Modified expression for predicting the bending resistance of a locally corroded pipeline and its experimental verification

Abstract

In practical service, transmitted pipelines may suffer from corrosion, which affects the safety of the component. For an engineering pipeline subjected to local corrosion, the pipe wall becomes thinner locally, and the bending load bearing capacity is inevitably reduced. Therefore, proper prediction of the bending resistance of a pipeline with locally corroded defects is very significant with respect to the safety assessement of a servicing pipeline. In the present paper, the effect of the length of local thinning in a pipe in the longitudinal direction is considered. A modification to the net-section collapse failure (NSC) criterion is then proposed. 3-point bending experiments for J55 pipe with artificially machined local thinning on the outer-surface of the pipe are conducted to verify the modified expression. Comparison of the predictions of the modified NSC with the experimental data indicates that the modified expression can predict the general variation tendency of the normalized bending resistance (M/M0) with the relative longitudinal defect lenght ($(L/\sqrt {Rt} )$). However, discrepancy between the theoretical prediction and experimental data is apparent for a small relative longitudinal defect leght ($L/\sqrt {Rt} \sim 1$ to 3). This discrepancy might result from the stress concentration effect, which has not been considered in the model.