Waldemar KAMRAT
Analytic hierarchy process application for investment effectiveness studies in power engineering industry
When making an investment decision it is usually the decision maker who encounters the problem of choosing the best option (strategy option in terms of physical tasks of an investment) and selecting the technology. This is a particular category of selection problems for which the assessment is considerably hindered. Complexity of the issues results, on the one hand, from the variety of technical, economic and environmental constraints - on the other hand, from many quality criteria which can only be arranged in the right way. The complexity of a decision problem, however, consists in the fact that individual investment projects can be assessed from different points of view with the help of both quantitative and qualitative criteria. In such cases the analytic hierarchy process can be very helpful.
Keywords: electric power engineering, analytic hierarchy process, investment effectiveness
Jerzy MADEJ, Bartłomiej BĘDKOWSKI
Numerical analysis of ventilating fans influence on electrical machines cooling efficiency
Presented are results and the course of analysis of an electric motor cooling efficiency depending on the applied ventilating fan type. The analysis was conducted with the use of numerical system equipped with tools essential for heat, liquids and gas flow analyses. The carried out numerical simulations allow to determine areas with elevated temeperatures which can have destructive influence on bearings, permanent magnets or other components and also on efficiency of the machine itself. Calculations of the air flowing through the motor were carried out for four different types of ventilating fans. The obtained results can be useful in electrical motors diagnostics as well as in design process of cooling systems. They also tell more about the real working state of the device, that in turn enables optimization of its application taking into account various working conditions and mounting locations.
Keywords: analysis of a heat and gas flow, electrical motors, cooling
Józef DREWNIAK, Jacek RYSIŃSKI
Fatigue life and reliability of power engineering machines and their elements
The designers of machines and devices, especially the ones working for the needs of power engineering, must pay a special attention during the design process to ultimate and fatigue strengths. However, it is not the only and sufficient approach to a design task because, for the users, the fatigue life and reliability of machinery are also very important parameters as they have direct influence on operating costs and maintenance planning. The fatigue life of machines and their parts, especially toothed wheels, used in power engineering is usually determined on the basis of fatigue tests, as the result of which we get the Woehler curve applicable in combination with one of the fatigue hypotheses e.g. Palmgren-Miner, Haibach or Corten-Dolan ones. This article presents a method of fatigue life evaluation based on fracture mechanics. Application of the boundary elements method allowed determination of fatigue crack propagation. After inserting the obtained data into the Paris-Erdogan equation we get the value of fatigue life measured in the amount of loading cycles. Due to the fact that this formula is the simplest one that can be used for determination of fatigue crack growth, some other equations e.g. Forman equation and Nasgro2/3 were used for comparison purposes. Once having the determined values of fatigue lives (since crack initiation, through propagation until the fatigue failure) one is able to evaluate reliability of any element of power engineering machines and appliances.
Keywords: power engineering machines and appliances, durability of elements of power engineering machines, reliability of machines and their elements
Sławomir MACKIEWICZ, Jacek SZELĄŻEK, Piotr GUTKIEWICZ
Ultrasonic testing of degradation process of steels used in power engineering
Discussed is the current state of various ultrasonic methods serving evaluation of steel degradation due to creep. Described are classical investigations based on correlation of changes in waves propagation velocity and the factor of attenuation of ultrasonic waves with the degree of material degradation. Presented are also new ultrasonic methods like investigations of nonlinear phenomena i.e. measurements of a nonlinear factor and an elasto-acoustic constant. The first one is based on the measurement of high-harmonic amplitudes generated during ultrasonic pulse propagation in a nonlinear solid. The second is based on measurements of elasto-acoustic effect i.e. the relation between ultrasonic pulse velocity and stress applied to the sample. More precisely described are investigations of acoustic birefringence caused by origination of oriented voids in solids during the last creep stage. Presented are results of birefringence investigations carried out on samples subjected to accelerated creep and on a sector of a thick wall pipe elbow damaged due to creep. Described is also an ultrasonic monitoring method of cicumference changes of a thick wall pipe working in creep conditions. Discussed are practical aspects of described methods application in industrial conditions. Acoustic birefringence measurement method and the technology of pipe circumference changes monitoring are completely nondestructive and demanding neither the use of expensive measuring equipment nor special preparations of the tested object and seem to be perfect candidates for practical application.
