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© 2019 The Authors. Fouling build-up is a well-known industrial problem and its accumulation is dependent on the conditions surrounding the structure. Conventional fouling removal methods are costly and also require an operational halt to carry out the procedure. The use of Ultrasonics has gained popularity in recent years as a non-invasive means of fouling removal but further research and development are required to improve and optimize the technology. Currently in industry, Ultrasonic horns are designed and optimized to generate high amplitude vibrations for various applications including welding, cutting and sonochemistry. Some research has been done to design horns for the generation of cavitation, but none specifically for fouling removal applications. This work investigates the addition of half-wavelength transducer horns of varying shapes (cylindrical, conical, exponential and stepped) to an existing 40 kHz cleaning transducer. Numerical modelling is carried out to optimize the length of the horn before manufacturing final geometries. Experiments were conducted to attach an ultrasonic horn to the transducer and to a carbon steel plate (300 mm x 300 mm x 2 mm), and to measure wave propagation across the structure using a PSV-400 3D Laser Scanning Vibrometer. This has shown that the addition of an ultrasonic horn improves the out-of-plane displacement across the structure, which correlates to an improvement in fouling removal for steel tube ultrasonic cleaning. 10.13039/501100000266-Engineering and Physical Sciences Research Council

The structural integrity assessment of thermoplastic pipes has become an interesting area of research due to its elevated usage in the liquid/gas transportation industry. Ultrasonic guided wave testing has gained higher attention from industry for the inspection of elongated structures due to the reduced inspection time and cost associated with conventional non-destructive testing techniques, e.g., ultrasonic testing, radiography, and visual inspection. Current research addresses the inspection of thermoplastic pipes using ultrasonic guided waves as a low cost and permanently installed structural health-monitoring tool. Laboratory and numerical investigations were conducted to study the potential of using ultrasonic guided waves to assess the structural health of thermoplastic pipe structures in order to define optimum frequency range for inspection, array design, and length of inspection. In order to achieve a better surface contact, flexible Macro-Fiber Composite transducers were used in this investigation, and the Teletest&reg, Focus+ system was used as the pulser/receiver. Optimum frequency range of inspection was at 15&minus, 25 kHz due to the level of attenuation at higher frequencies and the larger dead zone at lower frequencies due to the pulse length. A minimum of 14 transducers around the circumference of a 3 inch pipe were required to suppress higher order flexural modes at 16 kHz. According to the studied condition, 1.84 m of inspection coverage could be achieved at a single direction for pulse-echo, which could be improved by using a higher number of transducers for excitation and using pitch-catch configuration.

The application of the fundamental shear-horizontal wave mode for guided wave structural health monitoring is undoubtedly beneficial due to its nondispersive characteristics. Existing guided wave shear mode transducers are rigid and brittle, because of these characteristics, bonding them to irregular surfaces (i.e., curved surfaces) is challenging. There is a huge market interest in the development of a flexible shear mode transducer, which eases the transducer bonding process onto irregular surfaces and improves the surface contact between the transducer and the structure. This study presents a flexible shear mode transducer for structural health monitoring using low-frequency guided waves (20-120 kHz). The proposed transducer is manufactured using piezoceramic, and based on the results of this study, it exhibits the directional excitation of fundamental shear-horizontal mode at 20-120 kHz. Finite element analysis and laboratory experiments were conducted to study the behavior of the proposed transducer. Field trials were conducted on a liquid storage tank with an undulated surface (due to corrosion). The performance of the proposed transducer is also compared to the commercially available macro fiber composite transducers. The proposed transducer was driven by the industrialized ultrasonic guided wave inspection system; Teletest Focus+ in line with the application of tank floor inspection using ultrasonic guided waves. European Commission

Thickness-shear transducers for guided wave testing have been used in industry for over two decades and much research has been conducted to improve the resolution and sensitivity. Due to a geometric feature of the current state-of-the art transducer, there is an out-of-plane component in the propagation direction of the fundamental shear horizontal mode which complicates the signal interpretation. In such case, complex signal processing techniques need to be used for mode discrimination to assess the structural health with higher precision. Therefore, it is important to revise the transducer design to eliminate the out-of-plane components in the propagation direction of fundamental shear horizontal mode. This will enhance the mode purity of fundamental shear horizontal mode for its application in guided wave inspection. A numerical investigation has been conducted on a 3 mm thick 2 m circular steel plate to understand the behaviour and the characteristics of the state-of-the-art thickness-shear transducer. Based on the results, it is noted that the redesigning the electrode arrangement will suppress the out-of-plane components on the propagation direction of the fundamental shear horizontal mode. With the aid of this information current state-of-the-art transducers were redesigned and tested in laboratory conditions using the 3D Laser Doppler Vibrometer. This information will aid future transducer designers improve the resolution of thickness-shear transducers for guided wave applications and reduce the weight and cost of transducer array by eliminating the need of additional transducers to suppress spurious modes. This research was funded by Lloyd’s Registered Foundation and Loughborough University, grant number [30335], and the APC was funded by Loughborough University and Brunel Innovation Centre.

