Effect of chord-cut defects on the collapse response of thick-walled pipelines

Abstract

Corrosion defects can significantly reduce the ultimate bearing capacity of thick-walled pipelines in deep water. Uneven depth defects pose a serious threat to the integrity of pipeline structures. However, in the study of uneven depth defects, the influence of chord-cut defects is often overlooked. To study the impact of chord-cut corrosion defect on pipeline collapse response, a dynamic model is established. Two sets of full-scale pipeline experiments are conducted to verify the model. The validated model is used to obtain the pipeline collapse responses under different defect parameters, which include defect length, defect depth, defects’ location, and pipeline ovality. The changes in pipeline collapse pressure and collapse mode under different defect parameters are analyzed. The research shows the increase in defect length and the decrease in diameter-to-thickness ratio (D/t) will enhance the influence of defect angle θ on pipeline collapse configuration. And the change of collapse mode will lead to abnormal changes in collapse pressure. With the increase of internal defect length, the collapse mode variation rule is “∞” - “∩” - “P” - “U”. A collapse pressure empirical formula for pipeline with chord-cut corrosion defects is obtained. The empirical formula fits well with the numerical simulation results.