Miscellaneous Discussions on Series of Issues in Pressure Vessel Equipment Design – On the Design of Hydrogen-Handling Equipment

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Image 0, Introduction: There is a great deal of information available on hydrogen-handling equipment. This document merely provides a summary; it may not be comprehensive, and is intended only as a reference. When designing similar equipment, it is necessary to gather more relevant information to lay a solid foundation for the design process. 1. Materials for hydrogen-handling equipment: Based on the hydrogen partial pressure and operating temperature, select the appropriate material by referring to the Nelson curve provided in the title. A safety margin of over 20°C should be considered for the temperature; the reference materials recommend a temperature margin of 28°C, along with a pressure safety margin of 0.35 MPa as the hydrogen partial pressure increases. If 15CrMoR can be used, then there is no need to choose 14Cr1MoR or even 12Cr2Mo1R. As the content of Cr and Mo increases, the temper brittleness of the material becomes more severe, which imposes additional challenges on both manufacturing and operation. Raw material control J coefficient value. 2. Special treatment for allowable stress: The allowable stress is reduced by 25%. For example, according to the design standard JB4732-1995 (confirmed in 2005), when the main material is 15CrMoR and the design temperature is 250°C, the design stress strength is taken as 0.7×140 (or 150) = 98 (105) MPa. Note: For Cr-Mo steel materials used only in applications requiring resistance to medium and high temperatures under pressure, there is no need to reduce the allowable stress; such reduction is only applied when the material is used in hydrogen-handling equipment. 3. Heat treatment: All hydrogen-facing equipment must undergo degassing treatment; heat treatment immediately after welding can serve as a substitute for degassing treatment. The temperature for heat treatment should be below the tempering temperature of the material. 4. Design considerations for the structure: Avoid stress concentration. 5. Manufacturing precautions: Control the X coefficient and keep the sulfur content below 0.010%. Mn%+Si%≤1.1%. Whether to conduct a assessment of temper embrittlement shall be determined in accordance with the contract provisions. Limits on surface hardness of welded joints – Materials: Maximum Brinell hardness, HB. C-0.5Mo, MnMo, MnMoNi: 225; ≤0.5Cr: 225; 0.5Cr–2Cr: 225; 2.25Cr–9Cr: 241. 6. Inspection: For materials prone to delayed cracking, non-destructive testing during the manufacturing process should be carried out 24 hours after welding is completed ； UT or MT testing is conducted once again 24 hours after heat treatment is completed. References: [1] Industry standard HG/T20581-2011, Specifications for the Selection of Materials for Steel Chemical Storage Vessels: China Planning Press, July 2011. [2] Edited by Li Shiyu. Training Manual for Pressure Vessel Design Engineers. Xinhua Publishing House, August 2019. 【3】Written by Chen Zhaohui, Xu Feng, and Yang Guoyi. Answers to Questions and Examples Related to GB150-2011 \"Pressure Vessels\" (Questions 4-21). Xinhua Publishing House, October 2012. 【4】Written by the Basic Construction Department of the Chemical Industry Ministry and China Wuhuan Chemical Engineering Corporation. Questions and Answers on the Design of Chemical Industry Pressure Vessels; published by the Nitrogen Fertilizer Design Editorial Department, March 1993