Failure analysis on abnormal leakage of TP321 stainless steel pipe of medium temperature shifting gas in hydrogen production system

Due to the flammable and explosive characteristics of hydrogen gas, the safe operation of the equipment is particularly important. Any minor negligence may lead to serious accidents in the process of hydrogen production so great attention should be paid to the safety of each equipment in the production line. In this paper, the abnormal leakage failure of the TP321 stainless steel pipe that conveyed medium temperature shifting gas in a petrochemical factory was systematically studied. In order to find out the causes of the failure, the operating conditions, the material qualities of the failed pipe, the macroscopic and microscopic morphologies of the fracture, and the gas flow velocities were comprehensively analyzed. The results showed that the root causes of the failure were processing stripes and incomplete passivation film on the inner surface of the pipe due to inappropriate surface processing, which then initiated pitting corrosion and intergranular corrosion. Besides, the additional assembly stress between the pipe and fitting also produced larger longitudinal tensile stress, facilitating the initiation of stress corrosion cracking. Under the interaction of pitting corrosion, intergranular corrosion and stress corrosion cracking, the pipe leakage finally happened during its service. Based on these failure causes, some feasible countermeasures were then put forward for leakage prevention of similar structures or equipment in hydrogen production industry.

Automated summary

The study found that inappropriate surface processing led to processing stripes and incomplete passivation film on the inner surface of the pipe, which in turn caused pitting corrosion and intergranular corrosion. Additionally, the additional assembly stress between the pipe and fitting facilitated the initiation of stress corrosion cracking.