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In the current study, the problem of cracking on the stop valve body in a steam turbine related to a thermal power plant is assessed. The problem usually occurs consecutively and almost in identical locations for the power plant's stop valves. To do so, the steam flow path from the developed area at the boiler output to the turbine input is divided into three separate computational domains and numerically simulated. The obtained results of the simulation have been successfully verified using the actual data of the thermal power plant. The common factors affecting the formation of crack consist of contacting shell with cooled steam, expansion and contraction movement of a turbine, insufficient insulation, stop valve spring force, internal pressure, and fluid flow momentum are assessed. The von Mises stresses caused by each factor have been determined. It has been attempted to identify the main cause of cracking by comparing the obtained stress concentration points with the real coordinates of the crack. The results of the simulation revealed that the expansion and contraction movements of the turbine were the main cause of fatigue and crack in the stop valve body. Given the key role of the stop valve in generating power of turbines, the findings of this simulation can help to design sensitive equipment more accurately.

The present study concentrated on the metallurgical, micro- and macroscopic observations, hardness evaluation, as well as X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) analysis induced during the high-temperature operation of a pipeline that resulted in its relatively short-time failure. An ASTM A213-T12 superheater pipeline is used in a fossil fuel power-plant unit and is constructed by an array of steel tubes joined together by circumferential weldments. Macroscopic observations indicated a thinning and prolonged deformation of the superheater tube in the region close to the fire zone besides thick corrosion products on the other side of the pipe. Hardness measurements showed a remarkable decrease in hardness values of superheater metal near to the failure zone, indicating that grain coarsening or any other microstructure weakening must happen. Scanning electron microscopy (SEM) observations proved the ductile nature of cracking and justified the prolonged failure of the tube. The observed voids in the microstructure of the failed section demonstrated the occurrence of creep phenomenon. XRD and EDS analyses demonstrated the nature of sediments formed on the tube and described how the formation of these corrosion products contribute in the removal of any possible protective passive layer, exposing the tube to further corrosive deterioration and creating loop stresses which, in turn, will induce creep phenomenon and accelerate the occurrence of a failure in the tube.

System reliability of an offshore power plant with several gas turbine engines is analyzed in this study to understand the failure intensity of a selected gas turbine engines under varying maintenance activities. A set of event data of a selected gas turbine engine is considered to identify system failure intensity levels, where unknown maintenance actions were implemented (i.e. various repairs disturb the failure rate). A non-homogeneous Poisson process (NHPP) is used to model the age dependent failure intensity of the same gas turbine engine and the maximum likelihood estimation (MLE) approach for calculating the respective model parameters is proposed. Several failure intensity rates (i.e. varying failure trends) in these models (i.e. during the system age of the gas turbine engine) are observed. Furthermore, these varying failure trend models are evaluated with actual failure events of the same gas turbine engine by considering two goodness-of-fit tests: Cramer-von Mises and Chi-square tests. Finally, system reliability of the gas turbine engine under the failure transition, failure intensity, mission reliability and mean time between failures (MTBF) is also discussed in this study.

An essential section in the normal operation of a thermosolar power plant is the management of those effluents that are generated by the diverse processes that take place in the power plant equipment. Due to environmental regulations, it is necessary to develop an effluent treatment plant before all those fluids can be discharged into the environment. In such a plant, a neutralization process is performed, by adding certain chemicals, resulting in an environmentally safe spill. During the execution of this kind of facility in La Asturiana thermosolar power plant, all design requirements were fulfilled, without any incident. Nevertheless, during the commissioning of the facility, several pieces of equipment showed settlements that were much higher than the established limits, which led to a temporary shut-down of the facility. In order to discover the causes, evaluate the risk of repetition in other areas of the power plant and to be able to select the best corrective action, a forensic study was carried out. This study started with several field data tests and was concluded with the development of a computer model. The above mentioned study focused on one of the affected pieces of equipment, and on the surprising conclusions obtained with regard to the causes of the incident, which are developed in the present article.

