Preparation Of Polyurethane Gradient Material And Its Application In The Bending Stiffener

The bending stiffener is one of the most important equipment in the marine oil development process.It is mainly installed in the connection of flexible risers and umbilicals and floating equipment,so as to ensure that the flexible risers and umbilicals do not have excessive bending damage in various marine conditions.Polyurethane elastomer with high wear resistance,high elasticity,high strength,hydrolysis resistance and other excellent comprehensive properties,which is an ideal material for manufacturing bending stiffener of flexible risers and umbilicals.The structure of bending stiffener of flexible risers and umbilicals usually adopts three-section conical shape to realize smooth transition of bending rigidity.The polyurethane functionally graded material is a kind of material with the gradient of the performance along a certain direction.Polyurethane gradient materials with gradual elastic modulus can also realize the transition of bending rigidity.Therefore,the objective of this research is to prepare a kind of polyurethane gradient material with gradual elastic modulus and apply it to bending stiffener.First,casting polyurethane elastomer was prepared by semi-prepolymer method,and the effect of hard section content on its properties was studied.The structure and properties of the polyurethane elastomers were tested by infrared spectroscopy(FTIR),scanning electron microscope(SEM),tensile test,hardness test,viscosity test and thermogravimetric(TG).The results showes that the polyurethane elastomer was prepared successfully and the microphase separation structure was obvious.The study shows that with the increase of the content of the hard segment,the viscosity of the reaction liquid rises,and the life of the kettle reduces,and the thermal stability of the material increases.The content of the hard segment increases from 22.0% to 45.0%,the tensile strength and elongation at break increases first and then decreases,and the shore hardness increases from 60 A to 93 A,and the tensile modulus increased from 12 MPa to 106 MPa.Secondly,the CM grade polyurethane gradient materials were prepared by layer by layer pouring method,and their structure and properties were characterized by infrared spectroscopy(FTIR),scanning electron microscope(SEM),hardness test,absorbance test and tensile test.The infrared spectrum analysis shows that the position and shape of the stretching vibration peak of the amino and carbonyl groups changes obviously along the gradient direction,which proves that the structure of the material changes gradually.The same conclusion is drawn in the scanning electron microscope.The size of the hard section decreases and the distribution is more well-distributed along the gradient direction.The related properties show that the hardness and absorbance decrease gradually along the gradient direction.The tensile test along the gradient direction of polyurethane gradient material shows that the strain inside the material increases gradually along the gradient direction,which proves that polyurethane gradient materials with gradual elastic modulus have been prepared successfully.Finally,on the basis of polyurethane gradient material,a new concept of cylindrical bending stiffener was put forward.According to the practical application examples,the material design,size design and connection design based on the polyurethane gradient material bending stiffener are carried out,and the design results are analyzed with the finite element software.The results of finite element calculation show that the curvature of the flexible risers and umbilicals in the polyurethane gradient material bending stiffener protection section is less than the maximum curvature of the design,and the curvature distribution is hook,which proves that the polyurethane gradient material bending stiffener can protect the flexible risers and umbilicals.The cylindrical bending stiffener based on the polyurethane gradient material has the simple shape and can meet the design requirements of different working conditions through material design,which improves the utilization rate of the mould.At the same time,the polyurethane gradient material bending stiffener has a small volume,which improves the safety in use and economic performance to manufacture.