Evaluating impact toughness as a qualification testing requirement for welds

Steel structures with fracture-critical components and connections rightly require quality control to help prevent catastrophic failure. Specifically, fracture-critical welded connections require evidence of brittle fracture capacity, which can take the form of qualification testing or pre-qualification (which is based on previous qualification testing under design circumstances). In cases where the use of pre-qualified weld details are not applicable, qualification testing requirements can significantly influence project cost and schedule, especially on large complex projects. This paper focuses specifically on the fracture toughness (as quantified by impact toughness testing) aspect of qualification testing, which, for welded connections, often includes assessment of the weld metal, multiple locations in heat-affected zone (HAZ), and the base metal. The research presented herein incorporates a database of more than 400 weld qualification records, spanning over 30 years. The data includes significant variance across many welding parameters including, among others: i) base material, ii) welding process, iii) welding position, and iv) connection joint type (e.g., bevel, v-groove). The data indicates that the weld metal controls the impact toughness of the connection for the majority of base metals included in the study, regardless of welding parameter. While such conclusions are clearly limited to the parameters included in the database, the findings pose the potential for streamlining of fracture toughness qualification in welded connections. Specifically, the ability to characterize the fracture toughness of a welded joint solely based on assessment of the weld metal could reduce the schedule and cost impacts of qualification testing. •Fracture-critical welds rely on accurate characterization of fracture toughness.•Weld metal nearly always controls the fracture toughness of welded joints.•Steel specification impacts frequency of weld metal control of fracture toughness.•Within constraints, weld metal can characterize fracture toughness of welded joints.