Corrosion Behaviour of HVOF Sprayed Coatings on ASME SA213 T22 Boiler Steel in an Actual Boiler Environment

Abstract

In present study HVOF spraying process had been employed for depositing 93(WC-Cr3C2)-7Ni, 75Cr3C2-25NiCr, 83WC-17CO and 86WC-10CO-4Cr coatings on ASME SA213 T22. All the coatings were found dense and uniform having thickness between 200-250µm. All the coatings on ASME SA213 T22 used in present studies have provided resistance to corrosion in coal fired boiler environment in superheater zone when exposed for 10 cycles at 900°C. Each cycle consists of 100 hours heating followed by 1 hour cooling at ambient conditions. X-ray diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) techniques were used to analyse corrosion products. The results showed that among coated specimens 93(WC-Cr3C2)-7Ni and 75Cr3C2-25NiCr coatings has shown maximum and minimum resistance to corrosion respectively. The better corrosion resistance of 93(WC-Cr3C2)-7Ni coated steel alloys may be attributed to the formation of thin band of oxides of nickel, chromium; and carbides of tungsten.

Effect of burnishing on HVOF coated boiler steel against hot corrosion in actual boiler environment

“…The coated alloy's oxide scale spallates, as shown in BSE images (Figure 4b). Nickel and chromium oxides along with their spinels could be accountable for hindering the transference of degrading species through the applied coating [52,53]. Chromium and cobalt oxides, coupled with cobalt–chromium (CoCr 2 O 4 ) and nickel-chromium (NiCr 2 O 4 ) spinels, may have hindered CoO diffusing activities by preventing its production [28,54].…”

“…The cross-sectional EDAX analysis also confirms the formation of similar phases. Sidhu et al [55] and Singh et al [52] reported the presence of these phases during their investigation of appraising the hot corrosion performing of Ni-Cr coatings in coal-fired boiler environmental conditions. The cross-sectional analysis (Fig.…”

“…7c) also confirms the formation of similar phases. XRD and EDAX studies demonstrate the better performance of WC-CrC-Ni coatings due to the growth of chromium, magnesium, nickel oxides, and spinels [52]. WC-CrC-Ni-coated specimen followed by the burnishing process exhibited far much healthier hot corrosion resistance among other specimens.…”

Experimental Analysis of Hot Corrosion Behaviour of some Composite Coatings on Boiler Steel at Elevated Temperature

“…Otero et al (1987) had explained that Na 2 SO 4 − 60%V 2 O 5 leads to the spallation of the protective oxide scales formed on the surface of steel alloys due to which the surface comes into direct contact with the corrosive environment resulting in higher weight gain. Sidhu et al (2017) observed that steel alloys underwent extensive sputtering, spallation, peeling of scale and high weigh gain in Na2SO4-60%V2O5 environments. The high rate of weight gain was attributed to the formation of NaVO3, which acts as a catalyst and carries oxygen to the substrate causing high rate of oxidation of base elements of alloy (Rani et al, 2017).…”

“…After testing it was found that the corrosion resistance for coated material was more than that of bare material. Cr/Co-Al coating provided the thin layer of protective oxides (Cr2O3, Al2O3 and CoCr2O4), and these protective oxides provided protection against corrosion (Sidhu et al, 2017;Xi et al, 2017;Cabral Miramontes et al, 2018;Dorfman, 2018;Dudziak et al, 2018;Goyal, 2018). It is reported in the literature that the thermal spray coatings are effective to provide the resistance against corrosion, wear, oxidation and erosion in boilers and chemical process plants components (Poursaeidi et There is scope to develop composite coatings of Cr3C2-NiCr and to deposit these coatings on boiler steel to increase its corrosion resistance.…”