Fracture toughness and other mechanical metallurgy characteristics of pressure vessel steels

The objective of this work is to investigate the effect of specimen size and evaluation method on estimates of fracture toughness for three commercial pressure vessel steels in different heat treatment conditions. It is found that the fracture toughness values K_C recorded on large, 150 mm thick, specimens were consistently close to the lower bound envelope of the K_δC, K_JC and K_E values established on 20 mm thick specimens. Comparison of the various elasto-plastic fracture criteria ascertained on a single specimen shows that the variations in these values are relatively slight which implies that the evaluation techniques used in this study can be considered as giving results that are, for practical purposes, the same.     

Fracture toughness properties of HIC susceptible carbon steels in sour service conditions

Hydrogen Induced Cracking (HIC) in carbon steels is a well-studied mechanism, where diffusing hydrogen atoms accumulates at the steel imperfections/laminations to create gaseous hydrogen with very high pressure, leading to initiation and growth of internal cavities, so-called HIC. Measurements of relevant fracture toughness properties of non-HIC resistant steels in hydrogen environment is critical to predict and assess the initiation and growth of HIC. The present work attempts to quantify the effect of hydrogen on the fracture toughness properties (K_Q and CTOD) of an API X42 pipeline steel under simulated H₂S in-service conditions. The fracture toughness properties are measured in TL and SL directions: perpendicular and parallel to the pipeline wall thickness, respectively, following ASTM E1820, standard. Since the X42 is a non-HIC resistant steel, the measurement of the fracture toughness properties in the SL direction is more relevant in terms of HIC initiation and growth than fracture toughness properties in the TL direction. Indeed, parallel to the thickness of the pipeline wall, X42 steel shows microstructural features prone to HIC formation and growth. Steady state H₂S in-service conditions were simulated by charging the specimen for 48 h using a special electrolytic solution and then tested (ex-situ) to evaluate the fracture toughness properties. The steady state H₂S environment was obtained by measuring the Hydrogen Concentration (CH) in the bulk of the specimen, using Thermal desorption Spectroscopy at three levels of CH. It was observed that the K_Q was not affected in the SL direction, while it was reduced in the TL direction for 1.5 ppmw of CH. The CTOD showed mixed results in the TL direction while it was significantly reduced in the SL direction reaching a saturation at 1 ppmw of CH. Besides, microstructural analyses showed that the presence of inclusions coalescence in form of dimples promote the early failure, which is more pronounced in the hydrogen environment especially at higher levels of CH.     

Radiation embrittlement modelling for reactor pressure vessel steels: II. Ductile fracture toughness prediction

Modelling for the irradiation effect on ductile fracture toughness of reactor pressure vessel steels (RPV) is performed on the basis of ductile fracture criterion proposed earlier by the authors. The irradiation effect on mechanisms controlling ductile fracture is considered from a physical viewpoint. Modelling of the irradiation effect is carried out on the critical strain for smooth cylindrical specimens and on the local critical strain for cracked specimens. On the basis of the performed studies a scheme that allows an evaluation of the upper shelf level of the K_IC(T) curve for irradiated RPV steels is proposed.     

Exergoeconomic analysis and evaluation of energy-conversion plants—II. Analysis of a coal-fired steam power plant

A coal-fired steam power plant, which will be located in Southern Nevada, has been analysed with the aid of the method presented in Part I. The exergoeconomic analysis suggests that decreasing the exergy losses for the components steam boiler/reheater, feedwater preheaters, and low-pressure turbine may lead to a reduction in electricity cost although the capital costs will increase.     

Fracture toughness of weld metals in steel piping for nuclear power plants

To determine toughness behaviour of dissimilar welds in steel piping and obtain data to evaluate Leak-Before-Break for these welds, an experimental study on fracture toughness was carried out. This paper provides Charpy impact properties and fracture toughness data of base and weld metals of dissimilar welds in nuclear piping.     

