The Analysis Of Strength And Life Reliability Of Threaded Joint Of Pumping Unit’s Oil Pipe

The tubing of rod pumped well in the ways of oil exploration has the highest failurerate, and the failure of the tubing is one of the reasons why the pumping well pumpinspected. Causes of pipeline′s failure are complex, and the life of the tubing is a randomvariable interacted by many factors. Relevant statistics shows that the threaded joints arethe weakest link of the tubing; nearly80%of the failure occurred here. Considering theactual of tubing destruction, this paper focus on the tubing string strength of threadedconnection and the reliability of fatigue life, which can provide theoretical guidance forthe implementation of governance measures about the tubing string failure, lowerproduction costs, and improve overall economic benefits of oilfield developmentsignificantly. This article is mainly to carry out the following work:Combined with the works of pumping wells and operating parameters of oil wells,environmental loads of the tubing string is analyzed, the mechanical model of the tubingstring is created; According to the theory of multiphase flow, fluid pressure variations withdepth is decrypted in the tubing and casing-tubing annulus; the axial vibration of thetubing string is described by wave equation, and the simulation model about the tubingstring axial load distribution law is established. The main factors influencing the axial loadof tubing string are analyzed, which shows that submergence depth, water ratio and timesof stroke have more influence on the axial load and the submergence depth has thegreatest influence on the loads.The combination of thick-walled cylinder theory is applicated, the stress-strainmathematical model of tubing taper thread connecting is established in the role of themachine tight circle, internal and external pressure and axial tension; The effect of order inwhich the load is applied on the plastic zone size and the impact of stress and strain areanalyzed; and the destruction caused by thread several times on the shackle is analyzed.The result shows that the change is the strain rather than plastic zone size and the threadjoint should be changed after three times on the shackle.Non-thickening J55API round thread tubing connector as the object of study thetubing round thread connection is numerical simulated using nonlinear finite element software ANSYS with the J55API non-thickening tubing round thread connector; themechanical properties of tubing thread connection is studied under different loadconditions, these load conditions include the number of turns of the machine, tight internaland external pressure, axial tensile load and cyclic load and composite loads. The varationof torque with the number of turns of the machine and the varation of strain in thedangerous section with the axial tension loads and the cyclic load are got.Finally, the actual fatigue life of the dangerous section is estimated using the localstress and strain method. Based on reliability theory, the reliability model of fatigue life isestablished and the reliability prediction software about tubing string fatigue life isdeveloped, and the reliability of fatigue life about tubing string threaded connection ispredicted.