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.
Keywords: Ultrasound, coating, temperature compensation, corrosion rate estimation, real time