Vaclav Mentl

Application of Acoustic Emission for Identification of Differences in Fatigue Damage of Selected Materials for Power Plants

An acoustic emission is remarkable source of information about the fatigue process and its intensity under cyclic loading. Specimens made of reactor steel and INCONEL 713LC were subjected to bending fatigue loading in the high-cycle range. This study presents results of acoustic emission signal analysis. The main aim of this study is to propose a methodology for evaluation of the early manifestations of fatigue damage and to identify material changes in both materials by AE parameters. Signal comparison material indicates differences of damage mechanism in observed. An examination of crack initiation sites and microstructure has been also performed.Experiments were realized in cooperation between laboratories of Brno University of Technology and University of West Bohemia in Pilsen and its related to solving of project of the Czech Ministry of Industry and Commerce: “A diagnostic complex for the detection of pressure media and material defects in pressure components of nuclear and classic power plants“ and project New Technologies for Mechanical Engineering (NETME +).

Fatigue Tests – Important Part of Development of New Vehicles

In city of Pilsen (Czech Republic) modern transport engineering is developed. The Skoda Transportation (production company) has successfully been producing rail and road vehicles for many years (electric locomotives, trams, metro cars, trolleybuses, battery buses). This producer cooperates in developing these vehicles with the Research and Testing Institute (commercial research institute) and with the University of West Bohemia (public university). Fatigue tests are carried out by the Dynamic Testing Laboratory at the Research and Testing Institute and by the Regional Technological Institute, the research center of the Faculty of Mechanical Engineering at the university. The paper describes various fatigue tests and presents their practical realization in the mentioned laboratories.

Verification of the Trend of MPL Variation in Fatigue by Modern Methods

The paper presents experimental results concerning the variation of microplastic limit (MPL) during fatigue as determined by the measurement of changes in inductance L of specimens made from normalized low-C steel CSN 411375. Some indications have been obtained that MPL varies during fatigue with dislocation density. This was proved by nanoindentation, X-ray diffraction and transmision electron microscopy.

Utilizing electromagnetic properties to determine the micro-plastic limit of low-carbon steel CSN 411375

It is generally accepted that not all cyclic stresses below the fatigue limit are non-damaging. Particularly in spectrum loading, the inclusion of some cyclic stresses below the fatigue limit can reduce the fatigue lifeof acomponent. It is believed that the boundary between damaging and non-damaging stresses is the so-called micro-plastic limit (MPL) defined as a macro-stress at which dislocation pile-up stresses begin to obstruct the magnetic domains in rotation to the direction of the tensile stress. This paper shows that MPL can be determined from changes in magnetic permeability during tensile loading. In our work, changes in magnetic permeability were measured indirectly - by measuring changes in electrical impedance (a.c. resistance and inductance). Measurements were performed on normalized low-C steel CSN 411375, and the microplastic limit was determined by evaluating the Δ R- σ and Δ L- σ records.

Evaluation of Fatigue Damage by X-Ray Diffraction Technique of Steam Turbine Rotor Steels at Elevated Temperatures

In many industrial applications materials are subjected to degradation of mechanical properties as a result of real service conditions. The assessment of the remaining lifetime of components and structures is commonly based on correlated procedures including numerous destructive, non-destructive and mathematical techniques that should guarantee reasonable precise assessment of the current damage extent of materials in question and the remnant lifetime assessment. The assessment of the remaining lifetime by X-ray diffraction technique is based on the fact that mechanical properties of the most materials depend strongly on crystallite size and orientation of ingredients, which are the crucial parameters for the determination of the ageing state and the prediction of residual lifetime of the components. X-ray diffraction technique proved to be useful as a tool for the assessment of material degradation extent after a long-time service. Framework 5 project “XPECTION” [1] was dealing with this task with respect to high temperature creep degradation of boiler tube steels. In this presentation, the X-ray diffraction technique was applied to reveal subtle details of the microstructural changes induced by fatigue. Several steam turbine rotor steels were fatigue tested at elevated temperatures up to 600°C at strain control regime. After the tests, the X-ray diffraction method was used to correlate the extent of fatigue damage with the X-Ray diffraction patterns to be able to assume the life-time exhaustion caused by fatigue loading in service.Copyright

Remaining Lifetime Evaluation of High Temperature Components of Power Plant Steam Boilers: Case Studies

The energy producing power plants are designed for operational period of 20, 30 years. During this period, inspections are realized to investigate the operational capability of the respective components and the plant as a whole, and when the designed time is approaching its limit, the crucial questions are raised with respect to the following possible operation, its safety and risks that stem from the fact that the continuous degradation of material properties occured during the longtime service as a result of service conditions, e.g. high temperatures, fatigue loading etc. The inspection of the boiler and the assessment of its future operational capability should ensure the safe operation and minimazing the failure risks. In comparison with the more sofisticated and much more expensive methods that use numbers of variables that enter the evaluation process of the lifetime exhaustion, or the metallographic non-destructive or even destructive methods that do not result often in a quantitative lifetime assessment, a relatively simple assessment method was used to evaluate the remaining lifetime of the high temperature components. On the basis of accelerated creep test data performed on the degraded materials, the remaining lifetime hours were calculated for the three “safety” situations: 1. “ZERO SAFETY” (neither recommended k = 1, 5 safety coefficient for working stress nor +70deg Celsius increase of working temperature were taken into consideration). 2. “STRESS SAFETY” (1, 5 safety coefficient for working stress and working temperature were taken into consideration). 3. “FULL SAFETY” (1, 5 safety coefficient for working stress and working temperature +70 deg Celsius were taken into consideration). This paper summarizes the results of remaining lifetime calculation for three different cases of steam boilers inspected after longtime service by Skoda Research ltd. Recently. On the basis of performed examination, the results provided the customer the recommendations relating the future safe and reliable operation.Copyright