Study on the Determination Method of Minimum Pressurization Temperature Curves for Hydroprocessing Reactors Based on Hydrogen Concentration Distribution in the Reactor Wall

Abstract Hydrogen is a critical factor affecting the structural integrity of hydroprocessing reactors in petrochemical facilities. 2.25Cr1Mo steel, a typical material for the base layer of reactor shells, is prone to hydrogen embrittlement when exposed to high-temperature hydrogen environments, resulting in an increase in the ductile-to-brittle transition temperature and a reduction in the material’s resistance to brittle fracture. Although the material does not exhibit a significant loss of toughness at operating temperatures, it is susceptible to brittle fracture during startup and shutdown operations due to hydrogen embrittlement, compounded by temper embrittlement that occurs in 2.25Cr1Mo steel under high-temperature conditions. To prevent accidents associated with steel embrittlement, minimum pressurization temperature (MPT) curves are typically established for hydroprocessing reactors in engineering practice, ensuring that the internal pressure does not exceed specified limits when the reactor temperature is low during startup and shutdown operations. The determination of MPT curves is closely related to the toughness of the material. and the hydrogen concentration in the material has a direct impact on its fracture toughness. However, most existing methods for determining MPT curves do not accurately account for the hydrogen distribution in the reactor wall. This study addresses the issue of brittle failure in hydroprocessing reactors induced by hydrogen embrittlement during startup and shutdown operations. First, a numerical model for hydrogen diffusion in the reactor wall was established and validated. Subsequently, analytical methods were combined to investigate the effects of various factors—such as pressure, temperature, wall thickness, outgassing procedures, and cladding thickness—on the maximum hydrogen concentration, its location, and the distribution of hydrogen across the reactor wall during shutdown. Based on this analysis, prediction formulas for hydrogen concentration in the reactor wall, accounting for different influencing factors, were developed. Finally, MPT curves were established for defects of different sizes, incorporating the effects of hydrogen embrittlement and temper embrittlement. This research provides key technical support for ensuring the safe operation of hydroprocessing reactors.