Abstract: Corrosion in pipework is a major problem in the oil, chemical and other industries and there is an urgent need for the development of a quick method for the detection of corrosion under insulation. An attractive inspection method would be to use cylindrical Lamb waves which will propagate along the pipe wall from a transducer placed in a 'keyhole' cut in the insulation, echoes returning to the transducer indicating the presence of defects. This paper describes the results of an extensive set of field trials using the technique, together with the results of systematic laboratory and theoretical investigations of the reflection and mode conversion of the waves from part-circumferential defects. It is shown that propagation distances of over 50 meters in 3, 6 and 8 inch diameter pipes can be obtained using a dry coupled piezoelectric transducer system, and defects around half the wall thickness deep and there times the wall thickness in diameter can be detected. The method shows great promise for the rapid inspection of pipework for corrosion under insulation, and is also equally applicable to the detection of internal defects. Furthermore, it is shown that the mode conversion of the waves can be exploited in order to discriminate between part-circumferential defects and axially symmetric features such as welds. !8
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