Design And Strength Analysis Of Key Components Of Flexible Pipes For Deep-Sea Oil And Gas Transportation

At present,the transportation of oil and natural gas mainly relies on steel pipelines in China.Now corrosion of metal pipelines is becoming more and more serious.If the leakage accidents happens,it will not only affect the safety of production,but also cause immeasurable property loss and environmental pollution.Because of the reason,the research and application of non-metallic pipes are derived.In particular,the research on composite flexible pipes has attracted the attention of countries all over the world.Compared with rigid pipes,flexible pipes are more convenient to install and recycle due to their soft structure.The longer manufacturing length can reduce the use of connecting fittings and end fittings..Therefore,this paper selects the thermoplastic glass fiber reinforced flexible pipe as the research object,and carries out some basic research on its pipe body strength,joint structure,assembly process,special joint strength,pipe body in-situ strength,etc.The specific research work is as follows:(1)According to the design index and service environment of the thermoplastic glass fiber reinforced flexible pipe,it is determined that the material of the inner lining layer and the outer protective layer is high-density polyethylene with a thickness of 6 mm,and the material of reinforcing layer is glass fiber tape with a thickness of 24 mm;According to API RP 17 B standard,the strength of flexible pipes is checked based using this structure.The load types include: internal pressure load(30MPa);burst pressure load(90MPa);external pressure load(5MPa);Maximum tensile load(60T);combined load of internal pressure and external pressure(30 MPa and 5 MPa).The analysis results show that the designed flexible pipe body structure meets the requirements of the design index;(2)The characteristics and basic working principles of different flexible pipe joint types have been compared.Finally,the mechanical crimping joint is selected as the special joint type of thermoplastic glass fiber reinforced flexible pipe.According to the requirements of API RP17 B standard and the service environment of the joint,316 L stainless steel is selected as the material of special joint of thermoplastic glass fiber reinforced flexible pipe,and the crimping size of the special crimping joint for flexible pipe designed to ensure its service life and connection performance is calculated by empirical formula is 16.4mm;In order to ensure the reliability of the design,the finite element modeling and buckling performance analysis of the designed buckling joint are carried out.It is found that the connection performance requirements can be met when the internal expansion of the inner core of the joint is 5 ～ 5.9mm(radius direction)and the buckling of the outer sheath is 3.5-5mm(radius direction);The processed joint was installed and tested by blasting test.When pressurized to 90 Mpa,the pipe body and joint were not damaged,so the pipe body and special joint both met the design requirements;(3)According to the environmental condition parameters and the design requirements of DNV RP F109 for the stability of submarine pipelines,10-year return period waves +100-year return period currents are selected as the check conditions for the thermoplastic glass fiber reinforced flexibility designed and processed in this paper.The tube chooses a circular counterweight as its stabilization plan.At this time,its specific gravity is SG>1,and its lateral stability and vertical stability are less than 1,which meets the requirements of in-situ stability;,initial buckling,extended buckling,local buckling,combined stress and other aspects are checked,the results show that the design thickness 24 mm can meet the requirements;the finite element simulation analysis method is used to check,the results show that under the environment of 500 m water depth,the equivalent Mises stress of the inner lining layer and outer protective layer of thermoplastic glass fiber reinforced flexible pipe are 19.83 MPa and 16.47 MPa;respectively,which are lower than the yield strength of HDPE,which is 21 MPa.The calculation data of the reinforcement layer is substituted into the Hill-Cai strength theoretical calculation formula,the result is 0.03386,less than1,so it can meet the use requirements of in-situ strength.