Fatigue Resistance Design Of Umbilical Of Subsea Production

The subsea production system is an effective and economical development mode for the oil and gas exploitation in deepwater field. Umbilical provides electrical or hydraulic power, monitoring control signal and chemical injection for the subsea production system and is one of the important equipments of subsea production system.The umbilical bear harsh loads under installation and running in a tough environment. One of the most important damages is fatigue damage caused by floating body movement and environmental load. The failure of umbilical can lead to serious economic consequence. So the structure of the umbilical cable should be designed with the consideration of resistance of fatigue. However, it has a complex structure composed of multilayer and various materials with helically winding and non-adhesive form, which will lead the importance of consideration of the nonlinear stress of umbilical cable to predict its fatigue life. This work relies on the National High Technology Development Project (863Project)"Key Technology Research of Umbilical in Subsea Production System". Thus fatigue life analysis based on finite element analysis technique is utilized to study the fatigue life analysis and design of umbilical. The main work is as follows:1. Basic theories and methods of fatigue life analysis of umbilical of subsea production. Fatigue resistance design criteria and design methods of marine engineering structures are systematicly summarized. Finite-life design based on nominal stress method are introduced. Main factors that affect fatigue life are discussed. Fatigue resistance design and analysis model of marine structures are summarized detailed, especially umbilical anti-fatigue design process is summarized.2. Nonlinear stress analysis is carried out for the key components of subsea production umbilical. A fully three-dimensional finite element model of the dynamic umbilical is established considering the frictions and contacts between its components. The nonlinear stress state of steel tubes of the umbilical under different loads has been analyzed with the established FE model. The technique proposed in this manuscript will provide further understandings and technical tools for the application of the dynamic umbilical.3. Accurate umbilical fatigue life is predicted basing on a Spar offshore platform of the South China Sea, considering nonlinear stress distribution of the key components with the help of post development of the software of Orcaflex. It is different from the linear stress distribution assumption of traditional engineering design of structure of umbilical. Restructuring fatigue life analysis processes and analytical models of nonlinear stress of steel pipe of the umbilical are utilized to analyze fatigue life of umbilical under bending and tension.4. Influence of filler on umbilical fatigue life. Two-dimensional finite element model of the umbilical is established to analyze the effects of two filler configurations, dense filler and frame filler. Influence of different filler materials, different filler configuration and nonlinear material properties on fatigue life is quantitative are analyzed.