The probe and its mounting fixture are critical parts of the health monitoring of steam pipes. A high-temperature, piezoelectric transducer generates and receives ultrasonic waves, and the probe has to transmit the wave normal to the pipe surface. The mounting fixture is designed to allow for alignment of the probe even without a reference reflection, and thus enables blind alignment. In order to allow aligning of the probe normal to the surface of potential water condensation, and to secure intimate contact to the pipe surface, a novel mounting fixture was conceived and developed.
This system addresses a need for a monitoring system that provides assurance against potential accidents and system failures in steam pipe systems. An effective, in-service health monitoring system is needed to track water condensation in real time through the wall of the steam pipes.
The ultrasonic pulse-echo probe was described in “High-Temperature Ultrasonic Probe for In-Service Health Monitoring of Steam Pipes” (NPO-49045), NASA Tech Briefs, Vol. 39, No. 1 (January 2015), p. 20. The probe can sustain temperatures up to 250 °C, and uses a piezoelectric transducer to generate and receive the ultrasonic pulses. The system consists of a transducer alignment fixture and a strap. The strap includes a tension T-bolt with a spring for maintaining the tension in the strap for large temperature variations and coefficient of thermal expansion mismatch. The strap keeps the alignment fixture pressed against the pipe. The alignment fixture includes a frame, a transducer alignment guide, two strap pins, and three alignment bolts, and the guide determines the axis of the probe. It is attached to the frame through parallel flexures that maintain the guide alignment with respect to the fixture, and keep the transducer in contact with the pipe. The pins allow the strap ends to be attached to the alignment fixture, and contain a spherical surface for strap pin mounting. Three alignment bolts have sharp ends, and their position in the alignment fixture can be independently adjusted to align the fixture relative to the vertical direction.
The process of mounting the probe to the pipe has two steps. In the first step, the strap is attached to the pipe, and the probe alignment flexure is oriented to the local vertical direction. In the second step, bonding material is applied onto the probe face, and the probe is inserted into the guide, which is then pressed against the pipe to preload and secure the probe backing against the alignment guide.
When the health monitoring system is installed in a manhole, one of the concerns is the need to be able to align the probe without the presence of water surface inside the pipe. For this purpose, the mounting fixture is designed to allow for blind alignment capability.
This work was done by Yoseph Bar-Cohen, Mircea Badescu, Shyh-Shiuh Lih, Patrick N. Ostlund, and Stewart Sherrit of Caltech; and Nobuyuki Takano of CSU Pomona for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Technology Transfer at JPL
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-49046.