Progressive Damage Analysis Of Deep-sea Composite Risers

With the development of oil and gas resources to the deep sea,marine riser,which is an important component of the deep-sea oil and gas development system,has been difficult to meet the requirements of the design by using the traditional steel riser.The composite riser has many advantages over the metal riser,such as high specific strength,high specific stiffness and corrosion resistance.It has become a new choice for deep-sea riser design.However,composite materials are prone to damage due to their own defects in complex marine environment,which will cause incalculable losses.Therefore,the study on the damage of composite riser has important theoretical significance and practical value.The damage of composite materials is a gradual process.This paper is based on the principle of progressive damage,and simulated the damage process of composite materials by compiling the user subroutine function of finite element software.First of all,this paper studies the influence of the composite layer angle and the order of layer on the initial load,damage type,ultimate load and damage expansion.Then,the article with simplified structure of the marine riser,which is the composite riser with the metal liner and composite outer wrapped,as the object of the research,studies the effects of different structural design parameters on the strength of the composite marine riser and the failure of the different regions of the composite layer under the three stages of the inner lining metal deformation(elastic,plastic and failure).Finally,considering the possible problems in the actual production of the marine riser,a composite marine riser with an initial crack in the metal lining is designed,and the effects of the different initial crack size and the position of the initial crack on the damage of the marine riser composite layer are explored.This paper provides a theoretical reference for the application of composite materials in marine risers.From the above research results,found that the larger the layer angle,the smaller the initial load of the riser,the more single damage form and the smaller the axial strength,in addition,the design of the[0°/45°/-45°/90°]_T layer is more beneficial to the structure resistance to the axial tension load.The thinning of the lining of the riser makes the stress increase in the thickness direction,and the structure is destroyed in advance,which is not conducive to the internal pressure of the structure.When the winding angle at the interface between metal and composite material is 45°,the reduction rate of stress at interface is the maximum,and its resistance to pressure is stronger.The composite material loses most bearing capacity in the stage of metal plastic deformation.The boundary area of the riser controls the initiation and development of the structure radial damage,and the stress in the middle section of the riser is stable along the thickness direction,and it is not easy to cause damage.The initial crack has significant influence on the bearing capacity of the opposing tube.The increase of the deep and long size will make the cracking pressure of the metal lining and the damage initial load of the composite layer decrease,and the change of depth has a greater influence.Compared with the axial crack in the middle of the riser,the initial crack in the near end has a great influence on the damage of the metal lining layer,and has little effect on the damage of the composite layer.