Requirements for pressure vessel manufacturing

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Welding requirements: 1. Cross welds should not be used. The longitudinal seams between adjacent tube sections, as well as the welds used to join the end caps, should be offset from the longitudinal seams of the adjacent tube sections. 2. The gussets, pull plates, and other similar components welded to pressure vessels should be made of materials identical to those used for the vessel’s shell, or materials with similar mechanical and welding properties; they should also be welded using appropriate welding materials and welding techniques. The weld scars remaining after the removal of the temporary lifting lugs and pull plates must be polished smooth, and penetrant testing or magnetic particle testing must be carried out as specified in the drawings to ensure that there are no defects such as cracks on the surface. The thickness after polishing should not be less than the designed thickness of that area. 3. Forced assembly is not allowed. 4. When fit-up welding is performed between compressed components or between compressed components and non-compressed components, and if it remains as part of the weld metal, it shall be welded in accordance with the requirements for welds on compressed components. At the designated location 50 mm near the weld of the main pressure-bearing component of the pressure vessel, a welder’s code stamp shall be applied. For those that cannot be stamped, the welder’s code should be recorded using a schematic diagram, and this diagram shall be included in the product quality certificate and provided to the customer. Rework of welded joints: 1. The cause of the defect should be analyzed, and a corresponding rework plan should be developed. 2. For repairs, a detailed repair procedure must be prepared, and it can only be carried out after approval by the welding engineer in charge. The rework process should at least include the causes of the defects ； Technical measures to prevent the recurrence of defects ； Determination of welding process parameters ； Designation of welders for repairs ； Grade and specifications of welding materials ； Signatures of the person who developed the rework procedure and the person who approved it. 3. The number of repairs to the same area (referring to the area where the filler metal used for welding overlaps) should not exceed 2 times. If there are more than 2 revisions, approval from the technical director of the manufacturing unit is required. The number of revisions, the affected areas, the results of non-destructive testing after each revision, and the technical director’s approval signature must be recorded in the product manufacturing change report attached to the pressure vessel quality certificate. 4. The on-site records for repair work should be detailed, and should include at least the groove type and dimensions, the length to be repaired, the welding process parameters (welding current, arc voltage, welding speed, preheating temperature, interpass temperature, post-heating temperature and holding time), the grade and specifications of the welding material, the welding position, as well as the name of the welder and his signature. 5. For pressure vessels that require post-weld heat treatment, welding repairs shall be carried out prior to the heat treatment ； If welding repairs are carried out after heat treatment, heat treatment must be performed again after the repairs. 6. For pressure vessels made of austenitic stainless steel that require resistance to intergranular corrosion, the repaired areas must still maintain their original resistance to intergranular corrosion. 7. If repair is required after the pressure test, the repaired area must pass non-destructive testing in accordance with the original requirements. Pressure vessels that require repair due to leaks at welding joints or connections, or those for which the repair depth exceeds 1/2 of the wall thickness, shall also undergo a pressure test again. Control items 1. Groove geometry and surface quality. 2. The straightness of the cylinder body, the angle of its edges, the misalignment amount of the longitudinal and circumferential welds, and the difference between the maximum and minimum diameters at the same cross-section. 3. The loose area of multi-layer wrapped pressure vessels and the gap in the fitting surface of the pressure vessel fittings. 4. Splicing formation of the head and major dimensional deviations. 5. Dimensional tolerances and surface quality of the spherical shell. 6. Requirements for the butt joint of cylinders and end caps with unequal thicknesses. Surface quality 1. The shape, dimensions, and appearance shall comply with the specifications in the standards and design drawings. 2. There shall be no defects such as surface cracks, lack of penetration, lack of fusion, surface pores, arc pits, unfilled areas, and visibly visible slag inclusions; the slag on the weld seam and the spatter on both sides must be removed. 3. The weld seam should transition smoothly into the base metal. 4. The root depth of the fillet weld shall meet the requirements of technical standards and design drawings, with a smooth transition in shape.