Design of offshore gas pipelines against active tectonic fault movement

Abstract

Active tectonic faults impose permanent ground actions on offshore gas pipelines that threaten their safety and service life. The seismic fault movement deforms the pipeline and causes excess strains due to bending, along with axial compressive or tensile forces depending on the fault type. This may lead to buckling, severe cross-sectional distortion and even rupture. The assessment of an offshore pipeline crossing active faults considers the estimation of the potential fault displacement, the structural response of the pipeline, and the limit-state capacity. This paper explores the design options for improving the capacity of partially embedded offshore pipelines to tolerate fault differential displacement using equations that are fitted to the results of finite element simulations and allow the prediction of the critical co-seismic fault displacement, i.e. the value of fault displacement that leads to various forms of pipeline failure. Considering all the types of faults, the influence of the parameters affecting the performance of an offshore pipeline subjected to active seismic fault rupture is quantified and discussed. The proposed equations could be used as guidance in the preliminary route design of future medium-diameter offshore pipelines and in the assessment of the vulnerability of existing ones. An illustrative example is also presented to demonstrate the application of the proposed equations.