On-Site Ultrasonic Inspection of Highway Culverts
Thin galvanized steel culverts, 2.6 mm (0.1 in) thick, are used when constant or intense water flow from one side of the highway or road to the other has to be facilitated. The New York State Department of Transportation has long considered NDT detection of corrosion in culverts necessary for the realistic evaluation of their remaining safe life. This is a problem with immense economic consequences, because the potential of safe life extension of the vast number of culverts in New York State and their replacement cost. In this paper the development of a non-contacting NDT method for on-site inspection of culverts is presented. The culvert is accessible only on the inside and the measurement is complicated by the fact that this is in contact with water and air, and is covered with rust and dirt. It corrodes down to less than 0.5 mm (0.020 in) giving the surface an orange rind appearance. Contact or delay transducers could not be used due to the extreme conditions of the surface, which in many cases does not guarantee the parallelism necessary for the measurement. Of another concern was the indication in some critical cases of false readings which commonly result in the overestimation of the real thickness. The system developed utilizes commercial off-the-shelf ultrasonic equipment and piezoelectric transducers in a bubbler configuration. In order to optimize the transmission of the sound through the water stream and the culvert, a rubber shoe was utilized. A detailed description of the problem and of the solution is given.
KeywordsThickness Measurement Replacement Cost Strip Thickness York State Department Ultrasonic Inspection
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