CALCULATION OF CRACK GROWTH IN WELDED SPECIMENS UNDER SEAWATER CONDITIONS IN ORDER TO PREDICT FATIGUE LIFE OF OFFSHORE COMPONENTS

Welded components in the offshore field generally are designed that no cracks should occur. Under cyclic loading cracks must be taken into account. In the research work described, a suitable calculation method had to be proved to predict the crack growth behaviour of offshore components in seawater and under service-like conditions. Using Paris law, the crack growth behaviour of specimens which are similar to the component (welded V-shape specimens) may be predicted quite well in air, free corrosion, under cathodic protection (0860mV Ag/AgCl) and under a variable load sequence. The use of Wheeler's model including crack retardation yielded in a significant higher crack propagation life and therefore unconservative predictions of fatigue life.