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This study aims to report the oxidation behaviors of the T91 ferritic/martensitic steel (T91 steel) and 304 austenitic stainless steel (304 steel) in supercritical water (SCW) at 600°C.

The microstructure, elemental distribution and phase structure of the oxidation layers derived from the corrosion of the T91 steel and 304 steel were analyzed by scanning electron microscopy, Oxford Instrument X-ray spectroscopy, electron scattered diffraction and transmission electron microscopy.

The oxidation layers on the T91 steel and 304 steel have duplex structure. The two steels all suffer internal oxidation, and the phase of the internal oxidation layers are indexed as Fe-Cr spinel, although their morphologies are different. The formation of a continuous Cr-rich layer is not detected because of the relatively low Cr content of the steels, which is attributed to the corrosion property.

The accelerated corrosion and corrosion mechanism of the T91 steel and 304 steel with low Cr occurring in SCW at 600°C was clarified.

This paper aims to use the high-velocity oxy fuel (HVOF) spraying process for depositing 93(WC–Cr₃C₂)–7Ni, 75Cr₃C₂–25NiCr, 83WC–17C_O and 86WC–10C_O–4Cr coatings on ASME SA213 T91 to study the corrosion resistance of these coatings in an actual boiler environment.

The HVOF spraying process was used for depositing 93(WC–Cr₃C₂)–7Ni, 75Cr₃C₂–25NiCr, 83WC–17C_O and 86WC–10C_O–4Cr coatings on ASME SA213 T91. All the coatings obtained are found to be uniform, dense and having thickness between 200 and 250 μm. All the coatings were exposed in an actual boiler environment at 900°C temperature for 10 cycles. Each cycle consisted of 100 h heating followed by 1 h cooling at ambient conditions. X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy techniques were used to analyse corrosion products.

All the coated samples were found to be having higher corrosion resistance than the uncoated samples. Among coated specimens, 93(WC–Cr₃C₂)–7Ni coating has shown maximum and 75Cr₃C₂–25NiCr coating has shown minimum resistance to corrosion.

This paper is original research.

This paper aims to quantify atmospheric corrosion by image analyses. The corrosion extent, form and distribution of corrosion product on Q235B and T91 steels exposed to a Zhoushan marine atmosphere over one year are characterized by image analysis.

Image analysis of corrosion images were achieved using the gray value, wavelet analysis and fuzzy Kolmogorov–Sinai (K–S) entropy.

As corrosion becomes extensive, the gray value of corrosion images decreases, and the energy value of nine subimages after wavelength decomposition decreases. Fuzzy K–S entropy increases as localized corrosion propagates but decreases as uniform corrosion spreads.

The methods proposed in this work open a new way for fast corrosion evaluation of metallic materials exposed to atmospheric conditions.

It is well known that alloys, based on iron, were exposed to steam oxidation environment producing thick and non-protective oxide scale. More expensive stainless steels contain more Cr and are able to form more protective scales. The purpose of this research was to show ability to employ nitride coating on different alloys (T23, T91, E1250, 347HFG and HR3C) in order to enhance steam oxidation resistance.

The alloys were exposed to steam oxidation rig. Before the test, furnace was purged by nitrogen in order to remove moisture and oxygen. Di-ionised water was pumped from the reservoir using a peristaltic pump into the furnace. System was kept in the closed circle. To reduce solubility of oxygen, di-ionised water was constantly purged by nitrogen. The total exposure time was 2,000 h at 650°C under 1 bar pressure.

Due to the research, it was found that plasma nitriding process is detrimental for the protection of high-temperature structured materials; the high concentration and high activity of Cr produced a CrN phase. This phase is not stable in steam environment and underwent oxidation to Cr₂O₃ and further into volatile phase (CrO₂(OH)₂). Therefore, austenitic steels (E1250, 347HFG and HR3C) coated with nitride coating deposited by plasma nitriding process suffered similar degradation as the uncoated low Cr ferritic steel.

The main limitation of the research conducted in this study was corrosion resistance of the exposed materials.

To the best of the authors' knowledge, this report is the first of its kind to present nitrided alloys (ferritic and austenitic) exposed in steam oxidation.

The purpose of this paper was to evaluate corrosion resistance of superheater T91 material based on high temperature corrosion experiments with a condensate environment.

The contributions of water temperature, chloride concentration and corrosion time were considered and analyzed for modeling corrosion kinetics. The corrosion tendency also was predicted, and the results were compared with higher temperature exposures of T91 tube material installed in a biomass power plant.

High temperature exposure tests showed that the corrosion rates of T91 material would increase with temperature; there was a very evident corrosion acceleration point in 110°C. It was concluded that dimensional homogeneity analysis can serve as a viable evaluation method for T91 superheater material.

Dimensional homogeneity analysis was used as evaluation method for anti-corrosion performance of T91 superheater material.

The purpose of this paper is to obtain a single setting (optimal setting) of various input parameters of pack cementation process, i.e. halide salt activator, powder of master alloy and wt% of Y₂O₃ to obtain a single output characteristic as a whole namely resistance of hot corrosion for T91 steel.

