Failure analysis of a stainless steel hydrotreating reactor

This paper presents an analysis of a failed AISI 316L austenitic stainless steel (SS) hydrotreating reactor that produces flavors and fragrances. Pitting and cracking were observed mainly in the vicinity of the circumferential and longitudinal shell welds on the internal surface of the reactor by dye penetrant testing (DPT). Ultrasonic evaluation revealed the cracks were within near-surface area, therefore remedial grinding was performed to remove them. In situ metallographic investigation revealed that the cracks were predominantly transgranular and multi-branching. Thickness gauge, hydraulic pressure testing, and acoustic emission validated the reusability of the repaired vessel. Analysis of the catalysts showed the source of chloride. SCC (stress corrosion cracking) susceptibility testing of the identical material proved its liability to chloride SCC in the environment of the suspect catalysts. Studies revealed that the failure was caused by chloride SCC. Recommendations are made to prevent the recurrence of the similar failure.