Marek Chmielewski

Multiparameter magnetomechanical NDE

We present a new approach to microstructural magnetic nondestructive evaluation (NDE) based on multiparameter measurements of magnetomechanical properties. A steel specimen was magnetized with a C-core using a triangular waveform of order 1 Hz in frequency. Hysteresis loops were obtained for five quantities: magnetoacoustic emission (MAE) and Barkhausen effect (BE) intensities, magnetic flux derivative, external magnetic field strength, and magnetostriction. The ability to extract the magnetic flux second derivative and the derivative of the magnetostriction permitted the investigation of several new interrelationships between MAE and other magnetic properties. Approximate coincidences were observed between MAE peak field position and peaks in magnetic flux second derivative and derivative of the magnetostriction. These effects are discussed and reproduced using existing magnetic modeling of MAE and corresponding modeling of flux density and magnetostriction.

Comparison of Properties of Magnetoacoustic Emission and Mechanical Barkhausen Effects for P91 Steel After Plastic Flow and Creep

The correlation between magnetoacoustic emission intensity and mechanical Barkhausen effect intensity has been tested in the case of P91 steel having different microstructure states due to either plastic flow at room temperature or speeded-up creep, performed under stress 290 MPa at temperature 773 K. The plastic strain range for the first set of samples has been from 2.0% up to 10.5% and for the second one from 0.85% up to 10.0%. Both effects revealed analogous monotonous decrease of their intensities as a function of resulting plastic strain. The decrease was higher for plastic flow than for creep. Those results are well consistent with results of tensile tests of the as damaged samples.

Non-destructive characterisation of 2Cr-1Mo steel quality using magneto-acoustic emission

Summary form only given. The magneto-acoustic effect (MAE) is now intensively investigated and modelled in order to enable the application for NDE of the creep damage process. The main important feature of the MAE is that it decreases as the creep damage stage increase. This feature can be used for steel quality non-destructive assessment. We describe experiments with standard Polish 2Cr-1Mo steel at various creep damage stages in which properties of MAE were tested and compared to other magnetic properties such as hysteresis loop B(H), Barkhausen effect (HBE) and magnetostriction /spl lambda/. The creep damage stage of the samples was evaluated from microstructure analysis and mechanical properties tests. The aim of this work was to establish a correlation between observed MAE properties and magnetic properties of this steel.

Influence of Plastic Deformation on Stray Magnetic Field Distribution of Soft Magnetic Steel Sample

The effect of various combinations of conditions, i.e., presence of the Earths magnetic field during and after deformation on the distribution of stray magnetic field of S355 steel sample, which is locally deformed, was investigated. Some of the stages of the experiment were carried out in zero magnetic field. Compensation of the Earths magnetic field was obtained by the application of a pair of Helmholtz coils. These coils are able to produce homogeneous field compensating Earths magnetic field over the full length of the sample. Stray magnetic field measurements were carried out along the longest dimension of the sample using the probe consisting of mutually perpendicular sensors allowing the simultaneous measurement of two magnetic field components, i.e., tangential and normal to a surface of the sample. Research has shown that there is a correlation between the level of plastic deformation of the investigated sample and the distribution of stray magnetic field. It was found that the nature of stray magnetic field of the sample depends on presence of external magnetic field during unloading. An attempt was also made, with the finite-element analysis, to verify experimentally obtained stray magnetic field distribution of undeformed sample.

Multiparameter analysis of the Barkhausen noise signal and its application for the assessment of plastic deformation level in 13HMF grade steel

The paper presents the results of multiparameter analysis of Barkhausen noise (BN) signal properties. In addition to the commonly used quantifiers of the BN signal, such as amplitude, integral of the BN envelope or results of pulse count analysis, we propose an additional analysis based on the change in magnetizing current amplitude. As it turns out the character of the change of the BN signal (as a function of the plastic deformation level) measured for various magnetizing currents differs significantly. Being so, a comparison of the results obtained for at least two magnetizing intensities gives a much better description of a plastic deformation level. In addition to that we observe two monotonic changes in the BN signal properties—a systematic shift of the BN signal peak position and the increase in the frequency for which the maximum in the BN FFT spectra occurs.

