Transition metal joints for steam generators—An overview

The transition metal joint (TMJ) between an austenitic stainless steel and a chromium-molybdenum (Cr-Mo) ferritic steel used widely in steam generators of power plants has for a long time presented problems relating to premature failures in service. The direct (bimetallic) TMJ presently in use is designed for a service life of about 200,000 h; but such TMJs with iron-base weld metals have been failing in service within about one-third of their design lifetime, while their counterparts with nickel-base weld metals fail within about one-half of their design lifetime. The causes for such premature service failures of these TMJs are discussed in detail, leading to the development of improved TMJs. One of the improved TMJs with a trimetallic configuration of austenitic stainless steel/Alloy 800/Cr-Mo ferritic steel is discussed in detail, covering its development, characterisation and evaluation. Accelerated performance tests in the laboratory have indicated a four-fold improvement in the service life of the TMJ with this trimetallic configuration compared to the bimetallic configuration. The metallurgical details of these studies are also discussed in this paper.     

Performance comparison of neural architectures for on-line flux estimation in sensor-less vector-controlled IM drives

The sensor-less vector-controlled induction motor drive requires accurate estimation of speed and flux. The speed estimation depends on the motor flux, which has to be measured or estimated. The flux measurement is difficult and expensive and hence generally estimated. Conventional voltage model equations for flux estimation encounter major drawbacks at low frequencies/speed. Neural network-based estimator provides an alternate solution for on-line flux estimation. The on-line flux estimator requires the neural network model to be accurate, simpler in design, structurally compact, and computationally less complex to ensure faster execution time in real-time implementation for effective control. This in turn, to a large extent, depends on the type of neural architecture. This paper investigates three types of neural architectures for on-line flux estimation and their performance is compared in terms of accuracy, structural compactness, computational complexity, and execution time. The suitable neural architecture for on-line flux estimation is identified and the promising results obtained are presented.     

A novel NN based rotor flux MRAS to overcome low speed problems for rotor resistance estimation in vector controlled IM drives

This paper presents a new neural network based model reference adaptive system (MRAS) to solve low speed problems for estimating rotor resistance in vector control of induction motor (IM). The MRAS using rotor flux as the state variable with a two layer online trained neural network rotor flux estimator as the adaptive model (FLUX-MRAS) for rotor resistance estimation is popularly used in vector control. In this scheme, the reference model used is the flux estimator using voltage model equations. The voltage model encounters major drawbacks at low speeds, namely, integrator drift and stator resistance variation problems. These lead to a significant error in the estimation of rotor resistance at low speed. To address these problems, an offline trained NN with data incorporating stator resistance variation is proposed to estimate flux, and used instead of the voltage model. The offline trained NN, modeled using the cascade neural network, is used as a reference model instead of the voltage model to form a new scheme named as “NN-FLUXMRAS.” The NN-FLUX-MRAS uses two neural networks, namely, offline trained NN as the reference model and online trained NN as the adaptive model. The performance of the novel NN-FLUX-MRAS is compared with the FLUX-MRAS for low speed problems in terms of integral square error (ISE), integral time square error (ITSE), integral absolute error (IAE) and integral time absolute error (ITAE). The proposed NN-FLUX-MRAS is shown to overcome the low speed problems in Matlab simulation.     

The effect of diffusion barrier formation on the kinetics of aluminizing in inconel-718

Aluminizing of nickel alloy 718 was studied in order to reveal the effect of combined alloy additions on aluminide growth kinetics, as opposed to pure metal substrates. The low activity pack process was used and treatment was carried out at 1273 K using ammonium fluoride activator and Ni-50 wt% Al powder as an aluminium source for treatment times of 1, 2, 4 and 8 h. The aluminide coatings varied between 40 and 110 m in thickness. The microstructures consisted of a NiAl phase with a fine grain size containing small secondary-phase particles at the grain boundaries. The interface between the coating and the substrate was lined by a lamellar layer exhibiting a two-phase structure, which was enriched in chromium and niobium in addition to containing iron and nickel. Weight gain measurements indicated parabolic growth up to 2 h, beyond which the growth rate slowed down. Microstructures and composition profiles revealed that the interlayer, which was enriched in elements insoluble in NiAl, posed a barrier to interdiffusion of the reacting species and slowed down the growth kinetics of the aluminide.     

