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, stresses and strains field becomes multiaxial, worsening the fatigue resistance. Reel-lay method, is one of the most efficient and cost-effective methods of pipeline installation. However, if installed by 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 and formulation, and the load history through reel, aligner and straightener is simulated. The strain history of the whole modeling process in critical element is given, and the properties’ change after the load history is discussed. Then, principal stress criteria and Brown–Miller criteria (both combined with critical plane approach) based on FEA results were used to do fatigue life prediction of reeled and non-reeled model, respectively. The results indicate that reel-lay method does have a great influence on the fatigue life of steel tube umbilical, so the influence of installation on the umbilical fatigue must be considered when reel-lay method is adopted.