Weld Quality in Steels Construction

A weld must be of an appropriate quality to ensure that it will satisfactorily perform its function over its intended lifetime. Weld “quality” is therefore directly related to the purpose the weld must perform. Codes or contract documents define the required quality level for a specific project, meaning that a quality weld is one that meets the applicable requirements. Ensuring that the requirements have properly addressed the demands upon the weld is ultimately the responsibility of the Engineer.

All welds contain discontinuities, which are defined as an interruption in the typical structure of the material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics (AWS A3.0). Such irregularities are not necessarily defects. A defect is defined as a discontinuity that is unacceptable with respect to the applicable standard or specification. Defects are not acceptable; discontinuities may, or may not, be acceptable.

Welds are not required to be “perfect,” and most welds will contain some discontinuities. It is imperative that the applicable standards establish the level of acceptability of these discontinuities in order to ensure both dependable and economical structures. AWS D1.1 is the primary standard used to establish workmanship requirements. In general, these are based upon the quality level achievable by a qualified welder, which does not necessarily constitute a boundary of suitability for service. If the weld quality for each type of weld and loading condition were specified, widely varying criteria of acceptable workmanship would be required. Moreover, acceptable weld quality (in some cases) would be less rigorous than what would be normally produced by a qualified welder.

(D1.1-96, page 404, Commentary C6.8). This suggests that, in some instances, the D1.1 requirements exceed the actual requirements for acceptable performance. The Engineer of Record can use a “fitness for purpose” evaluation to determine alternate acceptance criteria in such situations. Some specific loading conditions require more stringent acceptance criteria than others. For example, undercut associated with fillet welds would constitute a stress riser when the fillet weld is loaded in tension perpendicular to its longitudinal axis. However, when the same fillet weld is loaded in horizontal shear, this would not be a stress riser, and more liberal allowances are permitted for the level of undercut.

to be continued…..

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