Collapse analyses of sandwich pipes under external pressure considering inter-layer adhesion behaviour

• Tests are conducted to evaluate the inter-layer stick-slip levels of the adhesives.
• Non-linear spring is used to simulate the inter-layer adhesion behaviour.
• Influencing factors on the pressure capacity and deformability of SPs are explored.
• Inter-layer adhesion behaviour strongly influences the collapse capacity of SPs.

Sandwich pipes composed of two relatively thin concentric steel pipes and a thick and flexible core in the annulus, are viewed as a significant potential for deepwater and ultra-deepwater applications in oil and gas transportation because they can simultaneously meet mechanical and thermal requirements. This paper presents a collapse capacity prediction of sandwich pipes with various inter-layer adhesion behaviour under external pressure. The solid polypropylene with favourable thermal insulation capacity and high compressive strength is used as the core layer material. The stress-strain curves of the polypropylene material are measured through the uniaxial tension and compression tests. The tests of simple shear specimen and sandwich pipe section specimen are conducted to evaluate the stick-slip levels of epoxy resin and 3M-DP8005 adhesives in two surface conditions of steel pipe, respectively. Then, the dedicated finite element model is developed and an extensive parametric study is conducted to explore the influences of geometric configuration, initial imperfection, material property, and inter-layer adhesion behaviour on the pressure capacity and deformability of sandwich pipes. It is observed that the inter-layer adhesion behaviour has a strong influence on the collapse capacity of sandwich pipes.