertaken to identify the cause of
cracking.
The RCA exercise involved an ‘Events and Causes Analysis’ and a concomitant failure
investigation which included Positive Metal Identification (PMI) of the alloy material, in-situ
microstructural examination of the alloy material, and chemical analysis of the incoming fluids.
PMI indicated that a mix up of materials had taken place wherein instead of the specified SS
316L cladding plate, a SS 321 cladding plate had been inadvertently used. The
microstructural examination revealed that the cracking was intergranular and was most likely
due to sensitization. Fluid analysis results indicated that sudden high spurts in chloride
concentration in the incoming process fluid had occurred, particularly during the last two years
of operation. The operating conditions of the scrubber unit coupled with the high chloride
concentrations were conducive to the development of Intergranular SCC in the 321 grade
stainless steel.
Keywords: Root Cause Analysis (RCA), stress corrosion cracking (SCC), 321 stainless steel