NG-18-104-R01 The Magnitude and Effects of Residual Stresses in Line Pipe

Abstract

The tendency of rings of line pipe to open or close upon being longitudinally severed results from circumferential residual stresses in the pipe. The objectives of this work was to: (1) To determine the nature and magnitude of the residual stresses which cause ring-opening and ring-closing in line pipe. (2) To determine the quickest and simplest way to measure such residual stresses. (3) To determine the effect of the residual stresses on the fracture initiation and propagation behavior of the line pipe. (4) To determine whether or not ring-opening or ring-closing residual stresses could be a useful means when intentionally induced in the pipe to improve its resistance to fracture initiation and propagation. With these objectives in mind the scope of the research program was defined to include: - A theoretical analysis of the forces and stresses producing ring-opening and ring-closing deflections - Experimental determination of ring-opening and ring-closing residual stresses in typical line pipe materials - Full-scale fracture initiation experiments to determine the effects of residual stresses on the failure stress levels of defects - Fracture propagation experiments on short vessels filled partly with water to determine the effects of residual stresses on the ductile fracture propagation characteristics of the line pipe.