Application of tri-vector analysis to identify the optimum coating thickness in induced draft fans

Abstract

An atmospheric plasma spray deposition process was adopted for coating regular-shaped, Stellite 6 powder directly on a rolled 3<math display="inline" altimg="eq-00001.gif"><mspace width=".17em"></mspace></math>mm size AISI 304 austenitic grade stainless steel substrate without any intermediate bond layers. Coating thickness as measured in a scanning electron microscope was obtained as 74 μμ<math display="inline" altimg="eq-00002.gif"><mi>μ</mi></math>m, 128 μμ<math display="inline" altimg="eq-00003.gif"><mi>μ</mi></math>m, and 215 μμ<math display="inline" altimg="eq-00004.gif"><mi>μ</mi></math>m. An experimental investigation of the functional behavior such as corrosion, microhardness, and erosion of the coated steel at different operating temperatures was undertaken to determine the suitability of its application in the industry. Erosion tests were conducted in an air jet tribo-tester utilizing alumina as an erodent with normal impingement angle at room temperature, 300∘C, and 600∘C. It was difficult to identify a single coating thickness that can be satisfactorily used for superior erosive wear properties with corrosion resistance. So modern management tools such as tri-vector and technology sieve analysis procedures as identification techniques were adopted for the selection of the best coating thickness by complying with the mechanical, erosion, and corrosion resistance properties. Steel coated with 128-μμ<math display="inline" altimg="eq-00005.gif"><mi>μ</mi></math>m coating thickness provides the best result for a combination of functional characteristics.