High temperature hydrogen attack (HTHA) is an intergranular damage mechanism that can occur in process equipment that is exposed to hydrogen at elevated temperatures (at least 400oF or 204oC), under dry conditions, when hydrogen disassociates into nascent (atomic) hydrogen, which is then driven into the steel by the temperature and pressure of the environment. The atomic hydrogen reacts with unstable carbides in steel to form methane gas, resulting in the formation of gas pockets that lead to material degradation. The damage that results from HTHA ranges all the way from superficial surface decarburization of the inside diameter (ID) surface to severe material embrittlement, loss of mechanical properties, and cracking.
This Asset Intelligence Report on High Temperature Hydrogen Attack (HTHA) serves as a primer to increase your familiarity with this topic. The report contains the following sections:
- Areas susceptible to HTHA damage
- An introduction to the Nelson Curve
- Methods of prevention/mitigation
- Effective inspection techniques
- Industry codes, standards, and best practices
- Further reading
This report is not intended to serve as a comprehensive resource for HTHA. Rather, it is just as the title suggests: a HTHA primer. Since the information is provided in a condensed format, we recommend printing and laminating copies that can be referenced by you and your co-workers at your convenience.
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