Damage and lifetime of fossil power plant components

This paper deals with a presentation of the different types of damage which may degrade the principal components of EDF fossil power plants. Examples of creep, fatigue, erosion and corrosion damage are outlined. Damage in EDF plants is compared with that described in different publications. Then, life assessment methods are presented. They are based on periodic inspections and mechanical analysis carried out to optimise the inspection frequency.     

Numerical assessment of thick walled power plant components under creep fatigue load with advanced models for deformation and lifetime

Abstract

Renewable energy sources are changing the operation mode of conventional power plants significantly. Load changes cause fatigue deformation and damage, where traditionally creep effects dominated. In thick walled components the fatigue is concentrated on the inside (where temperature changes are quickest), but through plastification and stress rearrangement during operation the deformation behaviour of the entire component is affected. In this work, the time and temperature dependent deformation of components is described by finite element analysis based on a viscoplastic deformation Chaboche type model. Creep fatigue damage is evaluated by a mechanism based creep fatigue crack growth model and applied by a post-processor program with automatic load cycle detection. An introduction to verification efforts within the HWT-II test rig (at GKM Mannheim) and by full scale component test (MACPLUS project) are given.     

Structural integrity assessment of different components of a power plant

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.     

Symptom based diagnostic system for nuclear power plant operations using artificial neural networks

Nuclear power plant experiences a number of transients during its operations. These transients may be due to equipment failure, malfunctioning of process systems and unavailability of safety systems. In such a situation, the plant may result into an abnormal state which is undesired. In case of an undesired plant condition generally known as an initiating event (IE), the operator has to carry out diagnostic and corrective actions. The operator's response may be too late to mitigate or minimize the negative consequences in such scenarios. The objective of this work is to develop an operator support system based on artificial neural networks that will assist the operator to identify the IEs at the earliest stages of their developments. These abnormal plant conditions must be diagnosed and identified through the process instrument readings. A symptom based diagnostic system has been developed to investigate the IEs. The event identification is carried out by using resilient back propagation neural network algorithm. Whenever an event is detected, the system will display the necessary operator actions in addition to the type of IE. The system will also show the graphical trend of relevant parameters. The developed system is able to identify the eight IEs of Narora Atomic Power Station. This paper describes the features of the diagnostic system taking one of the IEs as a case study.     

A photothermal line-scanning system for NDT of plasma-sprayed coatings of nuclear power plant components

The main pump of the nuclear power plant primary circulation system is one of the most important and critical components of the pressurized water reactor type nuclear power plant. For instance, the failure of plasma-sprayed coatings on the pump's shaft seal rings leads to shutdown of the entire reactor. However, suitable methods for NDT of these coatings have not been found in spite of the obvious need. In this study, a photothermal NDT technique based on line-scanning laser heating and infrared radiation detection was applied. The measurements were modelled numerically and then performed in four series. First, a newly coated seal ring pair was inspected; two adhesion defects were found. The defective pair was subjected to a trial run emulating the real conditions of use and after that was re-inspected. Twenty new adhesion defects were found. Another newly coated seal ring pair was inspected and found to be faultless, and it was installed in the nuclear power plant for a year. During the next maintenance stop the pair was inspected again, and a group of three adhesion defects was found. The detecting of adhesion defects in both the unused and stressed coatings demonstrates the applicability of the photothermal method.     

Vibroacoustic diagnostic system for power engineering equipment

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 39–41, May, 1988.     

Creep fatigue interactions in power plant components

Abstract

The increasing need for flexible electricity generation means that most components must perform under cyclic operating conditions. The multiplicity of generating options also means that defining a ‘typical’ cycle is difficult. Thus, in addition to the traditional hot and cold starts and stops, there are requirements for rapid load changes on many occasions followed by operation at generation levels of 30% of rated capacity. These transients and operation at low loads result in complex changes in local pressure, temperature and flow at different parts of a boiler system. Indeed, these differences, in combination with the use of metallurgically complex steels, are such that the range of potential damage mechanisms has increased. Understanding these mechanisms is not straightforward as less post service investigations and root cause analyses are being carried out. EPRI seeks to facilitate expert evaluation of service experience and collaborates on establishing lessons learned to establish best practice. Annual creep fatigue discussions have identified key issues and areas for development related to component design and performance under transient operation. Summary documents have helped guide this international effort in the field of creep fatigue. It is apparent that a coordinated effort is important to ensuring that outcomes are meaningful and impactful. Excellence in science and engineering is necessary to underpin technology which is used by the electricity supply industry to meet current challenges associated with safe and reliable operation of plant. The present paper summarizes achievements on creep fatigue behaviour arising from the EPRI collaborative work and describes on-going commitment to knowledge creation and technology transfer.     

A GIS-based prediction and assessment system of off-site accident consequence for Guangdong nuclear power plant

GNARD (Guangdong Nuclear Accident Real-time Decision support system) is a decision support system for off-site emergency management in the event of an accidental release from the nuclear power plants located in Guangdong province, China. The system is capable of calculating wind field, concentrations of radionuclide in environmental media and radiation doses. It can also estimate the size of the area where protective actions should be taken and provide other information about population distribution and emergency facilities available in the area. Furthermore, the system can simulate and evaluate the effectiveness of countermeasures assumed and calculate averted doses by protective actions. All of the results can be shown and analysed on the platform of a geographical information system (GIS).     

Measurement of thermal fluxes in power plant components

A method of recovering the thermal flux acting on a sensing element with respect to measurements of sensing element signals is described.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 6, pp. 990–994, June, 1985.     

Experience on in-service damage in power plant components

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.     

