Mechanical Analysis Of Flexible Pipes Under Torsion

Pipelines used in oil and gas transportation are divided into two main different types:unbonded flexible pipes and bonded flexible pipes.The material of the reinforced layers in unbonded flexible pipes is usually made of metals,each reinforced layer does not bond with each other.While the material of the reinforced layers in bonded flexible pipes is generally made of fibre glass,Kevlar,carbon fibre and so on,each layer is bonded by a hot melt process.The inner and outer layers of these two types are generally wrapped in plastic layers.Due to the differences of the materials used in reinforced layers and of the contacts between each layer,bonded and unbonded flexible pipes naturally have different mechanical behavior.Pipes may be subjected to torsional loads during transportation,installation and operation.Excessive torsional loads can cause torsional damage to the pipes.In this thesis,two typical unbonded flexible pipes and bonded flexible pipes,metallic strip flexible pipes(MSFP)and fibre glass reinforced flexible pipes(FGRFP),are studied,and their mechanical behavior under torsion are analyzed.The main contents are as follows:(1)The torsion experiment of three specimens and the material experiment of the steel strip and the plastic used in MSFP.The torque-torsion angle curves of the specimens under torsion are obtained,as well as the stress-strain curves of the steel strip and the plastic.(2)Finite element analysis of MSFP under anti-clock torque.The torque-torsion angle curve is obtained by this analysis and then compared with the experimental results.In the analysis,the layers of the reinforced layers and the plastic layers are taken out separately,and their stress,strain and deformation are analyzed.(3)The sensitivity analysis of MSFP is carried out via finite element method,the influence of steel strip layout,boundary condition,friction coefficient,winding angle,wall thickness of pipes and twist direction on its failure torque are analyzed.(4)Torsion experiments are performed on FGRFP.The torque-torsion angle curves of the specimens under torsion are obtained.Then torque-torsion angle curves are also obtained by analytical analysis and finite element analysis and compared with the experimental results.Finally,sensitivity analysis is carried out to analyze the effects of winding angle,thickness of reinforcement layer and ratio of diameter to thickness on torsional stiffness.