The application of synthetic focusing for imaging crack-like defects in pipelines using guided waves

Abstract

This paper deals with quantifying the performance of a technique for detection, location, and sizing of circumferential crack-like defects in pipelines using synthetically focused guided waves. The system employs a circumferential array of piezoelectric transducer elements. A torsional probing guided wave is excited using the array, which subsequently interacts with the reflecting features of the pipe, such as defects or weld caps. The recorded backscattered signals are synthetically focused to every point of interest in the pipe wall, to form an image of the reflecting features of the pipe. The defect image amplitude is used to estimate the defect depth, and the full width at half maximum of the defect image circumferential profile is used to estimate the circumferential extent of the defect. The imaging system is tested with data from finite element simulations and from laboratory experiments. It is found that reliable sizing of circumferential cracks in finite element simulations and experiments can be achieved if the circumferential extent of the defect is greater than 1.5 lambda(S), where lambda(S) is the shear wavelength at the frequency of inspection. This result is theoretically valid for any pipe size, any axial defect location, and any inspection frequency. Amplitude gains of around 18 dB over an unfocused system have been observed experimentally in an 8-inch pipe with a 9 dB SNR improvement.

Hybrid active focusing with adaptive dispersion for higher defect sensitivity in guided wave inspection of cylindrical structures

“…Therefore, the data acquisition time required to inspect the whole volume of the pipe will be considerably shorter compared with the other techniques [17,25]. However, the time saved at the data acquisition step is partially counteracted by increased computation time required for post processing the received signals.…”

“…The proposed technique is compared with active focusing [23] and time reversal focusing [11] and the comparison is based on Signal-to-Coherent-Noise-Ratio (SCNR) for a range of defects (circumferential extent ≤ 1.5λ). Furthermore the proposed technique is compared to the synthetic focusing based on the input signal to defect amplitude presented by Davies and Cawley [25].…”

“…A parametric study has been performed to investigate defect sensitivity of the HAF compared to the active focusing [23], time reversal focusing [11] and synthetic focusing [25] techniques. A set of fully penetrating, part-circumferential crack-like defects were considered in an 8inch Schedule 40 steel pipe (outer diameter -219.1mm and wall thickness -8.18mm).…”

“…This comparison is based on SCNR for a range of defects with circumferential extent of 3.5°, 7°, 15°, 30° and 60° (0.08 , 0.16 , 0.32 , 0.72 and 1.44 respectively). Furthermore the proposed technique is compared to the synthetic focusing based on the input signal to defect amplitude ratio published by Davies and Cawley [25].…”

Multidimensional guided wave dispersion recovery for locating defects in composite materials

“…They have been shown to propagate with relatively low attenuation and are sensitive to many forms of damage. Guided waves have been tested for a large variety of structures, including pipelines [13,14,15,16,17,18], bridges [19,20], concrete [21], steel cables [22,23,24], and aircraft components [25,26,27,28,29].…”