Diamond Technology

 

Polycrystalline Diamond Bearing Testing for Marine Hydrokinetic Application

B.A. Lingwall, C.H. Cooley, T.N. Sexton

diamond engineering

Polycrystalline diamond (PCD) bearings are engineered and designed for use in extreme environments because of their high strength and hardness 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 lived, and rugged. Another harsh environment that could benefit through the use of PCD bearings is underwater in marine hydrokinetic (MHK) energy machines. Through a grant from the United States' Department of Energy (DOE), US Synthetic Bearings performed tests to observe a PCD thrust bearing in a water environment; this paper discusses the data collected and the lessons learned from this testing. Laboratory test results that measured bearing capacity, hydrodynamic properties and diamond wear rates are presented that can help predict the performance of PCD in these MHK applications. Three important results were discovered during the MHK testing: First, when compared to a conventional test in oil, the bearing capacity was increased by using water as a cooling medium due to its higher convective heat transfer coefficient; the test was set up to simulate the ocean water flowing through the bearing. Second, the PCD thrust bearings were able to endure 6000 stops and starts in a test imitating years in life of a tidal stream power generator; no signs of damage or failure were observed. Third, the wear rate of the diamond would extend the life of a typical bearing in an MHK application; the wear rate even decreased as the surface finish of the bearing contact area improved over time. 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.