The Qnde Using Image Processing of the Magnetic Camera

Hwang

et al. 2007

KEM

The magnetic field distribution around a crack can be calculated more easily and quickly by using a dipole model than finite element method (FEM). This paper reports the development of numerical analysis software that uses an improved dipole model to analyze the magnetic field around cracks. The preprocessor in this software includes the crack formation software, which can distribute the magnetic charge per unit area, m, on the crack section area. Also the lift-off, measurement area and sensor interval, and magnetization direction can be considered in the preprocessor. Also, the postprocessor presents functions, such as the natural magnetic field distribution and ∂B/∂x, ∂B/∂y, as results. Also, the physical characteristics of the magnetic optical sensor and the Hall sensor are included in the postprocessor, and the magnetic field distribution can be changed to optical intensity and electrical signal distribution. The experiment results, which are obtained by using the magnetic camera on the crack, are compared with analysis results obtained by using the dipole model analysis software.

Section: Analysis and Experimental Results And Discussionmentioning

confidence: 99%

Development of Numerical Analysis Software for the NDE by Using Dipole Model

Lee

Hwang

et al. 2007

KEM

“…Correspondingly, D C ′ can be calculated from S C by using Eq. (8) because the section area is multiplied by L C and D C ′.…”

Section: = Fmentioning

confidence: 99%

“…A magnetic camera using Hall sensors has been developed to inspect and evaluate cracks [6][7][8][9]. The distribution of the magnetic field can be measured quantitatively; then, the crack can be evaluated with a scan type magnetic camera [10].…”

Section: Introductionmentioning

confidence: 99%

Nondestructive evaluation of a crack on austenitic stainless steel using a sheet type induced current and a Hall sensor array

Lee

2008

J Mech Sci Technol

Self Cite

Austenitic stainless steels (hereafter A-STS) such as STS304 and STS316 are paramagnetic metals. However, a small amount of partial magnetization is generated in A-STS because of the imperfect final heat treatment and mechanical processing. Surface cracks on paramagnetic metal with a partially magnetized region (hereafter PMR) are difficult to inspect. In this paper, we propose a method for high speed inspection and evaluation of a crack on A-STS. Cracks can be inspected with high speed by using 64 arrayed Hall sensors (HSA) with 3.5 mm spatial resolution and a sheet type induced current (STIC). Then, a crack can be evaluated quantitatively by using the detailed distribution of the magnetic field obtained by using single Hall sensor scanning (SSS) around the inspected crack area. Several cracks on A-STS with partially magnetized areas were examined and the experimental formulas were derived.

“…The specimen was magnetized by using a yoke type magnetizer, which had a 250mm of poles interval and 4,000 turns of coil at 0.34A input current. Also, the differential magnetic field to the magnetization direction, ∂H Z /∂x, was used in the experiment and analysis results because the ∂H Z /∂x data can eliminate the bad influence of the magnetic field from the poles of the magnetizer and the leaked magnetic field from the crack can be extracted efficiently by using ∂H Z /∂x [7][8][9].…”

Section: Improvement Of the Dipole Modelmentioning

confidence: 99%

“…Hence, nondestructive testing (hereafter NDT) and evaluation techniques for inspecting and evaluating cracks on the surface or near of surface of large structures, such as atomic and thermal power plants, have been developed. On the other hand, an NDT technique, namely, magnetic flux leakage testing (hereafter MFLT) can provide the magnetic field distribution of a specimen, and allow the quantitative evaluation of a crack with respect to crack position, direction, length and depth [1][2][3]. In addition, the distribution of the leaked magnetic field must be analyzed to evaluate a crack quantitatively with respect to its various shapes and sizes.…”

Section: Introductionmentioning

confidence: 99%

A Study of Magnetic Charge per Unit Area of Dipole Model for the NDE

Hwang

Choi

et al. 2007

KEM

Nondestructive testing using magnetic field is useful for detection of a crack on ferromagnetic material. The magnetic field distribution has to be obtained for quantitative evaluation of crack direction, size, and shape. Also, a crack can be evaluated by using the inverse problem analysis. However, an analysis method using a dipole model can be used to analyze the magnetic field distribution around a crack at a higher speed than the finite element method (FEM). Therefore, a dipole model simulation can provide useful information which can be used for the inverse problem analysis. However, the magnetic charge per unit area, m, and the permeability, μ, has been treated as constants. Therefore, analyzed results have been different from experimental results in most cases. This paper proposes the improved dipole model simulation method, which assumes that the magnetic charges per unit area exist at the section areas, edge lines and summits of a crack. Also, the magnetic charges per unit area were assumed to depend on the square of the crack depth. The improved method is validated by comparing its results with the experiment results obtained with the use of the magnetic camera.