Chloride attack is the primary cause of corrosion problem of concrete structures operate in marine environment. Therefore, concrete structures operate in such environment cannot escape from this corrosion related problem. This paper describes assessment of a reinforced concrete canal structure of power plant after 20 years of exposure in a marine environment. The work covers visual inspection of the structure, on-site and laboratory tests of the structure, analyses the current structural strength based on the tests, and proposing repair and/or strengthening for weak elements. Strength prediction is carried out using average and worst case scenarios. The strength calculations assuming average case scenario shows that by 2025 all the canal have no strength reduction due to corrosion. Calculation using the worst case scenario shows that all the canal by 2025 still comply with the limits specified in Indonesian Concrete Code, even though their strength has been reduced due to corrosion of the reinforcement.

Cooling towers are important heat exchangers in power generation industry comprising of centrifugal fans which are used for cooling purposes. The present research investigates the failure occurred on the fan blade supporting system, installed on the cooling tower of a power plant. Τhe tower is consisted of twenty fans. Their blades are supported onto a hub by “U” shaped holders. These specific fitments frequently undergo damages increasing plant downtimes as well as the risk of accidents. The study comprises of historical data recording, macroscopic examination, hardness measurements and chemical analysis of three failed components. Moreover, the microstructure and fracture surface morphology of failed components are thoroughly analyzed. Conclusions are presented regarding the failure mechanism and its propagation mode. Holders were totally break by low cycle fatigue. Improper material selection and poor design are mainly responsible for the repeated damage. Practical recommendations were delivered to avoid similar failures.

Turbine blade is one of the key parts in thermal power plant, its failure will bring the power plant out of operation. Premature failure of turbine blade in thermal power plant was reported frequently. The crack was detected on the top of the last stage turbine blade in a thermal power plant. The failure causes of turbine blade were determined based on the testing and analysis by different methods. The macro morphology of the crack was observed by optical light microscope (OLM) method. The fracture surface of crack was observed by scanning electron microscopy (SEM) method and the mechanical property of the failure turbine blade was analyzed by different mechanical testing methods. The analysis results showed that the high level microstructure stress existed in the heat affected zone in the part of the blade, which was the directly factor to cause the failure. The uneven distribution fine and course martensitic due to the unqualified heat treatment in the heat affected zone and the high-frequency hardening zone was the root cause of the failure. Suggestions were proposed to prevent the failure about turbine blade according to the testing and analysis results as well.

A failure analysis investigation was carried out on the secondary Superheater tubes of a boiler unit in a steam power plant. The tubes, made of DIN-16CrMo4 steel, failed by bulging and rupture only after about three years of operation. Metallurgical investigations revealed that microstructural degradation had mainly occurred at the external (fireside) tube surface. Long-term overheating was identified as the root cause of the premature failure.

Within the complexity of the design and execution of a solar power plant project, one of the main challenges falls on rainwater management, since there is the need to collect, conduct and store it for its use in the water-vapour cycle process. Therefore, the primary piping for rainwater transportation from the solar power plant is regarded as an essential installation for the operation of the plant. Within this framework, the appearance of pathologies in its conduction just a few months after the plant start-up is considered to be a critical problem, as it can endanger the electrical production of the facility. This problem has taken place at the solar power plant of “La Asturiana”, in Southern of Spain, with a solar field of 2 Mm2 in size and a gross generation capacity of 50 MW. The need to understand the reason for the pathologies, in order to prevent their reappearance, justifies a detailed analysis of the adopted design, as well as its execution. The research is completed with novel techniques for in-situ tests, which enable us to obtain rigorous data to be used in computer models with the aim of reproducing, in a controlled way, the execution conditions in order to establish the causes of the failure.

It is currently in the period of high-speed construction of pumped storage projects. However, the problems caused by vibration of pump turbine units, especially the runners, are very serious. It is of great significance to study the dynamic characteristics of pump turbine runner for the safety and stability of power station. In this paper, the natural modes of a pump turbine runner in the air and in the flow channels are calculated by numerical method. The influence and mechanism of the outer edge modification on the natural frequencies of the runner are studied. The results show that, for the object studied in this paper, the frequency of most modes will be decreased by thickening the outer edge. The frequency change can be attributed to two aspects, one is the change of the mass and the stiffness of the runner, and the other is the change of added mass of the water. Furthermore, the main mechanism of outer edge modification affecting the added mass coefficient is that the height of the radial clearance is changed.

