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Durgāpur, India

Ghosh D.,NDTand Metallurgy Group | Mitra S.K.,National Institute of Technology Durgapur
High Temperature Materials and Processes | Year: 2010

The slagging is a common problem of high temperature corrosion in fireside of waterwall tube of steam generator/ boiler of power plant component. The hematite (Fe2O3) layer very often exists on the fire side of the waterwall tube. The chemical interaction of hematite on the outer layer of the tube walls with molten pyrite (FeS2) at high temperature (if the fuel contains sulfur) may cause slagging/fire side tube wastage due to the high temperature corrosion. This is closely similar to slagging/fire side corrosion of the waterwall tubes at high temperature when sulfur bearing fuels are used in boiler. Plain carbon steel ASTM SA210 Grade Al is widely used for the construction of the waterwall tubes in the boiler. This papers highlights the mechanism and extent of high temperature corrosion of plain carbon steel in 67% of hematite (Fe2O3) and 33% pyrite (FeS2) in solid-solid and gas- solid reaction state. The samples are exposed in high temperature furnace in different reaction states as mentioned at a constant temperature of 923 K=750°C for 5 hours to study the high temperature corrosion behavior. The corrosion rates are calculated by weight gain method. The SEM and EDS study of the external scales of the samples are also carried out to examine the scale morphologies and constituent weight percentage of the elements of the external scales. It can be concluded from the results of the experiments that corrosion rate is much higher in solid-solid reaction state in comparison gas-solid reaction states with same proportion of hematite and pyrite The higher rate of corrosion in solid-solid reaction state is associated with external scale cracking/spalling and presence of appreciable amount of sulfur on the external scale.the lower corrosion rate in gas-solid reaction state is associated with the adherent corrosion resistant scale with finer grains of oxides and sulfides. Source

Ghosh D.,NDTand Metallurgy Group | Shukla A.K.,NDTand Metallurgy Group | Mitra S.K.,National Institute of Technology Durgapur
Surface Engineering | Year: 2013

This paper investigates the effect of cerium oxide (CeO2) coating on the high temperature corrosion behaviour of normalised and tempered 2·25Cr-1Mo steel in oxidation-sulphidation (SO2+O2) mixed gas environment. The CeO2 coating of two different coating thicknesses (150 and 300 μm) is prepared for experimental investigations. The isothermal corrosion study of uncoated and different CeO2 coated specimens is carried out in SO2+O2 environment at 973 K. The external scales of the post-corroded specimens are characterised after corrosion test by scanning electron microscopy and X-ray diffraction. CeO 2 coated specimens show higher corrosion resistance than uncoated specimen. The higher corrosion resistance of CeO2 coated specimens is associated with excellent scale plasticity and adhesion. The detailed mechanism of the corrosion is discussed in the paper. © 2013 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute. Source

Ghosh D.,NDTand Metallurgy Group | Shukla A.K.,NDTand Metallurgy Group | Mitra S.K.,National Institute of Technology Durgapur
Protection of Metals and Physical Chemistry of Surfaces | Year: 2013

The influence of superficial CeO2 coatings on isothermal and cyclic high temperature corrosion behavior of 2.25 Cr-1 Mo steel in oxidation and sulfidation (SO2 + O2) atmosphere have been reported in this paper. The CeO2 coating of three different depositions rate (0.15 mg/cm2, 0.30 mg/cm2 and 0.50 mg/cm2) were prepared for experimental investigations. The isothermal corrosion study of uncoated and CeO2 coated specimens was carried out in SO2 + O2 environment at 973K for 150 hours. The results clearly indicate that CeO2 coated specimen improves the high temperature corrosion resistance than uncoated specimens. The post corroded CeO2 coated specimen shows reduction of scale growth and improved scale adhesion to the substrate. The cyclic corrosion study was also carried out in both coated and uncoated specimen in same environment at 973K for 100 h. The CeO2 coated specimens on thermal cycling also shows significant improvement of the corrosion resistance without scale cracking and spallations. In contrary, the uncoated specimen in both isothermal as well as cyclic environment shows higher corrosion rate along with scale cracking and spallations. The results of the reaction kinetics have been substantiated by post corrosion analysis of alloy/scales combinations by SEM and XRD. The details mechanism of the corrosion in presence of CeO2 coating was further discussed in the paper. © 2013 Pleiades Publishing, Ltd. Source

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