Mode selection of guided waves for ultrasonic inspection of gas pipelines with thick coating
نویسندگان
چکیده
Mode selection of guided waves in an elastic steel plate with thick coating layer has been studied here. Eect of both thick elastic coating and damping of the coating layer on the dispersion and mode shapes has been investigated and modes that are less aected by elastic coating and damping have been identi®ed. For modeling the viscoelastic behavior of the coating layer, the standard linear solid is adopted and two damping factors are introduced into the Lam e constants. Viscoelastic property of the coating layer causes all wave numbers to be complex. In order to ®nd the complex wave numbers for a given frequency, a Rayleigh±Ritz type method is used to get approximate values of the complex wave numbers and then the IMSL subroutine zanlyt is employed to re®ne roots. It is found that a thick elastic coating introduces new dispersive modes and also, in general, changes considerably the modes of the bare steel plate, and that damping of the coating layer has signi®cant eect of the dispersion and mode shapes. However, we found that there are certain modes of the bare steel plate that are less aected by the thick elastic coating and damping. These modes could be selected for the ultrasonic inspection of stress-corrosion cracks in thin-walled gas pipelines with protective coal-tar coating. Ó 1999 Elsevier Science Ltd. All rights reserved.
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