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The oxidation behaviour of a wrought Ni‐Mo‐Cr alloy was studied under thermal cyclic conditions in air at 800°C for exposure periods of up to 1,000 h. The morphologies…
The oxidation behaviour of a wrought Ni‐Mo‐Cr alloy was studied under thermal cyclic conditions in air at 800°C for exposure periods of up to 1,000 h. The morphologies, microstructures and compositions of the oxide scales were characterized by scanning electron microscopy, energy dispersive X‐ray spectroscopy and X‐ray diffraction. Oxidation kinetics were determined by weight gain measurements. Results show that steady‐state oxidation was achieved within 1 h of exposure while partial scale spalling was observed after 400 h. The alloy grain boundaries intersecting the alloy surface showed preferential oxidation. They became depleted in Ni and enriched in Mo and Cr during transient oxidation. The scale initially formed at the surface was NiO which grew outwardly and laterally to cover the entire alloy. Upon continued oxidation, the scale developed into an outer NiO layer and an inner Cr2O3 layer while the presence of NiMoO4 was also observed within the scale.
To determine if the interim use of liquid waste as a fuel in a catalytic steam reformer unit had any deleterious effect on the long‐term life of the reformer tubes.
Standard metallographic techniques were used to prepare representative samples obtained from various sections of the reformer tubes for metallurgical evaluation. Microstructural characterization was carried out in a scanning electron microscope equipped with an energy dispersive X‐ray spectrometer. Imaging and elemental analysis was used for the identification of the alloy material, corrosion products and other microstructural features.
Hydrogen was produced in a catalytic steam reformer by cracking methane using natural gas as a fuel. Corrosion of reformer tubes occurred when natural gas fuel was replaced with a liquid waste. Use of liquid fuel waste accelerated the rate of oxidation at the outer tube surface. However, foreign species from the fuel were not transported into the tube material. The heat‐resistant steel casting used for this application was susceptible to precipitation of Si‐stabilized Ni‐Nb Laves phase, thus reducing rupture life of the component. Voids at grain boundaries indicative of creep damage were observed.
Although, the interim use of liquid waste fuel appeared not to have damaged the tubes, it was concluded that the expected service life of the tubes may not be realized because of the susceptibility of the material to precipitation of Laves phase. An Fe‐base superalloy UNS N08810 or UNS N08811 was recommended as a replacement material for this application.
This paper provides an account of a failure analysis study. It identifies incorrect materials selection for a particular application and suggests better alternative along with its justification. The information is deemed useful for plant designers and engineers working in the related industry.
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…
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 KP1, KP2 and KP3 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.
In this paper, a review of materials selection methods is presented. It initially discusses the importance of materials selection in various fields of scientific study…
In this paper, a review of materials selection methods is presented. It initially discusses the importance of materials selection in various fields of scientific study particularly in engineering design. Various tools and methods for the selection of materials are reviewed. These include materials handbook, materials data‐bases, materials selection charts, artificial intelligence systems, and other computeraided materials selection systems.