Fire side erosion–corrosion protection of boiler tubes by nanostructured coatings

Abstract

This article presents a systematic evaluation of erosion–corrosion (E–C) behavior of nanostructured Ni–20Cr coatings on two boiler steels. A nanostructured Ni–20Cr powder was synthesized using ball milling technique by the investigators. The powder was deposited on SAE‐213‐T22 and SA 516‐Grade 70 steels by high‐velocity oxy‐fuel (HVOF) spraying under set parameters. The uncoated and coated samples were exposed to super heating zone of a power plant boiler at 750 °C under cyclic conditions for 15 cycles. Each cycle consisted of 100 h of heating followed by 1 h of cooling. Attempt was made to study the kinetics of E–C using weight change and thickness loss data of the samples. Several characterization techniques such as XRD, SEM/EDS, and X‐ray mappings analyses were used to characterize the eroded–corroded samples. The coating was found to reduce the E–C rate of T22 steel and SA 516 steel by 85 and 84%, respectively, in terms of thickness loss. Moreover, the investigated nanostructured Ni–20Cr coating was found to be more effective to reduce the E–C rates of the steels in comparison with its conventional (Ni–20Cr) micron‐size counterpart. E–C resistance shown by the investigated coating under actual boiler conditions may be attributed to the presence of protective NiO and Cr2O3 phases in its oxide scale and its superior as‐sprayed microhardness.