Corrosion inside of pipes is a problem in power generation and other industries. Often these pipes are at high temperatures and inaccessible. It is important to detect and measure this corrosion so that plant may continue to operate safely. Ultrasound is a well-developed technique for this application. Manual scanning is widely used for this purpose. The problems of coupling the sound into the pipe wall and the very survival of the probe increase at higher temperatures. Often the locations of interest inaccessible or are under insulation that must be removed prior to the inspection. This paper describes a program to develop ultrasonic probes that can be permanently installed in critical locations to continuously monitor for corrosion. The probes are coupled to the pipe using metal foil at high contact pressure. The probes have been designed to survive at 500 degC for 5 years. Laboratory and field-testing at 300 degC is well advanced. Laboratory testing at 500 degC has now commenced.