Methodology for failure mode prediction of onshore buried steel pipelines subjected to reverse fault rupture

Oil and gas buried steel pipelines are vulnerable to permanent ground displacements, such as those resulting from tectonic fault activation. The dominant failure mechanism is strongly dependent on the type of faulting. The more complex case is the reverse fault type because the crossing pipeline is significantly compressed and bent and consequently, it may fail due to local buckling, upheaval buckling or tensile weld fracture. Which among those failure modes will be critical, depends on a set of parameters, comprising fault crossing geometry, diameter to thickness ratio (D/t) of the pipeline, pipeline steel grade, and backfill soil properties. An extensive parametric study is carried out, followed by statistical processing of the results in order to formulate simplified statistical models for the prediction of the predominant failure mode according to criteria set by the American Lifelines Alliance and EN 1998-4 standards. The study thus offers the first comprehensive attempt to quantify the qualitative criterion that deeply buried pipes with high D/t ratio tend to buckle locally, while shallowly buried pipes with low D/t ratio tend to buckle globally. Pipe designers may use the provided expressions to predict the predominant failure mode in order to either apply the necessary seismic countermeasures or re-design the pipeline if necessary.