HTHA stands for High Temperature Hydrogen Attack, which is a degradation mechanism that affects steels exposed to hydrogen at elevated temperatures and pressures. HTHA can cause cracking and failure of the steel, especially in welds and stressed areas¹.
HTHA occurs when atomic hydrogen penetrates the steel and reacts with the carbon present to form methane gas. The methane gas accumulates in the microstructure of the steel, creating internal pressure and weakening the material. Over time, this can lead to fissures and cracks that compromise the integrity of the steel².
HTHA is a serious problem that can occur in process equipment constructed of steel and used in applications involving hydrogen, such as petroleum refining, petrochemical production, and other chemical facilities. HTHA can also affect high-pressure steam boilers³.
To prevent HTHA, engineers need to select suitable materials for the operating conditions of temperature and hydrogen partial pressure. The Nelson Curves, maintained by the American Petroleum Institute (API), provide an authoritative guide for safe material choice based on empirical data and experimental tests. The Nelson Curves plot the limits of different grades of carbon and low-alloy steels against temperature and hydrogen partial pressure¹².
HTHA is a subtle and complex phenomenon that requires careful monitoring and inspection. Engineers should be aware of the risk factors and signs of HTHA, and follow the best practices and standards for managing HTHA in their facilities⁴.
¹: High Temperature Hydrogen Attack: Safe use of carbon steel
²: Mitigate a Subtle Cause of High-Temperature Hydrogen Attack
³: High Temperature Hydrogen Attack (HTHA) – TWI
⁴: Detecting and managing High Temperature Hydrogen Attack
Source: Conversation with Bing, 1/30/2024
(1) High Temperature Hydrogen Attack: Safe use of carbon steel. https://www.hse.gov.uk/safetybulletins/high-temperature-hydrogen-attack.htm.
(2) Mitigate a Subtle Cause of High-Temperature Hydrogen Attack. https://www.aiche.org/resources/publications/cep/2021/april/mitigate-subtle-cause-high-temperature-hydrogen-attack.
(3) Detecting and managing High Temperature Hydrogen Attack. https://pecm.co.uk/detecting-and-managing-high-temperature-hydrogen-attack/.
(4) High Temperature Hydrogen Attack (HTHA) – TWI. https://www.twi-global.com/technical-knowledge/job-knowledge/high-temperature-hydrogen-attack-htha-143.
Energy Risk Engineering Insights 