Effect of irregular seabed profile on upheaval buckling of buried offshore pipelines

Offshore pipelines are commonly buried in seabed 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 behaviour of buried offshore pipeline is investigated. The variation in the seabed profile is modelled 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 using optimised Latin hypercube (LHC) sampling technique. In order to assess the safety, a numerical model of pipeline-seabed system was developed in ABAQUS assuming linear elastic behaviour for the pipe material. The interaction between pipe and seabed soil was modelled 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.