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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

In-service mooring chains are subjected to harsh environmental conditions on a daily basis, which increases the necessity of integrity assessment of chain links. Periodic structural health monitoring of mooring chains is mandatory and vital in order to maintain the safety of floating platforms. Application of ultrasound for in-service mooring chain inspection is still in its infancy due to the lack of accessibility, in field operational complexity and the geometrical features of mooring systems. With the advancement of robotic/ automated systems (i.e. chain climbing robotic mechanisms), interest in in-situ ultrasound inspection has increased. Presently, ultrasound inspection has been confined to the weld area of the chain links. However, according to recent studies on fatigue and residual stresses, ultrasound inspection of the chain crown should be further investigated. A new application of ultrasonic phased array full matrix capture is discussed in this paper for investigation of the chain crown. Due to the complex geometry (i.e. curved and limited access) of the chain crown, a surface mapping technique has been added to the presented full matrix capture technique. The inspection method presented in this study is suitable for chain links both in air and underwater. A continuous water supply wedge was developed in order to supply couplant for in air inspection. Development of a technique which can be adapted for robotic inspection was considered, and an automated manipulator was used to carry out inspections. The design of the inspection method and the robotic manipulator is discussed in this article. The technique is validated with laboratory experiments. London South Bank Innovation Centre (LSBIC), the National Structural Integrity Research Centre (NSIRC) and TWI Ltd, Cambridge

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.

Fouling build-up in engineering assets is a known problem and, as a solution, the application of power ultrasonic for in-situ fouling removal has gained much attention from the industry. Current state-of-the-art fouling removal includes the use of hydraulic, chemical and manual techniques. Much research has been conducted to advance the knowledge on the potential uses of ultrasonics across different fouling applications, primarily in reverse osmosis membranes and heat exchangers. However, the optimization of in-situ ultrasonic fouling removal has not yet been investigated and is still in its infancy. The present study uses a previously experimentally-validated numerical model to conduct a parametric study in order to optimize the technique. Focus was given to the adoption of ultrasonics for large diameter pipes. Therefore, this investigation was conducted on a 6 in. schedule 40-carbon steel pipe. Parameters investigated include: optimum number of transducers to remove fouling in long pipes from a single transducer location; performance at elevated temperature; different fluid domains; optimum voltage; variety of input signals and incremental thickness of fouling. Depending on the particular studied conditions, the possible fouling removal of up to +/−3 m from a single transducer location is demonstrated in a 6 in. schedule 40 carbon steel pipe.

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.

Fouling formation on high value assets i.e. ships, offshore platforms, pipelines in the processing industry is a significant problem causing destruction to the environment and operations of the structure. Common fouling mechanisms in industry are deposit of scales, settlement and growth of marine organisms. It is an important factor, in order to assess the service lifetime and safety of these assets. Large sums of money are spent for removal and preventative methods to maintain efficient operation of the asset. Most of these methods are toxic and the environmental concerns associated with these techniques has led to studies on alternative methods to remove fouling. This paper proposes a non-invasive method of removing fouling using high power ultrasound. The acoustic cavitation phenomenon is related with the out-of-the-plane displacement occurring in structures for the fouling removal process. This is a cost and time effective method and more importantly, an environmentally sustainable method of fouling removal. Furthermore, this paper presents the research carried out at the Brunel Innovation Centre in this field. Through collaborative research projects, this technology has been developed for different fouling types specific to various industrial applications. A methodology has been established for the selection of the transducers and the hardware. The techniques effectiveness has been proven through experimental and simulation results.

This is an Accepted Manuscript of an article published by Taylor & Francis in Nondestructive Testing and Evaluation on 23/11/2015, available online: https://www.tandfonline.com/doi/full/10.1080/10589759.2015.1093628. Ultrasonic guided wave inspection is widely used for scanning prismatic structures such as pipes for metal loss. Recent research has investigated focusing the sound energy into predetermined regions of a pipe in order to enhance the defect sensitivity. This paper presents an active focusing technique which is based on a combination of numerical simulation and time reversal concept. The proposed technique is empirically validated using a 3D laser vibrometry measurement of the focal spot. The defect sensitivity of the proposed technique is compared with conventional active focusing, time reversal focusing and synthetic focusing through an empirically validated finite element parametric study. Based on the results, the proposed technique achieves approximately 10 dB improvement of signal-to-coherent-noise ratio compared to the conventional active focusing and time reversal focusing. It is also demonstrated that the proposed technique to have an amplitude gain of around 5 dB over synthetic focusing for defects

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.

