LAMRI SIDAHMED EL MAHDIOUDAD WAHID2026-09-272026-09-272026https://dspace.univ-temouchent.edu.dz/handle/123456789/7663The structural integrity of oil and gas pipelines is strongly influenced by the presence of defects that may develop during manufacturing, installation, or service. Among these defects, cracks and scratches are considered critical because they create stress concentrations that can reduce the load-carrying capacity of the pipeline and increase the risk of failure. Understanding the interaction between such defects is therefore essential for ensuring safe and reliable pipeline operation. This work investigates the interaction between crack and scratch defects in a buried API 5L X80 steel pipeline using the Finite Element Method (FEM). Numerical simulations were performed with ABAQUS to analyze the influence of defect geometry, including crack depth, crack width, scratch depth, scratch width, and scratch orientation. The distributions of Von Mises stress, equivalent plastic strain (PEEQ), and J-integral were evaluated to characterize the mechanical and fracture behavior of the pipeline. The results show that increasing defect dimensions leads to higher stress concentration and plastic deformation levels. Furthermore, the J-integral values increase with crack size, indicating a greater tendency for crack propagation. The study also highlights the influence of repair configurations on reducing the crack driving force and improving structural integrity. The findings contribute to a better understanding of defect interaction mechanisms in high-strength pipeline steels and provide useful information for pipeline integrity assessment and maintenance strategies.enThesis