Weld joint factor

Generally, the use of shims is intended to facilitate full penetration during welding. Nowadays, it is preferable to avoid using shims whenever possible; without them, the welding coefficient can be increased. Whether the welding coefficient is 1 or 0.85 depends on whether inspection is carried out using X-rays or through local testing.

The use of shims results in single-sided forming, and it is not possible to clean the root of the weld.

One type is permanently bonded to the weld metal (with most materials being the same as the base material), while the other type can be removed after welding (copper shims are used for steel welding, and flux shims are used for submerged arc welding). In both cases, these are used to ensure proper formation of the weld, thereby reducing defects such as inward indentation and burn-through in the back side of the weld. The joint factor is also related to the proportion of non-destructive testing

Before RT, remove the backing plate; in this case, it is equivalent to a double-sided welding process

For temporary shims, methods such as root cleaning and grinding on the back side can still be used. . Therefore, removing the backing plate before RT is equivalent to double-sided welding. Whether a backing plate is used during RT has an impact on the RT film; it may cover up some surface defects at the root, such as shrinkage cavities and similar issues.

"One type is those that can be removed after welding (copper shims are used for steel welding, while flux shims are used for submerged arc welding); shouldn’t such shims not be considered part of single-sided welding?

This post was last edited by jizhanwei22 on 2017-2-24 08:47. Question 1: A metal gasket is used with single-sided welded joints – what is the function of this gasket? ——Welding with shims is an auxiliary method for single-sided welding to achieve double-sided formation, aimed at ensuring welding quality (complete penetration). Question 2: Can a single-sided welded joint with gussets not achieve full penetration? ——Gussets are used precisely to ensure full penetration; even some welders (those with high skill levels) can achieve full penetration without gussets. Question 3: If single-sided welding is used to achieve full penetration without the use of backing plates, is the welding coefficient 1.0 or 0.9? ——Whether to use a welding joint coefficient of 1.0, 0.9, or 0.85 depends on the proportion of non-destructive testing. In the design, by specifying the weld joint coefficient, it is indicated that this weld must be fully penetrated. That is, only fully penetrated welds can give rise to a welding joint coefficient. However, the selection of the weld joint coefficient is only related to the non-destructive testing ratio.

Previously, the design drawings specified single-sided welding with gussets; however, considering issues such as the fit between the gussets and the weld seam as well as non-destructive testing requirements, we eliminated the gussets and opted for TIG welding as the root pass.

For those with shims, in terms of the fit during assembly, the quality of the underlying weld bead, and the quality of the non-destructive testing films, it is better to use TIG welding for the root pass.