Insight into integrity and corrosion behaviour of damaged pipe casing L80 13-3/8″ schedule 40 under marine conditions: A preliminary study

This study investigates the susceptibility of API 5CT L80 Type 1 to stress corrosion cracking (SCC) induced by mechanical drilling and excessive torque as a precursor in offshore environments, thereby limiting its application. The failure of casing has led to hydrocarbon leakage and damage, as micro-pits transitioned into microcracks in the horizontal direction, resulting in anodic dissolution and failure. The research encompasses a visual inspection of failed casings, which is contrasted with non-failed specimens, succeeded by microscopic examinations and material conformity tests (tensile and hardness test) to assess the crack mechanism and morphology through the utilization of scanning electron microscopy and energy dispersive X-ray (SEM-EDX) and X-ray diffraction, including high-resolution transmission electron microscopy (HR-TEM). Finite element analysis was employed to model crack growth, identify critical regions, and predict the direction of propagation. The tensile test results show a 0.57% increase in tensile strength for failed material, attributed to additional casing load absorption. The presence of martensite increased the hardness of the failed specimen to 16.7 HRC, although this value is lower than the standard 23 HRC. This observation corroborates findings from metallographic tests, which indicate issues related to corrosion and changes in microstructural integrity. Intergranular corrosion products, including oxides, sulfides, and chlorides, form due to the accumulation of cracks driven by mechanical stress at 870.05 MPa and impurity segregation. The finite element method aligns with experimental results, revealing that stress redistribution at the center of the pipe indicates localized stress concentration due to excessive torque in the Y -positive direction.