Damage under Thermo-mechanical Behavior of Tubular Structures

Abstract

Pipelines play a crucial role in the transportation of petroleum products, including gas, oil, and hydrogen, within the oil industry. However, their operation carries significant risks, including potential material and human damage as well as environmental harm. Among the components of pipeline networks, pipe elbows are particularly critical and susceptible due to stress intensification and bend curvature. They are more prone to various corrosion failure modes compared to straight pipes. The main objective of this thesis was to employ the Extended Finite Element Method (XFEM) to predict the damage occurring in pipe elbows with defects located at different positions. The analysis focused on the combined effects of internal pressure and in-plane bending moments, both in the closing and opening directions. The study was structured into three distinct sections: The first section aimed to predict the damage in pipe elbows with defects situated at various positions on the internal wall of the extrados. In the second section, the influence of service temperature on the damage of pipe elbows was investigated under combined internal pressure and opening bending moments. End-rotation curves were plotted for different service temperatures. The third section examined the effectiveness of two repair methods for critical defect positions: composite patch, and metallic patch. A parametric analysis was conducted to assess the impact of geometric parameters such as patch thickness, adhesive properties, and patch material on the repair's efficiency. The findings obtained from the study revealed that the damage in pipe elbows is primarily governed by the bending moment and the proximity of the defect to the critical elbow zone or maximum bending moment. Additionally, the behavior of the elbows under varying temperatures depends on the surrounding environment, which can lead to either brittle or ductile failure modes. The utilization of composite bonding, with different quantities of composite patches, enhances the critical moment, offering greater benefits in comparison to metallic patches. Furthermore, the research validates the precision of the suggested approach in forecasting the performance of the repairs.