PSI - Issue 64

Chris Mundell et al. / Procedia Structural Integrity 64 (2024) 191–198 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Research and Development studies 2.1. Sentec Research Proposals

Technology and product developers Sentec (part of the Xylem group) supplied a number of potential NDT solutions to the Moonshot ‘call for ideas’, building on their experience of developing innovative sensors and smart metering for gas, water and electricity sectors. Two proposals were identified that would attempt to tackle the most challenging aspect – determining how much corrosion has occurred within a tendon. These were direct impedance measurement and Radio-frequency (RF) coupled guided ultrasound. The direct impedance measurement involves continuous measurement of the tendon resistance and inductive/capacitive reactance, with the aim of detecting corrosion through the resistance changes within the steel. This would need to allow for changes in cable diameter and filtering out of changes in temperature and stress. It was identified from the outset that the technique may be affected by random changes in impedance due to joints and connections with reinforcement. For the RF coupled guided ultrasound involves the remote induction of a temperature gradient within the tendon via pulsed radio frequency. The induced temperature gradient is used to generate a high-power guided ultrasonic wave within the tendon, which is then measured by multiple receivers along the length of a section (from the surface of the concrete). 2.1.1. Progress to date – Direct Impedance At the time of writing, the direct impedance methodology has been proven through a series of small scale tests and numerical modelling. Validated and compared against numerical modelling, the team constructed a 1m long grouted line, which was then injected with an 80 MHz bandwidth pulse, which was drilled with a 1cm hole (simulating a defect). The system was able to measure a demonstrable difference and change in signal between wet and dry conditions. Demonstrating initial promise, the system does currently have a number of limitations and assumptions. These are namely:  Changes in condition are best measured as variations from a baseline, and as such generation of a baseline is required for optimum results  A direct electrical connection to the duct and strands is required to induce the signal into the system (with potential to use a current loop to couple a signal into the strand remotely at a later date)  Instances of connections between the tendon and metallic ducts, and further connections between duct and reinforcement will lead to a ‘short’ in the circuit and currently prevents further interpretation of the signal. 2.1.2. Progress to date – RF Coupled Guided Ultrasound The initial approach for this methodology was to attempt to induce a guided wave using an RF source, however it was determined through the course of the research that for situations where a duct is metallic, the power was predominantly absorbed by the duct. As such, the technology developed to trialing near field coupling via a magnetic field induced by a coil. With the revised methodology, the Sentec team were able to induce and detect a generated ultrasound signal from a standoff of 300mm. Through numerical studies, this was progressed to observing wave propagation through water filled voids within a duct, with a number of possible mechanisms for detecting and measuring the void. 2.2. Omnia Research Proposal Omnia Integrity is a company specialising in non-intrusive methods for asset inspections, with a focus on wave mechanics (guided wave and acoustic emission). The proposal team included partners with ARCES (Bologna University) and Vallen Systeme, specialists in guided wave mechanics and acoustic emission inspections respectively.