Axial Failure Analysis Of Non-bonded Flexible Riser Carcass Layer

The flexible riser is the transportation channel in the marine oil and gas production system,and its failure will bring huge economic losses and pollution of the marine environment.The flexible riser has a complicated structure,and each layer is composed of non-bonded assembly in a certain order,and there may be gaps between the layers.Under the external load,the flexible riser layers will exhibit complex mechanical properties,which has been a hotspot for research in industry and academic.At the 2013 OMAE conference,the Norwegian National Petroleum Corporation’s research team gave a detailed introduction to the tearing failure caused by the excessive axial force on the carcass layer.Therefore,it is significance to study the axial carrying capacity of the non-bonded flexible riser carcass layer.The paper studies the axial tearing mechanism of the carcass layer from the theoretical modeling and finite element numerical simulation to discuss the axial bearing capacity of the carcass layer:(1)The liner elastic theoretical model of the flexible riser under the axisymmetric load is established.The inner sheath outside the carcass layer is equivalent to a thick-walled cylinder,and the governing equation of the inner sheath is derived by the principle of elasticity-viscoelasticity correspondence.Considering the temperature variation along the radial direction,the time-temperature equivalent principle is used to obtain the variation of the strain and axial force of the inner liner along the radial direction.(2)This paper simplify the contact model between the inner sheath and the carcass layer,and use ABAQUS to simulate the shape of the inner sheath extruded into the carcass layer groove under the long time external pressure.The effects of the groove distance of the carcass layer,the external pressure and the thickness of the inner sheath on the creep of the inner sheath were analyzed.(3)This paper establishes a real three-dimensional model of the carcass layer and the inner sheath,simulates the shape of the inner sheath squeezed in the carcass layer.Considering the contact friction and the interlayer gap,the influence of the axial force generated by the inner sheath on the stress distribution and axial deformation of the carcass layer is analyzed.At the same time,it is also assumed that the inner sheath is neglected,the axial force is directly applied to the end of the carcass layer,and the friction loss of the carcass layer under the axial variable load is calculated by the energy conservation principle.