The influence of long-range residual stress on plastic collapse and local yielding of internally pressurized pipes

The determination of plastic collapse for cracked pipes is important in structural engineering design and component integrity assessment. Long-range residual stresses are usually treated as primary stresses which contribute to plastic collapse of pipes subjected to internal pressure. This paper explores the differences between load and displacement controlled conditions applied to the ends of thin- and thick-walled pipes. Both load and displacement control can represent long range or fit-up residual stresses if they are considered as primary or secondary stresses respectively. Both global collapse and local yielding for pipes containing partially and fully circumferential cracks are examined. Detailed three-dimensional (3D) finite element (FE) analyses are used to simulate the pipe and crack geometry and the boundary conditions. The cracked pipes are assumed to be open ended. For a defect free pipe the FE results for global collapse agree with analytical solutions for both load and displacement controlled end conditions. For high tensile end loads and displacements lower collapse pressures are found for displacement conditions, while it is the converse for high compressive end loading. However, when a crack is introduced it becomes evident that tensile or compressive displacement control has little impact on global collapse and therefore long-range displacement controlled (or residual) stresses do not contribute to collapse. On the other hand local net section yielding is strongly affected by either load or displacement controlled end conditions.