Ultrasonic Inspection and Imaging Projects
Remotely Operated Nondestructive Examination (RONDE) system
Using ultrasound to size up stress cracks
Examining the knuckle region of primary waste tanks is key in ensuring the integrity of Hanford's double-shell tanks. But it poses a significant technical challenge because the knuckle, where tank walls curve to meet the tank floor, is not entirely accessible using conventional measurement techniques. Pacific Northwest National Laboratory (PNNL) has developed a technology to solve this problem.
The Remotely Operated Nondestructive Examination (RONDE) system introduces sound waves from the more accessible region of the tank wall above the knuckle. Sound, divergent in nature, spreads out around the knuckle and along the bottom of the tank. Using a signal processing technique known as Synthetic Aperture Focusing (SAFT), this technology processes the returned sound waves to provide high-resolution images of the entire knuckle region. SAFT accurately detects and locates circumferentially oriented planar discontinuities such as stress corrosion cracks in the knuckle region.
In addition, PNNL has developed a two-transducer technique to accurately size a crack in both length and depth. This advanced nondestructive evaluation method, known as Tandem-SAFT, or T-SAFT, involves placing two transducers side-by-side and moving them back and forth in a pitch-catch mode to characterize the crack based on loss of signal.
Measurement begins as the sound wave hits the corner where the crack meets the inside surface of the tank and ends when the wave disappears over the tip of the crack. The location of the two transducers to each other is always known, allowing an accurate measurement of crack depth and length.
The RONDE imaging software presents the ultrasonic data in a two-dimensional top view, called a plan view, looking down through the test area, and a two dimensional side view of a cross-sectional plane through the test area. With its high-resolution imaging capability, the system can identify the welds that bound the knuckle accurately marking flaw location.
The RONDE system has been qualified to perform inspections of the knuckle region of Hanford tanks by passing a performance demonstration test (PDT), which confirms that it can detect and size cracks that could be circumferentially oriented in the knuckle region of a primary tank. Although still a prototype, the RONDE system will become a significant inspection device for the tank integrity program at Hanford and the data acquired can be used to help ascertain the condition of waste tanks.
Point of Contact Larry Casazza