Main Stop Valve Research Articles

Effect of long term aging on Microstructure and precipitates of valve bolts in power plant

10Cr11Co3W3NiMoVNbNB is used as the materials of Intermediate Pressure Control Valve, High Pressure Control Valve, and Main Stop Valve in some thermal power plant. After 45,000 hours of operation, the mechanical properties of this those materials has have been decreased greatly. By means of scanning electron microscopy, transmission electron microscopy and thermodynamic software simulation analysis, the conclusions can be drawn: under this operation environment, the coarsening of martensite lath and the dissolution-reprecipitation of second phases such as M23C6 carbides and MX phases are the main reasons which result in the decrease both in the room mechanical properties and high temperature mechanical properties of materials.

Evolution in Microstructure and Mechanical Properties of Inconel 783 Alloy Bolts after Long Term High-Temperature Aging at 700 °C

This paper described systematically the changes in microstructure and mechanical properties of Inconel 783 alloy after a considerably long time (equivalently 55,000 h, about 76.4 months) of thermal exposure. Based on the Inconel 783 alloy bolts of an intermediate pressure main stop valve used in a 1000 MW ultra-supercritical unit, the evolution of microstructures and mechanical properties were studied after 700 °C aging temperature with different aging times (1000 h, 3000 h and 20,000 h, corresponding to about 1.4 months, 4.2 months and 27.8 months, respectively), using an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD), a universal tensile testing machine and impact testing machine. The results indicated that the bolts aged for 1000 h in two temperatures, showing the second needle β phase, of which the quantity and size obviously increased with aging time. Meanwhile, the characteristics in quantity and shape of the primary β phase changed obviously with the aging time, which transformed to strip the Ni5Al3 and Laves-Nb-rich brittle phase in the matrix after aging for 20,000 h. The size of the γ’ phase grew bigger with aging time, and orientation distributions have been observed obviously at 3000 h aging in 700 °C. Compared with the 650 °C aging temperature, the coarsening of γ’ precipitates and second needle β, the orientation distributions of γ’ were more obvious at the 700 °C aging temperature with aging time, which resulted in the rapid decline in yield strength and tensile strength and obvious increase in the brittleness for Inconel 783 alloy bolts.

Effect of aging at 650 °C on microstructure and mechanical properties of GH783 alloy bolt

Taking the GH783 alloy bolt of intermediate pressure main stop valve used in 1000 MW ultra-supercritical unit as the research object, the optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) and mechanical performance tests were carried out to study the microstructure transformation and mechanical properties of GH783 alloy bolts at different aging stages under 650 °C aging environment. The results showed that the secondary needle β phase began to appear in the bolts aged for 1000 h, and the density of secondary β-phases in bolts aged for 3000 h significantly increased. When the aging time reached up to 20,000 h, the secondary β phase coarsened significantly. At the same time, as the aging time prolonged, the morphology and quantity of the primary β phase changed significantly. In terms of mechanical properties, the tensile strength and impact toughness of the bolts gradually decreased. This was due to the growing γ' phase, the formation of Ni5Al3 phase and the Nb-rich Laves phase in the structure during the aging process.

ИССЛЕДОВАНИЕ НЕКОТОРЫХ ПАРАМЕТРОВ КАПЕЛЬНОГО ОРОШЕНИЯ ПУТЕМ ГИДРАВЛИЧЕСКОЙ ОЦЕНКИ КАПЕЛЬНИЦ

The results of laboratory studies of the proposed drip irrigation system are given. Five different types of droppers have been investigated to quantify the hydraulic characteristics. The dependences of the uniformity of water flow through droppers with a change in the working pressure in the system are obtained. Laboratory studies of the experimental facility were carried out at the training and demonstration center of Kazan State Agrarian University. The experimental installation consists of a storage tank, a submersible pump, five P.V.C. main pipes with a length of 3 m and a diameter of 16 mm, stop valves of a drip line, pressure gauges, a main stop valve, a collector line, a return line, and droppers. Before starting the experiments, air was removed from the system and pressure at the inlet to each main pipe was adjusted to the required value. Immediately under each drip, 500 ml volumetric containers were placed to determine the volume of leaked water in two minutes. Significant uniformity of water consumption and the smallest deviations from the specified nominal flow rate were achieved with type A and C droppers (with pressure compensation) at an operating pressure of 0.2 MPa; with type B droppers (also with pressure compensation), water flow uniformity decreased with increasing pressure. The results of the research show that pressure-compensated droppers are less sensitive to pressure changes with an operating pressure of 0.35 MPa. Water consumption (q) for type A droppers increased by 5.27%, B - by 27.3% and C - by 9.1%. Dropper type D and E have the lowest uniformity of water flow at different pressure levels. Under actual irrigation conditions, it is recommended to install pressure gauges not only in the collector line, but also on the main pipes (preferably at the end of each main pipe) to determine the differential and pressure losses in the system.