The failure mechanism and the prevention method for TP347H stainless steel tube serviced in boiler reheater in a coal-fired power plant are presented in this paper. Through studies of detailed mechanical characteristics, microstructure, chemical composition and magnetic property, the mechanisms of reheater tube failure are found to be attributed to long-term overheating, second phase precipitating and coarsening along the grain boundary and formation of high content of deformation induced martensite (DIM) structure.

Blades of steam turbine are very important elements in power plant turbo aggregates. If blades of turbine fail, this will provoke further failures and high economical losses. Therefore, it is crucial to perform detailed research on reasons for failure of turbine blades to increase the reliability of turbine systems. The present paper deals with numerical simulation and research of erosion over blades in a low pressure stage of K-1000-6/1500 steam turbine working in a Nuclear Power Plant. Attention is paid to the effect of the amount of moisture in the stage; to the impact of droplets' diameter, their mass flow rate and forces acting on blade surfaces, to their aerodynamic behavior and influence on the energy conversion efficiency. Specific trajectories of water particles, reasons for the occurrence of erosion wear and erosion of certain parts of the streamlined surfaces are established and discussed. An approach to obtain incidence time to erosion effects appearance is formulated and implemented in the code. Research methodology and obtained results are applicable to determine specifics of erosion effects over streamed complex surfaces; replace expensive measurements campaigns; introduce approaches to decrease wetness in the last stages of condensation turbines and prolong the reliability of blades operated in wet steam conditions.

It is one of the main causes of conductor overheated fusing failure that the poor contact between conductors and the connecting clamp. In late October 2012, a typical case of that was discovered and dealt with by a power plant in Jilin, China. The project investigates the formation mechanism and development of the failure by laboratory tests combined with simulation method. The investigation indicates that there are two main characteristics of the infrared thermal image when conductors and clamps are poorly contacted—the temperature of the conductor is higher than that of the clamps, and the thermal image of the conductor shows it’s heat-producing like a equidistant helix. The characteristic thermal images provide some practical significance to determine and eliminate the equipment defects timely in inspection routines, thus improving the system reliability.

Dissimilar metal welding (DMW) finds extensive use in final sections of reheater tubing where the expected temperatures reach the maximum. Dissimilar weld failures are reported to occur at the weld interface, the heat affected zone and in the base metal depending on the operating parameters and stress level experienced during service. This paper presents a failure investigation of a reheater tube dissimilar weld failure, where the observed crack path cannot be described by any previously reported literature. The investigation leads to find the combination of i) tube restraint ii) shallow weld angle and iii) overheating conditions to be the root cause of failure. Recommendations are made based on the observations to prevent recurrence of reheater tube dissimilar weld failure.

This study concerns with erosion of Pelton turbine injector i.e. (nozzle spear tribo pair) by sediment particles for a typical power plant located in Himalayan belt of Jammu and Kashmir in India. Erosion of hydro turbine/runner and its allied parts by the sediment particles suspended in the river water is one of the challenging problems (faced by maintenance personnel of hydro power plants). Injector assembly is subjected to severe erosion which renders it dysfunctional in relatively short span of time compared to other parts of the hydro power plant. A detailed study regarding erosion measurement has been conducted using novel technique of 3D optical scanning to assess material loss and identify type of wear for spear and nozzle combination used at Chenani power plant (5 units each with a 4.66 MW capacity). Hydro-abrasive wear was quantified on the basis of measurement of material removed by process of erosion on spear and nozzle (virgin parts) compared with weight of eroded parts (scanned). The erosion was found to be 3.71% and 5% on spear and nozzle respectively (of virgin volume).

