Operation and maintenance schedule of a steam turbine. Fortran about the velocity distribution in the output of stator blades that have flow conditions of wet steam, in order to understand the causes that originate the erosion on the blades of the last stages in the low pressure section of steam turbines. In the first part of this work, the calculation presented of the transonic velocity field for the stream. Water droplets after condensation deposit mainly on the trailing edges of the stator. They direct the steam flow more efficiently than other nozzle types. Water droplet erosion 19 99 erosion of steam turbine blade due to the impaction of water droplets causes serious problems, such as performance degradation, high maintenance cost, and low availability, in many power plants. There is a number of other surface damage modes, such as extrusion, chip formation, tearing, brittle fracture, etc. The model is used to estimate erosion values for the analytical simulations of a ninestage wet vapor steam turbine and a twostage wet vapor potassium turbine. Steam turbines for geothermal power plants sst400 geo and sst500 geo with power output up to 120 mw industrial power scan the. The integration of the reverse engineering parts process into the steam turbine outage planning and execution ensures that parts can be supplied during ongoing overhauls.
Thin thermal spray tungsten carbide and stellite coatings provide wear resistance to turbomachinery. Corrosion fatigue of a lowpressure steam turbine blade. The probable explanation for this is that the pores in the surface of the blade where erosion has taken place are partlyfilled with water. This reduces turbine efficiency and can also limit capacity. Turbine blade erosion is initiated by a relatively small proportion of the water droplets in the steam separating out and collecting on the concave pressure face of the diaphragm blades, where a film is formed which is drawn towards the trailing edge by the drag of the steam. Pressure and heat is applied to the shield to thermoset the adhesive. From nuclear reactors to thermal power plants, the role of the steam turbine is both pivotal and result determining. A steam turbine is basically an assemblage of nozzles and blades. Solid particle erosion of the steam turbine blades also was an issue due to the plants cyclic operation. Over the last 100 years, ge has manufactured and installed a worldwide fleet of steam turbines. Erosion scarring and notch formation on last stage blade low pressure steam turbine consequences and impact of scarring and notch formation if left unattended last stage blade design and operation reasons for the formation of erosion damage mitigations, scarring and notch removal benefits gained from notch removal and blade dressing 3. Lsb erosion is the result of low velocity water droplets leaving the nozzle trailing edge and impacting on the. An arcuate anti erosion shield of stellite or the like has an inner surface with a film supported adhesive attached thereto and gasket strips formed from a fluoroelastomer along the edges thereof.
Protecting your steam turbine from corrosion power. The erosion caused by wet steam flow reduces the efficiency of the last stage rotor blades of condensing steam turbines, and makes their service life shorter. Figures 1 and 2 depict some very early turbine steam path failures showing rotating blade erosion and axial disc fatigue stodola. Unlikethesteamenginethesteamturbineisnotsubject tomuchwear.
Erosion of turbine blades results in rough surfaces that change steam flow paths. A steam turbine locomotive engine is a steam locomotive driven by a steam turbine. Leakage solid particle erosion moisture erosion steam path deposits. This study proposes a numerical and analytical coupling method for simulating unsteady steam flow through threestage stator and rotor blade rows of an intermediatepressure steam turbine operating in a power plant by considering both the secularchanged blades and the leakage flows in labyrinth seals. Numerical code, mesh blade, erosion blade, steam turbine, drop. Near the exhaust of a steam turbine engine also known as the penult stage or final. Water droplet erosion of stainless steel steam turbine blades. With the exception of plants that faced these issues, many coalfired power plants. Rotating lp turbine blades may be free standing not connectedtoeachother,connectedingroups,orallbladesinthe.
Pdf steam turbines are critical components of thermal power stations for generation of electricity. On predicting steam turbine blading erosion and turbine efficiency. Solid particle erosion of blades 2 93 hiope 3 erosion mechanisms 27 6 solid particle erosion of turbine blades 56 7 reduction of solid particle erosion 72 1 generals for solid particle erosion 2 2 prediction of particle behaviors 19 5 solid particle erosion of valves 48 4 erosion parameters 31. The last couple of stages of steam turbines are the most vulnerable to wde. Steam turbine blades droplet erosion protection hvaf. In the lowpressure stages of steam turbines more than. The failure comprised of surface damage that formed over the leading edge and a tangential crack that formed between the tierod hole and the damaged leading edge. Erosion process of 66 mw steam turbine rotor blades. Thus the most common causes of lp steam turbine blades is high cycle fatigue due to vibration, erosion due to impingement of water droplets, pitting corrosion and stress corrosion cracking 1 2. The erosion caused by wet steam flow reduces the efficiency of the last stage rotor blades of steam turbines and makes their service life shorter. The steam turbine generators used today produce approximately 85% of the electricity. Hvof coat refurbishment of worn compressor and turbine blades in san francisco bay area, california, usa. In a rare study that only focused on wde of inservice steam turbine blades, stanisa et al 17 monitored the wde damage evolution on low pressure cycle blades of a steam turbine at a power plant in krsko, slovenia. In its simplest form, a steam turbine consist of a boiler steam generator, turbine, condenser, feed pump and a variety of auxiliary devices.
