Fatigue Failure of Welded Tubular Joints

The fatigue of welded tubular joints, as found in offshore structures, is explored by developing a qualitative model. This model considers the influence exerted on the initiation and growth of fatigue cracks by secondary effects of the joints fabrication and behavior. The model is then used, along with basic concepts from fracture mechanics, to develop an analytical model for the prediction of fatigue failure. The behavior of the tubular joint undergoing fatigue is divided into three phases: primary phase—no noticeable effect from fatigue; transition phase—decaying behavior; and secondary phase—distinctly new behavior. Fatigue failure is then defined as a distinct change in the joint's load transfer characteristics (the end of the transition phase). Experimental data is presented to support both this definition and the theoretical prediction of failure.