Fitness for service assessment of a pressure vessel subjected to fire damage in a refinery unit

Abstract

Abstract The fire-damaged pressure vessel reactor, evaluated in this study, was a cylindrical vessel with design conditions of 460 psig (3.17 MPa) at 413 °C. The fitness for service (FFS) of the fire-damaged pressure vessel was assessed according to API 579-1/ASME FFS-1. First, the maximum temperature during the fire accident was determined based on deterioration of outer protective layer. Then, the possible damage was examined by hardness test, in-situ field metallography and metallographic replicas. Grain growth and spheroidized pearlite were observed in the base metal at the inner surface of the vessel. Outer surface of the vessel showed ferritic microstructure with smaller grain size as compared to the inner surface. Decarburizing and carbide formation were also visible at the outer surface. The lower hardness of the base metal at both sides of the vessel was compared to the standard value and related to the microstructure evolution during high temperature/fire exposure condition. The results of the FFS evaluation indicated that the vessel is not suitable for the current design conditions, and therefore a new maximum allowable working pressure was determined.