Metallurgical effect on hydrogen attack damage in C-0.5Mo steels
- Japan Steel Works, Ltd., Hokkaido (Japan). Muroran Research Lab.
- Fuji Oil Co., Ltd., Chiba (Japan). Dept. of Construction and Maintenance
- Chiyoda Protech Corp., Kawasaki (Japan). Dept. of Quality Assurance
- Idemitsu Engineering Co., Ltd., Chiba (Japan)
- Chiyoda Corp., Yokohama (Japan). Analysis and Materials Technology Center
- JSW Inspection Service Co., Ltd., Hokkaido (Japan)
Most equipment made of C-0.5Mo steel has been operating successfully for a long term in the petroleum and petrochemical industries. However, unusual incidents of hydrogen attack below the Nelson chart limitation imply that metallurgical variations such as microstructure and concentration of impurity elements have an important role in hydrogen attack resistance. The deletion of the Nelson curve is a major concern to the oil refining industry, which now has to assess the integrity of aged, existing equipment made of C-0.5 Mo steel. Engineering companies, vessel fabrications and oil refineries in Japan organized a private working group PVT to survey the past incidents of hydrogen attack by ultrasonic inspection and metallurgical examination. All damaged samples taken from retired vessels and piping after long term service possessed an unusual microstructure of proeutectoid ferrite and pearlite with quasi-carbides. On the other hand, all components with standard ferrite and acicular bainitic microstructures with Fe{sub 3}C were not damaged below the critical curve of Nelson chart 3rd edition. Autoclave exposure tests confirmed that these unusual microstructures transformed with slow cooling rates from austenitizing temperatures clearly cause significantly poorer hydrogen attack resistance in C-0.5Mo steels. Based on these surveys of the hydrogen attack incidents and laboratory scale examinations, a critical operating limit of temperature and hydrogen partial pressure was determined which accounts for variations in microstructure and the type of precipitated carbide.
- OSTI ID:
- 403564
- Report Number(s):
- CONF-960706--; ISBN 0-7918-1783-0
- Country of Publication:
- United States
- Language:
- English
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