The influence of post weld heat treatments on the structure,composition and the amount of ferrite in type 316 stainless steel welds

Microstructures of welds of AISI type 316 stainless steel have been examined with a view to establishing the changes that occur during postweld heat treatments in the temperature range 900 to 1100°C. The ferrite content of the weld zone has been estimated using a point count technique in the as-welded condition as well as after heat treatments. In addition, the compositional changes occurring in the ferrite phase have been determined using an electron microprobe analyzer. The ferrite content of the weld decreases continuously with an increase in the aging time. At the same time, the morphology of the ferrite changes from a dendritic network into a distribution of isolated near spherical particles. An analysis of the kinetics of the dissolution and the spheroidization of ferrite suggests that both these processes are controlled by interface diffusion; activation energies for these processes are 132 and 140.5 kJ/mol respectively. The influence of the heat treatment variables on the morphology and composition of the ferrite phase have been discussed.     

Microstructure of the heat-affected zone in 17–4 PH stainless steel

The microstructure of the heat-affected zone (HAZ) in bead-on-plate welded 17–4 PH stainless steel was studied with special reference to the roles of prior heat treatment and heat input during welding. The HAZ in solution-annealed condition consists of three different microstructural zones containing: (i) retransformed martensite and reformed austenite; (ii) overaged martensite; and (iii) under-aged martensite. In aged condition the HAZ consists of zones (i) and (ii), while in overaged condition it consists almost entirely of zone (ii). The HAZ in solution-annealed and aged conditions is characterised by steep gradients in hardness, while in overaged condition it has uniform hardness throughout. A good correlation was obtained between the calculated temperature distribution in the HAZ and the observed microstructural features.     

Stress-corrosion cracking of 15cr-15ni-2.2mo titanium-modified austenitic stainless steels

The stress- corrosion cracking (SCC) behavior of two alloys of titanium- modified austenitic stainless steels with different TiJC ratios in the 20% cold worked condition was studied in 45% boiling magnesium chloride (BP427 K) using the constant- extension rate testing (CERT) technique. The SCC susceptibility of the two titanium-modified alloys was assessed using the ratios of the values of ultimate tensile strength (UTS) and percent elongation in magnesium chloride and liquid paraffin, the susceptibility index (I), crack propagation rates (CPR), and stress ratios at different values of plastic strains. The results obtained on these alloys were compared with AISI type 316 stainless steel. It was observed that the two titaniummodified austenitic stainless steels had better SCC resistance than type 316 stainless steel, mainly due to their higher nickel content and, to a lesser extent, to the presence of titanium. Increasing the value of the TiJC ratio led to increased SCC resistance due to the availability of more free titanium in the solid solution. Fractography of the failed samples indicated failure by a combination of transgranular SCC and ductile fracture.     

Combustion,performance and emission analysis of dual fuel engine using tsrb biogas

In this work, an experimental investigation has been carried out to reduce the emission and improve the performance and combustion characteristics of direct injection compression ignition (DICI) engine fuelled with diesel and biogas in dual fuel mode. The anaerobic digestion method was used to produce biogas from tamarind seed and rice bran (TSRB). The diesel is injected by conventional injector setup and the biogas is inducted through the intake manifold with air in different flow rates such as 0.25, 0.50, 0.75, and 1.0 kg/hr. The emission, combustion, and performance test is conducted with a different flow rate of biogas with diesel and compared with diesel. Results show that the smoke and Nox emissions are lowered by 7.1and 23.27%, respectively compared to diesel mode.