Theoretical method to calculate pipeline thermal transient-induced walking rate considering nonlinear time-dependent soil resistance

Abstract

Submarine pipeline was widely used to transport oil and gas in offshore petroleum exploitation. In practice, deep-water pipeline experiences several times of maintenance every year. This periodic open-up and shut-down operation causes cyclic rise and fall in the temperature of a pipeline, resulting in the periodic expansion and contraction of the pipeline. Due to the characteristics of heating-up operation, the expansion and contraction movement are symmetrical about different points, and it leads to the pipeline walking phenomenon. As a key factor, the axial soil resistance affects the walking displacement heavily. The shearing generated by expansion and contraction of a pipeline section causes intermitted consolidation of soil and cyclic increment in the equivalent soil resistance coefficient. This paper analysed pipeline walking of a free-end pipeline laid on even seabed with consideration of cyclic soil strength hardening. New driving mechanism for pipeline walking caused by thermal transient due to the influence of time-dependent soil resistance was proposed. A common theoretical method to calculate walking displacement was also established.