Summary of Technical Requirements for Pressure Vessels (IV**)

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For low-temperature vessels, the technical requirements for low-temperature pressure vessels are as follows: 01 For 16MnDR and Ni-based low-temperature steels with a plate thickness greater than 20 mm (except in the quenched and tempered state), inspection shall be carried out on each sheet, with the quality grade to be at least Grade II. (GB150-2011) 02 For steel plates used in the manufacture of low-temperature pressure vessel shells, convex heads, and spherical shells, when their thickness exceeds the specified values, ultrasonic testing shall be carried out in accordance with the Standards for Non-Destructive Testing of Pressure Equipment, and the inspection level shall be at least Grade III. (HG/T20585-2011) For steel plates with a thickness greater than 16–20 mm, 20% of each batch shall be sampled, with a minimum of 1 sample per batch. Steel plates with a thickness greater than 20 mm shall be inspected one by one. (GB150 requires that the quality grade be no lower than Grade II.) 03 Seamless steel tubes used as the shells of low-temperature pressure vessels shall be subjected to ultrasonic testing one by one in accordance with the standards for non-destructive testing of pressure equipment. 04 Cryogenic spherical tanks with shell plate thickness ≥16mm shall undergo overall post-weld heat treatment. (GB12337) 05 When the thickness of the welded joints of pressure components exceeds 16 mm, stress-relief heat treatment shall be carried out after all welding work on the low-temperature pressure vessels or components is completed. The heat treatment process shall be consistent with the heat treatment schedule (temperature profile) specified in the welding process evaluation. (HG/T20585-2011) 06 Cases requiring 100% radiographic or ultrasonic testing: Cryogenic vessels with a design temperature below -40°C or weld joint thickness greater than 25 mm. (GB150-2011) For butt joints of low-temperature pressure vessels that meet one of the following conditions, 100% radiographic or ultrasonic testing shall be carried out: (HG/T20585-2011) Vessels containing explosive media with a design pressure greater than 0.6 MPa; those with a design pressure of 1.6 MPa or more; vessels whose shell plate thickness is greater than 25 mm; as well as low-alloy steels whose minimum tensile strength Rm specified by the steel standard is greater than 540 MPa, or those with an alloy element content of more than 3%.