Many of the thermal power plant small diameter pipes are used in high temperature and high pressure environment. Failure of small diameter piping welds is a recurring problem, especially wall thinning frequently caused by the corrosion. RT is very useful method to detect flaw in weld are...
Many of the thermal power plant small diameter pipes are used in high temperature and high pressure environment. Failure of small diameter piping welds is a recurring problem, especially wall thinning frequently caused by the corrosion. RT is very useful method to detect flaw in weld area. But, the government strongly regulated RT method during manufacturing and construction because of excessive expose to radiation. In the industrial world, substitution method of RT is need to keep the quality of power plant and has consider the UT method. But.it is difficult to detect the various defects using conventional ultrasonic examination, so developed technique that is phased array ultrasonic testing (PA UT) is considered to meet the code and customer’s requirement. However, this technique is not fixed how to setup the parameters, how to measure the length and through wall sizing using acquired data. Therefore, there is need to develop the standard process for detecting and correctly evaluate defects. This study compare the detectability flaw in the weld area between RT and PAUT and develop the optimized PAUT scan plan including several UT parameters using several shapes weld specimens to verify the ability of flaw detecting for different flaw types through the actual comparing experiments. Also this study verify that the reflected PAUT signal change in cause of post weld heat treatment (PWHT) of weld and adjacent area. The optimized PAUT detecting technique is based on the accurate analysis to be evaluate the flaw length and depth sizing using reflected signals from flaw. The optimized PA UT scan plan including several parameters receives ultrasonic beam regardless of the direction of the reflector, and used the technique of forming, steering focusing of ultrasonic beam to obtain signals with high signal to noise ration even in high attenuation materials. However, since the underlying physical phenomena of PA UT are the same as conventional ultrasonic testing, the technique should be established with sufficient demonstration in relation to measuring the length and depth sizing by ultrasonic signals. The experiment was carried out using several specimens including various artificial notches which have different lengths, widths and depths to verify the indication detection probability and the indication height measurement. Through this experiment, we can have many acquisition data depending on several acquisition combination and condition. The measurement method of the length and through wall sizing is not defined in the ASME code that only require the inspector workmanship. Also there is no study by now regarding how to evaluate the flaw size. Because of this, the confidence of PAUT is very low to customer and regulatory authority. The result of this study is that the most adjustable method is the PAUT that is verified to detect the various flaws and all area located flaw in the weld. The PAUT is verified excellent detectability for linear type flaw like as crack, lack of fusion compare to RT. Therefore the PAUT can enough apply to detect internal flaw of weld area substitute for RT. The PAUT data is not also changed depending on PWHT for the ferrite material weld. The geometric signal from the root phase shall be used comparison technique between incident angle and reflected angle from the reflector described this study. The important result of this study is how to evaluate the size of flaw based on the optimized detecting technique and define the sizing method similar to actual flaw size in the weld. Through the experiment for the technique of flaw sizing, it is verified the most important parameter to be define the amplitude drop method. Therefore this study is applied several amplitude drop method in accordance with reference code each length and through wall sizing. The result is that the 3dB drop and 6dB drop method is closest result to the actual size out of the flaw sizing experimental data. The result of experiment. The result of obtained through experiments is verified using the regressing equations to evaluate the optimal technique for sizing flaw length and through wall. The method of length sizing of flaws should be applied 6dB drop method based on the maximum amplitude from the reflected signals. This method comes close to distribution of actual artificial detects size. Although it is a different result with normal sizing method, the through wall sizing should be applied 3dB drop method based on the maximum amplitude. If applied the normal method, it may be overestimate compare to actual defect size and performed repair unnecessary. The result of study is verify the fracture mechanics and the evaluation standard in accordance with ASME Code case 2816. The result of this study is developed the best setup method to detect and sizing technique for the weld flaw. The result of study has a limitation for the application range of heavy thick weld zone and also stainless steel weld material. It is needed various study to be extended application parts for the many welding and material type.
