Attack (HTHA) Inspection
High-temperature hydrogen attack (HTHA) is observed in steel that is exposed to a temperature of 200 °C or more. At such a high temperature, atomic hydrogen diffuses in steel. This hydrogen reacts with carbon present in the steel and forms CH4. The methane that is formed bubbles and creates voids at the grain boundary.
MC + 4H = M + CH4
These bubbles exert pressure and also coalesce into fissures. The growth of voids and fissures weakens the metal, which leads to a major crack. This reaction decarburizes the steel, produces micro cracks/fissures and lowers toughness of steel but may not cause a loss in thickness.
- Supports the Inspection of large and wide areas
- Provides accessibility and convenience as external access is required only on one side (Opening of equipment or removal of the catalyst is not required)
- The depth of attack can be estimated
- Deep expertise required in interpretation
- Ignitial micro level degradation (Decarburization) cannot be estimated