Low Carbon Alloy Steel Solid Expandable Tubular Finite Element Analysis

The solid expandable tube technology is mainly developed to solve the problem that theborehole is so small that the tube cannot reach the purpose layer. The optimal extension toolis the key to the process. The material of solid tube should not only satisfy the expansionprocess but also should ensure it can be used normally after its expansion. So this paperfocused on the two parts.Based on the Chinese practice and foreign successful research experience, the paper putthe expansion process as the research object, on which we utilized the finite elementanalysis technology as the main research means. Firstly, based on the related theory ofelastic-plastic finite element contact problem, the paper constructed the mechanics model ofthe expansion tube in an expansion process and simulated the expansion process of the tube,with108mm in diameter and6mm in thickness. This paper studied the relationship betweenthe fluid pressure, which is needed to complete the expansion and the different expansionratio, and the expansive cone angle. It confirmed the best angle in different expansioninflation. The paper established a model of expansion fluid pressure’s strengthening powerbased on low carbon alloy steel stress-strain relationships. And it adopted the relationshipbetween resilience and expansion to modify the strengthening power model, by which weestablished the relationship model of expansion force, rate and cone angle. The modelcalculated the expansion force under different rate and cone angle, through which found outthe optimal cone angle, which is same to the finite element analysis result. Further more,we found that the real expansion force is slightly higher than the calculated result throughcomparing the theoretical value and the real value. Thus, it indicates that the model isvalidated on finding out the tube’s expansion force.Secondly, based on the research of108mm diameter solid tube, this paper put forward acalculation method on expansive force according to the function and principle bycombining the classical theory of plasticity with the finite element simulation algorithm.We got the expandable radial stress on ANSYS and calculated the expandable force by theclassical theory of plasticity and contact theory. A practical example is used to verify thecorrectness and reliability of the new calculation method. It is the main innovation of thepaper. Finally, upon analyzed the dynamic tensile test results, with the strain rate factor Z andMcCormick physical model, the paper set up low carbon alloy steel constitutive equation ofunderground temperature field. In the condition of underground temperature field, by usingthe finite element simulation method, we simulated the expansion process at the optimalangle under different inflations. A series of important conclusions are obtained, such as theequivalent stress cloud image of expansion process, the variation law of residual stress withthe temperature, collapse strength of expanded casing string, tensile strength andcompressive strength.