Polycrystalline diamond bearing testing for marine hydrokinetic application

Polycrystalline diamond (PCD) bearings are ideally suited for use in extreme environments because of their extraordinary thermal and mechanical properties. Past use of PCD in process-fluid-lubricated down-hole tool applications, such as those in oil and gas drilling turbines, have proven them to be robust, long lasting, and rugged. Another harsh environment where the use of PCD bearings makes sense is underwater in marine hydrokinetic (MHK) energy machines. Through a grant from the United States' Department of Energy (DOE), contract #DE EE0003633, US Synthetic performed tests to evaluate a PCD thrust bearing operating in a water environment. This paper discusses the data collected and the lessons learned from this testing. Laboratory tests that measured bearing capacity, hydrodynamic properties and diamond wear rates are presented that can help predict the performance of PCD in MHK applications. Three important results were discovered. First, when compared to bearings tested in oil, the bearing capacity was increased by using water as a cooling medium due to its higher convective heat transfer coefficient. Second, the PCD thrust bearings were able to endure 6000 stops and starts in a test imitating years of life of a tidal power generator with no signs of damage or failure. Third, the small observed wear rate of the diamond would extend the life of a typical bearing in MHK applications. In addition, it was observed that the wear rate decreased as the surface finish of the bearing improved. These key points and other subjects discussed herein illustrate that PCD thrust bearings can provide a robust, long lasting, and low maintenance bearing in MHK applications.