In order to detect material degradations in pressure vessel steel of A533B employed as a component material in light water reactors (LWRs), the leakage magnetic flux distribution on plate-type A533B specimens has been examined using a magnetic sensor of 120μm square GaAs Hall element. As reference data, the residual stress distribution has also been obtained by X-ray diffraction method where an irradiation spot was 1mm in diameter. The data of the leakage magnetic flux normal to the specimen surface (
Bz) measured by the Hall sensor were converted into the form of the first derivative d
Bz/d
x by calculating the gradient of the
Bz along the axial direction of the specimen (
x-axis), and the data of the axial residual stress (σ
x) obtained by the X-ray diffraction method were also transformed into the differential form dσ
x/d
x. It was found that there existed a correlation between the absolute value of the d
Bz/d
x and the dσ
x/d
x for the tensile specimens (correlation coefficient
r=0.282). Full width at half maximum (FWHM) for the frequency distribution profile of the d
Bz/d
x was calculated. The FWHM of the tensile specimens increased remarkably at the beginning stage of the plastic deformation where the Lüder's band was generated; The FWHM of the fatigued specimens increased with stress cycling. It was suggested that the leakage magnetic flux measurement by the GaAs Hall sensor was a promising non-destructive evaluation (NDE) method to detect the amount of plastic deformation and fatigue damage.
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