Jiseong Hwang

THE DETECTION PROBABILITY IMPROVEMENT OF THE FAR-SIDE CRACK ON THE HIGH LIFT-OFF USING THE MAGNETIC CAMERA

To evaluate cracks using magnetic flux leakage (MFL), the distribution of magnetic field (DMF) near the crack should be quantified. A narrow spatial resolution of DMF is demanded around the crack. Also the lift-off should increase over several mm to protect the sensors from environments such as high temperature, dust, and vibration. Furthermore, the MFL must be amplified to detect a far-side crack because the MFL will concentrate in the ferromagnetic specimen and will be weak. The magnetic camera and magnetic lens could be useful for high lift-off conditions such as in nondestructive testing of a far-side environment. The far-side crack detection probabilities, Max(∂B/∂x) and RMS(∂B/∂x), were improved by about 20~60% by using the magnetic lens. The crack can be easily detected by using the 1/4RMS algorithm. Finally, an equation that expresses the relationship between the volume of crack and Max(∂B/∂x) is proposed. This equation is based on the principle that the magnetic field is inversely proportional to the square of the lift-off and is useful for determining the crack volume when the lift-off is known.

Scan Type Magnetic Camera Images with a High Spatial Resolution for NDT Obtained By Using a Linearly Integrated Hall Sensors Array

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on the magnetized specimen by using a magnetic sensor such as the Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface crack on magnetized ferromagnetic materials. A scan type magnetic camera, based on the principle of MFLT, uses inclined Hall sensors array on the printed circuit board (PCB) to detect small cracks in high speed. However, the waveforms appear in the direction perpendicular to the scan, because the sensors are bonded at different gradients and heights on a PCB in spite of careful soldering. In this paper, the linearly integrated Hall sensors (LIHS) on a wafer are proposed to minimize these waves and to improve the probability of crack detection. The specimen took from a billet is used to determine the effectiveness of the LIHS in the multiple cracks detection.

Modeling of a scan type magnetic camera image using the improved dipole model

The scan type magnetic camera is proposed to improve the limited spatial resolution due to the size of the packaged magnetic sensor. An image of the scan type magnetic camera, ∂B/∂x image, is useful for extracting the crack information of a specimen under a large inclined magnetic field distribution due to the poles of magnetizer. The ∂B/ ∂x images of the cracks of different shapes and sizes are calculated by using the improved dipole model proposed in this paper. The improved dipole model uses small divided dipole models, the rotation and relocation of each dipole model and the principle of superposition. Also for a low carbon steel specimen, the experimental results of nondestructive testing obtained by using multiple cracks are compared with the modeling results to verify the effectiveness of ∂B/∂x modeling. The improved dipole model can be used to simulate the LMF and ∂B/∂x image of a specimen with complex cracks, and to evaluate the cracks quantitatively using magnetic flux leakage testing.

Quantitative Nondestructive Evaluation of the Crack on the Austenite Stainless Steel Using the Induced Eddy Current and the Hall Sensor Array

Nondestructive evaluation (NDE) has been effective in the prediction and evaluation of cracks on the surface of structures. Austenite stainless steel such as SUS304 and SUS316 is a paramagnetic metal with delta -ferrite structure. Small amount of partial magnetization is generated in the austenite stainless steel due to the final heat treatment and the mechanical working. The MOI (magneto-optical/eddy current imaging) was developed to inspect fatigue cracks and corrosions. But the surface cracks on the partially magnetized paramagnetic metals, such as austenite stainless steel, are difficult to inspect because the magnetic domains were saturated by external magnetization of the delta -ferrite. In this paper, the magnetic camera with the 64 arrayed Hall sensors by matrix (sensor matrix) was developed to confirm the real time inspection and quantitative nondestructive evaluation (QNDE). As the result, QNDE algorithm was proposed by using single sensor scanning, and the algorithm was introduced in QNDE by sensor matrix. Also, the cracks were inspected in the real time by sensor matrix, which were arrayed with 3.5 mm spatial resolution in square.

Magnetic images of surface crack on heated specimen using an area-type magnetic camera with high spatial resolution

A micro-array method using Hall sensors was proposed in previous research by the authors. That array method allowed a two-dimensional magnetic field measurement with high spatial resolution using simplified connections. A wide range of magnetic fields could be measured quantitatively with high spatial resolution. This paper proposes a nondestructive testing (NDT) method using a magnetic camera with the previous micro-array method to detect cracks in a specimen at high temperatures. Distilled water has a boiling point of 373.15 K at atmospheric pressure. Therefore, the Hall sensor array, which is submerged in the distilled water, can be protected from an external high temperature of several hundred degrees Kelvin until the container is broken. If the Hall voltage of each Hall sensor changes according to the external magnetic field at the boiling point of the liquid, we propose that the crack can be detected in a high temperature environment using a magnetic camera submerged in the liquid. Plate specimens made of SS41 stainless steel, with slits in the each specimen, were used to verify the proposed NDT method using a high spatial magnetic camera in a high temperature environment.

Inspection of Cracks on the Express Train Wheel Using a High Speed Scan Type Magnetic Camera

Abstract A novel nondestructive testing (NDT) system, which is able to detect a crack with high speed and high spatial resolution, is urgently required for inspecting small cracks on express train wheels. This paper proposes a high speed scan type magnetic camera, which uses the multiple amplifying circuits and the crack indicating pulse output system. The linearly integrated Hall sensors are arrayed in parallel, and the Hall voltages from each sensor in the scanning direction are obtained and amplified. High-speed NDT can be achieved by using the exclusive analog-digital converter and micro-processor because the ∂V H /∂x value, which provides the most important crack information, can be obtained by buffering and calculating. The effectiveness of the novel method was verified by examine using cracks on the wheel specimen model. †책임저자, 회원, 조선대학교 제어계측로봇공학과 E-mail : jinyilee@chosun.ac.kr TEL : (062)230-7101 FAX : (062)230-6858 * 조선대학교 일반대학원** 한국철도기술연구원 기호설명LIHaS : 선형으로 배열한 홀센서x, y : 스캔방향, 홀센서 배열방향∂V

Nondestructive evaluation using dipole model analysis with a scan type magnetic camera

Large structures such as nuclear power, thermal power, chemical and petroleum refining plants are drawing interest with regard to the economic aspect of extending component life in respect to the poor environment created by high pressure, high temperature, and fatigue, securing safety from corrosion and exceeding their designated life span. Therefore, technology that accurately calculates and predicts degradation and defects of aging materials is extremely important. Among different methods available, nondestructive testing using magnetic methods is effective in predicting and evaluating defects on the surface of or surrounding ferromagnetic structures. It is important to estimate the distribution of magnetic field intensity for applicable magnetic methods relating to industrial nondestructive evaluation. A magnetic camera provides distribution of a quantitative magnetic field with a homogeneous lift-off and spatial resolution. It is possible to interpret the distribution of magnetic field when the dipole model was introduced. This study proposed an algorithm for nondestructive evaluation using dipole model analysis with a scan type magnetic camera. The numerical and experimental considerations of the quantitative evaluation of several sizes and shapes of cracks using magnetic field images of the magnetic camera were examined.