Blade seals are used to prevent the steam leakage between the diaphragm and the shaft. The surface damage occurred on the leading edge was typical of pitlike. In the low pressure section of the steam turbines the damages are pronounced becoming remarkable in all the stages, since the generation of water liquid microparticles implies the impact on the blades having majors problems of erosion in the last stages by the increase of the humidity. Jun 04, 2018 in the case of back pressure turbine, the steam is not condensation. The rate of the deterioration is influenced by the turbine design, the steam quality, and the way the turbine is operated. Erosion of turbine blades results in rough, uneven surfaces that alter steam flow paths. Theoretical and numerical analysis of the mechanical erosion in steam turbine blades. A total destruction of the steam turbine can occur if a valve fails to close when the unit is tripped and driven equipment is no longer loaded. Ivusic b a faculty of technical studies, rijeka, and enin karlovac, karlovac, croatia faculty of mechanical engineering and naval architecture, zagreb, croatia abstract the erosion caused by wet steam flow reduces the efficiency of the last stage rotor blades of condensing. The first steam turbine rail locomotive was built in 1908 for the officine meccaniche miani silvestri grodona comi, milan, italy. Numerical code, mesh blade, erosion blade, steam turbine, drop distribution. Mechanisms of water droplets deposition on turbine blade. A final issue for gas turbines to consider is the blade cooling air that is bled for the compressor discharge and is then used as an internal cooling flow in the gas turbine hot section blades. The efficiency of the turbine depends largely on the blade.
Low pressure steam turbine last stage blade erosion. There have been numerous causes of steam turbine failures worldwide. Attheendofthetest,thebladewasremoved,allowed tocool,cleaned,driedinadesiccatorandweighed. Maintenance and overhaul of steam turbines wgp42 05. Low pressure steam turbine last stage blade erosion scarring, notch removal and refurbishments parsons 2019 10th international charles parsons turbine conference 1618th september 2019, cranfield university, uk mehran zanjani, ben morrell and dave carr.
Erosion in low pressure turbine stages is due to the high rate of expansion and the presence of wet steam. Most difficulties with these salts occur in the lp turbine. This is called an overspeed event and is the worst failure scenario for a steam turbine. The film is removed from the shield and the shield installed on the turbine blade. Us4842663a steam turbine blade antierosion shield and. They produce a larger pressure drop and therefore are more efficient than other nozzle types. Erosionfatigue of steam turbine blades sciencedirect. The drag of solid particles by the gas steam flow is another major problem during the operation of turbines. Hvaf systems for water droplet erosion resistant coating of steam turbine blades. Chapter 18 steam turbine deposition, erosion, and corrosion.
Erosion at the highpressure end of a turbine is usually caused by solid particles usually iron oxide present in the steam. Maintenance and overhaul of steam turbines hmn series steam turbine courtesy siemens power corporation. A lowpressure lp steam turbine blade of the steam turbine last stage of a thermal power plant had failed after it had been only a few years in service. Steam turbines st often exhibit leadingedge erosion on the laststage blades lsb of the lowpressure lp section. Recently, some stationary blade designs have also been leaned or bowed. Erosion behaviour and mechanisms for steam turbine rotor.
Erosion of steam turbine blade due to the impaction of water droplets causes serious problems, such as performance degradation, high maintenance cost, and low availability, in many power plants. Steam turbine blades are distinctly subjected to water droplet erosion wde caused by high energy impingement of liquid water droplets under high speed rotation. Apart from erosion of leading edges, erosion of the rotor blades trailing edges often occurs in condensing steam turbines due to impact of wet steam water. Nevertheless modern steam turbines are very efficient and operate with internal efficiencies within the range of 80 percent to 90 percent depending upon the steam conditions. A thermal spray equipment for robotic onsite repair of lowpressure steam turbine blades. Investigations of the processes of turbine blading erosion remain still an important part. A cfd investigation of droplet trajectories at different blade spans was used to design a set of blade like erosion specimens with a geometry reflecting real steam turbine blades. Krzyzanowski 1987, 1988, 1991 used for that purpose the calculated and measured erodet area of various turbine blade profiles. Major steam turbine problems, such as stress corrosion. Jan 10, 2018 a lowpressure lp steam turbine blade of the steam turbine last stage of a thermal power plant had failed after it had been only a few years in service. The best way to avoid erosion is to operate strictly as per manufacturerss sop standard operating procedures and operate it by following the recommended soc standard operating conditions. Pdf erosion process of 66 mw steam turbine rotor blades. This leads to, as mentioned above, turbine efficiency decrease and limited. In an extracting type turbine, steam is released from variousin an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sentstages of the turbine, and used for industrial process needs or sent to boiler feed water heater to.
