Questions regarding the evaluation of butt welds and fillet welds
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In our company, when performing fillet weld processes, we simply use the qualified butt welds as a reference, since those qualified butt welds are suitable for fillet weld processes within the same scope. So why go through the process of evaluating fillet weld specimens? Is it because it’s convenient?
The purpose of formulating rules for welding procedure qualification is to reduce the number of such qualifications. By taking into account the welding properties of the materials, the basic principles of welding procedures, and the requirements for welding management, it is possible to identify the underlying relationships among the factors involved in welding procedure qualification, and thereby establish corresponding substitution relationships, coverage relationships, and omission relationships. Clause 6.3.1.2 of NB/T47014-2011 stipulates that a welding process deemed qualified through the evaluation of butt weld specimens is applicable to both butt welds and fillet welds in welded parts.
Fillet welds cannot cover butt welds; conversely, butt welds can cover fillet welds
The evaluation of butt welds can cover fillet welds of any thickness, while fillet welds can only be evaluated as fillet welds. So, once the butt joint assessment has been done, there is no need to conduct an assessment for the fillet joint; however, if an assessment for the fillet joint is carried out, then an assessment for the butt joint must also be done.
It depends on the standards; ISO 15614-1:2012 is used for weld evaluation. This standard specifies that butt welds, as well as butt and fillet welds with full penetration or partial penetration, must be shown to be acceptable. If fillet welds are the main form of welding production, fillet weld tests should be conducted.
There is a qualified process assessment for butt welds, which is applicable to fillet welds of any thickness, as specified by the standard. For the process evaluation of butt welds, mechanical property tests are required, whereas for fillet weld evaluations, mechanical property tests are not feasible; only macroscopic inspections are carried out.
According to standard 47014, the evaluation of butt welds can replace that of fillet welds; however, the evaluation of fillet welds cannot replace that of butt welds. Therefore, in order to reduce the number of evaluations, it is sufficient to conduct evaluations only on butt welds.
The evaluation of butt welds can cover fillet welds of any thickness, while fillet welds can only be evaluated as fillet welds. So, once the butt joint assessment has been done, there is no need to conduct an assessment for the fillet joint; however, if an assessment for the fillet joint is carried out, then an assessment for the butt joint must also be done.