Simulated land-based turbine deposits generated in an accelerated deposition facility

This report presents a validation of the design and operation of an accelerated testing facility for the study of foreign deposit layers typical to the operation of land-based gas turbines. This facility was designed to produce turbine deposits in a 4-h test that would simulate 10 000 h of turbine operation. This is accomplished by, matching the net foreign particulate throughput of an actual gas turbine. Flow Mach number temperature and particulate impingement angle are also matched. Validation tests were conducted to model the ingestion of foreign particulate typically found in the urban environment. The majority of this particulate is ceramic in nature and smaller than 10 microns in size, but varies up to 80 microns. Deposits were formed for flow Mach number and temperature of 0.34 and 1150 degrees C, respectively, using MCrAlY coated coupons donated from industry. Investigations over a range of impingement angles yielded samples with deposit thicknesses from 10 to 50 microns in 4 h, accelerated-service simulations. Deposit thickness increased substantially with temperature and was roughly constant with impingement angle when the deposit thickness was measured in the direction of the impinging flow. Test validation was achieved using direct comparison with deposits from service hardware. Deposit characteristics affecting blade heat transfer via convection and conduction were assessed. Surface topography analysis indicated that the surface structure of the generated deposits were similar to those found on actual turbine blades. Scanning electron microscope (SEM) and x-ray spectroscopy analyses indicated that the deposit microstructures and chemical compositions were comparable to turbine blade deposit samples obtained from industry.