Optimized configuration of flexible joints for the protection of onshore buried steel pipelines against tectonic rupture

Safeguarding the integrity of onshore buried pipelines against earthquake hazard is a top priority for engineers, researchers, pipe operators, and regulators. The consequences of a potential failure caused by fault rupture can be counteracted by integrating flexible joints in the pipe in the fault vicinity to “absorb” pipe deformation, thus allowing pipe steel segments to remain virtually undeformed. A structural optimization approach for introducing flexible joints is presented. The strategy is formulated as a combined sizing and topology optimization problem, taking into account the number of joints, the distance between two adjacent joints, and the mechanical properties of the joints. The objective is to minimize the life-cycle cost of the protective measure by accounting for the primary parameters affecting its configuration, i.e., fault type and pipeline–fault crossing geometry. Genetic algorithms are employed for solving the optimization problem. All fault types and pipeline–fault crossing geometries are examined. An optimized topology configuration is obtained for each case, and the corresponding design considerations are discussed. The efficiency of flexible joints is demonstrated in comparison to unprotected pipes.