It is a fact that when a pipeline is installed by the reeling method, it will undergo cyclic plastic straining and the pipe will plastically deform. Due to the applied plastic bending moment, the residual deformation in terms of residual pipe ovality after reeling is difficult to predict by Finite Element Analyses (FEA) without a thorough understanding of the material characterization and changes under cyclic plastic straining.
The paper describes how the material behavior of seamless pipe under plastic strain reeling cycle has been characterized by a comprehensive material testing program including Bauschinger tests and perpendicular loading pre-straining tests. It turns out that for seamless pipe, by looking at the yield stress locus of the material after plastic straining, the reeled pipe material which initially shows isotropic behavior in the un-strained condition will change and evolve to show anisotropic behavior. The material in the hoop direction of the pipe will become more hardened than the material in the longitudinal direction of the pipe. The cross hardening characteristics of material under cyclic plastic deformation have been modeled using the “distortional plasticity” principle and implemented in a user subroutine of an FEA software package.
This paper includes the validation of the ovality prediction by FEA model using the developed material model against the ovality measurement from full scale bend tests at Heriot-Watt University as well as ovality measurements taken during the spooling test and trial of 16″OD pipeline at Carlyss spool base in 2013. The material testing of a sample cut out from Spoolbase test and trial, undergoes spool and un-spool 5 cycles, has been performed to confirm the distortional plasticity hardening behavior obtained from the small scale Bauschinger and perpendicular loading tests.