For pressure vessel welds, when gas shielded welding is used for the root pass, does this constitute double-sided welding?

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For the main welds of pressure vessels, it is essential to ensure the quality of the welded joints; the key aspects here are proper joint alignment and full penetration. What is underwelding? Underwelding refers to the condition in welding where the root of the joint is not fully melted; in the case of butt welds, it means that the depth of the weld does not meet the design requirements. The reasons for incomplete welding include issues related to the welder’s skill level and the welding process. The welder’s skill level is ensured through welder examinations and verified by non-destructive testing, whereas the welding process is related to factors such as the type of joint and the shape of the groove; it needs to be validated through welding procedure qualification. To ensure full penetration of thick steel plates, double-sided welding is generally employed, but certain single-sided welding methods can also meet the requirement for full penetration, such as single-sided welding with welding shims. For butt joints welded on one side, they can be considered equivalent to fully penetrated butt joints welded on both sides only if visual inspection and non-destructive testing confirm that full penetration has been achieved. Therefore, when the welding quality of gas shielded welding as a root pass meets the requirements for full penetration, it constitutes a welded joint equivalent to double-sided welding. Whether it constitutes a welding joint equivalent to double-sided welding is determined by its welding process, welding quality, and non-destructive testing.