Studying erosion wear of actual exservice turbine blades is also important because it can uncover some unknown parameters that also affect the erosion damage. Liquid droplet erosion is one of major concerns in the design of modern large fossil steam turbines. In blade cascades the saturated steam flows is a nebula of droplets. Figure 1a illustrates the sequence of the erosion process experienced in a steam turbine blade. After the surface has become uniformly pitted, there follows a tertiary period during which the material lost by erosion falls logarithmically with time and after about a year may almost cease. The method of repair of an eroded shield is disclosed in which the eroded shield is removed, welding material dissolved by acid, and the blade sandblasted. Request pdf erosionfatigue of steam turbine blades the premature failure of steam turbine rotor blades, manufactured in forged 12% crnimov martensitic. Investigation of corrosion fatigue phenomena in transient. The physical processes preceding blade erosion by wet steam in lowpressure turbines have been traced from the collection of water droplets larger than 30. They have found the oxides of silicate and sodium on fractured surface, which leads to the formation of corrosion pits and concluded that the blade failed due to corrosion fatigue. In general, a steam turbine is a rotary heat engine that converts thermal energy contained in the steam to mechanical energy or to electrical energy. Events leading to erosion in the steam turbine sage journals.
This report describes the construction and application of an analytical model of turbine rotor blade erosion in wet vapor turbines as performed under contract nas 7390. Leading edge erosion of coated wind turbine blades. Sep 17, 2011 the results obtained from studies of metal erosion processes are analyzed and generalized, which made it possible to establish the main regularities relating to surface destruction of blade materials under the effect of droplet impingement and determine how the size of liquid droplets and velocity at which they collide with the surface affects the rate of erosion wear for almost all blade. In 1924 krupp built the steam turbine locomotive t18 001, operational in 1929, for deutsche reichsbahn.
Steam turbine, drop distribution, erosion statorrotor blade, transonic flow. Steam can flow backwards and erode trailing edges of laststage turbine blades. In the last stage of the low pressure steam turbine the droplets localized have sizes that are generally greater than 100 m 10 and have a considerable slip relative to the vapor. Solid particle erosion of blades 3 93 hiope surface damage surface damage surface damage makes the structure and composition of materials quite different from their original ones.
These foreign particles can either be deposited over the turbine trail and blades see fig. The causes ni characteristics of the erosion of steam turbine blades, factors influencing erosion, and methods for preventing erosion are studied. Events can emanate from inadequate initial design, poor operation and maintenance, cycle chemistry environments, or lack of proper management support. An industrial steam turbine experiences performance deterioration over time. What is steam turbine description and characteristics. In these turbines the highpressure stage receives steam this steam is nearly saturated steam x 0. Analysis of liquid droplet erosion for steam turbine blades of composite material sandeep soni1 corresponding author. Erosion wear of the blades of wetsteam turbine stages. Water droplet erosion is one of the major concerns in the design of modern steam turbine because it causes serious operational problems such as performance degradation and reduction of service life. Steam turbines consist not only rotating blades called as rotor but also static blades. Latest technologies and future prospects for a new steam turbine. The entering steam still has a reasonable amount of superheat, but as the steam reaches the last few rows of turbine blades, some of it. These droplets have a significant influence on blade erosion, and the fact that the small nucleated droplets provide the source for entrainment of large droplets. Theoretical and numerical analysis of the mechanical.
Here the comparison of the calculated and measured erosion width. Hence the boiler feed water quality is not required as stringent as condensing turbine. Thus, the better the design of the blade, the more efficient the turbine will be. Since then turbines based on these principles have evolved in parallel and in fact merged to some degree. Why solid particle erosion is a concern turbomachinery. Hence the possibility of silicates and salts deposits does not occur in this turbine. Review leading edge erosion of coated wind turbine blades. Some aspects of erosion prediction of steam turbine. Any solid matter, such as sand particles, that is carried into this cooling flow, will deposit in the very fine blade cooling passages and plug them. Main root causes for performance deterioration are.
Theoretical and numerical analysis of the mechanical erosion. Steam turbines are not only employed to operate electric generators in thermal and nuclear power plants to produce electricity, but. Erosionfatigue of steam turbine blades request pdf. The steam must be reheated in order to avoid damages that could be caused to blades of steam turbine by low quality steam. Steam turbine basic parts mechanical engineering site. A numerical and analytical coupling method for predicting. They are less susceptible to steam erosion than other nozzle types due to their shape. Elsevier wear wear 186187 1995 395400 erosion behaviour and mechanisms for steam turbine rotor blades b. Astronuclear labor at or y preface this report describes the construction and application of an analytical model of turbine rotor blade erosion in wet vapor turbines as performed under contract nas 7390. Overspeed events not only cause very large or total destruction of the steam turbine. Difference between condensing turbine and back pressure.
In general, exservice steam turbine blades are usually studied by engineers and researchers to analyze the reasons for failure 16 19. To date there has been insufficient data on the erosion process which the steam turbine rotor blades are subject to during the operation, data which could be a basis for development and verification of mathematical models to estimate the service life of eroded rotor blades. Erosion behaviour and mechanisms for steam turbine rotor blades. Due to the accumulation that is formed on the stator blade, the erosion features in the following rotor blades is the consequence. Industrial power steam turbines for geothermal power plants.
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