Effect of Material Characteristics on the Properties of a Steel Pipe

The performance of a pipeline is related to both the stress levels to which the pipe is exposed and the characteristics of the pipe material itself. For steel pipe in particular, the grade of skelp used and its deformation history during fabrication can influence both the effective yield strength and subsequent (if any) plastic deformation of the final pipe product. To understand and quantify this relationship between pipe forming and pipe properties, three concurrent areas of study were undertaken: instrumented plant trials to understand and quantify strain history during pipe forming, characterization of the constitutive behaviour of pipe steel deformation under complex loading and the development of a finite element analysis (FEA) stress model to couple the effects of forming history and constitutive material behaviour on the mechanical performance of a steel pipe under an internal pressure. Strain gauge technology and digital imaging were used to measure dynamic strain histories and geometry of the pipe imparted by the forming process. These plant measurements provided unique insight into the dynamics of the forming operation and detailed data for the FEA model verification. A series of tension/compression tests were conducted on X-52 and X-70 steel to quantify the kinematic hardening behaviour of these materials under complex loading conditions. This data was used to formulate the constitutive equations of the steel in the FEA model. The numerical stress model was developed using the commercial finite element package ABAQUS. Loading simulations of the pipe using the FEA model were conducted to illustrate the effect of both steel characteristics and forming history on pipe performance.