| Summary: | 碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 104 === The main purpose of constructing the oil tank equipment in petrochemical refineries around the world is to store a lot of oil. However, if there were not providing the perfect security inspection for oil storage tank, the corrosion may cause the oil leaks and lead to the serious petrochemical industrial accident. In the conventional method for detecting bottom of oil tank, the inspectors need to go into the storage tank to conduct the complicated detection. However, the inspectors may be exposed to hazardous when they are on the inside of oil tank. The purpose of this thesis is to apply the phased array ultrasonic method to detect critical zone at the bottom of the tank. Consequently, inspectors can install the phased array ultrasonic transducer at the bottom of outside oil tank for detecting the corrosion directly rather than go to the inside of oil tank. In this thesis experiment is performed by the phased array ultrasonic method that can pulse multiple element transducers to detect the different sizes of pitting corrosion area in the critical zone of oil tanks and to discuss the experimental result and limit. The experimental results are scanned into different images to be compared to explain the causes of the test and the advantages of phased array ultrasonic system detection.
The results indicated that by using the phased array ultrasonic system combined with encoder could make the pitting corrosion area in the bottom of oil tank to image instantly on the signal of C-Scan and it could distinguish the site of the bottom welds and the defect, could also measure the diameter of the pitting corrosion. For the signal of S-Scan, it could image the cross-sectional of pitting corrosion; moreover the signal feature of vertical corner and corner angle of the defect can be used to determine the depth of defect, the minimum of depth is 1.5 mm. By the quantitative evaluation of the defect could discuss the defect geometry and the distance from the transducer to defect having an effect on the detection results. This thesis proves that applying the phased array ultrasonic system of detecting the critical zone from the outer oil tank has its advantage. Moreover, this method provided more security to the oil tank.
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