Recycling a hydrogen rich residual stream to the power and steam plant

The benefits of using a residual hydrogen rich stream as a clean combustion fuel in order to reduce Carbon dioxide emissions and cost is quantified. A residual stream containing 86% of hydrogen, coming from the top of the demethanizer column of the cryogenic separation sector of an ethylene plant, is recycled to be mixed with natural gas and burned in the boilers of the utility plant to generate high pressure steam and power. The main advantage is due to the fact that the hydrogen rich residual gas has a higher heating value and less CO₂ combustion emissions than the natural gas. The residual gas flowrate to be recycled is selected optimally together with other continuous and binary operating variables. A Mixed Integer Non Linear Programming problem is formulated in GAMS to select the operating conditions to minimize life cycle CO₂ emissions.     

主蒸汽温度的串级CMAC学习控制策略

结合CMAC学习控制器和串级控制系统,提出了主蒸汽温度的串级CMAC学习控制策略,其自适应性强,非常适合于计算机实时控制。仿真研究表明,该策略的控制品质良好,远远优于PID控制。     

VEGA206联合循环电厂汽轮机数字电调系统分析

简要介绍法国通用电器一阿尔斯通公司VEGA206联合循环电厂MICROREC汽轮机数字电液调节系统的主要特点，并对其生产过程中的应用情况及运行中出现的问题进行分析。     

Performance enhancement in coal fired thermal power plants. Part II: steam turbines

This paper presents the results of the performance enhancement study on 22 coal fired thermal power stations of capacities 30–500 MW. The oldest units (30 MW) have served for 33yr and the newer units (500 MW) have been in operation since 7yr. The turbine efficiencies are in the range 31·00–41·90% as compared to the design range of 34·80–43·97%. The isentropic efficiencies are in the range 74·13–86·40% as compared to design values of 83·20–89·10%. Considerable scope for efficiency improvement through low cost solutions: operational optimization, capital overhaul, simple modifications, etc., exists for all classes of units. The efficiencies can be restored to their design values. The developments in turbines over the last quarter of this century which have led to improved isentropic and thermal efficiencies must be adopted for existing units through retrofits, upgrades and revamps. The turbine efficiencies can be improved to 38·0% for 30 MW units and to 47% for 500 MW units. The maximum potential is for improvement in 210 and 500 MW units followed by 110 and 120 MW units. The potential for 30 and 62·5 MW units is rather limited because of their low capacity share, lack of interest in manufacturers to sell spares (because of the low volume of requirement) and large pay back periods for modernisation schemes. Copyright © 1999 John Wiley & Sons, Ltd.     

Comparison of power plant steam condenser heat transfer models for on-line condition monitoring

In this paper heat transfer models for large power plant condenser were examined. The goal was to develop a model capable of predicting not only the condenser pressure but the overall heat transfer coefficient. Such a model can be used for condenser condition monitoring. The results of a two-dimensional (2-D) condenser heat transfer model and single-point, zero-dimensional (0-D) model are presented together with the results from Heat Exchanger Institute (HEI) standards curves. Both 0-D and 2-D models can account for the effects of steam-side pressure drop and in a simplified manner also some effects of tube bundle geometry. For all models an experimental correction as a function of cooling water temperature was implemented to improve their accuracy. The results are presented in comparison with the measured plant data for three different tube bundle geometries, with and without the experimental correction factor. The 2-D model proved to be the most consistently accurate of the models both without the correction, and at varying steam and coolant flow with the correction applied. The results indicate significant local variation of pressure drop related effects, which the 0-D model failed to accurately predict particularly in cases of close temperature approach. In predicting the heat transfer coefficient the HEI model was the least accurate, significantly overestimating the impact of coolant flow rate change, and failing to match the measurements even with a correction applied.     

