Prediction of properties on large diameter welded pipe: case study on 32″ × 16 mm X65 HSAW pipe

Abstract

Large diameter welded pipes are amongst the most cost-effective transportation means for oil and gas. The production of those pipes involves different cold forming steps, as a result of which the mechanical properties on pipe will be different from the plate or coil properties. The steel manufacturer has several parameters at hand to control the properties of his final product. However, the pipe manufacturer only has a narrow process window, but eventually he is responsible for the properties of his product, i.e. the pipe. Furthermore, for some pipeline applications, the properties in both the transverse and longitudinal pipe direction must be within certain limits. This paper presents a Finite Element model which allows simulating pipe forming and subsequent mechanical testing and thus could be adopted to predict pipe properties from coil/plate properties. The complex hardening behaviour exhibited by pipeline grades is described by an extended version of the Levkovitch-Svendsen model, a constitutive model which accounts for isotropic, kinematic and distortional hardening. To validate the model, numerical predictions were compared to experimental results obtained from mechanical tests conducted on 32″ × 16 mm X65 HSAW (Helical Submerged Arc-Welding) pipes. The properties on pipe were evaluated by means of ring expansion tests and tensile tests on (flattened) full-thickness dog-bone samples and non-flattened round bar samples. Furthermore, tensile tests were performed in the transverse and longitudinal pipe direction and tests were conducted before and after hydrotesting. In general, the numerical predictions are in good agreement with the experimental data.