Aluminum Drill Pipes: Material and Design Developments

An extensive research program on the structural strength of aluminum drill-pipes is being conducted at COPPE/UFRJ. The main objective is to improve the fatigue performance of these components by selecting the appropriate aluminum alloy and by enhancing the mechanical design of the threaded steel connector. This paper presents the experimental test program and numerical analyses conducted on a drill-pipe of different materials (Al-Zn-Mg alloy) and geometries from those previously presented [1,2]. Small-scale specimens were tested to determine its uni-axial stress-strain and fatigue behavior. Full-scale fatigue test results are also presented. A finite element model of the drill pipe, including the tool-joint region, was developed. The model simulates, through different load steps, the tool-joint hot assembly, and then reproduces the physical experiments numerically in order to obtain the actual stress distribution. The correlation between full and small-scale fatigue tests is performed via multi-axial fatigue models. The weak points of the current practice design are highlighted for further development.