THE LAMB WAVE INSPECTION OF CHEMICAL PLANT PIPEWORK
David N. Alleyne, Alan M. Lank*, Peter J. Mudge* and Peter Cawley Dept Mechanical Engineering, Imperial College, Exhibition Road, London, SW7 2BX, UK *TWI, Abington Hall, Abington, Cambridge, CB1 6AL, UK
Keywords: Lamb waves, corrosion, pipe inspection, long range inspection, dry coupled transducers
ABSTRACT
Corrosion in pipework is a major problem in the oil, chemical and other industries. Many pipes are insulated which means that even external corrosion cannot be seen without removing the insulation, which would be prohibitively expensive. There is therefore 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 lagging, echoes returning to the transducer indicating the presence of defects. This paper describes the result of an extensive set of field trials using the technique, together with the results of systematic laboratory and theoretical investigations of the influence of defect depth and circumferential extent on the Lamb wave reflectivity. It is shown that propagation distances of over 50 metres in 3 inch and 6 inch diameter pipes can be obtained using a dry coupled piezoelectric transducer system, and defects around half the wall thickness deep and three 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.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 4, pages 2303 - 2306 Publisher:Ashgate Publishing Company
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