Abstract: In the periodic inspection process of pressure vessels beyond the design service life, the cracking of the surfacing layer on the inner wall of the thermal high pressure separator was a common defect in the inspection process, which seriously affected the safe operation of such equipment and the development of periodic inspection work. Taking two hot high-pressure separators in a petrochemical enterprise as the research object, the long-term cracking problem of surfacing layer found in previous periodic inspections was studied. According to the main damage mode of the equipment, combined with the data of crack macroscopic morphology, microstructure, hardness, ferrite content and strength verification, it was determined that the defect was stress corrosion cracking in a variety of corrosive media environment, and it was speculated that the small welding hot crack on the surface was the cause of crack initiation. The results show that the existence of the crack did not affect the safe operation of the container within a certain period and under specific allowable conditions. The research results could provide reference suggestions for the regular inspection of such equipment.