headsUP: LM6000 Sprint compressors

Prevent compressor-blade erosion

Lloyd Cooke, Liburdi Turbine Services

The LM6000 Sprint is equipped with water spray injection at the engine inlet for interstage cooling of the compressor. Water injection contributes to water droplet erosion of some compressor stages and such leading-edge erosion can cause serious problems. This dictates that the operator remove the engine every 12,000 hours and replace the blades in four compressor stages.

To minimize the need for costly re-blading, a titanium nitride coating can be applied to compressor blades to protect against erosion. TiN is a very hard, smooth, and thin coating that has been proven successful for many years in preventing erosion of compressor blades for aircraft turbo-prop engines.

Liburdi introduced the erosion protection coating over 10 years ago and since that time it has been used extensively on Rolls Royce and GE turbo-prop flight engines operating in harsh environments—for example, military helicopter and cargo planes landing on unimproved runways and ingesting dust and sand. The coating is tested and approved by Rolls-Royce and has been used on all USAF T56 engines operating in severe environments for the past eight years. It achieves three times the service life of uncoated compressor blades.

What Liburdi recommends for the LM6000 Sprint is known as Generation III of the original TiN coating. It offers superior toughness, corrosion resistance, and protection against water droplet erosion. Some operators are now considering applying this proven coating to blades in vulnerable compressor stages of the LM6000—in some cases along with the uncoated blades to compare the benefits. The intent is then to be able to have all compressor blades for the Sprint perform for full service intervals, just as the non-Sprint variant of the engine.

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