Comparison of nondestructive testing technologies used for inspection of welded joints
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The purpose of this research is to report on the comparison between different nondestructive test (NDT) methods applied for the detection of defects in welds. NDT methods such as Ultrasonic Testing (UT), Magnetic Particle Testing (MT) and Radiographic Testing (RT) may be applied for the detection of surface and subsurface defects in steel bridge members. However, each of these technologies may have a different response to the same defect, based on the physics of the technology. As a result, test results may vary between each of the techniques. Critical defects such as cracks may be detected by one technology, but not by another, leading to inconsistent results and undermining confidence in the test results. Inconsistencies between MT, UT and RT were identified in the study. In this research, MT, RT, and UT results from the inspection of the Sherman Minton Bridge were compared with physical test results obtained from cores taken at 21 different locations across the bridge. Comparisons for surface breaking cracks and subsurface defects (including cracks) were provided. This research also evaluated the limitations of MT, RT, and UT methods regarding defect types and disposition in welds and their locations on the tension tie chord of the bridge. It was presented through the study that RT missed many planar flaws compared with UT and laboratory results. The number of flaws detected by UT at the core locations was higher than any other method. Finally, ROC (Receiver Operating Characteristic) and POD (Probability of Detection) analysis were also conducted based on the results from 21 cores and results from field inspection of the Sherman Minton Bridge.
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