Optimization Design And Evaluation Of Flexible Composite Pipe Joint For Onshore Oil And Gas Fields

In oil and gas resources transportation engineering,pipeline gathering mode has advantages of high efficiency and low cost compared with road and railway gathering mode,so it has gradually become the main gathering mode of oil and gas resources.Traditional metal gathering and transportation pipelines are prone to corrosion and perforation failure phenomenon,leading to uncontrollable leakage of oil and gas resources.In order to avoid this problem as far as possible,flexible composite pipes with excellent corrosion resistance are widely used in the gathering and transportation projects of onshore oil and gas field pipelines.In the pipeline gathering and transportation project of onshore oil and gas fields,the pipes of flexible composite pipes are connected by metal clamped joints.The rationality of the zigzag structure of the metal clamped joints plays a decisive role in the safe service of the pipeline system.Structural incompatibility leads to fracture damage and destruction of the composite pipes as well as the failure phenomenon of pulling out,resulting in serious waste of resources and economic losses.Therefore,in this paper,3D modeling and simulation methods are used to optimize the size and structure design of metal clamping joint sawtooth structure of aramid fiber reinforced thermoplastic composite pipe,so as to provide technical support for material selection at the field gathering and transportation of oil and gas fields.The main work of this paper is as follows:(1)Selected flexible composite pipe nominal size DN100 aramid fiber reinforced thermoplastic composite pipe,nominal pressure is 6MPa.The materials used in the inner and outer layers and reinforcing layers of the aramid fiber reinforced thermoplastic composite pipe,namely high-density polyethylene and aramid fiber,were sampled in multiple groups.The tensile fracture strength,plastic strain and true stress values of the outer layer and reinforcing layer of the composite pipe were obtained by tensile test and numerical calculation,which provided data for the subsequent finite element simulation.(2)According to the relevant standards of oil tubing and the entity of the clamping joint,316 L stainless steel was selected as the metal clamping joint material.After dimensioning the joint and composite pipe,3D models of conventional clamping joint and piping system and new clamping joint and piping system were established and substituted into Abaqus for simulation.Taking the tensile fracture strength of the outer tube and the reinforced layer as the failure criterion,the stress and strain on the outer tube and the reinforced layer were analyzed after the ultimate working internal pressure load of 18 MPa was applied to the two kinds of clamping joints and piping system.In the conventional clamping joint and pipeline system,the maximum shear stress at the contact between the serrated joint structure and the inner layer of the composite pipe is 25.46 MPa,and the maximum shear stress borne by the outer layer of the composite pipe is 25.65 MPa.In the new type of clamping joint and piping system,the maximum shear stress on the surface of the inner high-density polyethylene layer of the composite pipe is24.95 MPa,and the maximum shear stress on the outer surface of the composite pipe is25.16 MPa.According to the above simulation results,the maximum shear stress on the outer layer of the composite pipe is greater than the required shear stress of high-density polyethylene21.9669 MPa after the connection between the two kinds of joints and the composite pipe,which indicates that the two kinds of joints are unreasonable,causing damage and damage to the aramid fiber reinforced thermoplastic composite pipe.(3)The tooth height size of the clamping joint saw tooth structure is too large,and the protruding tooth tip relative to the outer surface of the inner core tube and the inner surface of the outer sleeve will aggravate the fracture process of the outer layer of the composite tube when under pressure,and to some extent improve the possibility of failure of the outer layer of the composite tube.Therefore,the optimization treatment will be carried out to reduce the tooth height of the joint and keep the length of the tooth tooth unchanged.According to the requirements of structural strength and sealing performance,the optimal size of the tooth structure of the two kinds of clamping joint is obtained.The optimal size of the tooth structure of the conventional clamping joint and the new clamping joint are as follows: the tooth height of the conventional clamping joint is 1.6mm,the tooth length is 16mm;The optimum size of the new type of clamping joint sawtooth structure is 1.75 mm tooth height and 16 mm tooth length..The comparison and evaluation of two kinds of clamping joints with different serrated structures show that the maximum contact pressure between the new clamping joint and the inner layer of the composite pipe is obviously less than that between the conventional clamping joint and the inner layer of the composite pipe,which reduces the possibility of failure of the composite pipe.The superior performance of the new type of clamping joint proposed in this paper is highlighted.