ABSTRACT
This paper describes an automated remote ultrasonic thickness (UT) monitoring system using dry-coupled waveguide ultrasonic transducers at The Geysers. Dry-coupled waveguide UT transducers can provide remote real-time measurement of wall thicknesses on high temperature process piping without failure of the ultrasonic transducers and without the removal and reinstallation of insulation. An ultrasonic wall thickness monitoring system has been automated with battery powered UT sensors, wireless radio communication to a computer network gateway, and automated scheduled collection and storage of UT data in a database. The UT monitoring system software automates the data reduction tasks needed to make time plots of wall thickness trends and provides easy access over a computer network. The waveguide UT sensors were installed on steam well tie-in piping in a remote area at The Geysers steamfield to monitor steam piping thicknesses for a caustic steam scrubbing system used to mitigate severe HCl acid-dewpoint corrosion. The waveguide UT monitoring system provided early warning that severe internal corrosion was occurring and the caustic scrubbing system was not mitigating the HCl acid-dewpoint corrosion. The process piping and steam scrubbing equipment were modified and the automated waveguide UT monitoring system confirms that the process modifications were successful.
INTRODUCTION
The Geysers located in northern California is the world's largest complex of geothermal power plants and has over 80 miles of carbon steel steam piping from 8-inch to 48-inches in diameter. The standard piping material used is ASTM A53 Grade B. The steam chemistry at The Geysers has changed over the years to become more corrosive and economics do not support using long runs of very expensive high alloy materials. Acidic high temperature geothermal fluids are very corrosive and undetected internal corrosion can rapidly lead to extensive repair and replacement of piping, through-wall leaks or even ruptures. Frequent ultrasonic thickness (UT) measurements of piping are therefore required to assure integrity of carbon steel pressure piping and corrosion mitigation scrubbing systems are required to protect piping and extend service life.
