Numerical and Experimental Fracture Mechanics Assessment of Tubes in Sour Environment

Abstract

The structural integrity of tubular structures in sour environments is a critical concern for the safety and reliability of oil and gas extraction processes, particularly in harsh operating conditions. This thesis presents a comprehensive numerical investigation into fracture mechanics for steel tubes exposed to sour service conditions, focusing on sulfide stress cracking (SSC)—a form of hydrogen embrittlement exacerbated by the presence of hydrogen sulfide (H2S). A novel machine-learning-augmented Failure Assessment Diagram (FAD) methodology is developed to evaluate tubular integrity, incorporating key parameters such as material properties, residual stresses, and crack geometries. This approach overcomes the conservatism of conventional FADs, providing a data-driven framework tailored to specific material-environment interactions. The research further employs advanced computational modeling, including coupled chemo-thermo-mechanical phase-field simulations, to capture the complex interplay between hydrogen diffusion, temperature, and fracture energy degradation. These simulations provide a detailed understanding of the mechanisms driving SSC, highlighting the critical roles of environmental factors such as pH and H2S concentration, as well as material characteristics like microstructure and residual stresses. The study also includes several failure case studies, applying the developed frameworks to analyze real-world scenarios of tubular failures in ultra-deep gas wells and steel-reinforced thermo-plastic pipe systems subjected to H2S environment. By addressing the limitations of current standards and providing predictive tools for structural integrity assessment, this work contributes to safer and more cost-effective operations in challenging sour service conditions. The findings offer a pathway to improved material selection and optimized design practices for oil and gas infrastructure.

Date of Award	30 Apr 2025
Original language	American English
Supervisor	Imad Barsoum (Supervisor)