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An analysis of ultrasonic wave propagation in metallic pipe structures using finite element modelling techniques

Gachagan, A. and Reynolds, P. and McNab, A. (2004) An analysis of ultrasonic wave propagation in metallic pipe structures using finite element modelling techniques. In: 16th WCNDT 2004 - World Conference on NDT, 2004-08-30 - 2004-09-03.

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Abstract

This paper describes the development of a large finite element (FE) model representing ultrasonic inspection in a metallic pipe. The model was developed using PZFlex and comprises two wedge transducer components, water coupled onto the inner wall of a 36 inch diameter steel pipe. The 2MHz transducers are separated by 430mm and configured to generate/receive ultrasonic shear waves. One device is used in pulse-echo mode to analyse any reflected components within the system, with the second transducer operating in a passive mode. Importantly, to minimise the models computational requirements, an external pressure loading function was applied to the wedge component within the model to simulate the transducer excitation. A number of simple defect representations have been incorporated into the model and both the reflected and transmitted ultrasonic wave components acquired at each wedge. Both regular slot and lamination defects have been investigated, at three different locations to evaluate the relationship between propagation path length and defect response. These defect responses are analysed in both the time and frequency domains and good correlation with experimentally measured waveforms is demonstrated. Moreover, the FE modelling has produced visual interpretation, in the form of a movie simulation, of the interaction between the propagating pressure wave and the defect. A combination of these visual aids and the predicted temporal/spectral waveforms has clearly demonstrated the essential differences in the response from either a slot or lamination defect. It should be noted that these modelled representations correspond to a propagation path length in excess of 150 wavelengths. Consequently, it was necessary to incorporate denser meshing within the FE model and run the simulations on a multi-processor SGI computer facility to produce accurate results.