Publications
| Title | | Authors |
|---|---|
| Strength derating factors for pipeline steels operating at elevated temperatures « back |
D Benfell, P Morris and L Barsanti |
| 15th Joint Technical Meeting, Orlando, Florida, May 2005 | |
| Strength derating factors are used for pipelines and fittings, which operate in the region of gas compressor stations at temperatures above ambient. A number of codes provide guidance for such strength derating, but they are inconsistent in both the magnitude of strength reduction and the temperature below which such effects can be discounted. To assist in pipeline design, guidance is needed concerning the influence on properties resulting from exposure to elevated temperatures. A variety of mechanisms operate, even at relatively low temperatures, which can significantly influence both strength and ductility. The effects can be observed even after short-term exposure but the magnitude will vary with exposure time. A programme of work has been carried out to assess the effect that such elevated temperatures have on the tensile behaviour of pipeline steels. Codes specifying derating factors were first reviewed. A test programme was then carried out on UOE pipe covering grades X52 to X70 and test temperatures from ambient to 150oC. Results for all grades revealed a drop in 0.2% proof stress at 60oC when compared with initial room temperature values, followed by a levelling-out at temperatures above 100oC. These results showed a higher than expected loss of strength at the lower temperatures, although all steels still satisfied the specified minimum yield strength (SMYS) requirements for the particular grade. The results were verified with data supplied by EPRG members. The pipeline specifications reviewed do not have derating recommendations for temperatures below 100oC. The results from this work are presented together with a consideration of the mechanisms controlling strength derating and the treatment in different materials and design codes. Recommendations are made for the magnitude of the derating factor within different temperature ranges. | |
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