Pipeline Technology—Expansion and Global Buckling

Abstract

Abstract A pipeline is a long slender structure that in operation develops compressive axial force, with increasing internal temperature and pressure. The severity of the compressive force depends on the pipeline length, geometry, and seabed conditions. Long slender structures under compression are susceptible to Euler (column‐type) global buckling. This is commonly observed in railway tracks and pipelines. Pipelines may buckle upward (upheaval buckling) or sideways (lateral buckling). This leads to two distinctly different design strategies: (i) Upheaval buckling is considered in the design of trenched and buried pipelines. Upheaval buckling of a trenched pipeline is usually considered a failure condition, due to the loss of protection (from the trench) and the high level of strain that typically occurs. Therefore, the design aim is to prevent upheaval buckling by placing sufficient backfill over the pipe in the trench. (ii) Lateral buckling is considered in the design of pipelines laid on the seabed. Lateral buckling can often be tolerated in low temperature pipelines, or deliberately encouraged in higher temperature pipelines. The design aim is to encourage and control buckling at regular intervals along the pipeline, to relieve the axial compressive load in the pipeline and share the thermal expansion between adjacent buckles. The associated phenomenon of pipeline walking (axial ratcheting displacement) occurs due to differential expansion and contraction during startup and shutdown. Limits on allowable end expansion for pipelines susceptible to walking often require that walking must be controlled by the installation of pipeline anchors. This article addresses pipeline buckling and walking, highlighting the important aspects of pipe–soil interaction and mitigation measures to ensure that design limit states are not exceeded.