Expandable tubular technology is an effective method for saving on the costs of well drilling and completion. There are many applications for casing repair and slim hole casing design. The most essential aspect of post-expansion expandable tubular (EXP-T) is collapse resistance, which is affected by not only the expanded pipe properties, but also the axial restraint caused by sticking pipe in wells. This paper discusses the effect of expansion condition on the collapse and the prediction methods of the post-expansion collapse resistance by conventional formulas and numerical simulation. The test pipes for EXP-T were expanded at the various expansion ratios with/without axial restraint. Using the post-expansion pipes, full-scale collapse tests were performed. FEA (Finite Element Analysis) for pipe collapse considering the pipe geometries and the mechanical property was also carried out for predicting the collapse pressure of EXP-T after expansion. In addition, the accuracy of conventional formulas and FEM models for collapse prediction was inspected by comparing the collapse test results. These results reveal potential to improve the collapse resistance of the pipe expanded under the axial restraint. Good agreements were found between the collapse test results and the predictions by FEA are drawn.
UOE linepipes have orthotropic work hardening in which the longitudinal (L-) stress vs. strain (SS) curve is different from the circumferential (C-) one. The anisotropy is emphasized by the thermal aging during the anti-corrosion coating. However, there are few studies on the effect of the circumferential mechanical properties on the compressive strain limit required in strain-based design (SBD). This paper describes the combined effect of SS curves in L- and the C-direction on the buckling resistance using the newly developed yield function to model the orthogonal anisotropy. The coupon tests after thermal aging during the anti-corrosion coating indicate that the L-SS curve can maintain the round-house type while the long yield point elongation (YPE) appears on the C-SS curve. Using these mechanical properties, FE-models demonstrate that YPE in the C-direction reduces the compressive strain limit for pipes with high diameter/thickness (D/t) under high internal pressure. Hence, SS curves in the C-direction should be considered for more reliable prediction of the buckling resistance required in long distance gas pipelines.
This paper summarizes an experimental and numerical study aimed at understanding the collapse resistance of expandable tubulars (EXP-T), both before and after expansion, and at constructing a prediction method for post-expanded collapse. Post-expanded collapse resistance is one of the important properties for EXP-T, and the high-collapse EXP-T is necessary for the realization of expandable tubular monobore wells. Thus, a reliable prediction technique can be useful for casing-design utilizing EXP-T. However, the current collapse formulas widely used are not applicable to post-expanded pipes.To solve this subject, firstly, full-scale expansion and collapse tests were performed to compare collapse resistance between two materials. Secondly, two prediction methods were validated for post-expanded collapse: finite element analyses (FEA) and the statistic formula used in conventional OCTG.The test results demonstrated that post-expanded collapse resistance is significantly degraded by the increase in the diameter-to-thickness ratio. There was a large difference in the reduction ratio of the collapse between the conventional and trial material, and the FEA model is capable of evaluating the precise collapse strength of post-expanded pipes by modeling the collapse governing factors. It was also clear that the distribution of residual stress after expansion is opposite to conventional OCTG, although the residual stress deteriorates the collapse resistance after expansion. Moreover, by modifying the definition of the mechanical property of the pipe, the collapse prediction formula is capable of accurately calculating the collapse pressure after expansion. This result is caused by the difference in the shape of stress-strain (S-S) curves between conventional OCTG and post-expanded pipes.We expect that this research work will contribute to improving our understanding of EXP-T collapse, and will help form the technical basis for the reliability of EXP-T casing design.
Expandable tubular technology is an effective method for saving on the costs of well drilling and completion. There are many applications for casing repair and slim hole casing design. The most essential performances of expandable tubular (EXP-T) are the expandability and collapse resistance, which are affected by not only the expanded pipe properties, but also the axial restraint caused by sticking pipe in well.This paper discusses the geometrical and material factors governing pipe expandability, the effect of axial restraint during the expansion, and the collapse resistance of the expanded pipe. Two types of pipe were evaluated using pipe expander equipped with a function of the axial restraint. FEA for pipe expansion considering the pipe geometries and the mechanical property were also carried out for solving the fracture mechanism and deriving the design diagram of EXP-T. In addition, the full-scale collapse tests were performed for evaluating the collapse resistance of the expanded pipes and verifying the prediction using the conventional formulas.These results reveal the relevant combination of the pipe geometries and the material properties for preventing the expansion failure. A potential to improve the collapse resistance of the pipe expanded under the axial restraint is drawn.
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