Today, the use of shell and tube heat exchangers has become widespread and they are used in various industries under very diverse operating conditions. Specific operating conditions make it possible to consider and simulate the operating terms and failure conditions of these converters. In this study, the design of a shell-and-tube counter-flow heat exchanger in AutoCAD software is first considered, and the system is then meshed and simulated in ANSYS 2019 software. Simulation results of temperature, pressure, heat flux and fluid velocity within the system are reported in order to understand the system performance. Failure conditions are evaluated according to the ASME VIII Boiler and Pressure Vessel Code, and the results of equivalent thermal stress analysis and system lifetime under two extreme loading conditions are reported. The highest equivalent thermal stresses under these extreme load conditions occur at the joints of the tubes and tubes sheet and is equal to 641 and 931 MPa, respectively. Also, the lifetimes of tubes and tube sheets are 105 and 104 cycles respectively for the valley and peak load conditions.

The working principle of the Wells turbine, used in the ocean energy extraction, can sometimes lead to stall in the turbine blades and stators’ vanes, which is an unintended action considering that creates potentially damaging conditions to the mechanical components, plus reducing the efficiency of the take-off system. This work focused on the cracking damage caused to the earth-side guide vanes of the Pico Island Wave Power Plant due to the loading from turbulent air flow and consequent vibrations, as a result of turbine stall. Comprehensive analysis of the design and manufacturing phases, as well as of the constitutive metal properties (AISI 316L stainless steel), including the consequences of welding, was carried out. Strain gages were used to evaluate the loading profile in real-sea working conditions and different suggestions were made in order to postpone and prevent crack nucleation and propagation. The appearance of cracks seems to have been caused by mistakes made at both design and manufacturing phases, eliminating from the guide vanes the ability to endure the aggressive loads which they were subjected to. The lack of an active control strategy on the power plant resulted in consistent turbine stall events, thus contributing to the excessive loadings imposed to the vanes.

Steam turbine blades are the critical component in power plant, specifically low pressure blades are generally found to be more susceptible to failure. A mechanical, metallurgical and FEM based coupled methodology is used in the present failure investigation of low pressure steam turbine blade. The results of each investigation of turbine blade failure were then interpreted that leads to find the location of primary failure, sequence of failure and the root cause of its failure. All the three aspects of failure investigation are important in answering the questions raised for the failure and to avoid any future miss-happening.

The extreme spray water mass flow rate deviation was observed to occur in the middle temperature superheater of Sahand 2 × 325 MW Power Plant utility boiler, which severely affected its economic performance and safe operation. Boilers operating in these conditions led to failure in superheater tubes at the same place for two consecutive times in a three year span. Thus, the failure analysis of superheater tubes by investigating the visual inspection, chemical, scale and creep analysis was carried out. The brittle failure occurred in the superheater tubes after the fuel was changed from natural gas to heavy oil. Failure analysis showed that tubes were suffering from long term overheating which was instigated by high spray water flow rate. In order to rectify the boiler operating conditions, some modifications were applied in the boiler unit 1 and operating parameters on this boiler were compared with boiler unit 2. The results showed that the 8.33% reduction in heating surface area corresponds to 52.84 and 17.80% reduction in spray water mass flow rate for capacities equal to 300 and 260 MW, respectively.

Load and condenser pressure play an important role in overall life of turbine blades especially in the last stages of low pressure (LP) turbine. LP last-stage blades have greatest potential to stall flutter during low steam flow and high backpressure. Exhaust loss refers to the energy lost to the condenser as a result of the steam velocity going into the condenser. The faster the steam leaves the last stage blades, the greater the energy loss. Since the backpressure is a function of the plant cooling system, and the flow is a function of the initial plant design, the only cost-effective way to reduce the velocity is by increasing the area. This is achieved by increasing the length of last stage bucket. The two primary forces acting on the blades are the steady centrifugal force due to rotation and the fluctuating steam bending force. The best estimation of dynamic stresses in the blades due to the two known sources of vibration works out to be a small portion of the allowable value. But still, incidences of blade failure are regularly reported. Published reports on compilation of blade failures in power plants say that cause for large number of failure is not fully understood. One such cause on which very little is published is self excitation in long blades. Self excitation sustain until the condition remain conducive to vibration inside the turbine. In plants operating at low load and high back pressure the blades are most susceptible to self excitation wherein the blade vibrates in its lower mode. The paper deals with monitoring self excitation in an operating power plant. A Single long blade has been modeled to steady fluid structure interaction by Lagrangian and Eulerian meshing approach during low load and high back pressure. The effect of the steam inlet angle on the blade has been studied. The model simulates low steam flow condition to show increased blade response thus validating observation made in operating power plant.

