This paper reports on the design and application of a fatigue testing facility for drill pipes. A reversed bending load is applied using a rotating drill pipe in a four point static bend arrangement with the possibility of applying an additional static tension load. Drill pipes were tested with and without static tension at different cyclic bending stresses. The stress amplitudes ranged from 30 MPa to 230 MPa on the outside surface of the drill pipe. The test results show a consistent failure mode with a circumferential crack propagating in the groove of the first engaged thread of the pin, i.e. the male section of the joint. The fracture surface as well as ultrasonic monitoring of the sample during the testing suggest that the circumferential crack growth rate is fast, and final fracture occurs within a relatively small number of cycles as soon as a through wall crack has been formed. The S-N curve collected from a total of 18 samples shows a linear trend in the logarithm of the fatigue life versus stress amplitude.
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