Multiaxial Fatigue Analysis on Reeled Steel Tube Umbilical

Multiaxial fatigue analysis on reeled steel tube umbilical is proposed based on finite element analysis (FEA) results. Due to the complexity of the umbilical geometry, the stresses and strains field becomes multiaxial, worsening the fatigue resistance. The reel-lay method is one of the most efficient and cost-effective methods of umbilical installation. However, if installed by the reel-lay method, material properties of the umbilical change may have an influence in fatigue performance of the line. Finite element analysis is applied with contact formulation, and the load history through the reel, aligner, and straightener is simulated. The strain history of the whole modeling process in the critical element is given, and the properties' change after the load history is discussed. Then, the principal stress criterion and the Brown-Miller criterion (both combined with the critical plane approach) based on FEA results are used to do fatigue life prediction of reeled and nonreeled models. The results indicated that a reel-lay method has a great influence on the fatigue life of steel tube umbilical, so the influence of installation on the steel tube umbilical fatigue must be considered when the reel-lay method is adopted.