Abstract
Ten randomly selected first stage turbines unfailed blades were examined to evaluate the accumulation of deposits located on the blade stems under the platform of one marine gas turbine engine. The degradation of two failed blades from other marine gas turbine engines was also examined. Metallographic examination showed that the coating thickness under the platform and in the curved area of transition between the platform to the blade stem was either very thin, or in a few cases, non-existent on each unfailed blade. Type II hot corrosion was evident at these locations under the platform. Corrosion fatigue cracks initiated at several hot corrosion sites and had advanced through the stems to varying degrees. Cracking in a few blades had advanced to the point where failure would have been imminent.
Type I and II hot corrosion attack has been observed on certain marine gas turbine engines in the area of the first stage turbine hardware. In order to improve the service life and resistance to Type II hot corrosion of these turbine blades, laboratory testing of the current baseline coating and several candidate replacement coatings was initiated using a low-velocity, atmospheric-pressure burner-rig (LVBR). This paper examines the LVBR results of these high temperature coatings of various chemical composition and applied by several processes on Alloy M247 to determine the hot corrosion resistance relative to the baseline coating with the goal of replacing the current baseline coating with a better quality, more resistant, and better performing coating system.
