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Titanium and titanium alloy coiled tubing are widely used in the development operation of high corrosion resistance and ultra-deep oil wells because of their high specific strength, high corrosion resistance and high fatigue life. However, repeated bending and loading of coiled tubing can lead to the Bauschinger effect, resulting in a decrease in the yield strength and posing safety hazards to the coiled tubing. In order to investigate the relationship of yield strength of TA4 coiled tubing with the number of bending times under internal pressure (0 MPa and 35 MPa) and weld seam angle (0°, 90°, and 180°), bending fatigue tests and full-tube tensile tests were conducted. It is found that when the bending time is 1, the yield strength of CT will increase, while when the bending time is greater than 1, the yield strength of coiled tubing will decrease with the increase of bending number. In addition, the yield strength of coiled tubing decreases more significantly with the increase of internal pressure and weld angle. The increase of internal pressure and weld angle will lead to greater dislocation density and thus greater back stress, which will lead to greater backstress, so it will lead to greater Bauschinger effect.

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Study on Mechanical Properties Change During Repeated Bending of TA4 Coiled Tubing

  • 会议论文

  • 发表日期：

    2025年

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  • Zihan Li,
  • Wenjun Ye,
  • Songxiao Hui,
  • Yang Yu,
  • Xuwen Deng,
  • Yinqing Gong,
  • Changheng Li,
  • Xiongyue Ye,
  • Ronghui Fan

摘要

Titanium and titanium alloy coiled tubing are widely used in the development operation of high corrosion resistance and ultra-deep oil wells because of their high specific strength, high corrosion resistance and high fatigue life. However, repeated bending and loading of coiled tubing can lead to the Bauschinger effect, resulting in a decrease in the yield strength and posing safety hazards to the coiled tubing. In order to investigate the relationship of yield strength of TA4 coiled tubing with the number of bending times under internal pressure (0 MPa and 35 MPa) and weld seam angle (0°, 90°, and 180°), bending fatigue tests and full-tube tensile tests were conducted. It is found that when the bending time is 1, the yield strength of CT will increase, while when the bending time is greater than 1, the yield strength of coiled tubing will decrease with the increase of bending number. In addition, the yield strength of coiled tubing decreases more significantly with the increase of internal pressure and weld angle. The increase of internal pressure and weld angle will lead to greater dislocation density and thus greater back stress, which will lead to greater backstress, so it will lead to greater Bauschinger effect.