Instability Failure Analysis Of Sandwich Pipe Under External Pressure

Sandwich pipe plays an important role in the oil and gas exploitation in marine industry.The pipes used in deep ocean need to resist giant hydrostatic pressure.Compared to traditional single layer pipelines,the sandwich pipes have better mechanical strength and thermal insulation,which have good potential to be applied in deep sea oil industry.In the first part,an analytical formulation is derived to calculate the bifurcation pressure of sandwich pipe under external pressure.The core layer is viewed as a continuously distributed linearly radial spring.The core layer is fully constrained to the external and internal layer in the radial direction and free in the tangential direction.The system equilibrium equations are derived based on the principle of minimum potential energy,from which the bifurcation pressure of sandwich pipe under external pressure can be obtained.The comparison between formulations in literatures and finite element analysis results shows that they have a good agreement.Finally,some parameter analysis is done to discuss the factors that influence the bifurcation pressure of sandwich pipe under external pressure.In the second part,an FEA analysis is carried out to calculate the buckle pressure of sandwich pipe,and the influence of corrosion is considered the first time.First,an elastic bifurcation or buckle analysis of locally corroded sandwich pipe under external pressure is done,from which,the distribution figure of the buckle modal is obtained.Then the parameters which affect the bifurcation pressure are discussed.At last,analysis of post buckling is carried out in which the influence of plasticity is taken into consideration.The research in this paper can provide some guidance for design and safety evaluation for sandwich pipe in the marine industry.