Reliability of sprinkler system in Australian shopping centres –A fault tree analysis

The purpose of this research is to determine the reliability of sprinkler systems in shopping centres by utilising the fault tree analysis (FTA) method and the collection of data through a physical survey. As such, a comprehensive review of sprinkler systems in the low rise shopping centre buildings with less than four levels was conducted in two Australian cities: Melbourne and Adelaide. Data from eighteen buildings were collected and are presented in this paper. This study only includes wet pipe systems, as these are the most commonly found sprinkler system installations throughout Australia and New Zealand. Although Australian Standards and building regulations are taken as references, the methodology can be used in any other jurisdictions. The data related to the failure frequency, time required for repair and sprinkler downtime due to tenancy changes were collected during site surveys. This data has been used to carry out FTA to derive the likelihood of the failure of the sprinkler system. It is observed that the failure probability of a sprinkler system in Australian shopping centre buildings lies in a range of 1.4% and 9.8% (i.e. reliability range of 90.2% and 98.6%). Compared to a previous study on high-rise office buildings (Moinuddin & Thomas, Fir Saf J. vol 63 pp 52–68, 2014), the reliability of shopping centres is found to be 3%–4% higher. Similar to high-rise office buildings, sprinkler head's failure and isolation of the main stop valve during tenancy upgrades have significant effects on the reliability of the sprinkler system. However, more regulated sprinkler isolation and better maintenance of other components in the shopping centres result in better reliability.

Experimental and numerical study on loss characteristics of main steam valve strainer in steam turbine

In this paper, a kind of filter screen with special structure used in steam turbine’s main stop valve is simplified, and the three-dimensional modeling software is applied to build the filter screen test rig. The loss characteristics of it are investigated by using the method of wind tunnel test. Through the correlation analysis, a simple expression that reflects the total pressure loss of the strainer is obtained. The grid division and numerical simulation are performed on the minimum repeating unit (single crystal cell) which is taken from the whole strainer model and we compare the simulation results with the test data. Then the whole filter screen is simplified into a model of porous media and the feasibility is verified. The experimental results show that the loss coefficient of the strainer with different wind speed changes in a very small range under the same flow deflection angle. At the same wind speed, strainer loss coefficient will rise with the increasing angle, and when the angle varies from 0° to 25°, the increase amplitude of the loss coefficient is small; while it is great when the angel changes from 25° to 65°. Besides, the circumferential rotation angle of the strainer has little effect on its own drag performance. Through the numerical simulation of the single crystal cell of the strainer, its resistance characteristics can be qualitatively obtained. But there are still some deviations between the calculating results and the test data. While the value and variation of the loss coefficients obtained by using the porous media model for numerical simulation are almost identical to experimental data, indicating that the porous media model can better reflect the loss characteristics of real strainer.

