Research on multiaxial fatigue life of API drill collar thread in gas drilling.

According to the drilling tools failure statistics, fatigue failure of drill collar thread often occurs under a large weight on bit in gas drilling. So, this paper uses the multiaxial fatigue strength theory to study the drill collar's fatigue life. Pro/E software is applied to build a three-dimensional solid model of API drill collar thread and based on the model calculation results, the stress distribution of the API drill collar thread is analyzed. Then, according to the theory of multiaxial fatigue life, it is predicted that the fatigue life of the drill collar thread in gas drilling is about 2×105 times. The results provide a theoretical reference for identifying the fast failure mechanism of API drill collar thread in gas drilling. [ABSTRACT FROM AUTHOR]