Basic welding requirements of the Safety Technical Code for Special Equipment («Large Capacity Equipment Code»)

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For pressure vessels that comply with the safety technical specifications for special equipment (the \"Large Capacity Vessels Regulations\"), welding production must adhere to the strict requirements specified in Article 4.2.1, including weld procedure qualification, qualified welders, proper splicing and assembly of the pressure vessel, and repair of welds. 1. The definition of weld procedure qualification as given in NB/T 47014-2011 \"Weld Procedure Qualification for Pressure Equipment\" is: the process of conducting verification tests on the pre-weld procedure specification (pWPS) and evaluating the results, in order to ensure that the mechanical properties of the welded joint, its bending performance, or the chemical composition of the surfacing layer meet the specified requirements. Another purpose of welding process evaluation is to determine the appropriate process for achieving the welding quality specified by standards, through a series of process tests involving the selection and adjustment of welding methods, welding materials, and welding parameters, prior to the introduction of new products or materials into production in order to develop welding procedure specifications. The requirements for the welding procedure qualification of pressure vessels are as follows: 1) Before welding pressure vessel products, the welds of the pressure-bearing components, the welds that join to these pressure-bearing components, the fit-up welds incorporated into the permanent welds, the surfacing and repair welding on the surface of the base material of the pressure-bearing components, as well as any repair welds for the aforementioned welds, must all undergo welding procedure qualification or be supported by a welding procedure specification (WPS) that has passed such qualification. 2) The welding procedure qualification for pressure vessels shall comply with the requirements of NB/T 47014-2011. 3) The supervision and inspection personnel shall supervise the process of welding procedure qualification. 4) After the welding procedure qualification is completed, the Welding Procedure Qualification Report (PQR) and the welding procedure specification shall be reviewed by the welding responsible engineer of the manufacturing unit, approved by the technical supervisor, and, after being signed off by the supervision and inspection personnel, filed in the technical archive. 5) The technical records for welding procedure qualification shall be retained until such qualification becomes invalid; the welding procedure qualification specimens shall be retained for at least 5 years. 2. Welders 1) Pressure vessel welders must pass the assessments required by relevant safety technical specifications and obtain the appropriate \"Special Equipment Operator Certificate\" before they can carry out welding work within the scope of the approved tasks during its valid period. 2) Welders shall carry out welding in accordance with the welding procedure specifications or welding operation instructions and keep records of the welding process; inspectors from the manufacturing unit shall check the actual welding process parameters. 3) The welder’s code shall be stamped at a designated location near the welds of the pressure vessel’s pressure-bearing components, or the welder’s code shall be recorded in the welding records (including the weld layout diagram); the welding records are to be included as part of the product quality certification documents. 4) The manufacturing unit shall establish a welder’s technical file. 3. Welding and assembly of pressure vessels 1) Welding is not permitted for the spherical shell plates of spherical storage tanks. 2) Cross welds should not be used in pressure vessels. 3) Forced assembly is not allowed during the manufacturing of pressure vessels. 4. Requirements for repairing welds (including welding to fix defects in the base material) are as follows: 1) The cause of the defect must be analyzed, and a corresponding repair plan must be developed. 2) Repair work shall be carried out in accordance with Article 4.2.1 of the Large Vessel Code, either through a welding procedure qualification or with the support of a qualified welding procedure specification; detailed records of the repair work must be kept during welding. 3) The number of repairs to the same weld area should not exceed 2 times. If it exceeds 2 times, approval from the technical supervisor of the manufacturing unit is required prior to carrying out the repairs, and the number of repairs, the location, as well as details of the repairs must be recorded in the quality certification document for the pressure vessel. 4) For pressure vessels that require post-weld heat treatment, weld repairs are generally carried out before heat treatment; if repairs are done after heat treatment, it is necessary to determine whether stress relief treatment is required based on the depth of the repair welds. 5) For pressure vessels or pressure components with special corrosion resistance requirements, the repaired areas must still maintain a corrosion resistance level no lower than that of the original parts. 6) The repaired area must pass inspection in accordance with the original requirements.