Random fatigue analysis of drill-pipe threaded connection

Abstract

Threaded connections are widely used in connecting drill pipes into a drill string. During drilling operations, the threaded connections are subjected to various external loads, including the load from the unevenness of rock formation at the bottom, impact from the well bore and axial hook load etc. These loads are primarily random, and will cause fatigue damage to the connections during drilling operation. In this paper, a standard 4.5" API line pipe threaded connection is analysed to investigate the fatigue effect of the random loads. A static stress analysis is first conducted considering 'make-up' and 'tensile load' steps. Then modal analysis and random vibration analysis are carried out, with the excitation considered as random. The fatigue damage is predicted using the so called three-band technique based on the stress results obtained. Effects of parameters, such as the random excitation, location of the connection, and friction coefficient, on the fatigue are discussed.