Overheating of the final super-heater in a 660 MW power plant after service for 4700 h was investigated. The scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) was employed to observe the surface morphology and cross-section of the tube’s steam side and analyze the ingredient of oxide scales. Results show that exfoliation of iron oxides was detected at the steam side of the tube, resulting in the over-heating of the final super-heater. Compressive stresses in the oxide scale generated during the unexpected shutdown of the power plant, which was responsible for the exfoliation of iron oxides. Finally, the growth and exfoliation mechanism of the oxide scale were put forward to conduct the related prevention and control measures.

Compared with other types of coal mills, fan mill presents advantages of compact structure and less construction cost. Therefore, fan mill is widely applied in thermal plants. This work carried out root cause analysis of crack failures occurred in pulverizing wheels of fan mills, which are applied in 600 MW steam turbine units of a power plant in China. The cracks are observed in dovetail grooves with beaters installed, and they are with substantial depths and critical to the safety of the fan mills. To find out the failure cause, Finite Element Analysis (FEA) is carried out including: (I) modal analysis and transient analysis of the assembled pulverizing wheel to determine the dynamic characteristics; (II) stress and strain computation of the local structure to obtain the concentrated stress and strain, where operational loads and contact behavior between different components are taken into account. The results indicate that the initial stress and strain exceed the yield limit under the normal operational condition, which reduces the margin of safety. Moreover, the stress and strain increase significantly when the pulverizing wheel is worn, which greatly increased the risk of failure. To avoid crack failures caused by wearing, analysis with different wearing quantities is carried out to determine the optimal repair strategy.

Formation of steam-side oxide scale that can cause major failures in boilers is a large concern in fossil-fueled power plant operation. In this work, we attempt to simulate the implications of oxide scale formation and subsequently assumed exfoliation in the given length of an austenitic tube of ultra-supercritical (USC) fossil power plants under different presumed service conditions. The incremental procedures used to determine the average metal temperature and scale thickness over a period of time in superheater/reheater tubes at a specified steam temperature are presented. A number of simulation results for both formation and subsequent exfoliation of the oxide scales are presented and discussed. Based on the simulation results, the estimated scale growth and presumed exfoliation rate in austenitic steels at 650 °C seemed to be allowable. However, to run USC power plants with steam condition of around 650 °C, more detailed studies are required.

The improved ferritic steels that have very good creep strength such as grades 91 and 92 have been widely used for power plant applications. For example, a chromium–molybdenum–vanadium steel tube (SA213-T91) has been available in the market for two decades. The SA213-T91 material has better high temperature strength and oxidation resistance than those of the more widely used materials such as T11 and T22. In this paper, estimations of the oxide scale growth and temperature increase of 9–12% Cr martensitic steels of superheater tubes are carried out using an incremental procedure, utilizing the finite element simulations and the relation between the Larson Miller Parameter (LMP) and the scale thickness over a period of time. In order to show the superiority of T91 steels over T22 steels, two different steam temperatures are considered in the models for comparisons. The estimations showed as expected that the oxide scale growth and temperature increase of the 9–12% Cr steels were significantly lower compared to those of 2.25% Cr steels.

Based on laboratory testing and experience related to boiler operation, this paper presents the phenomenon of oxide exfoliation (spallation) from the surface of the tubes of superheaters made of austenitic alloys. A computational model is proposed to determine the rate of erosion of the boiler and the turbine components by solid particles carried by steam. A method is developed to calculate both the mass of iron oxides detached from the inner surfaces of the superheater tubes and the erosion time. Using the computational models developed, the rates of erosion of the reheater elbow and the turbine control valve are determined for certain exemplifying conditions. The calculation results indicate that a condensate purification system must be used because a noticeable loss of material might occur, especially in the turbine components, even at a single flow of steam contaminated with exfoliated iron oxides. Therefore, the exfoliated particles must be eliminated from the power plant cycle as soon as possible.

