On the spring-back and re-rounding mechanism of a plain dent on the sandwich pipe

Dent defect is a common cause of failure of the submarine pipelines, which not only leads to a reduction in the structural resistance of the submarine pipeline but also may induce the collapse of the submarine pipeline. The study aims to thoroughly investigate the dent spring-back and re-rounding characteristics of the inner and outer pipe of the sandwich pipe under lateral loading. This paper examines the sandwich pipe's dent spring-back and re-rounding processes through experiments and numerical simulations. The study shows that a higher bonding strength and a larger dent orientation angle will result in more excellent dent spring-back of the inner and outer pipes. The core layer material on the inner and outer pipe dent spring-back has a significant impact. Internal pressure improvement contributes to improving the indentation re-rounding ability of the inner and outer pipes. The larger the annular ratio, the closer the sandwich pipe inner and outer pipe dent re-rounding ability is. Finally, empirical formulas of the inner and outer pipe dent re-rounding coefficients are established, and the average errors are less than 10%. The research results can provide theoretical guidance for the safe operation of submarine pipelines containing indentations.