전단간섭법과 적외선 열화상 기법을 이용한 배관순환시스템에서의 원자력 압력용기 결함진단 및 정량평가

Abstract

Nondestructive inspection technology used in industrial field has been widely used the field of safety diagnostic tests such as industrial machinery, nuclear power plants, heavy and power plants, ports, car etc. The absence defect of industrial facilities through the test results quickly and accurately detect the defects, are responsible an important role in the industry by gaining the reputation of the product, such as the health, economy and reliability. There are many efficient NDT methods such as visual testing(VT), radiographic testing(RT), ultrasonic testing(UT), magnetic testing(MT), liquid penetrant testing(LT), eddy current testing(ET), acoustic emission(AE), thermography. Generally, VT, PT, MT, and ET are applied for the detection of surface defects and UT and RT are done for internal defects. Shearography was developed by Leendertz based on the concept to derive derivative for deformation after configuring proper optical interferometry. Since the initial discovery, Hung improved the methodology to acquire strain rate information. Original shearography was developed to measure slope, and it can be considered as strain gauge, which measures deformation slope in large area simultaneously. Where defect exists at rigid object, external force will create stress concentration. Rigid body deformation does not involve change in strain rate, and shearography method will be highly suitable to measure the defect in object, and it has less influence from disturbance. Due to these advantages, it has been widely used as non-destructive analysis technique. IR thermography utilizes optical energy as detection method. Unique IR energy signature is applied to target, and difference in IR energy from target is analyzed. This method is applied not only stress analysis, corrosion defect in metal, fatigue limit analysis, degradation of power facility, medical application, delamination of composite material, but also semiconductor, nuclear, defense, aerospace industries, that require higher reliability and safety standard. Therefore, its adoption into different field is expanding over the time. In this paper, shearography and IR thermography is used to measure wall-thinning defect according to internal temperature change in pipeline for circulation system of nuclear power plant. Sherography system is a commercial one from Dantec Dynacmics, German (Q-800 model), and it is composed of shearography sensor, diode laser inside of sensor, controller, and PC. Amount of shear is given in Y direction as 5 mm (0.333mm/pixel), and system utilizes commercial program, ISTRA 4D, for equipment control and filtering/grain treatment. IR thermography equipment is a commercial product from French company, Cedip 480M for acquisition of thermography image. Frequency of IR thermography is synchronized with function generator, and control PC for camera sensor control Emissivity of pipeline specimen is maintained as 0.95 by applying emission paint (KRYLON 4290 Ultra Flat Black). Internal temperature of test specimen in pipeline circulation system is set to 16℃ as ambient temperature, and is changed to 100℃. Using blower, temperature is quickly cooled to measure the surface of test specimen. Distance between pipeline and measurement equipment is 0.85m and 1 m, and blower is connected to function generator as sine wave with 0.1 Hz of frequency. Using pipeline circulation system, internal temperature of pipeline specimen is changed to 100℃ and blower is used to quench the specimen for measuring defect shape. As results, higher internal temperature of pipeline and deeper wall-thinning from the image will produce the bigger deformation of defect area. defect symptom of pipeline inside can be quantitatively estimated. Therefore, based on this result, estimation of defect, maintenance and replacement cycle for pipeline of nuclear power plant can be determined using the proposed method in this study.