| ISO13679 as the authority of the standard for evaluating the property of thread joint of tubing and casing,has been widely recognized within the industry.However,the standard has many disadvantages,such as long test cycle,high cost,harsh conditions,so that the actual application of the situation is not good.Therefore,in this paper,a kind of casing premium thread joint as a research object explores whether the computer simulation based on finite element method can be used as a substitute for full-scale physical evaluation in accordance with ISO13679 test procedure.First,based on the theory of elasto-plastic contact,this paper considers the geometric nonlinearity,nonlinearity of material and nonlinearity of boundary conditions in finite element analysis process,and establishes finite element model(FEM)of casing premium thread joint.On the basis of the FEM,according to the ISO13679 CAL ? A and B load envelope test procedure,it calculated the Von Mises stress and normal contact stress distribution of the casing premium thread joint under complex load,such as tensile,compression,internal pressure and external pressure.As well as the relationship between displacement,contact displacement,tangential contact stress and casing contact state was discussed.By introducing the thermal parameters of the material,the thermal stress and contact stress distribution of the premium thread joint of the casing were calculated under the condition of the C series thermal cycle test.The connection strength and the gas sealing of the premium thread joint were analysed via loading eight kinds path of ultimate failure,example the condition of high internal pressure stretch up to failure.Finally,the finite element calculation results are verified by two full-size physical experiments of the internal pressure to failure and stretch up to failure.The results found in this research include: In the envelope analysis,the stress distribution of the joint shows the middle lower than both the ends.The thread part and the pipe end near apex are succumbed locally.Tensile load is too large,the more detrimental to the seal,the internal pressure load obviously self-sealing effect.The stress value of the external thread is always greater than the stress value of the coupling,indicating that the external thread of the pipe is more likely to fail than the coupling.The way of "soft contact" instead of "hard contact" can effectively improve difficult convergence in the premium thread simulation after the introduction of friction.As the temperature changes from low to high,the yield strength ofthe pipe and the coupling decreases,and the sealing effect is worse.In the extreme state,the anti-tensile,anti-compression,anti-internal pressure and anti-extrusion ability of the casing premium thread joint are larger than the value of the API,and the failure modes are broken,blasting,crushing and so on.Which anti-internal pressure and anti-tensile results through comparing with the test results were found to be more consistent.The impacts of our obtained results are that it is feasible to evaluate the premium joint structure and seal integrity under the complex load according to the requirements of ISO13679 program,which can save the time and economic cost greatly and can replace the physical evaluation of the joint to a certain extent.At the same time,the computer simulation evaluation can also find the phenomenon that can not be observed in the physical experiment,which is of reference value for the optimization and improvement of the joint design. |
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