Abstract Scope |
Controlling unstable crack propagation in fracture-critical welded connections, such as those found in bridges, offshore structures, and other structures with highly cyclic loading, is commonly achieved through qualification testing. Charpy impact testing is often used to characterize the fracture behavior of the welded connection, which typically includes specimens in the weld metal, fusion line, and heat affected zone; this excess of specimens can be costly and wasteful. Analysis of a large database of weld qualification tests (30 years) for offshore structures indicates that in nearly 95% of cases the weld metal controls the fracture behavior of the welded joint; heat input appeared to be a parameter of interest. Validation of such a hypothesis could significantly reduce the cost and effort involved with qualification testing. However, previous data is limited to ultra-high-performance steels, and is not representative of standard industry steel grades. Mechanical fracture energy and metallurgical data were gathered for A572 Gr 50 plates over a range of heat input values. The results of this study indicate that weld metal properties (both mechanical and metallurgical) are unrelated to metallurgical changes in the base metal during the welding process. Heat input substantially impacts the size of the heat affected zone, and therefore the practice of fracture testing at predetermined distances from the fusion line is ineffective to characterize the fracture energy of the various regions of a welded joint. |