• Journal of the Korean Society for Nondestructive Testing
• /
• v.22 no.5
• /
• pp.483-489
• /
• 2002

The computer simulation has been done for non-insulated and insulated pipes which are vacant or half filled with liquid. The simulation results showed that the density profile on the radiography is continuous and symmetrical around the center of pipe in the case of vacant pipe. On the other hand the density profiles are not symmetrical and depend on geometrical setting for radiography in the case of half filled pipes. Finally, experimental testing on a non-insulated carbon steel pipe with artificial notches of different depth is carried out using Ir-192 and industrial film. Comparing the measured density profile on the radiograph to the calculated one, it has been shown that it is possible to evaluate thickness variation by measuring density profile on a radiograph.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.1
• /
• pp.45-52
• /
• 2003

A number of stress corrosion cracks in turbine rotor disk keyway in power plants have been found and the necessity has been raised to detect and evaluate the cracks prior to the catastrophic failure of turbine disk. By ultrasonic RF signal analysis and using a neural network based on bark-propagation algorithm, we tried to evaluate the location, size and orientation of cracks around keyway. Because RF signals received from each reflector have a number of peaks, they were processed to have a single peak for each reflector. Using the processed RF signals, scan data that contain the information on the position of transducer and the arrival time of reflected waves from each reflector were obtained. The time difference between each reflector and the position of transducer extracted from the scan data were then applied to the back-propagation neural network. As a result, the neural network was found useful to evaluate the location, size and orientation of cracks initiated from keyway.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.4
• /
• pp.328-333
• /
• 2003

It has been widely recognized that the residual stress of the weldment affect the integrity of steel structures and cause an initiation of crack in the welded regions. Since the power plants adopt a variety of welding processes, it is necessary to know the distribution and magnitude of residual stresses. This paper has attempted to investigate the validity of the saw cutting method and the indentation method to measure the residual stresses in the steel plates. The residual stresses in the specimens of hot reheater pipes, cold reheater pipes and feed water lines in power plants were determined by the saw cutting method and the indentation method. The data were compared and reviewed for the validity of the methods.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.4
• /
• pp.1509-1521
• /
• 2013

Social demand for the stability of structures lead to the development of the technology to accomplish it. The non-destructive seismic technique, which is able to assess structural integrity of infrastructures, belongs to this category. Seismic technique is focused on the measurement of seismic velocity propagating through the material, and has to utilize sensors coupled to material surface, which does not allow the testing to be performed on the fly. In this paper, a general vocal microphone, which works as a non-contact sensor, was adopted to facilitate seismic testing with mobility and efficiency improved. The target of using microphones was oriented toward quality assessment of compacted subgrade, stiffness evaluation and health monitoring of concrete structures. Experimental parametric study and field applications were performed to investigate reliability and efficiency of microphones. Finally, the optimal test configuration of microphones was suggested for resonance tests and surface-wave tests.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.19 no.2
• /
• pp.118-128
• /
• 1999

There are many ultrasonic measurement methods that are used in nondestructive testing applications. Some typical applications include material property determination, microstructural characterization. and flaw detection. Ultrasonic parameters such as velocity and attenuation are most commonly required in these applications. The accuracy and repeatability of testing results are dependent on both the hardware used to generate and receive the ultrasonic waves and on the analysis software for calculating these parameters. In this study, five analysis algorithms were implemented on a computer for measuring wave speed in a pulse echo. immersion testing configuration. In velocity measurements comparisons were made between the overlap. cross-correlation. Fourier transform. Hilbert transform, wavelet transform algorithms. Velocity measurement was applied to an isotropic steel sample using the five analysis algorithms. Frequency-dependent phase/group velocity and attenuation were also measured using the Fourier transform and wavelet transform algorithms on a composite laminate containing voids.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.30 no.4
• /
• pp.317-323
• /
• 2010

