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Browsing Theses by Supervisor "Chhibber, Rahul"
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Item Design and Development of Smaw Electrode Coatings for Dissimilar Metal Welds In USC Power Plants.(Indian Institute of Technology Jodhpur, 2020-07) Chhibber, RahulIn the present era of industrialization, the need for energy demands is increasing at a very fast rate. This calls for the increased load on power plants to produce the required amount of energy economically and efficiently. Supercritical power plants offer improved efficiency by consuming less coal and emits lower CO2. Power plant fabrication and maintenance is a challenging process due to the extreme service environments. Different components and structural establishments require the use of dissimilar metal welds for enhanced integrity and performance. The motivation behind this work was to develop shielded metal arc welding electrode coatings to ensure enhanced performance and minimize the problem of high-temperature failure. Shielded metal arc welding (SMAW) is a widely used welding process in weld fabrication, repair and maintenance. The information about welding consumables presently used is classified and limited in the public domain. The objective of this thesis is to design and develop highly basic electrode coatings to fabricate P22/P91 and P91/SS304L dissimilar joints for power plant applications. Mineral system CaO-CaF2-SiO2-Al2O3 was used to formulate coating compositions by extreme vertices mixture design approach. The developed coatings were experimentally characterized to investigate the physicochemical, thermophysical and wettability properties. The statistical regression analysis has been used to quantify the effect of coating ingredients on these properties. Multipass bead on plate experimentations was performed using developed electrodes. The qualitative and quantitative examination of beads were carried out to assess the suitability of laboratory-developed electrodes. The best performing electrode coatings were then used to fabricate dissimilar P22/P91 and P91/SS304L welds after being extruded on ER90S-B3 and Inconel-82 core wires respectively. The fabricated welds were characterized by mechanical and microstructural behavior. A comparison was also drawn between laboratory developed and commercially available electrodes used for these joints. The developed electrodes had better performance and showed enhanced properties as compared to commercially available electrode. Impact strength improved by 19% and 24% for P22/P91 and P91/SS304L welds respectively. Tensile strength for both the laboratory developed electrode joints remains comparable to the commercially developed electrode joint. High-temperature performance is the intended application for the above-mentioned joints. The base materials P22, P91 and SS304 along with welds P22/P91 and P91/SS304L were investigated for hot corrosion resistance. They were subjected to molten salt environments of alkali sulphates, alkali chlorides and vanadium pentoxide at high temperatures. The welds fabricated with laboratory-developed electrodes exhibited higher corrosion resistance as compared to commercial electrode fabricated welds under all conditions. The results obtained from this work indicate successful development of SMAW electrode coating designed explicitly for P22/P91 and P91/SS304L weld for application in USC power plants. The developed electrodes have better mechanical properties, high-temperature corrosion resistance as compared to commercially available electrode and acceptable microstructural stability.Item Development of Spectrally Selective Absorber Materials and Coatings for Photothermal Applications(Indian Institute of Technology Jodhpur, 2016-08) Dixit, Ambesh; Vijay, Vivek; Chhibber, Rahul"Solar energy is one of the most abundant renewable energy sources, which can be converted (i) directly into electricity using solar photovoltaic, and/or (ii) into thermal energy, which later can be used for numerous applications including electricity generation. The latter one is called as solar thermal technology, where Sun energy is concentrated onto a receiver for its maximum absorption with minimum thermal emission in the desired spectral range simultaneously for efficient conversion into thermal energy. An ideal spectrally selective absorber surface exhibits absorptivity “? ~ 1” in the solar wavelength range and emissivity “? ~ 0” in the infrared wavelength range to convert the entire incident solar irradiation into thermal energy, without any thermal loss. Thus, the development of such spectrally selective coatings is essential to meet the requirement. In addition, these coatings should withstand high operating temperatures and large thermal cycling, without any significant degradation in their solar thermal performance. Black chrome (Cr-Cr2O3) is one of the most extensively studied and commercialized spectrally selective absorber coatings for photothermal applications. Nevertheless, corrosion and thermal stability of black chrome coating are still challenging. The work has focused on improving the corrosion and thermal stability by introducing the nanoparticle (NP) in the black chrome spectrally selective coating matrix. The graphite encapsulated FeCo NPs are used in the black chrome electrolytic bath to synthesis FeCo(C) NPs modified black chrome thin films. These modified black chrome thin film structures have showed enhanced thermal stability and corrosion resistance, as compared to pristine black chrome structures. In addition, the work has also focused on design and development of reflector-absorber tandem spectrally selective coating structures for high temperature applications. These are based on Zr refractory material as a reflector in conjunction with ZrC-ZrN absorbers. The developed ZrOx/ZrC-ZrN/Zr/substrates structures suggest that these coatings can be used upto 700ºC in vacuum on SS substrates and upto 200ºC in ambient conditions without any significant degradation in their solar thermal performance. The corrosion studies on these structures are carried out in 3.5 wt.