Fatigue Life Prediction of Coiled Tubing

Abstract

Coiled tubings, which are used in drilling and washing up oil wells, receive various bending and straightening plastic deformations with operating internal pressure. Therefore the low cycle fatigue of coiled tubings is an important issue.
In this report, as objective to clarify fatigue properties of coiled tubings and to develop a fatigue life prediction method of coiled tubings, we carried out full scale fatigue tests, fatigue tests with small size specimen, and FEM analysis simulated the full scale fatigue tests. As a result, it was clarified that fatigue lives of high strength coiled tubings (T95) were longer than those of low strength coiled tubings (L80) with high internal pressure, and predicted fatigue lives were satisfied general allowable difference, factor of two.