Investigation On Nonlinear Buckling And Collapse Of Composite Structures For Deepwater Sandwich Pipes Under Complicated Load Combination

With the expanding of exploration and exploitation of offshore oil-gas resources into deepwater and ultra-deepwater regions, offshore pipelines are facing accumulating risks and challenges. The high hydrostatic pressure and low temperature environment require for higher demands of offshore pipelines, including pressure bearing capability, corrosion resistant ability and thermal insulation. Thus, the traditional single-walled offshore pipeline can no longer satisfy the bearing capacity and safe transportation requirements in deepwater and ultra-deepwater regions. The composite structure for sandwich pipe is a newly-developed technique for offshore pipeline bundles, acknowledged by growing numbers of people for its remarkable advantages in the exploitation and transportation of deepwater oil-gas resourses. Offshore pipeline has to sustain axial tension, flexure effects and hydrostatic pressure during the installation and service life. The material and geometric nonlinearity of sandwich pipes aggravates the complexity of the mechanical properties. Under the complicated external load condition, the offshore pipeline is vulnerable to local buckling. The buckle will propagate along the axial direction, resulting in the failure of the whole pipeline. The composite structure for sandwich pipe is prospective for exploitation and transportation of deepwater oil-gas resources. Moreover, it is of great practical significance to study the buckling instability mechanism under complicated load.In this paper, the adhesion behaviors between core layer and steel pipes are measured by experiments and compared with the results of numerical simulation. Considering the various inter-layer adhesion behaviors, accurate numerical simulation analysis on the buckling and collaspe of sandwich pipes under complicated load combination are conducted. The specific research work is mainly as follows:(1) Studies on the inter-layer adhesion behaviors of sandwich pipes. The tension tests of shear specimens and axial push-out tests of sandwich pipe specimens were carried out, and the corresponding curves of inter-layer shear stress-displacement were obtained using epoxy resin and 3M-DP8005 adhesives in the smooth and rough steel contact surfaces, respectively. The finite element models of the above experiments were established by general finite element software ABAQUS to simulate the test process. The results of numerical simulation and test datas were compared.(2) Investigation of the nonlinear buckling and sandwich pipes collapse under combined axial tension and bending. The finite element model of the composite structure for sandwich pipe under combined axial tension and bending was established. Nonlinear spring element between nodes was used to simulate the inter-layer adhesion behaviors. Based on the extensive parametric studies, the influence of the loading path, inter-layer adhesion behaviors, initial geometric imperfections and material properties on the buckling and sandwich pipe collapse were expositioned systematically.(3) Investigation of the nonlinear buckling and collapse of sandwich pipes under combined hydrostatic pressure and bending. The finite element model of the composite structure for sandwich pipe under combined hydrostatic pressure and bending was established. Based on a series of parametric sensitivity analyses, the effect of the loading path, inter-layer adhesion behaviors, initial geometric imperfections and material properties on the buckling and collapse of sandwich pipes were investigated.The research results show that the loading path has remarkble impacts on the buckling behavior of sandwich pipes under complicated load combination.The buckling behavior of sandwich pipes is significantly superior to that of the traditional single-walled pipes. In comparison to the initial geometric imperfection, geometric configurations of sandwich pipes and material properties of inner and outer pipes have a remarkable impact on the buckling behavior of sandwich pipes.