A Signal Processing Approach with a Smooth Empirical Mode Decomposition to Reveal Hidden Trace of Corrosion in Highly Contaminated Guided Wave Signals for Concrete-Covered Pipes

Abstract

Ultrasonic guided waves have been extensively applied for non-destructive testing of plate-like structures particularly pipes in past two decades. In this regard, if a structure has a simple geometry, obtained guided waves' signals are easy to explain. However, any small degree of complexity in the geometry such as contacting with other materials may cause an extra amount of complication in the interpretation of guided wave signals. The problem deepens if defects have irregular shapes such as natural corrosion. Signal processing techniques that have been proposed for guided wave signals' analysis are generally good for simple signals obtained in a highly controlled experimental environment. In fact, guided wave signals in a real situation such as the existence of natural corrosion in wall-covered pipes are much more complicated. Considering pipes in residential buildings that pass through concrete walls, in this paper we introduced Smooth Empirical Mode Decomposition (SEMD) to efficiently separate overlapped guided waves. As empirical mode decomposition (EMD) which is a good candidate for analyzing non-stationary signals, suffers from some shortcomings, wavelet transform was adopted in the sifting stage of EMD to improve its outcome in SEMD. However, selection of mother wavelet that suits best for our purpose plays an important role. Since in guided wave inspection, the incident waves are well known and are usually tone-burst signals, we tailored a complex tone-burst signal to be used as our mother wavelet. In the sifting stage of EMD, wavelet de-noising was applied to eliminate unwanted frequency components from each IMF. SEMD greatly enhances the performance of EMD in guided wave analysis for highly contaminated signals. In our experiment on concrete covered pipes with natural corrosion, this method not only separates the concrete wall indication clearly in time domain signal, a natural corrosion with complex geometry that was hidden and located inside the concrete section was successfully exposed.

Application of a flat variational modal decomposition algorithm in fault diagnosis of rolling bearings

“…However, the energy of noise is concentrated on small scales, and its wavelet coefficient rapidly decays as the scale increases. The expression of the tone-burst signal X(t) is simply a sine wave modulated by windows such as Hamming window 27 XðtÞ ¼ sin wt þ h ð Þ 0:08 þ 0:…”

Axial magnetized patch for efficient transduction of longitudinal guided wave and defect identification in concrete-covered pipe risers

“…Sixteen PZT pieces with dimensions of 20 mm × 5 mm × 0.5 mm were pasted onto the other end of the second riser evenly. The kind of PZT can trigger longitudinal mode efficiently, which has been used by many scholars . Moreover, considering the perimeter of the pipe riser (106 mm) and the width (5 mm) of the 130 kHz PZT, the number of the pasted PZT was enough.…”

“…Pulse‐echo guided wave testing mode permits inaccessible areas to be investigated to detect corrosion in pipe risers. Ultrasonic guided wave (UGW) is a low‐attenuation, rapid, and accurate nondestructive testing method. When defects occur in pipe risers, there are flaw echoes in the time domain.…”

Feature Extraction for Track Section Status Classification Based on UGW Signals

“…Similarly, time-frequency analysis methods, such as the Short-Time Fourier Transform (STFT) and Pseudo Wigner Ville Distribution (PWVD) have focused on the attenuation characteristics of UGW signals as well [18,19]. On the other hand, in [20] a signal processing approach with a smooth empirical mode decomposition applied to UGW signals was proposed. In [21,22], UGW signals were applied to pipeline flaw identification.…”