Experimental And Numerical Study On Buckling Effect Of Sandwich Pipe Under External Pressure In Deep Water

As oil and gas production moves to deep and ultra-deep waters,in order to meet the special working environment of deep sea,such as low temperature and high pressure,new pipelines with higher density and greater consistency are needed to transport crude oil.The sandwich pipe of composite structure which fully combines the middle part of inner and outer steel tubes has obvious advantages,so it is of great significance to study the sandwich pipe.In this paper,the experimental and numerical study of the buckling effect of sandwich pipe under deep water external pressure is carried out as follows:Experimental study on crushing of sandwich pipe and single layer pipe under deep water external pressure.Through the comparison of multiple groups of scale ratio experiments,the compressive strength of the sandwich pipe with good inter-layer bond was significantly improved compared with that of the sandwich pipe with insufficient bond,indicating that the inter-layer bond has an important influence on the structural strength of the sandwich pipe.At the same time,it is verified by comparative experiments that the compressive strength of sandwich pipe is much higher than that of single-layer pipe with the same outer diameter and has better structural strength.Numerical study on sandwich pipe and single-layer pipe.Through the uniaxial tensile test of the material,the stress-strain relationship of the material was measured,and the corresponding numerical model of the sandwich pipe and single-layer pipe was established by the finite element software.The deep-water finite element simulation under external pressure was carried out by the loading method of hydrostatic fluid.The accuracy of the numerical results and the finite element model was verified by the experimental data.Analysis of the influence of initial defect on sandwich pipe.According to the defect loading experiment and the deep-water external pressure experiment,compared with the sandwich pipe,the single-layer pipe is more sensitive to the maximum ovality of the defect,and the larger initial ovality defect has a significant influence on the collapse pressure value of the sandwich pipe,which reduces the anti-buckling ability of the sandwich pipe to a great extent.Considering the residual stress at the defect,the finite element models of defect loading and deep water external pressure were established,and a series of sensitivity analyses of the buckling effect of the sandwich pipe with initial ovality were carried out.Analysis of the influence of combined loading of bending and hydrostatic external pressure on sandwich pipe.Through the experimental study of four-point bending and external pressure and the study and analysis of the corresponding numerical model,it is shown that the bending moment has little influence on the buckling resistance of the sandwich pipe under external pressure in deep water.