Radiation embrittlement modelling for reactor pressure vessel steels: I. Brittle fracture toughness prediction

Modelling for the irradiation effect on brittle fracture toughness of reactor pressure vessel (RPV) steel is performed on the basis of the probabilistic model for fracture toughness prediction proposed by the authors earlier. The irradiation effect on parameters controlling plastic deformation and brittle fracture of RPV steels is analyzed. The physical mechanisms are considered which control the cleavage microcrack nucleation for RPV steels in the unirradiated and irradiated states and also in state after post-irradiation annealing. Prediction of the temperature dependence of brittle fracture toughness is performed as applied to irradiated 2.5Cr–Mo–V reactor pressure vessel steel. Modelling of the fluence effect and the phosphorus and copper content effect on brittle fracture toughness is carried out. It is shown that the probabilistic model based on a new formulation for brittle fracture criterion allows the adequate modelling for the irradiation effect on fracture toughness for RPV steel. Application of alternative models is discussed for fracture toughness prediction for irradiated RPV steels.     

Studies of the direct input of solar energy to a fossil-fueled central station steam power plant

Seven possible methods of absorbing solar energy as direct thermal input to an 800 MW, fossil-fueled, central station steam power plant have been studied. Irrespective of method, the solar heat is first collected by an array of flat mirrors and concentrated on a tower-mounted absorber where it is transferred into the power cycle. The heat absorbing methods studied were heating of feed-water, evaporation of water, superheating of steam, combined evaporation and superheating, reheating of steam, air preheating, and combined air preheating, and feedwater heating. Factors considered were relative capital cost, energy conversion efficiency and complexity of design, operation and control. Combined evaporation and superheating proved to be the preferred method because of its high utilization of solar energy, relatively low indicated capital cost and only moderate complexity in design, operation and control. Feedwater heating also has very desirable capital cost, design and operating aspects, but suffers from the drawback that over 30 per cent of the solar energy absorbed is, in effect, lost because of degradation of the steam cycle efficiency.     

A method of economical load dispatch for steam turbine unit of thermal power plant

In this paper, by combining the equality differential increment theory (EDIT) with the equivalent polyhedron body (EPB) searching extremum strategy, a method of economical load dispatch for the steam turbine unit of the thermal power plant has been presented. Simultaneously, a method for the order of load shedding and the related optimal economic operational modes of each turbine unit in decreasing its load are ascertained. According to the methods, the results of the optimal economical dispatch of the peak loads, the order of load shedding and the related optimal economic operational modes of each turbine unit while decreasing the load of a certain thermal power plant have been obtained. These results are applied in the thermal unit, and its economic benefits are shown to be obviously higher than that of applying the relative efficiency of each turbine unit. The methods can be used as a reference for obtaining the optimum economical load dispatch for similar thermal power turbine units. Copyright © 2007 John Wiley & Sons, Ltd.     

火力发电厂灰场对土壤及浅层地下水的影响研究

火力发电厂灰场的粉场灰对土壤和浅层地下水均有影响,其对浅层地下水影响的大小,主要取决于排灰场土壤的类型及污染物的种类和浓度,从模拟试验结果可知,土壤对砷,氮,六价铬的吸附能力远小于汞和铅。     

燃气-蒸汽联合循环电站机组配置及选型分析

对联合循环电站燃气轮机选型、蒸汽系统的选择、余热锅炉和汽轮机选型、机组轴系配置、动力岛布置、主要辅助设备的选择等方面进行了分析研究,为联合循环电站的设计和研究方向提供了建议。     

联合循环电厂汽轮机供热运行的若干问题

国内某联合循环电厂由于汽轮机缺乏非设计工况下抽汽供热运行经验且需要参与电网调峰,经过对联合循环机组特性分析和现场运行数据的整理、优化,在保证机组安全的前提下,确定了汽轮机供热量和机组调峰能力,为指导运行人员操作和确定机组电网调峰能力提供了依据。     

