As a result of full-scale and accelerated fatigue tests, a new data on coiled tubing (CT) fatigue life is now available. For a full-scale field test, operators set up an operational coiled tubing unit and induce stress/strain conditions identical to field conditions by moving pressurized CT from the reel to the well and back to the reel. Accelerated tests are performed with a laboratory bending machine that applies stress/strain cycles to the pressurized specimen. These cycles are similar to actual stress/strain cycles applied to CT over the reel or over the tubing guide. In this case, the specimen is 6 to 7 ft long. It is fixed at one end and simulates a cantilever with an alternating load at the other end.

Fatigue tests are performed on 1.25 to 3.50-in. OD CT sizes having the following minimum yield strengths:

  • 70,000 psi (70k tubing)

  • 80,000 psi (80k tubing)

  • 100,000 psi (100k tubing)

An existing CT fatigue life model is refined to account for the tested CT sizes and materials. Main features of the model are described.

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