The failure of industrial boilers has been a prominent feature in fossil fuel fired power plants. The contri-bution of one or several factors appears to be responsible for failures, culminating in the partial or complete shutdown of the plant. The use of high sulfur and ash containing fuel, exceeding the design limit of temperature and pressure during operation, and poor maintenance are some of the factors, which have a detrimental effect on the performance of materials of construction[1-4]. Among the many forms of corrosion mechanisms operating in tube failures in different parts of the boiler, ash corrosion and galvanic corrosion were the prime failure mechanisms predominantly found in bank tubes which arise due to use of low quality feed coal as fuel and poor cleaning proc-edures, respectively [5,6]. These types of failures are manifested by the accumulation of ash deposits on the fireside, which impart excessive fireside heat input and accumulation of corrosion products on the waterside of the tube [7], which induce localized corrosion. In the present paper, a comprehensive analysis of a boiler bank tube failed in one of the captive power plant of 77 x 2 MW capacity located in the northwest region of INDIA is presented.

Coal-fired boiler tubes are generally exposed to high internal pressure and high temperature of steam and flue gas. The common cause of any metallurgical failure of a superheater tube is due to the tube metal temperature higher than that as originally specified [1]. Tube metal temperature may increase gradually over many years due to the growing oxide scales inside tube or elevate rapidly caused by loss of internal steam or water-coolant flow. Internal pressurized tubes are critical components in water-tube boiler and steam superheater elements. Tubes in such application are vulnerable to high temperature upset condition, undergoing severe creep deformation or even final rupture. Therefore, boiler tubes in power plants have finite life because of prolonged exposure to high temperature, stress, aggressive environment, corrosive degradation, etc. However, uses of suitable boiler tube material in thermal power plants are required to ensure that the materials are safely used under higher temperatures and pressures for a long period of operation [2]. Many works concerning the failure problems in water-tube boiler have been reported. The North American Electric Reliability Council (NERC) reported that the coal-fired boilers are among the highest economic risk components in any other power plant. By far, the greatest number of forced outages in all types of boiler is caused by failures [3]. Elimination of boiler tube failure could save the electric power industry about $5 billion a year [4]. Metallurgists from French, Inc. [1] published data of the top 10 causes of failures where creep (long-term overheating) is 23.4%, followed by fatigue (13.9%) (thermal 8.6%, corrosion 5.3%), ash corrosion (12.0%), hydrogen damage (10.6%), weld failures (9.0%), high temperature (short-term overheating) (8.8%), erosion (6.5%), oxygen pitting (5.6%), caustic attack (3.5%) and stress corrosion cracking (2.6%). In general, 30% of all tube failures in boilers and reformers are caused by creep [5–7].

By analyzing the measured temperature, fatigue life, and damages due to continuous appearance of crack within the interior of the combined cycle power plant’s intermediate temperature (IT) and high temperature (HT) super heater header and finned tube weld, the causes of the damages were identified.

In this paper failure analysis on the SA213-T12 superheater tube by visual inspection, in situ measurements of hardness and finite element analyses is presented. A primary superheater tube has failed with a wide open burst after running at around 28,194 h. Heavy clinkers were found to almost entirely cover the primary superheater region. In situ hardness measurements were carried out on the selected primary superheater first row tubes at the middle region between furnace rear screen tube and primary superheater blower flow path. Hardness measurements are also taken on the as-received failed tube. Finite element analyses on possible features prior to failure are also conducted in order to illustrate and deduce the failure mechanism and failure root cause. Localized short-term overheating of the tube due to localized and concentrated flue gas flow resulted in a failure of the primary superheater tube.

