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A unique project was completed in Mid-2014 at the Unit 3 turbine refurbishment, Grand Coulee Dam, located in Washington State. This project was the result of extensive testing conducted at the Bureau of Reclamation’s engineering department, where over 50 products were evaluated.
The purpose of applying a thick epoxy gel coating to the 6,400 sq. ft. exit chamber of the penstock was to repair the surface primarily to correct cavitation. During earlier inspections, the penstock was determined to have extensive pitting and corrosion of the concrete surface, which creates cavitation on the surface of the concrete as water exits the dam. This cavitation creates a small degree of back pressure on the total flow and may decrease the efficiency of the turbines.
Even a very slight improvement in the flow characteristics (Hazen-Williams flow coefficient) could increase the efficiency of power production, as any improvement could represent a significant amount when 7,000 MW per day (21 Billion KW) per year is generated. This is a very unique application of a specialized repair epoxy gel, which has excellent bond strength and high compressive strength. The gel does not require a prime coat, and can be easily and effectively installed in one step to a damp substrate. Proper surface preparation using high pressure water and diamond grinding where needed, insured that the single step coating of the epoxy gel gave a uniform and well bonded surface using standard trowel techniques. When the turbine is restarted later this year, improved efficiency results will be provided by the BOR, which will better document the improved flow characteristics and power generated.
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