Navneet Arora

Availability analysis of steam and power generation systems in the thermal power plant

The paper discusses the availability analysis of a steam generation system consisting of three subsystems A, B and D and a power generation system consisting of four subsystems E, F, G and H arranged in series, with three states viz., good, reduced and failed. Taking constant failure and repair rates for each working unit, the mathematical formulation is done using the Birth-Death process. Expressions for steady state availability and the MTBF (mean time between failure) are derived. The graphs are given, depicting the effect of failure and repair rates on the system availability. The results are supplied to the plant personnel, to plan the policies for failure free running of the systems for a long duration.

Use of bimetallic welds in nuclear reactors: Associated problems and structural integrity assessment issues

Abstract The bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system in itself is the critical part of a nuclear reactor. Any failure of this system can lead to grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. The present paper is an effort towards identifying and understanding the problems affecting the BMWs and is as well an attempt to highlight the current issues in the structural integrity assessment of structures having these welds. The basic aim of this work is to provide a clear understanding of the current structural safety issues and their importance in underpinning the use of BMWs in modern nuclear reactors.

Dry erosion wear performance of Inconel 718 microwave clad

Abstract This paper reports on the dry erosive wear performance of Inconel 718 clads deposited on SS-304 substrates through microwave hybrid heating technique. Clads were deposited using a domestic microwave applicator at 2·45 GHz and 900 W. The microstructural observations of the Inconel 718 clad indicate good metallurgical bonding with the substrate and revealed no visible interfacial cracking. The microhardness of the clads was assessed using a Vicker’s microhardness tester and the average microhardness in the clads was 564±22 HV. Erosive wear performance of the clads was evaluated using an air jet erosion test setup as per ASTM G76 standard. The effect of varying impact angle was studied; the results have been discussed with the help of SEM images of the worn surfaces. It was observed that the improved erosive performance of the Inconel 718 clads was due to presence of strengthening intermetallic phases (Ni3Ti, Ni3Al) in the tough Ni–Fe–Cr matrix.

Solid Particle Erosion Behavior of WC-CoCr Nanostructured Coating

In the present study, solid particle erosion resistance of high-velocity oxy-fuel (HVOF)-sprayed WC-CoCr coatings was evaluated. Erosion testing was conducted using alumina (Al2O3) powder as the erodent with three different impact angles (30, 60, and 90°) and impact velocity was kept constant. The coatings were deposited using two different powders; one was composed of conventional WC particles and second one contained nanoscale particles mixed with CoCr binder material. Erosion testing was carried out at room temperature using an air-jet erosion test setup. The effect of varying impact angles was studied and discussed with the help of scanning electron microscopy images of worn surfaces of coatings. The results showed that coating properties like microhardness and fracture toughness have a strong influence on the erosion behavior. During erosion testing, material was removed by fracturing and pullout of WC grains from the binder matrix. The morphology of the eroded surface also showed cutting, lip, and groove formation in the binder matrix caused by the repetitive impacts of erodent particles. It was observed that coating with nano-WC grains exhibited higher erosion resistance compared to conventional coating.

Stochastic analysis and maintenance planning of the ash handling system in the thermal power plant

Abstract This paper discusses stochastic analysis of the ash handling system in a thermal power plant. The system consists of four subsystems Ai, Bj, C and Dk in series, with three possible states: good, reduced and failed. Failure and repair rates for each subsystem are taken to be constants. Using a probabilistic approach, the differential equations are generated and the expression for steady state availability is computed. Taking data from the thermal power plant, situated in North India, the behaviour of each working unit is analysed. Problems and remedies with appropriate maintenance schedules have been discussed. The results are discussed with the plant personnel and are helpful to the management in predicting the behaviour of each operating unit, so that timely decisions can be taken for maintaining the system in upstate for a long duration.