Possibility of Application of Magnetoacoustic Emission for the Assessment of Plastic Deformation Level in Ferrous Materials

The paper presents the results of an attempt to use the magnetoacoustic emission (MAE) signal for the nondestructive evaluation of plastic deformation levels in samples subjected to tensile loading. Four varied materials have been investigated: 13HMF, CSN12021 and P91 steels and commercially available Armco Iron. As it turned out various magnetic and magnetoacoustic properties of materials subjected to plastic tensile deformation behave in different ways for various materials, yet it is universally true that the steepness of the magnetic hysteresis loops decreases, thus leading to the increase in the separation of the “knee” portions of those loops. The MAE signal, being directly connected with the processes taking place for the magnetic field intensity at which those “knees” are observed (namely the 90° domain wall creation/annihilation and movement) can be used for the detection of that increased separation. As a suitable parameter we propose either the MAE peak separation (if two maxima are visible) or the separation between the peaks obtained for increasing and decreasing magnetizing field. An important feature of those parameters is that in all the investigated materials we observe a monotonous increase of such separation.

Barkhausen Noise Properties Measured by Different Methods for Deformed Armco Samples

The main goal of this research is the comparison of Barkhausen effect (BN) properties evaluated by means of two different methods: 1) using a ¿point probe¿ appropriate for industrial application; and 2) using a surrounding coil. The point probe contains ferrite core with searching coil perpendicular to the surface, and the sample is magnetized with a C-core electromagnet. Three quantities have been measured using first method: V1- rms voltage over many periods, Nc-number of BN pulses with amplitude higher than a given threshold, V2-maximal value of the flux derivative in the C-core. In the second method, the sample is magnetized with external solenoid and voltage signal induced in surrounding coil is analyzed providing several quantities: hysteresis loop of magnetic flux density, envelopes of BN rms voltage and pulse count rate over one period of magnetization, In-an integral of the rms envelope, N-total number of pulses, ¿ m-maximal value of differential permeability. The samples made from Armco iron sheet have been plastically deformed by tensile load at room temperature up to ¿ p =20%. The differences in BN properties revealed by these two methods are discussed qualitatively and explained.

An In-Depth Study of the Barkhausen Emission Signal Properties of the Plastically Deformed Fe-2%Si Alloy

This paper presents the results of the in-depth study of the Barkhausen effect signal properties for the plastically deformed Fe-2%Si samples. The investigated samples have been deformed by cold rolling up to plastic strain epsivp = 8%. The first approach consisted of time-domain-resolved pulse and frequency analysis of the Barkhausen noise signals whereas the complementary study consisted of the time-resolved pulse count analysis as well as a total pulse count. The latter included determination of time distribution of pulses for different threshold voltage levels as well as the total pulse count as a function of both the amplitude and the duration time of the pulses. The obtained results suggest that the observed increase in the Barkhausen noise signal intensity as a function of deformation level is mainly due to the increase in the number of bigger pulses.

On the possibility of the application of magnetoacoustic emission intensity measurements for the diagnosis of thick-walled objects in the industrial environment

This paper presents the results of measurements of the magnetoacoustic emission (MAE) signal performed on thick-walled pipelines in the industrial environment, and discusses the possible ways of their further analysis. Even though the direct measurement of the MAE does not allow for the determination of the MAE intensity, the paper proves that it is possible to separate the useful signal from the background noise either by means of hardware analogue filtering or by the application of the numerical analysis of the signal. Both the fast Fourier transformation (FFT) and wavelet analysis allow for the characterization of the MAE signal, the intensity of which can be much lower than the background noise level. Implementation of the hardware filtering, even though resulting in a lower signal-to-noise ratio, allows us to measure only the useful data, simplifying greatly the analysis needed. It should be emphasized that the application of software made with the help of the LabVIEW package allows for the implementation of the numerical analysis directly in the measuring set, enabling thus the direct assessment of the correctness of the obtained results during the tests in the industrial environment.

A new eddy current method for nondestructive testing of creep damage in austenitic boiler tubing

A new nondestructive eddy current technique is described for testing for incipient creep damage in austenitic steel boiler tubing in power plants. It is used because as incipient creep damage is formed, a magnetic oxide scale forms on the outside of the boiler tube in concentration proportional to the incipient creep damage; simultaneously in the base metal under the scale, a magnetic ferrite phase also forms in the grains and grain boundaries, which is in smaller concentration, but which is also in concentration proportional to the incipient creep damage. The eddy current signal can be processed in such a way that it varies monotonically and nearly linearly with the magnetic phase concentration and monotonically and nearly linearly with the incipient creep damage. Various aspects of the measurement are analysed and discussed—for example, liftoff, wall thickness, and diameter dependence. Using a zero point value to assess oxide layer permeability and dependence on conductivity is also discussed. Comparison is made between measurements and finite element modelling results.