S-N curves for welded tubular joints
- NCEL, Urbana, IL (United States)
The objective of the project was to develop a welded tubular joint database to assess the fatigue design curves (X and X{prime}) in the American Petroleum Institute design code (API RP2A). Changes in the curve-fitting method and screening criteria (primarily the exclusion of the very thin tubular joints) produced results different from those reported previously. The current results show that the X and X{prime} curves are too conservative and that a new curve should be adopted. The Department of Energy T{prime} curve was found to be consistent with the screened tubular joint air data and is recommended for use in API RP2A. The weldment size effect exponent (n) of 0.25 in the current version of API RP2A was found to be too small, and a higher value of 0.30 consistent with the Department of Energy recommendations is recommended. The fatigue test results for tubular joints tested in air and tubular joints tested in sea water with cathodic protection are the same at long fatigue lives. At short fatigue lives, tubular joints tested in sea water with cathodic protection exhibit fatigue lives a factor of 2 shorter than tubular joints tested in air. Tubular joints tested in sea water under conditions of free corrosion exhibit fatigue lives a factor of 3 shorter than tubular joints tested in air at both long and short lives. This study confirms the recent recommendations of the DOE as regards the suitability of the T{prime} curve and their recommended design curves for freely corroding and cathodically protected tubular joints tested in sea water.
- OSTI ID:
- 205408
- Report Number(s):
- CONF-950695--; ISBN 0-7918-1309-6
- Country of Publication:
- United States
- Language:
- English
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