SINTEF/TWI joint study on fatigue of tubular joints: Overview and background
- Norwegian Inst. of Tech., Trondheim (Norway)
- TWI, Cambridge (United Kingdom)
Fatigue design of tubular joints is based on SN curves. The design curves are essentially empirical and have been derived by a procedure which on a notional basis corresponds to a lower 97.7% confidence limit of experimental data, i.e. a notional probability of failure of approximately 2.5%. It follows that the appropriateness of the curves is crucially dependent on the experimental data being representative of real life structural behavior. Key words in this respect are: geometry, size of test models; materials, welding, technological factors; load configuration, load history; environment; duration of tests, number of cycles to failure; assessment of a characteristic stress. The current fatigue design curves, which are applied for North Sea structures, are based on the 1984 revision of the UK Department of Energy Guidance Notes. The basic SN curve was derived from tubular joint data which were obtained by testing various tubular joint geometries under constant amplitude loading in air. After derivation of a 95% confidence band, the following assumptions were made, essentially on the basis of small scale testing: Variable amplitude loading may be accounted for by a cumulative damage calculation, with the implicit assumption that failure will occur at a damage sum of unity. The fatigue limit was taken at N=10{sup 7}, and modeled according to Haibach; Under cathodic protection, the fatigue life in sea water is the same as in air; Effect of size may be accounted for by a plate thickness correction, {Delta}S={Delta}S{sub o}(t{sub o}/t){sup 1/4}. The Norwegian offshore structures code and design recommendations have adopted the UK code, although the code applies a more conservative assumption concerning the fatigue limit (taken at N=2{center_dot}10{sup 8} with a horizontal cut-off).
- OSTI ID:
- 27935
- Report Number(s):
- CONF-940230--; ISBN 0-7918-1266-9
- Country of Publication:
- United States
- Language:
- English
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