Evaluation of Tensile Failure of Girth Weld Repair Grooves in Pipe Subjected to Offshore Laying Stresses

Abstract

The repair procedure for removal of a girth weld defect in offshore pipelines involves arc-gouging a groove into the defective area. Since high bending stresses in the pipes exist at the repair station, the concern was whether the weld repair groove may cause failure of the pipes. An experimental research program was conducted to determine the critical length and depth of repair grooves. Experiments were conducted on 100, 150, and 762-mm-dia pipes. A plastic instability failure criteria was developed and verified to predict the failure stresses for carbon steel pipes. The failure criterion is given as a function of three nondimensional parameters. These parameters are groove depth to pipe thickness ratio, groove length to pipe circumference ratio, and longitudinal stress to flow stress ratio. Stable versus unstable (i.e., leak versus break) behavior is also predicted from the failure criteria.