Toward characterizing the effects of environmental and operational conditions on diffuse-field ultrasonic guided-waves in pipes

Abstract

One of the main challenges in real-world application of guided-waves based nondestructive evaluation (NDE) of pipelines is their sensitivity to changes in environmental and operational conditions (EOC) that these structures are subject to. In spite of many favorable characteristics of guided-waves for NDE of pipes, their multi-modal, dispersive, and multi-path characteristics result in complex signals whose interpretation is a difficult task. Studies that have considered the effects of EOC variations either fail to reflect realistic EOC scenarios (e.g., limited to particular effects of specific EOCs, like time shifting effects of temperature in plates) or lack the necessary understanding of the effects of EOC variations on different aspects of the developed damage detection approaches. Such gaps limit the extensibility of these approaches to pipeline applications outside of controlled environments. This paper motivates the idea of analytically incorporating the effects of temperature and flow rate variations into damage diagnosis of pipes, through a number of case studies. A review of the existing literature on guided-wave based testing is also provided. For damage detection, a linear supervised classification method, namely linear discriminant analysis (LDA), is applied to experimental guided-wave data recorded from a hot water piping system under regular operation. Principal components, obtained through principal component analysis (PCA), and Fourier transforms of the signals are two sets of damage-sensitive features (DSF) that are examined for LDA-based classification. The effects of temperature and flow rate difference among testing and training datasets on (A) detection performance and (B) goodness of fit of the method to the data are investigated.