Leszek Piotrowski

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.

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.

Designing a magnetoacoustic emission measurement configuration for measurement of creep damage in power plant boiler tubes

We discuss design features that are needed for magnetoacoustic emission (MAE) measurement of creep damage in the outer walls of boiler tubes. MAE is used because it decreases monotonically with increasing creep damage. Features of magnet design for boiler tube inspection are presented. Relationship of total MAE to Barkhausen noise path integrals is discussed. Also, dependence of MAE on frequency and tube wall thickness is delineated. Finally, measurements are discussed which show how azimuthal asymmetry in creep damage is echoed in azimuthal asymmetry in MAE. All tests were performed on 2Cr–1Mo Polish steel tube specimens.

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.

Investigation of magnetic and magnetomechanical hysteresis properties of Fe–Si alloys with classical and mechanical Barkhausen effects and magnetoacoustic emission

Grain oriented Fe 3.5% Si sheet samples with a Goss (GO) microstructure and Fe 3.5% samples with nonoriented (NO) grains were tested using two Barkhausen effects, the classical Barkhausen effect (HBE) and the mechanical Barkhausen effect (MBE), as well as the magnetoacoustic emission (MAE). The aim of the work was to present further evidence that the B(H) hysteresis with effects like HBE and MAE, and magnetomechanical hysteresis with MBE are correlated via internal stress barriers pinning domain walls (DWs). In the case of a GO alloy, the long axis of the sample was parallel to the [100], [110], and [111] directions with respect to the rolling direction. The HBE and MAE were measured using a C-core electromagnet supplied with a triangular wave form of current intensity. The MBE intensity was recorded during a monotonous increase of shear stress using a torque machine. The maxima of MBE intensity for the “first load” mode for a NO sample and for three GO samples indicate an internal stress distribution pin...

Study of microstress state of P91 steel using complementary mechanical Barkhausen, magnetoacoustic emission, and X-ray diffraction techniques

The paper deals with assessment of microstress state of martensite P91 steel using three complementary techniques: mechanical Barkhausen emission, magnetoacoustic emission (MAE), and X-ray diffraction (XRD) profile analysis. Magnetic coercivity Hc and microstructure were investigated with inductive magnetometry and magnetic force microscopy (MFM), respectively. Internal stress level of P91 steel was modified by heat treatment. Steel samples were austenitized, quenched, and then tempered at three temperatures (720 °C, 750 °C, and 780 °C) during increasing time (from 15 min up to 240 min). The microstrain level ei was evaluated using Williamson–Hall method. It was revealed that during tempering microstrain systematically decreases from ei = 2.5 × 10−3 for as quenched state down to ei = 0.3 × 10−3 for well tempered samples. Both mechanical hardness (Vickers HV) and magnetic hardness (coercivity) decrease almost linearly with decreasing microstrain while the MAE and MBE intensities strongly increase. Temperi...