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Mandatory requirements for Cr-Mo steel containers: For Cr-Mo (Cr-Mo-V) steel containers, the following requirements apply: 01 The materials of the main pressure-bearing components in the wellhead equipment and bottomhole equipment of gas storage wells must be Cr-Mo steel forgings of grade III or higher (including grade III), in compliance with the requirements of NB/T 47008. 02 Low-alloy chromium-molybdenum steel cast containers, with a design pressure not exceeding 4.0 MPa and a design temperature range of 0°C to 450°C. 03 The surface of welded joints must be inspected using magnetic particle (MT) or penetrant testing (PT). 04 During regular inspections, the length for surface defect detection shall be no less than 20% of the length of the butted weld. 05 For welded joints that have a tendency to reheat cracking or delayed cracking (referring to Cr-Mo steels and low-alloy steels with Rm≥540 MPa), magnetic particle or penetrant testing should be performed on their surfaces. For materials prone to delayed cracking, surface testing should be carried out at least 24 hours after welding; for materials prone to reheat cracking, additional non-destructive testing should be conducted after heat treatment. 06 When the thickness of the steel plates used for the shell (excluding the plating layers of multi-layer containers) is greater than 25 mm, ultrasonic testing shall be conducted on each plate, with a qualification grade of not lower than II. 07 For 12Cr2Mo1VR steel plates designed for temperatures above 300°C, high-temperature tensile tests at the design temperature are required to be conducted in batches; the yield strength values are given in Appendix B. 08 20MnNiMo, 12Cr2Mo1V, and 12Cr3Mo1V all require the use of secondary refining processes. 09 For grade III or IV forgings of 20MnMoNb, 20MnNiMo, 12Cr2Mo1V, and 12Cr3Mo1V designed for temperatures above 300°C, the design documents shall specify that high-temperature tensile tests at the design temperature be conducted in batches (for grade III) or on a piece-by-piece basis (for grade IV); the yield strength values are given in Appendix B. 10 For steel forgings of 12Cr2Mo1, 12Cr2Mo1V, and 12Cr3Mo1V intended to meet the requirements against temper embrittlement, the technical documents shall specify the special requirements regarding their chemical composition and mechanical properties.