There is an increasing interest in using ultrasonic guided waves to assess the structural degradation of above-ground storage tank floors. This is a non-invasive and economically viable means of assessing structural degradation. Above-ground storage tank floors are ageing assets which need to be inspected periodically to avoid structural failure. At present, normal-stress type transducers are bonded to the tank annular chime to generate a force field in the thickness direction of the floor and excite fundamental symmetric and asymmetric Lamb modes. However, the majority of above-ground storage tanks in use have no annular chime due to a simplified design and/or have a degraded chime due to corrosion. This means that transducers cannot be mounted on the chime to assess structural health according to the present technology, and the market share of structural health monitoring of above-ground storage tank floors using ultrasonic guided wave is thus limited. Therefore, the present study investigates the potential of using the tank wall to bond the transducer instead of the tank annular chime. Both normal and shear type transducers were investigated numerically, and results were validated using a 4.1 m diameter above-ground storage tank. The study results show shear mode type transducers bonded to the tank wall can be used to assess the structural health of the above-ground tank floors using an ultrasonic guided wave. It is also shown that for the cases studied there is a 7.4 dB signal-to-noise ratio improvement at 45 kHz for the guided wave excitation on the tank wall using shear mode transducers.

Fouling build up is a known problem in the industry. Accumulation of fouling can occur in different structures e.g. offshore pipes, ship hulls, floating production platforms. The type of fouling that is being accumulated is dependent on environmental conditions surrounding the structure itself. Current methods that are deployed for fouling removal spans over hydraulic, chemical and manual means. Current technologies such as DynaJet (cavitating water jets) and Hydrex's underwater ship hull cleaner have both advantages and disadvantages, where one common disadvantage is to put the operation of the structure to a halt in order to commence the fouling removal process. Currently, ultrasonic baths are used for cleaning by generating cavitation bubbles which implode on the surface of fouling, particularly in Reverse Osmosis applications. Conventionally, components that have accumulated fouling are placed into an ultrasonic bath which yet again, requires to stop the operation of the structure for fouling removal process to commence. Application of high power ultrasonic transducers are proposed in this work as a means to remove fouling on a structure whilst in operation. The work presented in this paper consists of the designing of bespoke high power transducers, transducer array design and development of bespoke power amplifiers to drive the high power transducers. The Polytec 3D Laser Doppler Vibrometer has been incorporated into this investigation to study the fouling removal process. Results shows the potential of using high power ultrasonic transducers for fouling removal in marine structures due to the wave propagation across the structure that is under excitation.

Copyright © 2019 by the authors. Fouling accumulation in pipelines is a well-known problem in industry across various applications. The build-up of fouling within a pipe can reach a detrimental state, leading to pipe blockages that, in turn, result in pipe bursts. As pipelines transport fluid up to hundreds of meters, a method to prevent and remove fouling at long distances is required to support an engineering structure without the requirement of halts for maintenance to be carried out. Underwater pipelines are currently deployed which must ensure that pipelines carrying crude oil do not reach a detrimental state which leads to pipe leaks or pipe bursts, resulting in a discharge of oil into the surrounding water. This work discusses an optimized ultrasonic cleaning transducer array which undergoes marinization. The marinized transducers are characterized for impedance and wave propagation across a fouled 6.2 m long, Schedule 40, 6-inch diameter carbon steel pipe. This study has shown that the addition of marinized material dampens the vibrational output from the High-Power Ultrasonic Transducer (HPUT) configuration. This reduction in vibration is most significant when the structure is filled with water, resulting in a marinized HPUT configuration dropping by up to 85% and a non-marinized HPUT configuration dropping by up to 80% Innovate UK, grant number 102491

"(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.