Ultrasonic testing (UT) has long been a key method for detecting defects and service-induced degradation in nuclear and fossil plant components and for supporting remaining component life assessment. But it comes with some tradeoffs.
Manual scanning with handheld transducers allows quick and easy testing of large areas at low cost, but the results are mostly qualitative and can be plagued with false positives. This requires a conservative approach, which means shorter inspection intervals and sometimes-unnecessary repairs and replacements.
Automated UT using mechanized scanners can produce highly accurate three-dimensional (3-D) scans of component interiors, which can be stored, reconstructed, and manipulated, enabling quantitative flaw analysis and better decision-making. These inspection systems, however, are expensive, cumbersome, time-consuming and difficult to operate, and cannot always reach critical areas in an operating plant.
The ideal UT system would be small and handheld, yet capable of high-resolution 3-D scanning. A research project led by the Electric Power Research Institute (EPRI) is developing just such a tool, which it refers to as an “acoustic mouse” (Figure 3).
3. Small but powerful. This prototype handheld 3-D ultrasonic testing transducer is under development by the Electric Power Research Institute (EPRI). Courtesy: EPRI
The challenges for a handheld 3-D UT system are twofold: precise tracking of the transducer position—necessary for 3-D imaging—and a portable transducer design that allows high-resolution image capture at a reasonable level of data processing. These functions, according to EPRI, also needed to be integrated “within a hardware and software system supporting seamless operation of manual scanning, position-tracking, 3-D imaging, computer encoding, data visualization and analysis, and condition assessment technologies.”
EPRI began work on the project in 2009, recognizing that advances in ultrasonic scanning developed for medical and geophysical applications held promise for UT of power plant components. Developmental work has focused on improving signal processing, pattern recognition, and other methods to support accurate position tracking and data reconstruction.
Previous UT scanners required high-channel transducers for 3-D image reconstruction, while large ultrasonic apertures are necessary to achieve depth focusing throughout the interior of thick-section components. The EPRI project has developed new linear and matrix sparse-array configurations with the potential to achieve the same results as larger scanners using a smaller number of array elements and a smaller number of channels.
Small, Handheld, Powerful
Tests of the prototype developed by EPRI, showed it was capable of generating high-quality real-time computer-encoded images of simulated defects and internal features in reference blocks and component mockups (Figure 4).
4. Real-time 3-D. EPRI’s “acoustic mouse” has proven capable of generating high-quality 3-D scans in testing. Courtesy: EPRI
Though the EPRI acoustic mouse is not yet being manufactured, EPRI is currently working with instrument manufacturers and plant owners to develop commercial models and support code qualification for the instruments, as well as develop training programs for their use. The first models are expected to be commercially available in 2016.
—Thomas W. Overton, JD is a POWER associate editor.