The accumulation of fouling within a structure is a well-known and costly problem across many industries. The build-up is dependent on the environmental conditions surrounding the fouled structure. Many attempts have been made to detect fouling accumulation in critical engineering structures and to optimize the application of power ultrasonic fouling removal procedures, i.e., flow monitoring, ultrasonic guided waves and thermal imaging. In recent years, the use of ultrasonic guided waves has been identified as a promising technology to detect fouling deposition/growth. This technology also has the capability to assess structural health, an added value to the industry. The use of ultrasonic guided waves for structural health monitoring is established but fouling detection using ultrasonic guided waves is still in its infancy. The present study focuses on the characterization of fouling detection using ultrasonic guided waves. A 6.2-m long 6-inch schedule 40 carbon steel pipe has been used to study the effect of (Calcite) fouling on ultrasonic guided wave propagation within the structure. Parameters considered include frequency selection, number of cycles and dispersion at incremental fouling thickness. According to the studied conditions, a 0.5 dB/m drop in signal amplitude occurs for a fouling deposition of 1 mm. The findings demonstrate the potential to detect fouling build-up in lengthy pipes and to quantify its thickness by the reduction in amplitude found from further numerical investigation. This variable can be exploited to optimize the power ultrasonic fouling removal procedure.

Inspection of cylindrical structures using the first longitudinal Ultrasonic Guided Wave (UGW) mode has so far been predominantly neglected. This is due to its attenuative and dispersive behaviour, at common UGW operating frequencies (20-100 kHz). However, with the current knowledge on the level of attenuation in the first longitudinal wave mode and dispersion compensation techniques, the first longitudinal guided wave mode no longer need to be neglected. Furthermore, the first longitudinal guided wave mode has higher number of non-axisymmetric modes compared to other axisymmetric modes in the operating frequency. This will enhance the flaw sizing capability which makes the first longitudinal guided wave mode a viable prospect for UGW inspection of cylindrical structures. This study has been performed to investigate the potential of exciting the first longitudinal guided wave mode in isolation. Numerical investigations have been conducted to investigate the pure excitation of the first longitudinal guided wave mode. It has been shown that the first longitudinal guided wave mode can be used in UGW inspection effectively in isolation by adopting transducers with out of plane vibration for excitation. This can reduces the cost and weight of UGW inspection tooling. Numerical results are empirically validated.

"(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works." Ultrasonic Guided Waves (UGW) can be used to inspect and monitor a structure from a single test location. Piezoelectric transducers are commonly dry-coupled with force to the surface of the waveguide in order to excite UGWs. These UGWs propagating within the waveguide will interact and reflect from known features, thus possible damage could be detected. In this paper the interaction of UGWs with piezoelectric transducers is reported and investigated. An Finite Element Analysis (FEA) approach has been used to conduct a parametric study in order to quantify the effect of the waveguide diameter on the guided wave response. Laboratory experiments are carried out to measure the effect of the force on the dry-coupled piezoelectric transducers and the corresponding guided wave response including reflections and mode conversions. A test rig is used to apply and measure the force on the piezoelectric transducers. For verification, a 3-Dimensional Laser Doppler Vibrometry (3D-LDV) scan is performed on the waveguide in order to quantitatively identify the modes of interest. The conclusions reached this paper, particularly with respect to the quantification of the wave mode properties, lead to useful recommendations which can contribute to field inspection scenarios.

This paper presents a Split-Spectrum Signal Processing (SSP) with applications to Long Range Ultrasonic Testing (LRUT). The problem of coherent noise due to Dispersive Wave Modes (DWM) in the context of ultrasonic scattering is addressed and a novel solution by utilizing the SSP technique is proposed for reduction of the effects of DWM in the received signal. The proposed technique investigates the sensitivity of SSP performance to the filter bank parameter values such as processing/filter bandwidth, and filter overlap. Therefore, as a result the optimum values are introduced that improve the signal to noise ratio (SNR) significantly. The proposed method has been compared with conventional approaches for synthesized signals for a 6 inch pipe by applying the different recombination SSP techniques. The Polarity Thresholding (PT) and PT with Minimization (PTM) methods were found to give the best result and substantially improve the SNR performance by an average of 10 dB.