Influence of Surface Condition on the Inspection of Steel Bridge Elements Using the Time-of-Flight Diffraction Method
Publication: Journal of Bridge Engineering
Volume 15, Issue 6
Abstract
Prior studies on the time-of-flight diffraction (TOFD) method have focused primarily on ground smooth, clean surfaces of steel. In practice, however, the surface of an existing bridge element will be covered with rust or have several layers of paint. The main objective of this study was to evaluate the influence of the surface condition of steel elements (i.e., painted or rusted) on the ability of the method to accurately detect and size flaws. These objectives were met by performing a number of tests on plates with saw cuts or implanted fatigue cracks with different surface conditions. These included ground smooth and polished, rusted, and painted surfaces. The data show that rusted surfaces will reduce the amplitude of the ultrasonic signals, but they will not impair the ability of the TOFD method to detect and accurately size flaws. A painted surface will also cause a reduction in signal amplitude. More important, however, is the appearance of additional wave signals that could be interpreted as false indications. While these additional signals do not obscure the presence of actual flaws or affect the accuracy of the TOFD method to size the flaws, they make flaw detection more difficult. Based on the results of this study, recommendations for field inspection on rusted or painted surfaces using the TOFD method are provided.
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Acknowledgments
The writers would like to acknowledge the Wisconsin Alumni Research Foundation (WARF) for providing funding for this study. Thanks are extended to the Federal Highway Administration (FHWA) for supplying some of the test specimens used in this investigation. The assistance of Mr. Bruce Karow, Mr. Robert Hubing, and Mr. Joel Alsum of the Wisconsin Department of Transportation is gratefully acknowledged. Special thanks are extended to Dr. Peter Bosscher (deceased) (Univ. of Wisconsin-Madison) and Dr. Glen Washer (Univ. of Missouri) for their valuable input and assistance during this investigation.
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© 2010 ASCE.
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Received: Feb 9, 2009
Accepted: Jan 6, 2010
Published online: Oct 15, 2010
Published in print: Nov 2010
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