Reliability of subsea pipelines against lateral instability

Abstract

An approach for the reliability assessment of subsea pipelines against on-bottom lateral instability is presented in this work. Combined stresses/lateral displacement acting on offshore pipelines due to combined hydrodynamic loads including wave/current effects are computed using a non-linear finite element model. The model takes into account the effect of pipe–soil interaction. The resulting combined pipe stresses/lateral displacement are used as input for reliability assessment. Probabilities of pipeline overstress/lateral movement due to hydrodynamic loading are computed using a finite element reliability code. First-/second-order reliability methods are used for computation of safety indices. These values are then compared with target safety levels as set in pipeline design codes. Three case studies for actual pipelines off the shore of Egypt are analysed using the proposed approach. Results show that computed safety levels are within the target values. The proposed approach can be a valuable tool for the pipeline designer/operator for assessment of pipeline safety and reliability with respect to on-bottom stability.