Erosion-corrosion of plasma as sprayed and laser remelted Stellite-6 coatings in a coal fired boiler

Unacceptable levels of surface degradation of metal containment walls and heat exchanger tubing by a combined erosion-corrosion (E-C) mechanism have been experienced in some boilers. The recent use of coatings to protect the heat exchanger tubes of fluidized bed combustor from E-C problems has been suggested by many authors. The laser remelting of the surface coating is suggested as a promising technique to improve its physical properties.Aim of the present investigation is to evaluate the erosion-corrosion (E-C) behaviour of plasma as sprayed and laser remelted Stellite-6 (St-6) coatings on boiler tube steels in the actual coal fired boiler environment. The cyclic experimental studies were performed in the platen superheater zone of a coal fired boiler where the temperature was around 755 °C and the study was carried out upto 10 cycles each of 100 h duration followed by 1 h cooling at ambient temperature. Coated steels were found to possess higher resistance to E-C than the uncoated steels. The highest degradation resistance has been indicated by the T11 steel coated and subsequently laser remelted.