Fatigue Life Evaluation of Coiled Tube under Coupled Load of Internal Pressure, Bending and Torsion
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摘要: 针对连续管在作业中易出现疲劳失效等问题,进行了连续管在内压、弯扭耦合加载下疲劳寿命评估。首先分析了耦合加载下连续管低周疲劳失效机理,基于Brown-Miller疲劳寿命模型建立了连续管疲劳寿命数值计算模型,开展了内压和弯曲加载下连续管疲劳实验,实验结果证实该数值模型是可行的。计算了内压和弯曲耦合加载下连续管低周疲劳寿命,以及内压和弯扭耦合加载下连续管低周疲劳寿命。计算结果表明,连续管最大塑性应变和疲劳敏感区出现在轴向拉伸面和压缩面,与现场连续管失效情况是一致的。通过计算得到了连续管安全服役的临界扭矩值和内压值。Abstract: It is necessary to evaluate the fatigue life of coiled tube (CT) under the coupled load of internal pressure, bending load and torsion. First, the failure mechanism of low cycle fatigue of CT under coupling loading is analyzed. Based on Brown-Miller fatigue life model, a numerical calculation model of CT fatigue life is established. The low cycle fatigue life of CT under the coupling load of internal pressure and bending load is calculated. And also the low cycle fatigue life of CT under the load of internal pressure, bending load and torsion is calculated. The calculation results show that the maximum plastic strain and fatigue sensitive areas of CT appear on the axial tensile surface and compression surface, which is consistent with the failure of CT on oil field. The critical torque value and internal pressure of CT are obtained by calculation for CT safety service.
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Key words:
- coiled tube /
- torsion /
- plastic deformation /
- fatigue life /
- coupling load
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图 7 连续管疲劳测试装置示意图
Figure 7. Schematic diagram of coiled tube fatigue test device
1. Straight mode; 2. Flexing mode; 3. Sample; 4. Fixtures; 5. Base; 6. Accumulator; 7. Check valve; 8. Supercharger; 9. Liquid pool; 10. Air valve; 11. Micro air compressor; 12. Valve; 13. Connecting pipe; 14. Cylinder;15. Support; 16. Active connector; 17. Pressure relief valve
Material type Outer diameter/mm Wall thickness/mm Elastic modulus/MPa Poisson’s ratio CT-800 60.325 4.775 210 000 0.3 Yield stress/MPa Cyclic strain hardening
coefficient/MPaCyclic strain
hardening indexSection shrinkage/% 552 785 0.1 58.18 表 2 有限元模拟值与实验值对比
Table 2. Comparison of finite element simulation results and experimental results
Internal pressure/MPa Experimental value/N Finite element value/N Error/% 65 50 45 10 65 49 45 8 65 52 45 13 表 3 内压、扭矩对连续管疲劳寿命的影响
Table 3. Influence of internal pressure and torque on fatigue life of coiled tube
Torque/(N·m) Fatigue life Torque/(N·m) Fatigue life 0 MPa 30 MPa 60 MPa 0 MPa 30 MPa 60 MPa 1000 >107 >107 >107 7300 8650 352 4000 >107 >107 >107 7400 2090 280 5500 >107 >107 >107 7420 745 234 5800 >107 ≥107 ≥107 7450 349 196 6000 >107 1331 111 7480 238 145 6200 >107 856 38 7500 179 122 6400 ≥107 623 1 7700 18 6800 36 890 408 -
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