The high-temperature hydrogen corrosion environment has the greatest impact on equipment lifespan
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Considering the corrosive environment in refining units, the high-temperature hydrogen corrosion environment has the greatest impact on the service life of equipment. It occurs under the high-temperature and high-pressure hydrogen-rich conditions in units such as hydrocracking and hydrorefining, where hydrogen atoms penetrate into the steel and react with carbides to produce methane, leading to internal decarburization and intergranular cracks. This is a type of irreversible, permanent embrittlement damage that directly undermines the mechanical properties of the steel, causing sudden brittle fractures in the equipment well before its designed service life expires. In some hydrogen-handling devices, if the wrong materials are used, the actual service life may be less than 30% of the designed lifespan. In contrast, high-temperature sulfur corrosion primarily results in a uniform thinning of the wall thickness, and the remaining service life can be predicted through regular thickness measurements ； Low-temperature sulfur corrosion can have its corrosion rate effectively controlled through process-based anti-corrosion measures, and the impact of both on equipment lifespan is much lower than that of high-temperature hydrogen corrosion.
The original poster’s analysis is very thorough; the Nelson curve and PWHT mentioned in the replies are also key points. I would like to add a few more details that are often overlooked in actual operation and maintenance: aside from material selection and heat treatment, it is recommended to closely monitor changes in hydrogen partial pressure and operating temperature during routine monitoring. This is especially true during periods when the equipment’s load is adjusted or during catalyst regeneration, as short-term fluctuations in these two parameters can cause the materials to enter a state sensitive to hydrogen erosion. Furthermore, regular ultrasonic testing (UT) combined with phase contrast imaging can detect intergranular microcracks earlier than thickness measurement alone—however, such tests require significant expertise, so it is recommended to entrust them to qualified external testing agencies. If the evaluation of older equipment is involved, reference can be made to the section on the failure mechanisms of refining equipment in API RP 571, which provides detailed criteria and typical cases for hydrogen attack damage. Of course, the specific plan needs to be determined based on the process parameters of your equipment as well as the records related to that equipment. If possible, it would be advisable to hire a corrosion engineer to conduct a specialized risk assessment, as the operating conditions vary significantly from one piece of equipment to another.