Low alloy heavy-walled hydroprocessing reactors in the refining industry, which operate at elevated temperatures and high hydrogen environments, need to be designed for protection against brittle fracture especially during start-up and shutdown. While developing minimum pressurization temperature (MPT) envelopes for these reactors, both temper and hydrogen embrittlement effects must be considered. However, there are no specific rules to evaluate loss of toughness due to hydrogen embrittlement in the design Codes / fitness-for-service Standards. Earlier, Japanese steel and pressure vessel manufacturers (JSPVM) developed a methodology to estimate MPT envelope for Cr-Mo steel pressure vessels. Recently, a state-of-the-art fracture mechanics based methodology is published in Welding Research Council (WRC) Bulletin 562 to determine MPT envelopes for equipment operating in high-pressure hydrogen environments. Meanwhile, API RP 934-F draft provided guidance on developing MPT envelops for heavy wall Cr-Mo vessels. In this paper, a brief summary of the JSPVM, API and WRC approach is presented with flow charts. A case study of establishing the MPT envelopes for a typical hydroprocessing reactor using WRC, JSPVM and API approach is presented and the results are compared and discussed. The advantages and potential savings of using recent WRC approach are highlighted.

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