Research On Bearing Capacity And Structure Optimization Of Clamp Joint Of Fiber Reinforced Plastic Composite Pipe

In the process of pipeline installation and service,the joint is the most critical and most vulnerable part of the entire pipeline system.Metal buckling joints have become the first choice for the connection of fibre-reinforced plastic composite pipes for oil and gas gathering and transmission due to their high strength,strong pull-off resistance,easy and fast installation and low cost.In order to ensure the safe and stable transmission of oil and gas pipeline systems,and to make them withstand various loads while having good load-bearing and sealing performance,this paper uses finite element software to simulate the buckling process of fibre-reinforced plastic composite pipes and their buckling joints,to optimise the buckling amount of joints,to investigate the load-bearing performance of pipes and joints under different loads,and to establish the connection between the structural parameters of joints and sealing performance,so as to effectively guide the use and optimisation of these composite pipe joints.This study was carried out to investigate the load-bearing performance of pipes and joints under different loads,and to establish the relationship between the structural parameters of joints and sealing performance,in order to effectively guide the use and optimisation of these composite pipe joints.The main research contents and results are as follows:The finite element clamping assembly model of DN150/ PN2.5MPa fiber-reinforced plastic composite pipe and its clamping joint was established by using ABAQUS finite element software,and the simulation results were close to the burst pressure of the actual pipe hydrostatic test with a relative error of only 3.54%,indicating that the established finite element model was accurate and reliable.Based on the sealing principle of the buckled joint,the sealing criterion of the joint was proposed,and the maximum contact stress and effective sealing area on the sealing surface of the pipe and the core tube of the joint were used as the basis for judging the sealing performance;the influence of the assembly buckling amount on the sealing performance of the joint was analyzed,and the optimum buckling amount of the joint was determined to be 5.5 mm.Based on the above finite element model,the ultimate load carrying performance of the pipe system was analysed under a single internal pressure,tensile and torsional load,and the influence of the structural parameters(tooth angle,tooth height and number of teeth)on the sealing performance of the joint core tube was investigated.It was found that the ultimate loading values for the pipe system were 13.504 MPa internal pressure,84.7 mm tensile length and 0.821 Rad torsional radius,and that the sealing performance of the joints decreased with increasing internal pressure and tensile load,but improved with appropriate torsional load.In addition,increasing the height of the joint’s teeth can effectively improve the sealing performance of the pipe body,but the angle of the joint’s teeth and the number of serrations should not be too large or too small,otherwise the interference between the pipe and the joint is not conducive to contact.Based on the single-load analysis,the load-bearing and sealing performance of the piping system under combined load was further investigated.It was found that when the piping system was subjected to a combined internal pressure and tensile load,the maximum contact stress on the sealing surface of the pipe and the effective sealing area were significantly reduced,and the tensile limit value under the combined load decreased by a quarter compared to that under the single load,indicating that the pipe had a certain negative impact on the tensile performance of the joint in normal service;when the piping system was subjected to a certain torsional load under the internal pressure load,the When the pipe system was subjected to a certain torsional load,the sealing performance of the joint improved and the limit value of torsional arc was close to the limit value of single torsional arc,indicating that the torsional load had less influence on the bearing and sealing performance of the pipe system.Under combined loads,the core structure parameters of the joint have the same effect on the sealing performance as under a single load,i.e.the saw tooth height effectively improves the sealing performance of the joint,while the tooth angle and number of teeth should not be too large or too small,but should be appropriate.The optimum core structure parameters were determined by comprehensive analysis to be 60° tooth angle,1.75 mm tooth height and 13 teeth.