Strain capacity analysis of the mismatched welding joint with misalignments of D 1,422 mm X80 steel pipelines: An experimental and numerical investigation

Abstract

Anomalies as misalignment, microcrack are inevitable for large diameter high strength steel pipelines. To ensure the strain capacity of mismatched welding joint with misalignments of D 1,422 mm X80 steel pipeline, a comprehensive study via wide plate experiments and finite element model simulations was conducted. The full-scale tensile experiment of a X80 pipe wide plate with weld joint was conducted. Strain distributions on the plate was derived by DIC technic. Trends of CMOD at the precrack in the weld joint with tensile strains monitored. A FE model was established to inverse the wide plate experiment and prove the accuracy of numerical model’s prediction results for crack driving forces. Using the same modeling method, a parametrical 3D numerical simulation model for X80 line pipe with cracks in automatic welding joints was established. The double V-shaped groove type welding joint was precisely considered in the geometric model. Difference of the stress-strain relationships of yielding-to-tensile ratio of the BM, softening rate of the HAZ and strength matching coefficient of WM were considered in the material model. A CTOD extracting program coded was employed. Parametric analysis was performed to investigate the effects of load conditions, strength matching coefficient of WM, yielding-to-tensile ratio of BM and softening rate of HAZ on the strain capacity with a critical fracture toughness adopted in pipeline industry. Based on the derived results, mismatched ratio requirements of D 1,422 mm X80 pipes were listed, which provides guidance for the welding parameter design and safety evaluation of automatic welding joints.