Keywords: steels used in power engineering, steel degradation, ultrasonic testing
Michał KWIECIEŃ
Technical condition of a mounting system is a key to failure-free and long lasting pipeline operation – on the example of diagnosis of an OP-230 boiler steam pipeline hanger system
Diagnostics of mounting and hanger systems is a part of a broadly defined diagnostics of high-pressure steam pipelines. The only guarantee of a proper work of the whole system are regular inspections and currently made repairs. Abandonment of such activities can lead to occurrence of local stress accumulation in a pipeline material what in turn creates favourable conditions for its quicker wear-out. All inspections carried on during the start-up and shut-down procedures are in favour of elimination of even the tiniest defects. And when outlays on reconstruction of mountings or hangers are relatively small then the replacement of, for instance, pipeline elbow needs much bigger expenses. That is why the care about the high-pressure pipeline mounting system is of a fundamental importance for its long-time and safe operation. Presented is a mounting system applied for a pipeline connecting OP-230 boiler and its TG unit. The system is quite characteristic and often met in power engineering. Also the arising problems with mountings work are similar in many cases.
Keywords: steam pipelines, safety systems, pipeline hanger system
Wojciech BIELIKOWSKI
Non-typical corrosion damages of WP-120 boiler waterwall tubes outer surface (debate article)
Technical expert opinions concerning damaged elements of boilers and turbines, going to determine the causes of these damages, must be based on a vast amount of knowledge from various technical branches and experience in the field of power engineering equipment functioning. In most cases the so-called „a good piece of engineer’s work” is quite sufficient to expertize and determine the damage cause in a comprehensive and, to a large degree, an explicit way. But, alas, it is not sufficient when we deal with damages of a boiler heating surface on the side of exhaust gases. Sometimes the interpretation of a damage cause becomes an intellectual challenge for an expert and does not necessarily ends successfully (often with more or less probable hypotheses). Presented is one of such opinions which did not end with an explicit determination of corrosion damage causes of a WP-120 boiler waterwall tubes outer surface. Described results can be helpful for a reader trying to consider the problem. Some of the phenomena accompanying the tube corrosion process are very rarely met.
Keywords: WP-120 boiler waterwall tubes, corrosion damages
Zbigniew KOWALEWSKI
Damage measures in creep investigations of construction materials
Presented are selected damage measures used for description of degradation of construction materials subject to loading conditions inducing creep phenomena. Apart from the commonly known measures some new concepts of damage. Discussed is also their suitability for detection of an early stage damage on the example of testing of the power engineering steels applied currently as constructional elements in power plants.
Keywords: creep, fatigue, damage, power engineering steels, damage measures
Marek AUGUSTYNIAK, Grzegorz W. WIŚNIEWSKI
Selected applications of Finite Element Method in design and diagnostics of energy systems and components
The authors’ own experience and results of contacts with producers of power system elements show that the demand for CAD/CAE software becomes more and more popular and more valuable. Particular role is played here by the Finite Elements Method with its various options and implementations. Analysed are technical and economic benefits which can be obtained when using FEM at the stage of exploitation of fuel sources, conversion of fuels into heat/electricity and energy transmission. The given examples illustrate variety of the above mentioned methodology applications for e.g. acoustic inspection of boreholes, HV cables insulation or boiler designing. Skilfully applied computer aided 3D system can be complementary to the 1D modeling system enabling growth of savings, durability of engineering constructions and enhancement of diagnostic methods.
Keywords: conversion, energy transmission, construction durability, turbines, boilers, pipelines, offshore, Finite Element Method
Leszek PIOTROWSKI
Magnetic adaptive testing – nondestructive testing method of changes in microstructure of power enegineering steels
Magnetic adaptive testing (MAT) is a new, promising method of evaluation of changes in material microstructure. Its main advantage is the fact that it allows to determine the hysteresis loop parameter optimal from the point of view of investigated changes in microstructure. Presented are results of P91 steel samples tests after austenitization (T = 1050oC; t = 1 h), air cooling and then tempering in temperatures T = 720, 750 and 780oC for a period of 15-240 minutes. Measurements of magnetic hysteresis loop showed that the change of classical hysteresis loop parameters (coercion field, maximum differential magnetic permeability) enables easily distinguish the tempered sample from the others, but the dynamics of changes during tempering process is not very big. Application of MAT method allowed to find parameters that are characterized by a higher change dynamics, both in the whole range of tempering times and in the final stages of this process.
Keywords: material structure changes, magnetic adaptive testing, hysteresis loop parameters