Resilience of HP/HT pipelines to combined seismic and thermal loadings

Abstract

Resilience of unburied high pressure/high temperature (HP/HT) pipelines with different outside diameter-to-wall thickness (OD/t) ratios and subjected to the combined action of both earthquake and thermal loads is studied numerically. Unlike most of the existing research on buried or trenched pipelines, the current work analyses the resilience to combined seismic-thermal actions of an unburied pipeline laid on the seabed and resting on a sleeper. By using finite element analyses (FEA), the thermal and seismic responses of pipelines with different OD/t ratios are captured. The pipeline-soil and pipeline-sleeper interactions are modelled using Mohr-Coulomb constitutive contact behaviour. Empirical equations of critical temperatures causing lateral buckling in pipelines with OD/t between 10 and 50 are developed. Rayleigh damping coefficients are calculated following modal analyses, whereby the pipeline-soil system frequencies are found. Resilience to failure under combined seismic and thermal actions is load-path dependent; the earthquake imposed on a laterally buckled pipeline represents the most detrimental scenario. It is understood that the introduction of seismic load can amplify the buckle amplitudes beyond the pre-defined controlled buckle amplitude and thus cause overstressing and/or local buckling in the buckle crown segment. Local buckling due to the interaction between thermal and seismic loading is found to be more pronounced in pipelines with OD/t > 40.