Software system “DIORES” for the operation diagnosis of a steam power plant unit

Despite the long operating experience with steam power units in the Electric Power System of Serbia (out of which some are at the end of or had even passed their planned working lives), unfortunately, there is a lack of data for their operating regimes, process parameters and performance deviations, the economy and operating states for the previous period. These data would not only be useful for optimal process control, but also for the planning of maintenance, retrofits and repowering of power plants. For these and other equally important reasons, the software system for the diagnosis of operating conditions, control of economy and operating states of different components has been developed for the referential steam power unit. A better control of the process and operating state, thanks to the use of the results obtained with this software system, will bring a lasting benefit to the efficiency and economy increase. Furthermore, it will enable an increase of reliability and availability of steam turbine units and make their working life longer. The basic characteristics of this software system and some of the results obtained by its testing using the available data base for referential unit operation are presented in this paper.     

Energy,exergy and exergoeconomic analysis of a steam power plant: A case study

The objective of this paper is to perform the energy, exergy and exergoeconomic analysis for the Hamedan steam power plant. In the first part of the paper, the exergy destruction and exergy loss of each component of this power plant is estimated. Moreover, the effects of the load variations and ambient temperature are calculated in order to obtain a good insight into this analysis. The exergy efficiencies of the boiler, turbine, pump, heaters and the condenser are estimated at different ambient temperatures. The results show that energy losses have mainly occurred in the condenser where 306.9 MW is lost to the environment while only 67.63 MW has been lost from the boiler. Nevertheless, the irreversibility rate of the boiler is higher than the irreversibility rates of the other components. It is due to the fact that the combustion reaction and its high temperature are the most significant sources of exergy destruction in the boiler system, which can be reduced by preheating the combustion air and reducing the air–fuel ratio. When the ambient temperature is increased from 5 to 24°C, the irreversibility rate of the boiler, turbine, feed water heaters, pumps and the total irreversibility rate of the plant are increased. In addition, as the load varies from 125 to 250 MW (i.e. full load) the exergy efficiency of the boiler and turbine, condenser and heaters are increased due to the fact that the power plant is designed for the full load. In the second part of the paper, the exergoeconomic analysis is done for each component of the power plant in order to calculate the cost of exergy destruction. The results show that the boiler has the highest cost of exergy destruction. In addition, an optimization procedure is developed for that power plant. The results show that by considering the decision variables, the cost of exergy destruction and purchase can be decreased by almost 17.11%. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural theory and thermoeconomic diagnosis: Part II: Application to an actual power plant

In this second part of the paper, the new advances on thermoeconomic diagnosis presented in the part I are applied to the Escucha power plant, which is a 160 MW conventional coal fired power plant sited in Aragón (Spain). As a result the validity of the methodology is proved and quantified.The methodology is validated using a specific simulator of the Escucha power plant cycle, mainly based on [ASME Power Division, Paper no. 62-WA-209, 1974] method. This simulator reproduces with high accuracy the cycle behavior for different operating conditions, either in design and in off design conditions. The error is lower than 1% in most of cases. The simulated results, i.e. temperatures, pressures, mass flow rates, power and so on, are considered as plant measured and validated values. In this way all measurement uncertainties are avoided.A complete thermoeconomic diagnosis is presented applying the Structural Theory of Thermoeconomics. The impact of the component inefficiencies on the fuel plant consumption, and the effect of a component inefficiency (intrinsic malfunction) on the rest of the plant components (induced malfunctions and dysfunctions), are analyzed and quantified. The methodology is validated quantifying its accuracy.     

Effect of hydrogen charging on the mechanical properties of advanced high strength steels

The present work investigates the influence of hydrogen on the mechanical properties of four multiphase high strength steels by means of tensile tests on notched samples. This was done by performing mechanical tests on both hydrogen charged and uncharged specimens at a cross-head displacement speed of 5 mm/min. A considerable hydrogen influence was observed, as the ductility dropped by 8–60%. In order to demonstrate the influence of diffusible hydrogen, some parameters in the experimental set-up were varied. After tensile tests, fractography was performed. It was found that hydrogen charging caused a change from ductile to transgranular cleavage failure near the notch with a transition zone to a fracture surface with ductile features near the centre.