Sulfidation: Turbine Blade Corrosion

A large number of Pratt & Whitney Canada (P&WC) PT6 Service Bulletins and maintenance manuals have been used in the preparation of this article. For this reason the specific recommendations are most closely applicable to P&WC PT6 engines, but the...

It is important to check the most current procedures recommended by the engine manufacturer to determine whether a motoring wash (simply using the starting motor to rotate the engine) or a running wash (engine started up and running) should be performed. In general, motoring washes are now considered preferable to running washes. Either way, be sure to use the cleanest water available. While some manufacturers say that “any water safe to drink” can be used for washes, others recommend deionized (distilled or demineralized) water only. In addition, chemicals mixed with the water for cleaning the engine (i.e. performance recovery wash) vary relating to their corrosive, hazardous waste, and biodegradable characteristics. Regulations regarding their use and disposal in various environments vary from state to state and country to country.

Also, technicians should be aware that the more pure the wash water is, the “hungrier” it is for attracting the very contaminants one is trying to extract from the engine. Therefore, stainless-steel storage tanks or other metal containers with approved epoxy coatings are recommended. Glass and fiberglass containers should be avoided. Polyethylene containers are acceptable only if they are of the nonpigmented, detergent-grade quality. Even immersing one’s finger in deionized or demineralized water can raise the specific conductance tenfold and thereby reduce its effectiveness.

Be sure to consult the engine manufacturer’s recommendation for types of chemicals, pressure equipment, flow rates, temperatures, and other safety-related procedures.

When it is time to repair or replace hot section parts, install alternative parts that have a higher resistance to sulfidation. Sermaloy J (silicon aluminide) has been proven to either double or sometimes quadruple the resistance to sulfidation. Diffused aluminide has been shown to have a higher resistance to oxidation at elevated temperatures. When selecting new parts during hot section repair/overhaul it is important to be aware of the sulfidation history (or lack thereof) of your engine. Traditionally P&WC has provided hot section parts with diffused aluminide coatings. It is important to select the coatings that are best equipped to address your particular operating environment.

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