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Welding quality issues: The main welding quality problems in pressure vessels include the following: 01 Welded parts do not meet the required dimensions. If the length (or width) of the welded part decreases and its flatness fails to meet the requirements, this is mainly due to welding deformation caused by weld shrinkage. Such defects often cannot be corrected to an acceptable level, resulting in the waste of the welded part. 02 The weld size and shape do not meet the requirements of the drawings and technical standards. Generally, such defects are relatively easy to fix to meet the requirements. 03 Process defects in welded joints can be divided into surface defects and internal defects. Surface defects such as surface cracks, pores, and undercutting are generally detected by the naked eye or using surface non-destructive testing methods. Internal defects such as cracks in welds and the heat-affected zone, as well as pores, slag inclusions, lack of fusion, and incomplete penetration within welds must be detected using non-destructive testing methods like radiography or ultrasonics. Full penetration of the weld joint is a fundamental requirement in pressure vessel design, and it is a focus of attention for designers, manufacturers, inspectors, and owners alike. Many accidents have been caused by incomplete welding at the joints between manholes or connections and the shell. Incomplete penetration refers to the phenomenon where the root of a weld joint is not fully melted during welding. The causes of incomplete penetration can be attributed to issues related to both the welder’s operational skills and the welding process. The welder examination rules now include tests for pipe-to-plate corner joint specimens; whenever grooving of the plate is required for welding manholes, nozzles (including the welding of tubes in shell-and-tube exchangers to the tube sheet), etc., candidates must pass the test using these pipe-to-plate corner joint specimens. 04 The performance of the welded joint or the chemical composition of the weld does not meet the requirements. Information on performance and chemical composition can only be obtained through the testing of welded specimens of the product or by performing non-destructive inspections on the product itself.