Chemical & Process Technology: High Temperature Hydrogen Attack in metal & alloy

Friday, September 14, 2007

High Temperature Hydrogen Attack in metal & alloy

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.

Recent Activities On High Temperature Hydrogen Attack

"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 Japan.

In USA, API summarized these data as Publication 941 – “Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants” in 1970 and, since then, it has been widely used for material selection in hydrogen service, operation and maintenance in petroleum and petrochemical plants. In Japan, some organizations such as JSM, JPVRC and PVT have been tackling HTHA problems since 1970’s, and they suggested some assessment procedures for HTHA. Importance is how to evaluate this equipment to keep plant integrity."