In this paper, the failure of the bolts that fasten the draft tube of a 95-MW Francis turbine is presented. The fracture of the bolts is especially frequent when the machine operates at partial load. Fracture surface analysis and stress measurements under several power levels were done. Stress was also measured, while pressure relief in the spiral case was performed. Finally, stress measurements were conducted while pressured air was injected at the stay vanes and the machine was operating at partial load. With the strain measured, stress on the bolts was calculated. The fracture surface analysis showed that fatigue is the failure mechanism. Stress measurements revealed that strong vibration and broad stress variation is present when the machine operates at powers below 80 MW. Air injection effectively decreases vibration and stress fluctuation, but pressure relief in the spiral case did not show any beneficial effect.

Samples of 2.25Cr–1Mo steel in the form of tubes have been examined in the new condition and after extended service in a power station. The differences in microstructure in terms of precipitates have been characterized using a TEM; the various precipitates present have been identified individually by using extraction replicas and energy dispersive spectroscopy analysis. The area fraction of each type of precipitate was calculated. The results have shown that the quantity of M7C3 precipitated within grains as well as on grain boundaries decreased markedly with the time in service while the quantity of M6C increased in both regions. It was observed that precipitates of Mo2C and (CrMo)2CN, detected after aging respectively on the samples with the shorter and the longer aging times, were present only within grains. The procedure used was not accurate for identification and quantification of small VC and (VNb)C precipitates. The results of the relative quantity of M7C3 and M6C, as a function of time in service, particularly on grain boundaries, showed a well defined interdependence. These results can be used as a complementary analysis for creep damage and remaining life estimation for this class of steel operating at high temperature under steady state conditions.

Since the optimum operation of a generator is highly affected by increasing in temperature, a cooling system is used to control the temperature. Employing a fan as a cooling system for the generator at the end sides of its rotor is a practical method [Montazer Ghaem Gas Turbine Power Plant. Gas turbine generator manual, Iran, 2004]. In some cases, fracture of blades causes short circuit between rotor and stator and consequently generator explosion and huge financial loss. Since fracture in cooling fan blades has been occurred five times in our case study, in this research, the emphasis has been placed on failure analysis and preventing methods from the fracture in this generator’s fan blades. Survey and analysis of the above-mentioned problem have been conducted in different ways, which the main titles results are as follows: • All of these failures have been happened after the first operation of gas turbine or at the early after operation 100 h after gas turbine repairs [Alsthom Company. Failure report for gas turbine fan blades, 1997]. • Metallurgical and structural analyses on the failed blades have not shown any microstructure degradation. • Studies on the ruptured surfaces using scanning electron microscope (SEM) have shown that fracture has been happened as a results of high cycle fatigue (hcf). • Calculation of alternative stresses has indicated that this stress is less than fatigue endurance limit of blade material and none of these stresses and forces could result in fracture. • Modal analysis of blade has indicated that the blades natural frequency has been limited too close to the blades operational frequency. It means that making changes in blades installation conditions; blade natural frequency approaches the operational frequency and consequently causes the resonance. Analysis results show that the final fracture of blades is due to fatigue conditions in resonance state and growth of existent tiny probable cracks.

Turbine blades in a power station exposed to a temperature of about 800 °C were refurbished after 40,000 h of operation. However, after only 900 h of service at the same temperature, a number of refurbished blades were fractured. Various electron microscopy techniques as well as computational modeling were used to develop a one-to-one correspondence between microstructure and temperature distribution. Fracture was found to occur by a ductile intergranular mode. Although there was no evidence for overheating during service, the results showed that the blades initially contained γ′ precipitate-free zones alongside grain boundaries, which could accelerate intergranular failure consistent with the observed fracture mode. It was concluded that the blades were damaged by improper heat treatment during refurbishing.

Investigation is conducted following the discovery of significant deformations and the presence of cracks in the vicinity of welded joints at the superheater tubes of a heat recovery steam generator (HRSG) in a Malaysian Electricity Company’s power plant. This study performs the finite element (FE) analyses in order to identify the possible root cause failure of the deformed superheater tubes using software package of MSC PATRAN/NASTRAN. The locations of maximum stress induced by the deformed tube are determined. The correlation between the maximum stress and allowable restriction condition is presented, and it shows good correlations with the findings obtained from the visual inspection on site.