Many of the thermal power plant small diameter pipes are used in high temperature and high pressure environment. Failure of small diameter piping welds is a recurring problem, especially wall thinning frequently caused by the corrosion. RT is very useful method to detect flaw in weld area. But, the government strongly regulated RT method during manufacturing and construction because of excessive expose to radiation. In the industrial world, substitution method of RT is need to keep the quality of power plant and has consider the UT method. But.it is difficult to detect the various defects using conventional ultrasonic examination, so developed technique that is phased array ultrasonic testing (PA UT) is considered to meet the code and customer’s requirement. However, this technique is not fixed how to setup the parameters, how to measure the length and through wall sizing using acquired data. Therefore, there is need to develop the standard process for detecting and correctly evaluate defects. This study compare the detectability flaw in the weld area between RT and PAUT and develop the optimized PAUT scan plan including several UT parameters using several shapes weld specimens to verify the ability of flaw detecting for different flaw types through the actual comparing experiments. Also this study verify that the reflected PAUT signal change in cause of post weld heat treatment (PWHT) of weld and adjacent area. The optimized PAUT detecting technique is based on the accurate analysis to be evaluate the flaw length and depth sizing using reflected signals from flaw. The optimized PA UT scan plan including several parameters receives ultrasonic beam regardless of the direction of the reflector, and used the technique of forming, steering focusing of ultrasonic beam to obtain signals with high signal to noise ration even in high attenuation materials. However, since the underlying physical phenomena of PA UT are the same as conventional ultrasonic testing, the technique should be established with sufficient demonstration in relation to measuring the length and depth sizing by ultrasonic signals. The experiment was carried out using several specimens including various artificial notches which have different lengths, widths and depths to verify the indication detection probability and the indication height measurement. Through this experiment, we can have many acquisition data depending on several acquisition combination and condition. The measurement method of the length and through wall sizing is not defined in the ASME code that only require the inspector workmanship. Also there is no study by now regarding how to evaluate the flaw size. Because of this, the confidence of PAUT is very low to customer and regulatory authority. The result of this study is that the most adjustable method is the PAUT that is verified to detect the various flaws and all area located flaw in the weld. The PAUT is verified excellent detectability for linear type flaw like as crack, lack of fusion compare to RT. Therefore the PAUT can enough apply to detect internal flaw of weld area substitute for RT. The PAUT data is not also changed depending on PWHT for the ferrite material weld. The geometric signal from the root phase shall be used comparison technique between incident angle and reflected angle from the reflector described this study. The important result of this study is how to evaluate the size of flaw based on the optimized detecting technique and define the sizing method similar to actual flaw size in the weld. Through the experiment for the technique of flaw sizing, it is verified the most important parameter to be define the amplitude drop method. Therefore this study is applied several amplitude drop method in accordance with reference code each length and through wall sizing. The result is that the 3dB drop and 6dB drop method is closest result to the actual size out of the flaw sizing experimental data. The result of experiment. The result of obtained through experiments is verified using the regressing equations to evaluate the optimal technique for sizing flaw length and through wall. The method of length sizing of flaws should be applied 6dB drop method based on the maximum amplitude from the reflected signals. This method comes close to distribution of actual artificial detects size. Although it is a different result with normal sizing method, the through wall sizing should be applied 3dB drop method based on the maximum amplitude. If applied the normal method, it may be overestimate compare to actual defect size and performed repair unnecessary. The result of study is verify the fracture mechanics and the evaluation standard in accordance with ASME Code case 2816. The result of this study is developed the best setup method to detect and sizing technique for the weld flaw. The result of study has a limitation for the application range of heavy thick weld zone and also stainless steel weld material. It is needed various study to be extended application parts for the many welding and material type.
주제어
#Phased Array Ultrasonic Test Radiographic Test Post Heat Treatment specimen weld flaw Regression ASME Code amplitude drop method flaw sizing
학위논문 정보
저자
이동진
학위수여기관
창원대학교 대학원
학위구분
국내석사
학과
재료공학과
지도교수
홍현욱
발행연도
2020
총페이지
82
키워드
Phased Array Ultrasonic Test Radiographic Test Post Heat Treatment specimen weld flaw Regression ASME Code amplitude drop method flaw sizing
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