Fatigue of Drill Pipes Used in Mini-Horizontal Directional Drilling

摘要

In order to analyze the fatigue life of mini-horizontal directional drilling (mini-HDD) rod, a fatigue test machine was constructed at the Trenchless Technology Center. This paper describes the testing procedure and the results of the testing. Five preliminary tests were carried out to test the equipment set up and during these tests, the strong impact of make up torque and joint lubrication on the fatigue life was observed. Seven tests were then carried out at different drill string curvatures to construct an S-N curve for mini-HDD drill pipe. During this series of tests, six failures occurred and one test was terminated without failure. The S-N curve derived from the test results was found to match well with prior research for larger drill pipe used in oil field drilling. Simulation of drill joints was carried out to investigate the stress concentrations within the joint and the theoretical stress condition in different phases of the drilling process was compared to the normal stress assumptions used in practice. The S-N curve results can be used to provide an indication of the cost of drill rod fatigue by using some illustrative assumptions about curved drilling and drill rod usage.