Structural Design Capacity of X120 Linepipe

Abstract

A new high strength steel linepipe with a specified minimum yield strength of 120 ksi (X120) has recently been introduced to industry. The newly developed linepipe meets all mechanical property targets of an X120 grade material as verified through an extensive small and large-scale experimental program. Design equations have been developed and verified with full scale testing that allow pipeline designs that take full economic advantage of the higher strength of X120. This paper focuses on the development and verification of capacity equations for bending loads, external pressure (collapse) loads, combined bending and external pressure loads, and internal pressure (burst) loads. The corresponding response of the pipe was investigated with finite element analysis (FEA). Analytical equations that predict the burst, bending, and collapse capacities were then established based on parametric studies performed using FEA models. To gain confidence in the models, full size pipe tests were conducted and the results compared to FEA. The testing demonstrated that the FEA models accurately predict the behavior of the X120 pipe. Modifications to the existing equations were made when necessary to ensure the capacity equations correctly capture the pipe response for higher D/t ratios and for the higher strength X120 material. Material sensitivity studies show that the new equations accurately predict the X120 behavior over the range of load conditions evaluated.