Research On The Mechanical Proerties Of Steel Strip Reinforced Flexible Pipe Under Internal Pressure Related Load

Flexible pipes are experiencing rapid application in oil&gas exploitation field nowadays due to their superior peoperties compared to conventional steel pipes.Different kinds of flexible pipe possess different properties,as a newly emerging flexible pipe,steel strip reinforced flexible pipe(steel strip PSP)integrate the virtues of fibre reinforced flexible pipe and steel wire reinforced flexible pipe:superior anti-internal/external pressure capacity and relative low price,this has made it an appropariate choice for onshore&offshore application.However due to its inherent attribute,some issues should be confronted directly:1)a reliable theoretical model is needed to analyze the mechanical properties of steel strip PSP;2)the swaged endfitting may change the boundary condition of the pipe wall and thus inducing Stress Concentration Effect(SCE)in the pipe wall;3)the bolt-nut connection may loose due to corrosion or creep and further lead to leak accident.Based on the description above,this thesis aim to tackle these problems and the main contents are arranged as follow:1)The mechanical properties of steel strip PSP under internal pressure related load conditions are analyzed.The stress distribution on each layer is analyzed with FE model and theoretical model to show that the innermost reinforcemtn layer contributes most to the pipe anti-internal pressure capacity,the on-axias stress on this layer is introduced as the criteria to predict the burst pressure of the pipe.The interaction effect of combined load on the pipe mechanical behavior are analyzed.2)The Stress Concentration Effect(SCE)in pipe with swaging end-fitting was studied.The deformation expression of pipe wall near end-fitting is deduced with thin wall cylindrical theory by treating the swaged endfitting as rigid body.The deformation discontinuity of pipe wall in this area is proven theoretically.The pressure difference between the upper surface and lower surface of a layer is derived based on force balance condition,and is set an independent parameter for calculating the pipe wall deformation.Burst pressure obtained from this model and classic elastic model are compare with experiment data saperately to show the feasibility of this model.3)The sealing performance of bolt-flange was investigated and the criteria of sealing performance was proposed.The gasket strain variation under pretight and working condition is investigated.With FE method the contact force and contact condition between gasket and flange is simulated,result shows that the Stress Concentration accurs in the contact part.This situation is relieved by changing a new type of gasket.Sealing test under internal/external pressure are conducted in ABAQUS and it can be found under specified condition the flane connection exhibit good sealing performance.