Advancements in Fatigue Testing and Analysis

Abstract

Abstract 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.