Mechanical resistance of stepped lamination defects in a welded section of oil and gas pipeline: a finite element analysis

The mechanical resistance of API 5L X52 steel with stepping lamination in the base metal (BM), heat affected zone (HAZ) and welding bead (WB) was studied by using the finite element method (FEM) in the present work. Both internal working pressure in the pipelines and internal pressure in the stepping laminations were studied to analyze the mechanical behavior of the pipelines. 3D FEM models and kinematic hardening were activated in the software used, while tests for the mechanical properties (true stress–strain curve) of BM, HAZ and WB were also conducted. The results demonstrated that stepping laminations in the BM–HAZ–WB zone reduced the ability to support internal pressure; therefore, the failure pressure (P_f) is also reduced. Pipeline failures occurred when the Von Mises stresses reached or exceeded the ultimate tensile stress (σ_UTS) of the material in the outer and inner wall and the stepping lamination sizes were too large. Failure in pipelines with stepping laminations occurred on the left side of the crack on the outer wall of the BM–HAZ zone; on the inner right side of the stepping laminations, the failure takes place on the inner wall in the WB.