Design And Performance Study Of Thermoplastic Flexible Pipe Materials For Marine Environment

With the development and explore of deep-sea oil and gas resources,the demand of submarine pipelines is increasing day by day.However,steel pipes are mainly vised for the oil and gas transportation in China,and corrosion problems are prominent.Due to the excellent characteristics of light weight and corrosion resistance flexible pipes,which have become the development trend of ocean pipelines.In this study,according to the service environment of marine flexible pipes,the composite thermoplastic flexible pipes have been proposed.The effects of fusion technology and laying methods on the properties of thermoplastic pipes are analyzed,and the service properties of thermoplastic resins and composite plates are investigated.Based on the application background and investigation and analysis,thermoplastic PE and PP resins were chosen as alternative materials for inner and outer lining,respectively.Thermal analysis showed that the melting temperature of PE resin was lower than that of PP resin;the tensile and compressive strengthes properties of PP resin and room temperature were better than those of PE resin.Though the strength properties of PE and PP resin are decreased at 80?,the strength of PP was still higher than that of PE;the friction coefficients of PE and PP were lower under low and high loadings,and the friction coefficients of PP resin were lower than those of PE,but the friction coefficients of PP resin were lower under low loads.The loss rate is higher than PE,but it is opposite under high loadings With the increase of ambient temperature,the compressive strength of PE and PP decreased,while the compressive strength and tensile strength of PP were higher than those of PE.In seawater and oil environment,the quality of PE and PP both were changed slightly,the moisture absorption rate was low,the tensile and compressive strengthes also were decreased slightly,but the tensile strength and yielding strengthes of PP were higher than those of PE.According to the data support and analysis obtained from the experiments,PP resin was determined to be the outer protective layer material for flexible pipes and PE resin was the inner lining materialThe glass fiber reinforced polypropylene composite material was selected as the reinforcing layer material of thermoplastic flexible pipes for marine environment through service environment and investigation and analysis.Thermal analysis shows that the optimum melting temperature,pressure and time of glass fiber reinforced polypropylene composite plate are 200?,4500 Pa and 300 s,respectively;the hardness of glass fiber reinforced polypropylene composite prepared under the optimum melting condition is 12.3 HV,and the interlaminar shear strength is 17.3 MPa;with an increase of the angle of the lamination,the shear strength decreases,the number of layers in the direction of 0°increases and the shear strength increases.The increase is approximately linear;the closer the angle is to 90°,the lower strengthening effect of glass fiber tape on tensile properties;with the increase of cross angle of fibers,the hardness decreases slightly.The uniform and stable performances can be obtained by using the cross-laying method with different angles of overlay seam arrangement.The interfacial bonding quality between fibers and resins is significantly improved when the fusion temperature is 200?,the fusion pressure is 4500 Pa and the fusion time is 300 s.In the environment of seawater and oil,which both have little effect on the mechanical properties of glass fiber reinforced polypropylene composite plate when the soaking time is less than 13 days.The soaking test at 60? accelerates the process of corrosion.The mechanical properties of glass fiber reinforced polypropylene composite plate in the soaking test at 60? all decrease faster than that in the normal temperature soaking test.At the same soaking temperature,the mechanical properties were decreased with the increase of soaking time.The results show that the glass fiber reinforced polypropylene composite plates has a better service performance in seawater and oil environment.