Analysis Of Ultimate Bearing Capacity Of T/TT Pipe Joints Of CFRP-reinforced Marine Jacket Platform

Fixed jacket platform structure is mostly used in oil production platforms of shallow sea oilfields.The working environment of jacket platform is very risky,which will cause irreversible corrosion damage to offshore platform due to long-term erosion by sea water.Once corrosion occurs,the bearing capacity of the platform will be reduced.Tubular joint is an important part of jacket platform,which plays a vital role in the strength of the platform.In order to improve the bearing capacity of the joints,increase the safety factor of the platform and prolong the service life of the platform,the commonly reinforcement methods are grouting clamp reinforcement,external stiffening rings reinforcement,doubler plates reinforcement and doubler plate.Although the above-mentioned methods significantly improve the bearing capacity of tubular joints,there are still many shortcomings.At present,most of the reinforcement means need to be welded Welding reinforcement will produce residual stress and welding defects,which will affecting the durability and aesthetics of the structure.Carbon Fiber Reinforce Polymer(CFRP)have some advantages,such as high strength,welding-free,flexible operation and short repair cycle.The elastic modulus of CFRP is similar to that of steel,which is conducive to the coordinated deformation between CFRP and defective pipeline,thus achieving the purpose of reinforcing.CFRP has very strong tensile strength along the fiber direction,and the fiber itself is very soft.These determine that CFRP can formulate reasonable reinforcement schemes for different structures and damage status of the platform,so as to realize the comprehensive optimization of platform maintenance schemes.In this paper,the effectiveness of CFRP to improve the static performance of tubular joints is studied by means of test and finite element simulation,which provides theoretical basis and technical guidance for practical engineering application.The main research contents are as follows:1.Two sets of T/TT tubular joints with corrosion defects were designed by scaling the size of T/TT tubular joints in jackets of existing offshore platforms.The strengthened and unstrengthened T/TT tubular joints were tested under axial compression.The failure modes,deformation and ultimate bearing capacity of CFRP strengthened tubular joints and unreinforced tubular joints were observed.2.Based on ABAQUS finite element analysis software,T-joints and TT-joints before and after reinforcement were simulated respectively,and the correctness of the model was verified.Sixty T-joints with different size parameters and Sixty TT-joints with different size parameters were selected.The finite element analysis model of CFRP strengthened tubular joints with different dimension parameters(diameter-thickness ratio of chord,diameter ratio of brace to chord)was established.The influence of diameter-thickness ratio of chord,diameter ratio of brace to chord and the number of CFRP strengthened layers on the ultimate bearing capacity of tubular joints was studied.3.Aiming at the present situation of dent damage of tubular joints in practical engineering,two T-joints with different size of dent defects were established based on the correct finite element analysis model,and the effect of dent defects on the ultimate bearing capacity of tubular joints was studied.CFRP was used to reinforce T-joints with dent defects,and the reinforcement effect of winding 5-layer and 10-layer CFRP on T-joints with dent defects was studied.