High Temperature Condition Monitoring with a Novel, Flexible, Thin Film Sensor

Ultrasonic inspection is the go-to tool for a range of industrial NDE applications. There are, however, severe limitations when applying the technology in high temperature environments. For sectors such as oil & gas and nuclear power this makes the monitoring of assets at elevated temperatures challenging; often requiring costly and inconvenient shutdown. Suitable sensors can be permanently fitted to high temperature infrastructure and this will significantly improve monitoring and reduce asset downtime. The work presented here demonstrates fit and forget sensors which have consistent output at elevated temperatures and are durable enough to withstand the industrial environment. An additional benefit of these sensors is that they are truly flexible, which allows them to conform to curved surfaces (e.g, pipes) without the need for a couplant material. A proprietary piezoelectric thin-film material is used to produce many consistent single element contact transducers. The material is a metal oxide-based alloy, deposited with a novel reactive sputtering process onto a flexible metallic substrate. The performance of the transducers is measured over long-term heating and cooling cycles at 250°C. The transducer is fixed to a section of steel pipe on a hot plate. Backwall reflections of the steel pipe are recorded every minute throughout the cycling using standard ultrasonic equipment. Results obtained showed that the sensors operated effectively through repeated heating, demonstrating that they can withstand prolonged temperature and operation. Typical amplitude data from 3 sequential heating cycles (duration 7 hours) is shown in Figure 1. As shown, the output remains stable whilst held at elevated temperature, with no statistical significance in the output amplitude (Students T-Test, p<;0.08).