An analysis of the hydraulic system of the natural circulation loop of the waste-heat boilers of combined-cycle gas turbine units is performed. It is demonstrated that the standard method of ...hydraulic calculation of steam boilers based on an evaluation of the reliability criteria of the hydraulic system and the thermal regime of the evaporator tubes is incorrect. The existence of loop-wide hydraulic persistence of flow in the low-pressure evaporator in natural circulation caused by elevated resistance of the steam-outlet tubes is demonstrated for the first time. Recommendations are given for increasing the reliability of the hydraulic system of the low-pressure evaporator loop and selecting an optimal combined water and chemical regime to prevent erosion wear of the metal of the inner surface of the evaporator tubes.
Performing high-quality repair on aging hydro power equipment is a challenging issue for utilities. Weld repair deteriorates the mechanical properties of the base metal in and around the ...heat-affected zone. For martensitic stainless steel runners, there is no way to perform post-weld heat treatment (PWHT) on site to restore those properties without dismantling, a very expensive job for such large components, typical of power utilities. To perform in situ high-quality repairs on such components, a new robotic heat treatment process is developed. Heat is generated and controlled using a flat spiral coil mounted on a compact, portable robot and moved over the area needing heat treatment. Unlike conventional induction heating, which requires a customized coil, this new approach combines a universal coil and a flexible robot to heat a broad range of complex shapes. One critical aspect is to set heating and path parameters in order to generate a target spatial and temporal temperature field. This paper proposes a numerical method combining thermal finite element analysis and a non-linear optimization algorithm to set these parameters. The temperature resulting from the electromagnetic field induced by the coil is modeled using an average heat input source to improve computation speed. Good agreement is obtained between numerical and experimental results for PWHT under laboratory conditions.
Methods for restoring steam turbine rotor blade erosion damage are reviewed. Favorable factors and shortcomings of the methods considered are analyzed. The most promising method for restoring rotor ...blades by laser-powder surfacing is recommended.
Cut face roughness analysis under waterjet cutting Verchenko, A. V.; Tamarkin, M. A.; Kishko, A. A.
Vestnik Donskogo gosudarstvennogo tehničeskogo universiteta (Online),
06/2017, Volume:
17, Issue:
2
Journal Article
Technology is provided for restoring erosion damaged rotor blades of the last stages of steam turbine low-pressure cylinders (LPC) using laser-powder surfacing and application of an erosion-resistant ...coating. For this method there is typically low heat input into the blade basic metal, which improves its restoration reliability. Results are obtained for comprehensive experimental studies on specimens and blades, confirming the high quality of welded joints obtained by laser surfacing of nickel alloy proposed for restoring the blade profile of blade steels ÉI961-Sh and 15Kh11MF-Sh, and application of a stellite-6 erosion-resistant coating. The possibility is concluded of using the laser-powder surfacing method during refurbishment of steam turbine LPC rotor blades.
Finite element analyses are used to simulate the response of glass impacted by solid particles. The Sun-Khaleel stress-based continuum damage mechanics (CDM) model is used to describe the ...constitutive behavior of glass. The contribution of different cracking systems in the strength degradation of glass is explicitly taken into account by the anisotropic CDM model which is enhanced by coupling with a vanishing element technique. Focusing on the initiation and propagation of the ring/cone crack, a combined numerical and experimental approach is proposed to estimate the CDM stress limits. The changes in contact characteristics due to erosion damage mechanism in glass are then studied using the developed predictive tool. In accordance with available experimental observations, it is found that the impact-induced damage reduces the energy restitution coefficient and increases the contact time.
► Development of an anisotropic model including damage and a failure criterion. ► Identification of model parameters using a hybrid numerical/experimental approach. ► Prediction of cracking patterns in glass subjected to impact loading. ► Demonstration of a nice agreement between numerical trends and experimental data.
This article investigates the effect of kinematic excitation on the vibration stress state of blades in the mistuned disk of a last stage high-power steam turbine. Turbo-machines often experience ...deviations in blade geometry and bandage connection conditions, leading to variations in the cyclic symmetry of the blade-disk system. Additionally, erosive damage can occur in the blades due to high humidity in low-pressure cylinders. Repairing damaged blades introduces changes in their natural frequencies, further broking the cyclic symmetry. The objective of this study is to assess the influence of the broken cyclic symmetry on the stress state of blades in the last stage of a high-power steam turbine. A finite element model is developed to analyze the vibrations of the blade-disk system, considering kinematic excitation caused by the movement of the shaft's center. The computational studies reveal resonant regions and changes in maximum equivalent stresses in the blades. The results demonstrate that kinematic excitation affects the stress distribution in the blades, with increased stresses observed near the rotation frequency. The findings emphasize the importance of considering kinematic excitation when evaluating the vibration reliability of blades in mistuned disk configurations. Understanding the stress behavior and its relationship to cyclic symmetry can contribute to prolonging the safe operation of repaired blades and ensuring the reliability of steam turbine systems.
The effect of laser surface alloying of type 316 stainless steel on the erosion resistance in mercury has been investigated. The alloying was produced by melting predeposited Al–Si powder and a ...portion of underlying substrate with a pulsed Nd:YAG laser beam. The microhardness of the modified layer was found to be 2.5 times higher than that of untreated steel. The erosion test of laser alloyed surface and steel in mercury was carried out by using the electromagnetic impact testing machine. The laser alloyed surface was found to be less damaged after 10
5 cycles of impacts compared to untreated stainless steel. However, after 10
6 cycles the erosion resistance of the modified layer is much lower than that of untreated steel. Liquid metal embrittlement in contact with mercury and residual stresses were considered as factors impairing the erosion resistance of the laser alloyed surface.
This research was done to slow the decrease in the use of windbreaks by preparing windbreaks database showing their effectiveness in preventing wind damage in Otofuke, Tokachi region in Hokkaido, the ...northernmost prefecture in Japan. The main research method was using the windbreak data within the GIS (geographic information system). It was shown that the total length of windbreaks in Otofuke increased from 242.3 km in 1995 to 255.0 km in 2003, which was a 12.7 km increase in 8 years. It was shown that the tree species used in the windbreak in Otofuke are Larix kaempferi (Lamb.) Carriere (74.9%), Betula platyphylla sukatchev var. japonica (Miq.) Hara (9.5%), Abies sachalinensis Fr. Schm. (3.0%), Picea glehnii (Fr. Schm.) Masters. (0.5%) and other trees (12.1%). The tree trimming of windbreak of tree height over 20 m decreased at 54 km, and the planting of windbreak of tree height of 10 m or less increased 7 km. In spite of increased the extension of windbreaks slightly, the sheltered areas by windbreak decreased 1,400 ha. It was proved that the windbreak was useful for prevention of wind erosion damage through the relations between the sheltered areas by the wind-break and the place of the wind erosion damage.
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