Evangelos HRISTOFOROU
Laboratory of Electronic Sensors, National Technical University of Athens, Zografou Campus, Athens 15780, Greece

Faultless steel production and manufacturing based on stress monitoring and rehabilitation

Faultless steel production and manufacturing (FASTEP) represents a new method and technology for surface and bulk stress distribution monitoring and rehabilitation in steels, based on stress distribution monitoring and rehabilitation by localized induction heating. Stress distribution is monitored by monitoring differential permeability distribution; our group has proven that residual stresses depend on such differential permeability. Three types of permeability meters sensors are presented. The first one employs Hall sensors in a permanent magnet – soft magnetic bar yoke arrangement, offering permeability monitoring independent on the ambient field. The second one is a rather classic coil-coil arrangement with precise calibration, while the third one is based on a force sensing element set between a permanent magnet and the under-test steel. Measurements of the same type of steel have been realized, using all three types of sensors, illustrating a good agreement and low uncertainty. The rehabilitation has been realized by induction heating, using high current pulse generator, based on high voltage generator. The localized heating has been modeled by finite elements, calibrated by a precise infrared camera. Results illustrate that stress nonuniformity is improved two orders of magnitude by using stress monitoring and then induction heat annealing.

Yasuhiro KAMADA
Iwate University, Morioka, Japan

Application of magnetic hysteresis loop and electromagnetic acoustic resonance measurements to assure nondestructively the materials quality in automobile components

Magnetic hysteresis loop (MHL) measurement is one of the powerful tools to estimate mechanical characteristics of steels nondestructively. It is applicable to assure the materials quality during manufacturing process and also to diagnose materials degradation during operation. This report focuses on the former topic and shows two examples. The first example is the estimation of hardness in hot-stamped steels by measuring MHLs. Hot stamping is a process for both hardening and forming of steel materials, which is a critical technique for making light and strong automobile components. Using two parameters of coercivity and remanence in MHLs, we have succeeded in determining Vickers hardness even without knowing the information on thickness of surface oxide layers. This nondestructive testing is now adopted for quality assurance in production process at a car factory. The second one is the nondestructive evaluation of both tensile strength and Brinell hardness on cast irons with different matrix microstructures and graphite morphology. MHL properties are sensitive to the matrix microstructures but not to the graphite morphology. The combination of MHL and electromagnetic acoustic resonance (EMAR) measurements is the key success factor.

Gabor VÉRTESY
Hungarian Academy of Sciences, Centre for Energy Research, Budapest, Hungary

Nondestructive investigation of reactor steel degradation by magnetic adaptive testing

Degradation of nuclear pressure vessel steel material was investigated by a novel magnetic nondestructive testing method, so called Magnetic Adaptive Testing (MAT), which is based on systematic measurement and evaluation of minor magnetic hysteresis loops. In first series of measurements reactor steel material samples were aged by special step cooling thermal treatments. This process was used for accelerated evaluation of thermal ageing sensitivity. The main consideration at the selection of the thermal treatment was to produce similar microstructural changes, which occur at irradiation. Three Charpy specimens from 15Kh2NMFA material and three Charpy specimens from A508 Cl2 material were measured. It was found that this type of degradation can be easily followed by magnetic measurements. Charpy impact test was also performed and the result was compared with the magnetic parameter. A good, reliable and closely linear correlation was found between the properly chosen magnetic descriptor and transition temperature in case of 15Kh2NMFA material. In the second series of measurements samples having different chemical compositions were irradieted by neutrons, and then measured by this magnetic method in a hot cell. It was found that neutron irradiation caused well measurable changes in the magnetic parameters. Magnetic parameters were sensitive both to the neutron fluence and to the temperature of irradiation. Our experiments prove the applicability of MAT in nuclear industry.

Bolesław AUGUSTYNIAK
NNT Ltd, Gdansk

Magnetic NDT – chance for industry 4.0

Presentation provides arguments which proof the thesis that magnetic non-destructive techniques have special and unique features which make that these techniques are highly recommended for application at industry 4.0 area. Review of relation between industry 4.0 and NDT starts presentation and basic features of magnetic NDT types of inspections are also described. The main part of presentation deals with the examples of novel magnetic techniques of steel construction inspection proposed by NNT for 4.0 industry market. Three following issues are addresses: 1) stress state assessment with Barkhausen noise detection, 2) microstructure damage detection with magneto-acoustic emission and eddy currents, 3) noncontact detection of cracks by means of magnetic flux leakage and by magnetostrictive pulses techniques. Summary of the features of the as given examples of magnetic NDT techniques and final remarks end the presentation.

