The plastic bending that occurs at surface causes large residual stresses in coiled tubing (CT) as it is run in and out of a well. When an axial force is applied to the CT it stretches more than pipe which has never been bent. Thus the conventional stretch calculations often used are incorrect for CT applications.

This paper presents equations which model the elastic/plastic stretch of CT. The results from these equations are compared to a computer model which was developed based on CT elongation research.

This paper also proposes a method to be used for stuck point depth calculations which avoids the plastic stretch complication.

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