The manual ultrasonic examination for the nuclear power plant piping welds has been demonstrated by using KPD(Korean Performance Demonstration) generic procedure. For automated ultrasonic examination, there is no generic procedure and it should be qualified by using applicable automated equipment. Until now, most of qualified procedures used pulse-echo technique and there is no qualified procedure using phased array technique. In this study, data acquisition and analysis software were developed and phased-array transducer and wedge were designed to implement phased array technique for nuclear power plant in-service inspection. The developed procedure are qualified for performance demonstration for the flaw detection, length sizing and depth sizing. The qualified procedure will be applied for the field examination in the nuclear power plant piping weld inspection.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.28 no.4
• /
• pp.352-357
• /
• 2008

The detection of micro cracks in materials at the early stage of fracture is important in many structural safety assurance problems. The nonlinear ultrasonic technique (NUT) has been considered as a positive method for this, since it is more sensitive to micro crack than conventional linear ultrasonic methods. The basic principle is that the waveform is distorted by nonlinear stress-displacement relationship on the crack interface when the ultrasonic wave transmits through, and resultantly higher order harmonics are generated. This phenomenon is called the contact acoustic nonlinearity (CAN). The purpose of this paper is to prove the applicability of CAN experimentally by detection of micro fatigue crack artificailly initiated in Aluminum specimen. For this, we prepared fatigue specimens of Al6061 material with V-notch to initiate the crack, and the amplitude of second order harmonic was measured by scanning along the crack direction. From the results, we could see that the harmonic amplitude had good correlation with COD and it can be used to detect the crack depth in more accurately than the common 6 dB drop echo method.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.4
• /
• pp.18-24
• /
• 2015

Non-destructive testing (NDT) methods are widely used in the construction industry to diagnose the defects/strength of the concrete structure. However, it has been reported that the results obtained from NDT are having low reliability. In order to resolve this issue, four kinds of NDT test (ultrasonic velocity measurements by P-wave and S-wave and the impact resonance methods by longitudinal vibration and deformation vibration) were carried out on 180 concrete cylinders made with two kinds of mix proportions. The reliability of the NDT results was analyzed and compared through the measurement of the actual compressive strength of the concrete cylinders. The statistical analysis of the results was revealed that the ultrasonic velocity method by S-wave is having lowest coefficient of variation and also most capable of stable observation. Analytical equations were established to estimate the compressive strength of the concrete from the obtained NDT results by relating the actual compressive strength. Moreover the equation established by the ultrasonic velocity method by S-wave had the highest coefficient of determination. Further studies on the stability of non-destructive testing depending on various mixing conditions will be necessary in the future.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.30 no.4
• /
• pp.386-395
• /
• 2010

The steam generator management program(SGMP) has recently defined the procedures for the qualification of eddy current hardware and technique. These procedures provide two basic methods for qualification. The first way is to qualify the equipment or the probe by using the flaw mechanism and method of the pulled tubes from the heat exchangers or the artificial flawed tubes. The second way is to verify the equivalency with the characteristics of the qualified equipment or probe. In this case, the qualified equipment or probe may be modified to substitute or replace instruments or probes without re-qualification provided that the range of essential variables defined in the examination technique specification sheet are met. This study is to describe the result of the comparative performance evaluation of bobbin coil eddy current probes manufactured by KEPCO Research Institute and probes manufactured by a foreign manufacturer. As a result of this study, although there were minor differences between the two kinds of probes, it was evaluated that the two kinds of probes were almost identical in the significant performance characteristics described in the KEPCO Research Institute guideline.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.304_306
• /
• 2009

본 논문은 IEEE std 400에서 규정하고 있는 케이블 시험방법 중 Type 1, 파괴시험법(DC, 상용주파 내전압, 그리고 VLF내전압 시험)은 절연물 손상을 발생시키므로 예방진단에 사용될 수 없고 그렇지 않은 Type 2. 비파괴시험법에 대해 주로 소개하였다. 이와 추가하여 한전에서 사용 중인 IRC(Isothermal Relaxation Current) 측정법에 대해 간략하게 소개하고 더불어 IEEE Std 400에서 제시하고 있는 $Tan{\delta}$측정법의 문제점 및 개정 방향을 소개하고, 마지막으로 IEEE Std 400.3의 PD신호의 분석을 통해 결함위치와 열화정도를 평가 진단하는 기법에 대해 서술하고저 한다.