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Case Studies

Laser Scanning Confocal Microscope: EPRI For the Greater Grid

Keyence Corporation of America

3D Laser Scanning Confocal MicroscopyPalo Alto-based Electric Power Research Institute improves throughput and accuracy of metallurgical studies using 3D Laser Scanning Confocal Microscopy from Keyence.

Whether it’s flipping on a light switch or opening the refrigerator door, the residents of industrialized nations have come to expect low-cost, clean, and reliable electric power. Delivery of that power is often easier said than done, however. The world’s electrical grid is fueled by a diverse array of technologies, including nuclear power, natural gas and coal-fired plants, hydroelectric dams, wind farms, geothermal sources, and even the solar cells on residential rooftops. Connecting these disparate sources of electricity is a monumental task, never mind the need to closely manage their output and keep all of us safe while doing so. To say it’s a complex endeavor is a gross understatement.

The Power of Collaboration
Yet that’s exactly the mandate of Dr. John Shingledecker and his peers at the Electric Power Research Institute (EPRI), a non-profit company that serves the public by performing research and development related to all aspects of electricity. Based in Palo Alto, CA with major offices in Knoxville, TN and Charlotte, NC, EPRI was established in 1972. It is a member-funded organization, with more than 1,000 electric utilities, government agencies, public and private firms contributing financial aid, and representing approximately 90 percent of the electricity generated in the United States as well as 30 countries internationally. Members also participate in industry leadership, collaborating on EPRI’s ongoing research projects and future direction.

High resolution 3D color height map used to characterize a high-temperature erosion test coupon.

“We’re a unique organization,” says Shingledecker. “An independent and collaborative research and development company, one that shares its findings with the public, the electric supply chain, and our international participants. Because of this, we are an important source of information for everyone in the industry, and help promote efficient and safe generation of electricity from fossil fuels, renewables, and nuclear power sources as well as its transmission and distribution, with a focus on end-use efficiency and overall effect on the environment.”

Studies in Charlotte
No matter how it’s generated, electrical power sources require metal and machinery to operate. This is true for the turbines buried deep within the Hoover Dam or the massive gearboxes driving the windmills of the desert Southwest. One apparent exception to this is solar power, but even here, material research plays a key role in improving output from photovoltaic cells.

Quantifiable differences in high temperature wear behavior of potential high-temperature wear resistant coatings/claddings for valves after high-temperature laboratory wear testing.

Power generation is grueling work. Metals become fatigued over time by extreme pressures and temperatures, with high stakes indeed in the event of a failure. Shingledecker and EPRI work hard to manage and help prevent that fatigue. The organization’s material laboratory in Charlotte, NC studies new kinds of metallic alloys and other materials for use in future power applications. Legacy systems are monitored as well—samples of metal tubing from utility boilers, for example, or the coatings of valve stems used in steam turbines, are collected and analyzed.

The primary tools used for such work have traditionally been optical microscopy, scanning electron microscopy (SEM), and contact profilometers. Yet despite their long track record, these instruments are often less than ideal. Contact measuring techniques present the possibility of surface damage, particularly with soft metals or where scaling and oxidation exists, a common occurrence in steam-based power generation. Further, details smaller than the stylus tip are impossible to measure. Optical microscopes are generally limited to around 0.2 μm feature size and roughly 1500X magnification, and suffer lighting constraints. This is why SEM is often the tool of choice when very high magnification is needed, but this requires lengthy artifact preparation, is limited in the amount of three-dimensional (depth) information offered, and does not easily generate large area images.

Beyond Legacy
To identify the root causes of material failures, or predict those failures years in the future, the team in Charlotte needed a better tool. Shingledecker and his team of materials engineers surveyed a range of equipment and vendors in the area of microscopy and metrology. After reviewing the available options, they selected a Keyence VK-X160K 3D Laser Scanning Confocal Microscope. “Power plants are obviously quite large, and much of our research is done on commensurately large material samples—a welded structure, for example. Producing lots of images with the SEM and piecing them together can be difficult and time-consuming.”

The VK-X microscope sports a 408 nm wavelength semiconductor laser, motorized stage with 100 mm (3.93 in.) X-Y travels, and optics capable of 28,800X magnification. There’s no need to prepare specimens before measurement, nor is a vacuum chamber required as with SEM—just set the sample on the stage and start measuring. Z-axis display resolution as high as 0.5 nm is possible, and 130 nm in the X and Y axes. Images are displayed via a high-resolution CCD camera, displaying subtle differences in surface relief and stunning large area metallurgical maps.

Unetched (as-polished) laser image of the inner diameter surface of a shot-peened 304 H stainless steel superheater tube after ~24,500 hours of service.

Taking a Hard Look
Some examples of this include 3D analyses of hard-facing alloys used for erosion resistance in high-temperature valves. Laser microscopy of samples exposed to erosion tests in the laboratory and evaluated with the VK-X clearly showed surface perturbations that were indistinguishable using traditional 2D methods, resulting in reliable—and quantifiable—measurement of material erosion rates. The VK-X offered similar results during analyses of the 30 μm thick, nanostructured TiSiCN coating EPRI and a collaborating utility were evaluating in-service on a valve stems, clearly displaying the amount and depth of material loss during service.

EPRI found that images can be collected “in air” [SEM requires vacuum to operate] and there is no need for conductive surfaces as with SEM [which is challenged by coated or oxidized surfaces]. The end result? Technicians can take more samples, more quickly, making overall throughput of the lab that much greater. “When the metallographers and engineers say that something makes their life easier, it means we can do more work,” Shingledecker says. “Our people spend more time focusing on the results, as opposed to time spent getting the results. That helps us toward our end goal: development of welds and materials that can endure harsher conditions. This in turn enables the industry to build more efficient, safer power generation technology for future generations.”

About Keyence
KEYENCE has steadily grown since 1974 to become an innovative leader in the development and manufacturing of automation equipment worldwide. Our products consist of automation sensors, static eliminators, barcode readers, measuring instruments, vision systems, laser markers, and digital microscopes.

 

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