Changes in Tensile Properties Due to Cold Bending of Line Pipes

Abstract

The changes in the tensile properties of line pipes due to cold bending were experimentally and analytically investigated. Full-scale cold bending experiments were performed on API X60 and X80 grade line pipes. The reduction in the yield stress of the cold bends due to the Bauschinger effect was approximately 20% and 35% for X60 and X80, respectively. In order to evaluate the changes in the tensile properties of the pipes quantitatively, finite element (FE) analyses and small-scale experiments were conducted. The FE analytical model for simulating the strain distribution at various bending angles was verified with the results of the full-scale experiments. The tensile properties of the cold bends were in good agreement with those of the small-scale experiments using uni-axially prestrained specimens. Based on the present results, an estimation method was proposed for evaluating the distribution of the tensile properties after cold bending with the analytical model using the results of the tensile tests for prestrained specimens.