Material damage evaluation and residual life assessment of primary power plant components using specimens of non--standard dimensions

Abstract

Obtaining information on the mechanical condition of service exposed primary power plant components can be problematic because of the need to sample significant quantities of material for testing direct from the component. To address this problem, techniques using specimens smaller than the ‘conventional’ ones described by commonly used test standards have emerged. Several experimental techniques that have been developed and validated with the aim of assessing mechanical condition, particularly from the point of view of fracture toughness, are reviewed. These involve the use of specimens reconstituted from previous tests or of subsize or even miniaturised specimens. The ability of these tests to reproduce data from full sized specimens and their range of applicability is discussed.     

Estimating the remanent creep life of power plant components

This paper examines the current status of remanent creep life assessment methods for power plant components. Consideration is given mainly to predictive techniques based on post-service examination and testing with application to low alloy ferritic components in fossil plant. The requirements for producing methodologies, namely the development of mechanistic and parametric models for creep damage and failure, are discussed together with aspects on the measurement of the relevant creep damage feature or property. Techniques considered include physical and mechanical property measurement, metallographic examination, strain measurement, and accelerated creep and rupture testing. Methods based on accelerated testing are discussed in detail; extrapolative techniques and application of the life fraction rule are considered both from an experimental and mechanistic viewpoint. Finally, attention is given to the choice of representative stress to apply to uniaxial data. The influence of material parameters on the representative stress is emphasized and upper and lower bounds appropriate to creep brittle and creep ductile material states are considered.     

Use of R5 in plant defect assessment

The R5 defect assessment procedures are widely used to assess components in Nuclear Electric's Advanced Gas-Cooled Reactor plant. In this paper, the use of R5 is illustrated by calculating the creep- fatigue crack growth in a specific component. The resulting crack size is compared with the limiting crack size calculated using R6. The implications of considering ductile tearing in the latter calculation, the possible interaction of tearing with creep crack growth, and the use of leak before break arguments are discussed.     

热电厂采用热电冷联供的适用性分析

利用等效发电效率概念,以300MW级抽凝式供热机组为例,对热电冷联供的适用性进行分析。在目前电、热价格以及发电机组装备水平的基础上,提出城市热电厂推广使用热电冷联供的约束性条件。     

Electric power system customer interruption cost assessment

A common approach used in quantifying the worth or benefit of electric service reliability is to estimate the customer costs (monetary losses) associated with power interruptions. Customer surveys are often used to determine interruption costs. The Power Systems Research Group has recently conducted surveys of Canadian electric utility customers in the residential, commercial, industrial, and agricultural sectors. These surveys were sponsored by the Natural Sciences and Engineering Research Council and eight participating utilities. This paper presents summary results of these surveys with emphasis on the costs of interruption.     

Development of life assessment procedures for power plant headers operated under flexible loading scenarios

A finite element methodology for thermo-mechanical fatigue analysis of a subcritical power plant outlet header under realistic loading conditions is presented. The methodology consists of (i) a transient heat transfer model, (ii) a sequential anisothermal cyclic viscoplastic model and (iii) a multiaxial, critical-plane implementation of the Ostergren fatigue indicator parameter. The methodology permits identification of the local thermo-mechanical stress–strain response at critical locations and prediction of fatigue life and cracking orientation for complex transient, anisothermal, cyclic elastic–plastic-creep material behaviour. Measured plant data, in the form of steam and pipe temperature transients and steam pressure data, are employed to identify heat transfer constants and validate the predicted thermal response, with particular attention given to plant start-up and attemperation effects. The predictions indicate out-of-phase temperature-strain response at the header inside surface and in-phase response on the outside surface. Cooling transients are predicted to control damage and crack initiation at the inner bore, whereas heating transients are predicted to have a more damaging effect at weld locations. A representative test cycle is presented, which is shown to capture the salient thermo-mechanical cyclic damage of the realistic cycle. The predicted results correlate well with industrial experience in terms of crack (initiation) orientation, location and life.     

Application of the fault tree analysis for assessment of power system reliability

A new method for power system reliability analysis using the fault tree analysis approach is developed. The method is based on fault trees generated for each load point of the power system. The fault trees are related to disruption of energy delivery from generators to the specific load points. Quantitative evaluation of the fault trees, which represents a standpoint for assessment of reliability of power delivery, enables identification of the most important elements in the power system. The algorithm of the computer code, which facilitates the application of the method, has been applied to the IEEE test system. The power system reliability was assessed and the main contributors to power system reliability have been identified, both qualitatively and quantitatively.     

基于故障危害度的飞机电源系统可靠性评估

基于故障危害度对飞机电源系统进行可靠性评估,首先建立可靠性评估模型,该模型考虑各故障样本对飞机电源系统供电可靠性危害度影响,将出现的故障按照对电源系统安全、性能、任务及维修等指标的影响程度进行等级分类,从故障的失效机理出发建立相应的分布模型;然后采用分布计算和二次分布等算法进行系统整体可靠性指标评估。应用该模型对飞机电源系统进行了故障统计分析,计算了飞机电源系统的可靠性指标。     

An analytic model for situation assessment of nuclear power plant operators based on Bayesian inference

Simulation-based human reliability analysis (HRA) methods such as IDAC seem to provide a new direction for the development of advanced HRA methods. In such simulation-based HRA methods, the simulation model for the situation assessment of nuclear power plant (NPP) operators is essential, especially for addressing the issue of errors-of-commission (EOCs). Therefore, we propose an analytic model for the situation assessment of NPP operators based on Bayesian inference. The proposed model is found to be able to address several important features of the situation assessment of NPP operators, and is expected to provide good approximations to some parts of the situation assessment. A comparison with an existing model and identification of several other features of the situation assessment of NPP operators that should be further addressed are also provided.