Abstract
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.
