The inside of a hydro turbine is typically exposed to erosion from sediments in the water as well as possible corrosion due to varying water chemistry. Traditional pipeline coatings are often not possible due to mechanical interfaces with moving parts and tight tolerances.
Stark Engineering Consulting was requested to inspect, diagnose and rectify severe corrosion issues inside a small Kaplan turbine. The inspection revealed that the original electroless nickel coating had failed throughout the machine, leading to severe pitting corrosion of the turbine runner hub, distributor and seal supporting cone. Previous in-situ paint repairs had proved to be difficult to apply and ineffective.
Although the runner was replaced by a stainless version, it was uneconomical to replace the distributor and seal supporting cone. Instead we recommended a repair procedure including:
1. machining of critical clearance surfaces to ensure sufficient clearance with moving parts
2. full sandblasting of the pieces
3. rebuild and repair with a 2-part repair composite paste
4. final topcoat of low-friction 2-part epoxy coating
Now, 15 months later, an internal inspection has revealed that the coating is in excellent condition, giving our client good hopes that this economical solution is proving to be durable.