Effect of Irregular Seabed Profile on Upheaval Buckling of Buried Offshore Pipelines

Abstract

Offshore pipelines are commonly buried in seabeds for protection against damage, for better insulation, and to prevent upheaval buckling induced by thermal and pressure loadings. The seabed imperfection is one of the important design parameters determining the burial depth in order to achieve the required uplift resistance for a given pipeline. In this paper, the effect of variability in seabed profile on the performance of upheaval behavior of buried offshore pipeline is investigated. The variation in the seabed profile is modeled using random field theory. The field-observed imperfection height and correlation length are used to draw the samples of seabed profile for Monte Carlo simulation (MCS) using optimized Latin hypercube (LHC) sampling technique. In order to assess the safety requirement, a numerical model of a pipeline-seabed system was developed in a commercial finite element software ABAQUS assuming linear elastic behavior for the pipe material. The interaction between pipe and seabed soil was modeled using pipe-soil interaction elements in ABAQUS. The effect of irregular seabed on the performance of offshore pipeline against upheaval buckling was quantified on the basis of the probability of failure calculated using the simulation results. Analysis results showed that the irregular seabed profile can significantly increase the vulnerability of the pipeline (failure probability) during upheaval buckling. Results further revealed that the reliable distribution of seabed feature heights and lengths using surveys of out-of-straightness is required even from the front-end engineering design (FEED) phase to eliminate the unexpected pipe failure.