Improved assessments of wave-induced fatigue for free spanning pipelines: Fid-Bau Portal

Improved assessments of wave-induced fatigue for free spanning pipelines

Sollund, Håvar A. / Vedeld, Knut / Fyrileiv, Olav / Hellesland, Jostein

Highlights • The dynamic response of free spanning pipelines to direct wave action is described. • An efficient time-domain algorithm for assessing wave-induced fatigue is developed. • Effects of multi-spans and multi-mode response are investigated for the first time. • Shortcomings of analysis methods from recognized design standards are identified. • Frequency-domain solutions accounting for multi-mode response are derived.

Abstract For subsea pipeline projects, the costs related to seabed correction and free span intervention are often considerable. Development of reliable methods for fatigue analyses of pipelines in free spans contributes to minimize costs without compromising pipeline integrity. Assessment of wave-induced fatigue damage on multi-span pipelines is investigated, and improved analysis methods are suggested in this paper. A time-domain (TD) algorithm is developed, which accounts for non-linear hydrodynamic loading and dynamic interaction between adjacent spans. The proposed TD approach is employed to evaluate linearized frequency-domain (FD) solutions from recognized design standards and to study the dynamic response of multi-span pipelines to direct wave loading. Differences between multi- and single-span analyses are described for the first time, and the common assumption that the main fatigue damage contribution comes from the fundamental mode is demonstrated not to hold for multi-spans. An improved FD solution capable of predicting multi-mode response is derived and demonstrated to give accurate fatigue life estimates for multi-span pipelines.