% NaCl electrolyte solution and observed that these structures are highly corrosion resistance. The corrosion rate is ~ 0.000054 (mm/y), which is much lower, as compared to both stainless steel and copper substrates. These studies suggest that the developed ZrOx/ZrC-ZrN/Zr structures may be used for high temperature applications under the adverse conditions such as saline environmentsItem Experimental Investigation on Development and Structural Integrity Assessment of Glass to Metal Joint(Indian Institute of Technology Jodhpur, 2018-05) Chhibber, RahulThe joining of glass with metal plays an important role in various applications including vacuum tube, Solid Oxide fuel cell, electronics component, parabolic trough receiver tube (PTRT).The presented research is focused on the development of novel glass-metal joint for PTRTs. The initial aim of present investigation was to select a suitable glass-metal joint combination on the basis of wettability, surface roughness, pre-oxidation time, microstructural and X-ray diffraction studies. Later, an unmatched glass-metal joint between borosilicate glass and austenitic stainless steel SS 304 was developed after selecting the suitable glass-metal joint combination. 40SiO2-54B2O3-4Na2O-2Al2O3 material was used as the glass sealant to join the SS304 metal ring and borosilicate glass tube. The chemical compositions of glass sealant were investigated by changing SiO2/B2O3 ratio by using statistical design of experiment approach for SiO2-Al2O3-B2O3-Na2O system. The effect of SiO2/B2O3 ratio in glass sealant on wettability, glass transition temperature Tg and crystallization temperature Tc, thermal conductivity, adhesion and density were studied.Item Experimental Investigations on Dissimilar Metal Welds For Offshore Applications(Indian Institute of Technology Jodhpur, 2021-10) Chhibber, RahulThe structure and components of pipeline steel suffer a significant loss of properties due to the corrosive marine environment. It is joined with high corrosion-resistant alloys in critical zones using different welding processes. The joint of primary interest in this study is a dissimilar weld between pipeline steel API X70 and high corrosion resistant alloy super duplex stainless steel SDSS 2507. The joint find application in the marine splash zone for drilling riser and branching/sub branching sections of oil-gas distribution pipeline network. A methodology has been proposed to develop shielded metal arc welding electrodes for fabricating the said joint. The developed coating for shielded metal welding electrodes in the laboratory utilizes CaO, CaF2, TiO2, and SiO2 as major constituents. The coating composition has been characterized for physicochemical, thermophysical, wettability and structural properties to assess their suitability. Regression analysis was used to establish the influence of individual coating constituents and their interactions on properties. A mining waste red ochre from iron ore tailings after experimental characterization has been used in an as-is state as a constituent of electrode coating. The addition of mining waste has been proposed as an alternative to the commercial ferro-alloy powders, thereby making the process environmentally sustainable. The developed coating compositions were extruded on austenitic stainless steel 309L grade filler wire to fabricate shielded metal arc welding electrodes. The electrodes were then used to apply a multi-pass bead on the plate, which was examined qualitatively and quantitatively. The two most suitable coating compositions and commercial grade 309L electrodes have been used to fabricate the dissimilar weld from SMAW process. Mechanical and metallurgical characterization of the welds was done to compare the laboratory-developed electrodes' performance and assess their suitability. A dissimilar weld between API X70/SDSS 2507 steels was also fabricated using gas tungsten arc welding (GTAW) process using two candidate fillers: (i) austenitic stainless steel (ASS) 309L and (ii) super duplex stainless steel (SDSS) 2594. The weld made with ASS 309L filler has skeletal morphology ferrite precipitated in an austenite matrix. In contrast, the super duplex filler has the precipitation of reformed austenite. The welds were examined for mechanical, microstructural, and corrosion behavior. Elemental analysis shows a significant gradient of alloying elements (Cr, Ni, Si, Mo) at the X70/weld interface. ThermoCalc has been used for Scheil's solidification calculations and equilibrium phase estimation. An attempt has also been made to study the effect of heat treatment on wear and corrosion properties of super duplex stainless steel. The wear properties have been studied in the dry and wet medium matching the actual service conditions. Cyclic corrosion study was performed to compare the corrosion resistance of pipeline steel with super duplex stainless steel in an as-received and heat treated condition. The work carried out and results reported in this thesis are of direct application to the offshore oil-gas exploration and transportation sectors.