Coiled tubing is now routinely used in operations at stress and strain levels that are significantly greater than prior experience. These operating conditions have identified limitations in both the fatigue models and their underlying fatigue test data. A new experimental fatigue test program was undertaken to extend the strain and stress range used in testing. The test plan was formulated in terms of three non-dimensional variables based on the five physical variables. Data binning the three indenedant variables allowed the development of a full factorial test plan. By using the coefficient of determination as a measure of goodness of fit it was possible to test different hypotheses, including eliminating one of the three three non-dimensional variables. This fact greatly simplified the analysis and understanding of the data, and offers the possibility of significantly reducing the number of fatigue tests required to develop accurate models. The dependence of fatigue life, diametrical growth, and fracture length on the remaining two non-dimentional variables, strain and normalized hoop stress, are shown graphically. The lessons learned in this program are used to make recommendations for future fatigue test programs.
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Avakov, V.A., Foster, J.C., and Smith, E.J.; "Coiled Tubing Life Prediction", OTC paper 7325-MS, Houston, Texas, May 1993.
Christian, A. 2010. Local Strain Approach for Fatigue Life Prediction of Coiled Tubing with Surface Defects. PhD dissertation, University of Tulsa, Tulsa, Oklahoma (2010).
Tipton, S.M., Newburn, D.A.; "Plasticity and Fatigue Damage Modeling of Severely Loaded Tubing", Advances in Fatigue Lifetime Predictive Techniques, STP 1122, American Soc. for Testing and Materials, Tulsa, Oklahoma (1992) 369&-382.
Newman, K.R. Development of a New CT Life Tracking Process. Paper SPE 163884 presented at the SPE/ICoTA Coiled Tubing and Well Intervention Conference & Exhibition, The Woodlands, Texas, March 2013.
Newman, K., Kelleher, P.; CT Fatigue Modeling Update. Paper SPE 179049 presented at the SPE/ICoTA Coiled Tubing and Well Intervention Conference & Exhibition, Houston, Texas, March 2016.
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