Cavitation-resistant coatings for hydropower turbines

Abstract : Operating hydropower turbines to obtain the ultimate power output often results in cavitation (the rapid formation and collapse of vapor pockets in a flowing liquid in regions of very low pressure) in the turbine area. The level of cavitation typically destroys organic coatings in a relatively short time. Traditional metallizing to repair cavitation damage has resulted in unsatisfactory performance. Other coating systems, such as those deposited by High Velocity Oxygen Flame (HVOF), have been laboratory tested and shown to hold promise but have not been evaluated in actual long-term field applications. This study evaluated HVOF-applied coating systems that hold promise for long-term cavitation resistance and apply the most promising products to turbine areas for long-term field performance data. Work consisted of evaluating existing published and unpublished data on cavitation-resistant materials and selecting the most promising systems for field application. Those systems were then applied to areas of a turbine to evaluate their long-term performance. After 1 year, it is clear that many of the coatings have failed. Two of the coatings, however, appear to be virtually unchanged from the time of application and may be found to provide long-term resistance to damage caused by cavitation.