Investigation into Arc Behavior during Twin-Wire Submerged Arc Welding

Behavior of leading and trailing arcs in twin-wire submerged arc welding has been investigated with help of transient heat transfer analysis. An appropriate heat transfer model with dissimilar heat sources at leading and trailing arcs has been considered. The model has been simulated with different combinations of model parameters. Computed and experimentally measured temperatures have been compared and geometrical and heat distribution differences between leading and trailing heat sources have been suggested. The behavior of leading and trailing arcs along with comparison between the current and the conventional approach has been presented and discussed. The simulation indicates that the leading arc has a major share in producing penetration where as the trailing arc is more responsible for melting.

On microstructure, hardness and wear behaviour of flame sprayed Co base alloy coating deposited on mild steel

Abstract In the present paper, the influence of preheat and post-spray heat treatment temperature on microstructure and adhesive wear behaviour of flame sprayed Co base hard facing alloy (EWAC 1006 EE) coatings on mild steel has been reported. Coatings were deposited by oxyacetylene thermal spraying torch. Thermal spraying of substrate was carried out at two preheat temperatures, i.e. 300 and 350°C. The post-spray heat treatment of the coatings was carried out at three different temperatures: 650, 750 and 850°C, for 2 h. Wear resistance of coatings was evaluated using ring on block wear system at 40 N normal load and 1 m s−1 sliding speed of ring. Hardness of coating, base metal and interface was tested using Vickers hardness testing machine. Optical studies of the microstructure of the substrate, interface and coating were carried out to investigate the influence of preheat and post-spray heat treatment temperatures. It has been found that an increase in post-spray heat treatment temperature enhances the hardness and wear resistance of the coating.

Statistical modeling of deposition rate in twin-wire submerged arc welding:

Abstract The present article offers statistical modeling of deposition rate in twin-wire submerged arc welding. ‘Best subset selection method’ and ‘Mallows criterion’ have been used for model development. The deposition rate has been experimentally measured under varying process parameters including welding current, welding voltage, welding speed, contact-tube-to-workpiece-distance, and wire-diameter. Models for two polarities — direct current electrode positive and direct current electrode negative — have been presented. The models have been validated and have been further confirmed with the data points other than that used for model development. The models have been checked for their predictability and also compared with the models developed with conventionally used technique. The developed models of deposition rate in twin-wire submerged arc welding can be used for practical purposes with admissible error in prediction and better predictability compared with conventional models. The effects of process parameters on the deposition rate have also been presented.

Effect of Electrode Coatings on Diffusible Hydrogen Content, Hardness and Microstructures of the Ferritic Heat Affected Zones in Bimetallic Welds

Bimetallic welds (BMWs) have been a necessity within the steam generators of nuclear power plants, where the heavy section low alloy steel components are usually connected to stainless steel primary piping systems. These welds represent zones with metallurgical discontinuities, which tend to localize the strains and cause failures. The other critical issues which must be taken care of while welding of bimetallic joints include solidification cracking, thermal fatigue and residual stresses in welds. The occurrence and severity of all these problems associated with bimetallic welds depend upon the type of welding process used along with the other variables like welding consumables, heat input etc. In shielded metal arc welding (SMAW), welding electrode consumables/coatings play an important role in deciding the weld metal quality. The development of welding electrode coatings is quite difficult due to very rapid complex reactions taking place during welding and the involvement of many controlled process variables. The present paper is an effort to highlight the general issues and challenges for the systematic and scientific development of welding electrode coatings for bimetallic welds. The experimental procedure contains three sets of coated electrodes having varying ferro-alloys, silica and carbon content. In the first set of electrodes, non-ferrous elements are also introduced into the weld metal through flux addition. Further, the welded joints are subjected to various tests and then evaluated to ascertain their mechanical as well as metallurgical behaviour.

Estimation of Gurson material parameters in bimetallic weldments for the nuclear reactor heat transport piping system

Bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system itself is the critical part of a nuclear reactor. Any failure of this system can lead to very grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. This paper describes the experimental efforts towards estimation of Gurson material parameters of base metal and weld metal regions of a BMW so as to use the micromechanical modelling approach for addressing the structural integrity issues in BMWs.