Hot Corrosion of Shipboard Gas Turbine Blades

Abstract

Turbine blades removed from the first stage of a shipboard gas turbine engine for excessive degradation were characterized. Scanning electron microscopy coupled with energy-dispersive spectroscopy, X-ray diffraction, and inductively coupled optical emission spectroscopy was used to characterize corrosion deposits and features of field hardware that are not typically obtained in controlled laboratory settings. Corrosion was associated with deposits of varying compositions on the airfoil, beneath the platform, and within cooling passages. Deposits on the airfoil were primarily sodium sulfate presumably derived from seawater. Deposits below the platform and within cooling channels were crystalline aggregates of Ca, Mg, Al, and Si compounds presumably derived from dust and sand. FactSage thermochemical calculations were performed for gas turbine environments, and results are used to explain variations in deposit chemistry. The results show that solid sodium sulfate may not be retained in some gas turbine conditions, leaving the deposits rich in Ca and Mg compounds.