SPE Projects, Facilities & Construction
Volume 4, Number 4, December 2009, pp. 106-123

Summary

Estimating fatigue damage under wind-driven sea loading is of primary importance in the design of steel catenary risers (SCRs) serving floating hosts. For design, the wind-driven sea is modeled as a stationary random process. The resulting dynamic stress in the SCR is also a stationary random process. Spectral methods provide closed-form fatigue damage estimates in terms of statistics for stationary random stress processes. Cycle-counting methods, such as rainflow cycle counting, provide an alternative damage estimation approach that is generally applicable and requires simulation of stress time series. The cycle-counting approach requires more computation than spectral methods. Damage estimates using the cycle-counting method may be lower than spectral damage estimates; however, a substantial amount of simulation may be required to quantify the difference.

This paper considers fatigue damage in SCRs attached to both tension-leg platform and semisubmersible hosts. Spectral and cycle-counting estimates are generated and compared. Accuracy of the estimates is discussed, and guidelines for damage estimation are presented. It is demonstrated that the differences between spectral and cycle-counting estimates of lifetime fatigue damage arise primarily from assumptions made regarding the spectral shape of the stress processes of interest.

© 2009. Society of Petroleum Engineers

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History

• Original manuscript received: 18 February 2008
• Meeting paper published: 5 May 2008
• Revised manuscript received: 23 March 2009
• Manuscript approved: 28 March 2009
• Published online: 14 January 2010
• Version of record: 14 January 2010