Marek AUGUSTYNIAK
Gdańsk Univ. of Technology / InnoKompas consulting group

Energy from the sea wind – achievements, challenges and potential for diagnostics

Facing the installation of first Polish offshore wind farms in the near future, it is reasonable to discuss the state-of-the-art in the field of inspection of the wind turbines, and identify the optimal development strategy of local companies producing WT components or delivering dedicated NDT services. The presentation shall comprise the following topics:
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Introduction – Offshore wind power in numbers.
Vocabulary nuances: SHM / CM / CBM / NDT; four levels of damage detection.
Major players on the market: commercial companies, national and supernational wind energy-related organizations, major WT-NDT laboratories.
Levels of Wind Turbine monitoring (farm / WT / components), and failures specific for each component – blades, tower, foundation, generator, gearbox. Complexities of maintenance optimization.
Three mature CM techniques: vibration, oil particulate analysis, fibre optic strain gauges; challenges specific to offshore wind generation.
NDT approaches, in particular devoted to composite blades – complex, anisotropic structures; contact vs non-contact methods; special focus on electromagnetic methods.
Signal processing and computer-aided interpretation of stochastic and ambiguous data; simulation (FEA) role in NDT support: generating database of possible cases for artificial intelligence.
Standardization of NDT techniques for wind turbines.
T echnological trends and their limitations (e.g. wireless sensor systems – energy harvesting).
Complementary challenge: inspection of windfarm operating vessels, e.g. Jack-Ups.
Back to bird’s eye view: perspectives for wind energy in Poland and its Baltic zone.
Acknowledgement
The review was prepared in cooperation with FEM4CAD – the company specializing in modelling of offshore jack-up vessels and InnoKompas consulting team.

Jerzy OKRAJNI
Silesian University of Technology, Gliwice

Diagnosis of the technical state of power plant components using computer modeling methods

The paper will present the results of research on elements of conventional power plants after many years of their operation. The course of changes in the time of their operation parameters including the pressure, temperature and steam flow rate will be discussed. On this basis, the issue of formulating boundary conditions for the analysis of temperature fields, stresses and strains in selected elements with a complex shape will be presented. Examples of local stress-strain characteristics determined on the basis of the FEM analysis will be presented. The problem of selecting material durability criteria depending on the nature of thermal and mechanical loads will be presented. Particular attention will be paid to the relationships between the assumed boundary conditions and the results of calculations in the context of the possibility of validating computer models based on the results of temperature tests at selected points of the components. The results of the FEM analysis will be compared to the experience of power plant users.

Aphrodite KTENA
National & Kapodistrian University of Athens, Greece

Magnetic permeability as a metric for NDT

Magnetic permeability is a macroscopic property of magnetic materials which reflects the existing microstructure at the time of measurement and its interaction with external stimuli such as applied fields, mechanical stresses, temperature. However, the interpretation and correlation of magnetic permeability with microstructural parameters or inherent magnetic properties requires particular attention as it refers to a deeper understanding of the magnetization process of the material. In practical applications, the measurement of the differential magnetic permeability as a function of the applied magnetic field, μdiff=dB/dH, is used instead of μ=Β/Η. In the present study, we investigate the dependence of μdiff on the strain and grain size of the material investigated and the use of μdiff as a metric for the determination of the tensile field in steels. The results are compared with 2D VSM measurements and other parameters such as those obtained from Barkhausen noise measurements. For the study of the effect of the grain size on the magnetic response, the RMS voltage of Barkhausen noise shows a more consistent behavior than μdiff. However, μdiff is proposed for the evaluation of mechanical deformation of magnetic materials, such as steels. Finally, we propose the use of the first derivative of differential permeability as a supplementary metric in the region of plastic deformation.

Marcos FLAVIO DE CAMPOS
Federal Fluminense University, Volta Redonda RJ – BRAZIL

Achievements in micromagnetic techniques of steel plastic stage evaluation

The investigation of plastic deformation and residual stress by non-destructive methods is a subject of large relevance for the industry. In this article, the difference between plastic and elastic deformation is discussed, as well as their effects on magnetic measurements, as hysteresis curve and Magnetic Barkhausen Noise. The residual stress data obtained with magnetic measurements is compared with data obtained by the hole drilling method and x-ray diffraction measurements. The residual stress level obtained by these three different methods is different, because these three techniques evaluate the sample in different depths. Effects of crystallographic texture on residual stress are also discussed. The magnetoelastic term should be included in micromagnetic methods for residual stress evaluation. It is discussed how the micromagnetic energy Hamiltonian should be expressed in order to evaluate elastic deformation. Plastic deformation can be accounted in micromagnetic models as a term that increases the coercive field in soft magnetic materials as the steels are.

