Friday, September 14, 2007
High Temperature Hydrogen Attack (HTHA) is a form of degradation caused by hydrogen reacting with carbon to form methane in a high temperature environment.
C + 4H --> CH4
The methane forms and stays in grain boundaries and voids however it does not diffuse out of the metal. Once it accumulated in the grains and voids, it expands and forms blister , weaken the metal strength and initiate cracks in the steel.
High-strength low-alloy steels are particularly susceptible to this mechanism, which leads to embrittlement of the bulk parent metal (typical C-0.5 Mo steels). The embrittlement in the material can result in a catastrophic brittle fracture of the asset.
Following is a picture of Blistering in metal due to High Temperature Hydrogen Attack.
This paper summarizes the research and investigation activities related to HTHA, including the general information about HTHA.
"Exisitng C-0.5Mo steel in hydrogen service is still our concern in industries. High Temperature Hydrogen Attack (HTHA) has been one of the major problems in petroleum and petrochemical industry because of its effect. Since the original Nelson Curves was suggested in 1949 to define the operating limits for steels used in hydrogen service to avoid HTHA, a number of research and investigation activities on HTHA have been carried out mainly in The United States and
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