Analysis of torsional instability and reliability of marine flexible pipelines.

During the installation of marine flexible pipelines, components, such as flexible risers, umbilicals, and cables, subject to wave motion and ship yaw can cause torque on such pipelines. In addition, marine flexible pipelines are subjected to low tension at the touch down zone (TDZ), which could result in the torsion instability phenomenon of flexible pipeline in the TDZ, thus forming a loop. Moreover, when the tension on a marine flexible pipeline increases, the radius of the loop decreases and kinks can form, which could result in damage or fracture of the flexible pipeline, affecting its normal operation. In this study, the formation mechanism of a flexible pipeline loop is thoroughly analyzed considering the end torsion, tension, and environmental loads. The bending failure response surface function of the flexible pipeline is constructed considering the randomness of design parameters, e.g., elastic modulus, diameter, and density, and the probability of torsional instability of flexible pipeline is analyzed using both the first-order second moment and Monte Carlo simulation methods, both of which could give almost the same level of accuracy, while the first-order second moment method is computationally less expensive. • The formation mechanism of a flexible pipeline loop is thoroughly analyzed. • The bending failure response surface function of the pipeline is constructed considering the randomness of parameters. • The reliability of torsional instability of flexible pipeline is analyzed using two reliability methods. [ABSTRACT FROM AUTHOR]