Retesting of materials for pressure vessels

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Material re-inspection: Generally, when accepting materials, pressure vessel manufacturing units only need to verify the validity of the material quality certificate and the consistency between the material markings and the quality certificate. When necessary, the pressure vessel manufacturing unit shall also re-test the materials used for major pressure-bearing components, etc. Situations requiring re-inspection: Material re-inspection is an important control step in the manufacturing process of pressure vessels. Therefore, the items requiring re-inspection are: (1) Grade IV forgings for Class III pressure vessels that have been purchased. (2) Materials of major pressure-bearing components for which the authenticity of the quality certificate cannot be confirmed, or regarding which there are doubts about performance and chemical composition. (3) Overseas materials used to manufacture primarily compressive components, as well as overseas-grade steel plates (steel strips) manufactured domestically. For materials manufactured by overseas material manufacturing units, as well as steel plates (steel strips) of foreign grades produced by domestic material manufacturing units, in principle, re-inspection should be conducted using domestic inspection and testing method standards (referenced standards, i.e., basic standards). The main contents of such re-inspection generally include inspecting the surface quality and markings of each piece of material, re-testing the chemical composition of the material on a furnace-by-furnace basis, and re-testing the mechanical properties of the material according to the approval. (4) Austenitic stainless steel flat sheets used for manufacturing primarily compressive components. For austenitic stainless steel, the leveling process results in a decrease in its elongation after fracture. Therefore, leveled plates made of austenitic stainless steel must have their mechanical properties re-tested according to batch numbers. For users of entire coils, after the leveling process, a set of test specimens for re-testing should be taken from each of the head, middle, and tail sections of the leveled plate. (5) Materials required to be re-inspected as specified in the design documents. (6) For electrodes used in cryogenic containers, retests on the moisture content of the coating or the diffusible hydrogen content in the deposited metal shall be conducted by batch, in accordance with the relevant electrode standards or design documents. For low-temperature vessels, the electrodes used are all low-hydrogen or ultra-low-hydrogen electrodes; re-inspection is carried out to ensure a low water content in the electrodes as well as a low level of diffused hydrogen in the deposited metal ； For the other re-inspection requirements mentioned above, the chemical composition shall be re-inspected by heat number, and the mechanical properties shall be re-inspected by batch number. In other cases: Apart from the situations where re-inspection is required as mentioned above, for steel plates that, according to TSG 21 and GB/T 150.2, must undergo ultrasonic testing one by one, if the steel manufacturing unit fails to provide a certificate of ultrasonic testing for the plates, it shall also conduct re-inspection via ultrasonic testing on each plate, in accordance with the testing requirements and acceptance criteria specified in the aforementioned safety technical specifications and standards. Containers with specific structures, as well as containers made of non-ferrous metals and their composite plates, that fall within the scope of GB/T 150.1 shall be re-tested in accordance with the re-test requirements specified in TSG 21 and/or GB/T 150.4. Among them, GB/T 12337 also requires that the electrode used for welding the spherical shell seams and those seams that are directly welded to the sphere have their diffused hydrogen content in the weld metal retested by batch. Containers within the scope of application of JB 4732 shall be re-inspected in accordance with the re-inspection requirements of TSG 21 and GB/T 150.4.