화력발전소 주증기배관에서 밸브 차단에 따른 수증기 충격 특성에 관한 연구

본 연구는 화력발전소 최종과열기에서 고압터빈 사이 배관과 고압터빈을 지난 곳에 있는 체크밸브와 1차 재열기 사이 배관을 포함한 수증기 배관시스템에서 터빈의 급작스런 사고로 인해 터빈으로 들어가는 수증기를 차단할 때 발생하는 수증기 충격이 배관시스템에 미치는 영향을 분석하는 연구이다. 이를 위해서 수격현상 해석에 많이 사용하는 Flowmaster 소프트웨어로 배관시스템을 모델링하고 시간 변화에 따라 배관 내부의 압력, 질량유량률의 특성을 파악하였다. 이러한 특성으로부터 수증기 충격이 주로 영향을 미치는 곡관에서 수증기 충격에 의한 힘을 도출하였다. 본 연구를 통해서 수증기 충격은 주증기 차단 밸브 직전의 곡관과 체크밸브 이후에 바이패스 배관과 연결되는 곡관에서 수증기 충격에 의한 힘이 가장 크게 나타남을 밝혀냈다. 본 연구에서는 이렇게 도출한 힘의 기본 자료를 이용하여 차후 연구에서 화력발전소 수증기 배관시스템의 수증기 충격 시 곡관과 지지대의 안전성을 진단하는 토대를 구축하였다. The present study has been carried out to analyze the effect of steam hammering on the steam piping system including the final superheater, the high pressure turbine, check valve and the first reheater by sudden stoping of main stop valve in a power plant. For the present steam hammering analysis, the well known Flowmaster software has been used to model the steam piping system and the time dependent characteristics of pressure and steam mass flow rate has been conducted. Using the result of the unsteady pressure and steam mass flow rate, the forces acting on the elbows in the piping system has been derived. From the present analysis, it has been elucidated that the elbow just before the main stop valve and the elbow near the connection pipe between bypass pipe and check valve had the largest force among the elbows in the steam piping system. The structural safety diagnostics study on the elbow and the supporting structures of the steam piping system of a power plant will be conducted in the future by the present results of the forces acting on the elbow.

Numerical 3D simulation of the erosion due to solid particle impact in the main stop valve of a steam turbine

Solid particle erosion in a steam turbine main stop valve bypass valve has been investigated by means of computational fluid dynamics. Previews attempts to couple fluid mechanics and erosion modeling and improvements in the hydrodynamics models together with improvements in the erosion models are reviewed. The solid particle bearing steam flow through the valve was investigated using a 3D numerical model and the finite volume code Fluent V6.0.12, looking for a reduction of the erosion process. The flow simulation was carried out for the valve original and modified designs with changes of the angle of particle impact on the valve surface. Numerical predictions have been carried out using the Renormalization Group (RNG) k– ε turbulence model. To account for the influence of turbulent fluid fluctuations on particle motion, the stochastic tracking Discrete Random Walk model is used, which includes the effect of instantaneous turbulent velocity fluctuations on the particle trajectories. The removal of wall material due to erosion is calculated using the Finnie model developed for ductile materials. The numerical predictions showed a 51% reduction of the erosion rate for the valve modified design due to changes of the particles trajectories and impingement angle (angle of particle impact). The results obtained show that numerical simulation can be used in a predictive manner to solve a real practical design problem.

Improvement of the Turbine Main Stop Valves with Flow Simulation in Erosion by Solid Particle Impact CFD

The flow field in a steam turbine main stop valve bypass valve (MSVBV) has been investigated by means of CFD simulations. Because the entire flow to the turbine during start ups is carried by the MSVBV it is subject to serious solid particle erosion problems and requires frequent replacement to avoid the catastrophic damage which can occurred when the MSVBV skirt eroded through causing large pieces of metal to be carried directly into the turbine. For some of the most important geometric parameters of the MSVBV, design recommendation have been made.

Improvement of the Turbine Main Stop Valves with Flow Simulation in Erosion by Solid Particle Impact CFD

Improvement of the Turbine Main Stop Valves with Flow Simulation in Erosion by Solid Particle Impact CFD

The steamhammer problem: dynamic shock loading of critical reactor piping systems

In the course of both pre-operational testing and power operation of commercial nuclear power plants, relatively large amplitude transient vibrations of steam piping systems have been experienced with damage to the piping supports in at least one recent case. These transient vibrations result from ‘steamhammer’ or dynamic shock loading induced by pressure and momentum transient conditions generated in the piping by sudden changes to the flow conditions, such as are produced by sudden valve opening or closure. In particular, vibrations have been experienced in by-pass and discharge lines as a result of relief valve discharge, and in main steam lines as a result of sudden main stop valve closure. Piping in both BWR and PWR reactor systems has been found to be susceptible to these conditions. This paper is concerned with the evaluation of the pressure and momentum transients resulting from sudden valve operation, and the determination of the dynamic response of the piping to the induced transient loading. The characteristics of the transient conditions existing immediately following both sudden valve opening and closure as encountered in BWR and PWR plants are discussed. The procedures used to calculate the transient time history functions are outlined. The derivation of the loading induced in the piping by the pressure and momentum transients is discussed and the determination of the dynamic response of the piping is presented. The procedures described in the paper are illustrated by actual examples from BWR and PWR plants, and the significance of steamhammer effects relative to other loading conditions is discussed.