Combined Effect of Pressure, Temperature and Soil Stiffness on Pipeline Strain Demand in Geohazard Zones

Abstract

Pipelines subject to ground deformations produced by geohazard loads carry high importance on pipeline analysis, design, and assessment due to risk of structural failure. An appropriate approach for evaluation is the finite element method (FEM), providing efficient and sophisticated results. Methods proposed by Zheng et al. (2021) using finite element analysis (FEA) software Abaqus/Standard provide highly accurate results by simulating a displacement-controlled analysis of buried steel pipes subject to ground displacement of varying magnitudes and direction. This paper aims to further develop this pipe strain demand assessment by including variable effects of internal pressure and temperature of steel pipes buried in soils of different stiffness. The developed strain demand criterion considers inelastic material behaviour for different grades of steel pipe, as well as bi-linear soil force-displacement interaction, accounting for soil plasticity (ALA, 2001). Assuming the effects of thermal expansion are negligible prior to ground motion initiation, the pipe loads can be assessed by modelling a pipeline with initial temperature and pressure loads, followed by a ground motion in a series of steps. Several case studies were performed by modelling an X65 grade pipeline subject to ground displacements varying from 100 to 1000 mm, across a length at the midsection of the pipe. Simulations are assessed with a specified temperature increase, and internal pressure required to induce an operating hoop stress of up to 80% of the specified minimum yield strength (SMYS). By assessing the pipeline in soils of different stiffness (low, intermediate, high) at different increments of ground displacement, an accurate representation of the material stress/strain response can be acquired for each respective case. This research may provide guidance for further studies of pipelines involving internal pressure & temperature.