Influence of Plastic Deformation Capacity on Failure Behavior of Pipelines

Abstract

Plastic deformation capacity parameters affect the deformability of steel in the plastic stage and then affect the limit pressure of pipelines. This paper investigates the influence of plastic deformation capacity parameters on the limit bearing capacity of pipelines. These parameters include yield-to-tensile ratio ($\sigma_{y} /\sigma_{u}$), percentage uniform elongation ($\delta$) and strain hardening exponent (n). Based on the Swift strain hardening model, the relational expression of the plastic deformation capacity parameters is theoretically deduced. Ninety-five groups of material tensile test data have been collected. Based on these test data, the variation tendency of the plastic deformation capacity parameters has been analyzed statistically, and the empirical formula of the key parameters has been fitted numerically. Twenty groups of finite element examples are designed to analysis the influence of yield-to-tensile ratio and uniform elongation on the limit pressure of pipeline. Results show that, with the improvement in strength grade of steel, the plastic deformability of steel decreases; the recommended critical plastic deformation capacity indexes are: (1) pipeline steel below X65, $\sigma_{y} /\sigma_{u}$ ≤ 0.85 and $\delta$ ≥ 10%; (2) pipeline steel for X70–X80, $\sigma_{y} /\sigma_{u}$ ≤ 0.93 and $\delta$ ≥ 8%.