High Resolution Ultrasound Wall Thickness Measurements through Polyester Coating and Real-Time Process Control

Epoxy-, polyester-, paint and similar coatings are often used for external corrosion protection on pipelines and other process equipment. It is well known that ultrasound transducers can determine wall thickness through such coatings. This paper explores how the sensitivity of high resolution pulse-echo ultrasound measurements from permanently installed immersion sensors are affected by measuring through a 300 μm layer of polyester powder coating compared to measuring on plain steel. The results show that the standard deviation is below 6 nm for both specimens. Further, there is no degradation in the resolution when measuring through coating. Actually, the results show that measuring through the coating gives better resolution. This result is verified by examining the received acoustic energy from the two specimens by using a 1D signal model.

For many real-time corrosion monitoring applications it is important to estimate the corrosion rate as fast as possible. This paper also explores how one can incorporate the abovementioned ultrasound wall-thickness measurements into a recursive Kalman filter for optimal parameter estimation and process control. The results show that reliable corrosion rate estimates are obtained and that these correlate well with the measured temperature.