COMPONENT LONGEVITY

By:  John Molloy

Introduction

An industrial combustion turbine can ingest over 1000lbs of air per hour of operation.  Entrained within the air is a spectrum of mineral, salt, moisture, and VOC, and other compounds that are present in the local atmosphere.  Locally high concentrations of potentially corrosive species may also be present due to surrounding industries or even effluent from the power plant itself, such as cooling tower drift, evaporation cooler deposits, or water treatment effluent.

In addition to disrupting the flow path area of the compressor blades and vanes, with a consequential drop in compressor efficiency, these contaminants can also serve as sites for under-deposit corrosion cells that have implications for component life as well as risk for catastrophic failures.  Compressor waterwashing with detergents has been utilized with some success by utilities as a method for mitigating the effects of deposit accumulation.  Nevertheless, tenacious deposits can accumulate over time.  The presence of moisture in the deposit can also result in activation of a corrosion cell that can corrode the typical stainless steels used for blade and vane construction.  Higher strength PH stainless steel blades and vanes suffer a larger loss in fatigue endurance limit from pitting, and tend to suffer more airfoil liberations due to cracking initiated at pitting.

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