This document analyzes the structural integrity of several tubes of material P91 [1] , [2] , [3] used in a power plant. The appearance of three failures in different steps of the plant construction process requires a detailed an in-depth analysis to be performed in order to determine whether this will lead to the generalised failure of the rest of components or whether, on the other hand, the actions performed after the failures (post-weld heat treatment) are enough to ensure the correct operation of the plant.

Two principal groups of failure mechanisms appear in power plant components. On one hand, each component is usually known to suffer at least potentially from certain failure mechanisms that are expected and largely accounted for in design, manufacturing and assembly of the plant. Such mechanisms include for example creep, fatigue and corrosion under the foreseen service conditions. Even these mechanisms can contribute to real failures, because the real plant and its components may not turn out to fulfil the requirements, or because the plant is used longer or under different conditions from those initially expected. On the other hand, something unexpected can also happen in real service, so that other than expected failure mechanisms may intervene. Examples are shown on both types of failure mechanisms. Creep damage can be expected to limit the component life in superheaters and hot steam lines. Inspections on creep damage are widely used to indicate minimum life, or allowable time to next inspection. In general, unexpected failures are therefore not very common even after exceeding the nominal design life. However, unexpected mechanisms such as internal thermal shock cracking in the steam lines can result in failures much earlier than design life limit. Such damage is much more difficult to accommodate in the inspection and preventive maintenance programs, because it is more difficult to observe and inherently missed from the expected mechanism list.

In this paper, a series of failures of the welded joints in a power plant exhaust flue have been investigated. On-site investigation and experimental evaluations revealed that knife-line attack, embrittlement of weld metal detected due to sigma phase formation and thermal fatigue are responsible for the failure. The flue is made of stabilized austenitic stainless steel (type 321) and works at 520–550 °C.

Fatigue is a limiting factor in structural component life. Design calculations are performed according to conservative methodologies that shorten component life. Fatigue Monitoring Systems are an alternate that register the component service conditions. This work studies the application of one of those systems to determine the fatigue usage of the safe end of the feedwater system nozzle of the Santa Maria de Garona nuclear power plant. The transients recorded are compared to the ones evaluated in the design specifications and the fatigue usage is compared with the one provided in the stress report. The main conclusion is that the fatigue monitoring system calculates a fatigue usage that is significantly lower than the design one, this is due to two main reasons: actual transients are less severe than design ones, and the number of occurrences of actual transients is lower than specified.

The failure analysis of a disc and a few of the rotor parts of a turbo-generator of a 10 MW captive power plant has been made. It was found that a part of the rim of the 23rd disc, which had cracked by fatigue, became unstable and was flung off. This hit the diaphragm and the diaphragm carrier in its vicinity and led to their catastrophic failure.

The paper presents a method for estimating the degree of fatigue damage in an engineering ferritic–bainitic steel. A dislocation microstructure chart is first established from laboratory fatigue tests. Misorientation measurements are carried out after fatigue failure between dislocation cells produced by cyclic loading in ferrite grains and between dislocation cells in bainite originated by the heat treatment. There is shown to be a clear dependence of these values on the strain amplitude. On this basis, the analysis of the microstructure of a steel taken from a component which failed in service allowed the determination of the strain amplitude value to which the component had been subjected.

A service exposed (80,000 hr) economiser tube of a 60 MW boiler of a thermal power plant was investigated for the detailed metallurgical assessment necessary for remaining life estimation. The investigation included hot tensile tests, hardness measurement, microscopy and thickness measurement. Analysis revealed that there was no degradation of mechanical properties and microstructural features. The reduction in tube thickness was primarily due to oxidation and corrosion/erosion processes. Taking into account all the experimental data and mechanics aspects of the tube an estimated remaining life of 20,000 hrs was calculated and thus recommended for further use.

The failures of six pressure vessels are described: Sizewell boiler (1963), John Thompson ammonia converter for ICI Immingham (1965), Cockenzie power station boiler drum (1966), Typpi Oy heat exchangers (1970), Robert Jenkins pressure vessel (1970) and the Union Oil Co. amine absorber tower (1984). The failure investigations and findings are summarized.