[ \text{Fe}_3\text{C} + 4\text{H} \rightarrow 3\text{Fe} + \text{CH}_4(g) ]
Author: [Generated for Academic Review] Date: April 2026 Abstract High-Temperature Hydrogen Attack (HTHA) is a damaging degradation mechanism affecting carbon and low-alloy steels exposed to hydrogen at elevated temperatures and pressures. Historically mislabeled as “HTRI crack” due to early studies at the Heat Transfer Research Institute, HTHA involves the internal decarburization of steel and the formation of methane bubbles at grain boundaries, leading to fissuring and loss of mechanical properties. This paper provides a comprehensive analysis of HTHA, including thermodynamic and kinetic foundations, metallurgical transformation, nondestructive examination (NDE) challenges, and modern mitigation strategies. The transition from carbon steel to Cr-Mo steels with post-weld heat treatment (PWHT) is evaluated. Recent advances in advanced ultrasonic backscatter techniques and risk-based inspection (RBI) are discussed. The paper concludes with case studies and future directions for hydrogen service in the context of a hydrogen economy. htri crack
For alloy carbides (e.g., Cr₂₃C₆, Mo₂C): The transition from carbon steel to Cr-Mo steels
