Is root welding using gas shielded welding considered equivalent to double-sided welding?

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Clause 4.5.2.2 of GB150 stipulates the welding joint coefficients for steel pressure vessels as follows: (1) Double-sided welding: Butt joints and fully penetrated butt joints equivalent to double-sided welding. How to understand a \"fully penetrated butt joint equivalent to double-sided welding\"? Is root welding using gas shielded welding considered equivalent to double-sided welding? This provision was established primarily to ensure the quality of welded joints, with an emphasis on butted joints and full penetration. What is lack of penetration? 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, while 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 in 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 only, 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 root pass of gas shielded welding meets the requirement of full penetration, the resulting weld joint is equivalent to a double-sided weld. Whether it constitutes a weld joint equivalent to double-sided welding is determined by its welding process, welding quality, and non-destructive testing.