Zahi, MESSAOUD2025-05-292025-05-292025-02-27http://dspace.univ-chlef.dz/handle/123456789/2091THESIS to the fulfilment of the requirements for a DOCTORATE Field: Mechanical engineering Specialty: EnergeticThe aim of this project is to experimentally study the effect of semi-elliptical defects on API X52 pipeline steel and its repair by welding and by patching with hybrid composites made of natural fibers and synthetic materials. Tensile tests were performed on API X52 steel samples, with and without semi-elliptical defects through the variation of a/c and a/t ratios, and then the samples repaired by welding and composite patches were tested and compared with the results of origin material samples. The experimental results of mechanical properties indicate the effect of defects on the integrity of the pipeline of energy transport through the different ratios of a/c and a/t. It was observed that a/t ratio defects are more dangerous than the ratio a/c, especially when the ratio a/t is higher than 0.5. It is clear that both welding repair and composite patch methods can be considered as a solution for maintaining the integrity of the piping systems.CorrosionAPI X52 steelDefects Semi-ellipticalPipelineRepairingThesis