M. J. SABLIK
Applied Magnetic and Physical Modeling, San Antonio, TX, USA, 78240

Prediction of magnetic properties of a plastically deformed silicon steel

This is a review of how to use the theory of magnetic hysteresis as provided by Jiles, Atherton and myself to predict magnetic properties of plastically strained magnetic materials. For this purpose, one uses Ludwik’s Law for strain-hardening stress to compute the dislocation density and insert it into the computation of magnetic hysteresis. A nonlinear extrapolation is used across the discontinuous yield region to obtain the value of stress at the yield point that is used in fitting Ludwik’s Law to mechanical data. The computed magnetic hysteresis exhibits sharp shearing of the hysteresis loops at small deformation, in agreement with the experimental data. Magnetic hysteresis loss is also shown to follow a Ludwik-like dependence on the residual strain, but with a smaller Ludwik exponent than applies for the mechanical data.

L. B. MAGALAS
AGH University of Science and Technology, Krakow

Novel applications of high-resolution mechanical spectroscopy to NDT

High resolution mechanical spectroscopy (HRMS) enables extremely accurate measurement of the absolute value of modulus of elasticity (E and G) and their subtle (previously unmeasurable) relative changes in materials subjected to various processes of heat treatment, thermo-mechanical treatment or plastic deformation. It means de facto new possibilities of diagnostic tests of metallic materials after different period of their exploitation in industrial conditions. The value of modulus of elasticity obtained in this way, correlated with the measurement of the amount of dispersed mechanical energy, makes it possible to track subtle module changes caused by the evolution of microstructure, dislocation structure, density of point defects, the share of quantitative phases and the possibility of detecting the appearance of small quantities of new phases, analysis of the process of separation, micro-cracks, etc. These changes are very difficult to detect in classical microscopic and diffraction studies, which means that such information is difficult to obtain in classical NDT.
In this paper we will present new methods of analysis of deformations of non-elastic metal alloys based on optimized interpolated discrete Fourier and Hilbert transform. These results greatly improve accuracy and reduce the background level of mechanical energy dissipated by the sample by nearly two orders of magnitude. This major leap forward in new mechanical spectroscopy research methods has been achieved through the use of unique A/D and D/A converters, the elimination of measurement errors associated with digital sampling and signal processing, and the use of dedicated proprietary software processors. The developed solutions have enabled a step- change in the development of measurement methods used so far and the creation of high-resolution mechanical spectroscopy, HRMS, both in the resonance and subresonance ranges. The results of tests obtained with the HRMS method can be used in non-destructive tests to diagnose degradation of materials used in e.g. rolling mills and critically loaded pipeline elements. From the point of view of NDT tests, the following information is extremely important o the possibility of carrying out tests in industrial conditions and without the necessity of cutting out the sample from the tested installation/machine. There is no single answer to this problem. In some situations, a standard measurement under industrial conditions is sufficient. In most cases, however, it is necessary to take a sample of small geometrical dimensions and perform tests under laboratory conditions. Such samples can be taken during planned overhauls of rollers, pipelines or other equipment and are usually sufficient for HRMS testing.
In conclusion, it should be emphasized that it is advisable to supplement routine NDT procedures with advanced scientific research, which often brings completely new information.
and shed new light on the difficult-to-recognize processes of material degradation. This conclusion applies both to materials used in miniature devices, such as metal alloy components used in high- performance mechanical pressure gauges, and to components used in sophisticated gravity wave tests and less exciting standard NDT industrial tests.
The great practical importance of research into material degradation processes forces us to constantly search for new solutions and methods and to take a new look at “old” problems. We have achieved this goal through the use of multidisciplinary solutions from various scientific disciplines far beyond material engineering and non-destructive testing.

Zbigniew RANACHOWSKI
Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw

Application of the acoustic emission method in the diagnostics of technical objects

In the presentation the general description of effects related to generation and propagation of Acoustic Emission (AE) signal is included. The pending European standard, i.e. procedure description are also discussed. The details of instrumentation designed to process the AE signal are described. The presentation is replenished with the informations dealing wih the preferred methods of characterizing of AE signal, that is the AE descriptors, such as: hits, events, detection level, spectral content. The presentation also lists the most frequent examples of the method application, i.e: location of the AE sources, guard sensing, testing of reinforced concrete elements, Kaiser & Felicity effects, testing of non-pressurized and pressurized vessels, testing of fiberglass pipes, high-power transformers, Diesel engines and austempered steel rods. Some of these application examples are of commercial type and some other are as far as now of the laboratory stage. Remarks on merits and drawbacks of the presented method when compared to other NDT tests are stated.