Continuous Thickness Monitoring - Experience from the Field and Lessons Learned

Since 2005 the Imperial NDE group has been developing permanently installed ultrasonic sensors for wall thickness monitoring. A waveguide based sensor is particularly attractive as it isolates the test specimen from the transduction, signal processing and communication components of the sensor. For applications in industry the reliability and sensitivity to wall loss is particularly important. A corrosion monitoring system has been commercialised via Permasense Ltd. and several thousand sensors have been installed in petrochemical plants around the world. As a result ultrasonic measurement data is available at an unprecedented rate and repeatability. This paper will present lessons learned from application of this SHM system in the field and an analysis of the influence of the different parameters that influence the wall thickness trend analysis. While the paper focuses on the particular thickness gauging sensor that has been used the understanding gained has much wider applicability to other SHM problems.