Provisions regarding “full penetration welding” in pressure vessel standards
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Welds of Class A and B pressure vessels must be fully penetrated. German AD specifications require that welds must be free of cracks, lack of fusion, or incomplete penetration. Welds of classes A and B recommended by ASME in the United States and JIS8243 in Japan are also all double-face butt welds or equivalent to double-face welding. In GB/T 150.1, both cases where the welding joint factor is taken as 1 or 0.85 require full penetration welding; furthermore, the Type A and Type B butt joints specified in Appendix D of GB/T 150.3 also require full penetration welding. As for the welded joints between the nozzle and the shell, they have high restraint and significant stress concentration; for fatigue loads, they often serve as the origin of crack initiation. From a manufacturing perspective, these types of welds are also the most difficult to control and the most prone to problems among all welds. This should also be a focus of the design. Standards such as TSG 21-2016 and SH/T 3074-2018 specify that the weld joints between nozzles and shells should achieve full penetration across the entire cross-section. Relevant standards also recommend the use of a saddle-shaped groove cutter to improve the precision of groove preparation, reduce labor intensity, and ensure welding quality. Among the various main standards for pressure vessels, TSG 21, SH/T 3074, HG/T20583, etc., all specify that joints of types A, B, and D must be fully penetrated by welding. Let’s take a look at each of them separately. It should be noted that among the welding types for nozzles and shells recommended in GB/T 150.3 and HG/T 20583, there are structures where full penetration welding is not required. Should full penetration welding be necessary, this should be emphasized in the design documents; it can be stated as follows: The weld joints between pressure-bearing components shall be fully penetrated.
In general, according to the standards for pressure vessels, welds of categories A and B must be fully penetrated; that is, there should be no cracks, lack of fusion, or incomplete penetration in these welds. The Class A and Class B welds recommended by the German AD regulations, the American ASME, and the Japanese JIS8243 also require double-sided butt welding or an equivalent to double-sided welding. In GB/T 150.1, when the welding joint coefficient is set to 1 or 0.85, full penetration is also required; moreover, the Type A and Type B butt joint configurations specified in Appendix D of GB/T 150.3 also require full penetration. For the welding joints between the take over and the shell, cracks are likely to occur due to high restraint and stress concentration, making them a key focus in manufacturing and design. Standards such as TSG 21-2016 and SH/T 3074-2018 clearly stipulate that the weld joints between nozzles and the shell must be fully penetrated across the entire cross-section. It is also recommended to use a saddle-shaped hole-cutting machine for processing, so as to improve the accuracy of the groove preparation and the quality of the welding. Other major standards also explicitly require full penetration for Type A, B, and D joints. If it is necessary to emphasize full penetration of the joint, this can be explicitly stated in the design documents. .
It is also possible to achieve full penetration; generally, a margin is left in the inner hole, which is then bored after welding