Mechanical Behaviors And Reliability Analysis Of Steel Strip Reinforced Flexible Pipes

Steel strip reinforced flexible pipe(SSRTP)is regarded as promising alternative for submarine pipelines for its good performances and characteristics.During the operation and service phases,SSRTP will inevitably experience significant environmental loads as well as the service load and a number of uncertainties,which represent great challenges.Those are important aspects affecting the integrity and security of the SSRTP's utilization in installation and service.In order to ensure the security and reliability of SSRTP in the application,the mechanical responses of SSRTP subjected to different load conditions and the corresponding design safety factors should be carefully estimated.The major research contents are summarized as follows:1)Buckling stability of SSRTP subjected to external pressureThe collapse behaviors of SSRTP subjected to external pressure are investigated experimentally and numerically.A hyperbaric chamber is utilized to conduct the full-scale laboratorial tests of SSRTP,and the commercial software ABAQUS is used to simulate its collapse behavior.The results obtained from the experiments and the simulations are compared to verify the reliability and accuracy of the proposed finite element model.Also,a simplified estimation is presented to calculate the collapse pressure of SSRTP,which can be regarded as its lower limit value.In addition,a series of parametric studies were performed to investigate the influential factors on the collapse pressure of the pipe,such as the initial imperfection,the geometrical configurations,the friction coefficient between contact surfaces,etc.2)Behavior of SSRTP under combined bending and external pressureThe collapse response of SSRTP as a result of the combined loading is simulated by ABAQUS.The accuracy and reliability of the proposed FEM is verified by the good agreement with the results obtained from the full-scale laboratorial test.The influence of initial bend radius and additional parametric study on the collapse buckling was discussed throughout the proposed model.3)Mechanical behavior of SSRTP subjected to tensionA finite element model that takes into account of the geometrical and material nonlinearity as well as the sliding and friction interactions between the layers is created using ABAQUS.Full-scale laboratorial tests involving SSRTP under pure tension is conducted.The relationship between the axial load and the extension of SSRTP acquired from the experiment is compared with that of numerical simulations.Good agreement between the two sets of results illustrates the accuracy and reliability of the established finite element model.The detailed responses of the PE and reinforcement layers of the pipe under pure tension are analyzed.The impact of the steel strip reinforcement layers in undertaking the axial tension load and the effect of friction coefficient between the layers are also studied.4)Mechanical behavior of SSRTP under combined axisymmetric loadsA theoretical model estimating the tension stiffness under axisymmetric loads is established,which takes the PE material's plasticity into consideration.Additionally,a finite element model is developed by ABAQUS to verify the feasibility of the proposed theoretical model,and the results from full-scale tensile tests of SSRTP are also adopted to verify its validity in calculating the tension behavior.Based on the parametric study,some interesting conclusions can be obtained which may be useful for the practical application of SSRTP.5)Reliability-based safety factor for SSRTPReliability-based safety factors for SSRTP are calibrated,which mainly takes the loading case of external pressure as example.The partial safety factors are obtained by introducing a target reliability index and using a combination of Monte-Carlo simulation&FORM.The relationship between the safety factors and the coefficient of variation for key basic variables as well as the impact of different distribution types for both the resistance and load effect parameters on the calibrated results are investigated.Recommended design safety factor for SSRTP is given similar to the widely used design safety factor for conventional metallic pipes.The calibration process presented in this thesis is relatively easy to understand and to carry out.This also applies to cases with multiple components and even requiring complex iterations in relation to the mechanical model.