The multi-criterion methodology based on Taguchi approach and utility concept has been used for optimization of the multiple performance characteristics namely hot corrosion rate K_P1, K_P2 and K_P3 for pack cementation coated T91 steel in chlorine and vanadium environment.

All the three pack cementation parameters, namely, halide salt activator, powder of master alloy and wt% of Y₂O₃ had a significant effect on the utility function based on analysis of variance for multiple performances. The percentage contribution of halide activator (1.54 percent), master alloy powder (4.66 percent) and wt% Y₂O₃ (93.79 percent). The results indicated the beneficial influence of yttrium on the chemical stability of the protective layer in presence of chlorine and vanadium environments. The optimal parameter settings obtained in this study is A2B2C1, i.e. halide salt activator (NaCl), powder of master alloy (92Cr-8Al) and 1wt% of Y₂O₃.

The outcome of this study shall be useful to explore the possible use of the developed coating for high temperature components. Unfortunately, the pack cementation was normally limited by the diffusion and reaction kinetics involved, which has a detrimental effect on the mechanical properties of work pieces. Therefore, reducing pack cementation temperature is required for widespread application of the pack coatings.

Pack coating at optimum conditions can be used for surface coating technologies to economically improve high temperature oxidation, corrosion resistance of components.

The multi-criterion methodology based on Taguchi approach and utility concept has been used for first time for parametric optimization of wt% Y₂O₃ modified chromium- aluminide coatings for T91 steel.

Molten sulphate-vanadate induced hot corrosion is the main reason of failure of boiler tubes used at high temperatures in thermal power plants. The hot corrosion can be encountered by applying thermal spray coatings on the alloy steels. In this perspective, this paper aims to attempt to investigate the effect of carbon nanotubes reinforcement on Cr₂O₃ composite coatings on hot corrosion behaviour of ASTM-SA213-T22 steel in a corrosive environment of Na₂SO₄ – 60%V₂O₅ at 900^°C for 50 cycles.

The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900^°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques.

During investigations, the carbon nanotubes (CNT) reinforced Cr₂O₃ composite coatings on T22 steel were found to provide better corrosion resistance in the molten salt environment at 900^°C. The coatings showed lower weight gain along with formation of protective oxide scales during the experiment. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.

The addition of CNT has resulted in reduction in porosity by filling the voids in chromium oxide coating, with interlocking of particle and has blocked the penetration of corroding species to enhance the corrosion resistance of the composite coatings. The corrosion rate was found to be decreasing with increase in CNT content in coating matrix.

It must be mentioned here that high temperature corrosion behaviour of thermally sprayed CNT-Cr₂O₃ composite coatings has never been studied, and it is not available in the literature. Hence, present investigation can provide valuable information for application of CNT-reinforced coatings in high temperature fuel combustion environments.

This paper aims to investigate the hot corrosion behavior of Ni-Cr and Cr3C2-NiCr coatings, deposited on T11, P91 boiler steels by detonation gun spray coating (D-Gun) process to enhance high temperature corrosion resistance.

Hot corrosion studies were conducted in secondary super heater zone of boiler at 900 °C for 10 cycles on bare and D-Gun coated steel specimens. The microhardness and porosity values of as-sprayed coatings were measured before exposing the specimens in the boiler environment. Each cycle consisted 100 h of heating in the boiler environment followed by 20 min of cooling in air. The weight change measurements were performed after each cycle to establish the kinetics of corrosion using thermogravimetric technique. X-ray diffraction, SEM techniques were used to analyze the corroded specimens.

Uncoated boiler steel experienced higher weight loss. The Cr3C2-NiCr coating was found to be more protective than Ni-Cr coating. The phases revealed the formation of oxide scale on coated specimens, mainly consist of nickel and chromium, which are reported to be protective against the hot corrosion.

There is very limited reported literature on hot corrosion behavior of Ni-Cr and Cr3C2-NiCr coatings deposited on the T11 and P91 substrates by detonation gun (D-gun) spray technique. T11 and P91 alloy steels have been chosen for this study because these two alloys are used to manufacture boiler tubes used in Indian thermal power plants.

In Indian thermal power plants, the main cause of boiler tube failure is the presence of molten sulphates and vanadates, which deteriorate the tube material at high temperatures. To combat the hot corrosion failure of metals, thermal spray technology is adopted. This study aims to investigate and study the effect of hot corrosion behaviour of carbon nanotube (CNT)-reinforced ZrO₂-Y₂O₃ composite coatings on T-91 boiler tube steel in a molten salt environment at 900 °C for 50 cycles.

A plasma spray technique was used for development of the coatings. The samples were exposed to hot corrosion in a silicon tube furnace at 900 °C for 50 cycles. After testing, the test coupons were analysed by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and cross-sectional analysis techniques to aid understanding the kinetics of the corrosion reaction.

CNT-based reinforced coatings showed lower weight gain along with the formation of protective oxide scales during the experimentation. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.

It is pertinent to mention here that the high temperature behaviour of CNT-reinforced ZrO₂-Y₂O₃ composite on T-91 steel at 900°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at elevated temperature.