Analysis And Design Of The Sealing System In Unbonded Flexible Pipe End Fitting

End fitting is a necessary accessory for unbonded flexible pipe, which provides connect and seal functions for link between the pipe and the terminal. The sealing system determines the operating pressure and the application depth of pipeline. Typical sealing systems of end fitting are implemented basing on a contact pressure effect. The current research of unbonded flexible pipe has just started in China, and the sealing performance of the end fitting is behind international average level, which severely restricted the use of domestic pipeline.Firstly, this paper introduces the structure characteristic of unbonded flexible pipe and end fitting. The current situation of research and application in sealing system is stated, which clarifies the significance of this study. Secondly it introduces the common seal problems in engineering, and focuses on the static sealing principle and method. Analysis method of those sealing methods relying on contact pressure effect is summarized and corresponding seal criteria is discussed and presented. Hertz contact theory is introduced, and the calculation code for the contact between cylindrical and elastic-plastic half space is established. Thirdly the seal performance of serrated tooth which is a typical structure on contact surfaces, is analyzed via theoretical and numerical method. The sealing performance under different cross-sections and materials is discussed. The conclusion is that the circular tooth has a better performance, and the materials with high Young's modulus and high yield strength behave better. The amplification factor is introduced to simplify the analysis of sealing structure with serrated tooth. Fourthly, a seal ring for end fitting is designed through contact pressure calculation amplification factor and seal criteria. Then sensitivity analysis, seal testing and self-sealing performance analysis are also performed via numerical method. Finally the acceptance test of sealing system inside end fitting is designed and conducted. Considering the introduced acceptance criteria, test data show that the sealing system is qualified to the service conditions.Research of this paper is sponsored by Hi-Tech Research and Development Program of China (863 Program,2012AA090314). This work has guiding significance for the analysis and design of the sealing system in flexible pipe end fitting in China.