By Kevin Sliman
A team of researchers at Penn State is investigating how contaminants in power plant water cycles affect the integrity of steel pipes and tubing in power generation systems.
The team is being led by Derek Hall, an energy engineering researcher in Penn State's John and Willie Leone Family Department of Energy and Mineral Engineering. Hall’s team includes Akash Ganesan, one of Hall’s doctoral students, and Serguei Lvov, a professor of energy and mineral engineering and materials science and engineering.
They are collaborating with the Institutes of Energy and the Environment’s Center for Quantitative Imaging to expand their understanding of corrosion processes in extreme environments.
The objective of the project is to provide evidence of how different water contamination levels and contamination types change the extent of damage observed from corrosion processes in a laboratory setting. The sponsor of the research is the Electric Power Research Institute (EPRI), which looks to validate its boiler and turbine steam cycle chemistry guidelines.
“The guidelines are designed to help power plants manage chemistry process-related issues to minimize risk of corrosion-related failures,” said Brad Burns, area manager of process operations and chemistry for EPRI. “The key factors are time and concentration of corrosive contaminants. Penn State has the capability to simulate boiler water conditions with temperature, pressure and water chemistry. Our goal is to learn about when active corrosion initiates through use of both electrochemical methods and the nano-computed topography scans.”
According to Hall, corrosion risks are notoriously difficult to study.
“Normally, we need to destroy samples during the process of detecting any localized corrosion or corrosion damage under the naturally forming surface oxide layers,” Hall said. “In this study, we are using nano-computed tomography to nondestructively monitor how base metal and corrosion product layers change with extended exposures to corrosive fluids.”
Hall said that this work helps power generation systems, such as coal, nuclear, geothermal and natural gas-fired plants, understand how to minimize corrosion risks while operating their systems in concert with renewable energy systems. Some sources of power, like solar and wind, are intermittent by nature and require other sources to adjust their electrical power outputs to stabilize the grid.
“Water cycle power plant systems are designed to run at an optimal power output and operate less efficiently when changes occur,” Hall said. “Now, they are being asked to shift their power output much more frequently, so operators need to manage corrosion risk in more dynamic operating conditions.”
As more renewable sources are added, the frequency of power shifting and cycling increases.
“Many systems reliant on water cycles struggle to adjust quickly,” Hall said. “The current energy transition is putting considerable pressures on how power plant operators manage their systems.”
Burns said project outcomes will help with reliability and availability of the assets to produce power by creating guidelines that will help manage risk to ensure this can be done longer term.
“Industry guidelines set limits on how long you can operate with certain levels of contaminants within your water cycle,” Hall said. “However, these limits are based on industry experiences, which vary considerably. Some plants may see severe damage in short amounts of time, whereas others observe minimal damage under the same conditions. We aim to provide experimental data to better pinpoint the causes of damage due to high contamination levels to better define these limits and the implications of operating beyond them.”
Burns said Penn State offers key technologies that help EPRI achieve their goal.
“We also gain tremendous benefit from collaborating with Derek and his team,” Burns said.
The monitoring is being completed with a piece of equipment called the Zeiss Versa 620. The nondestructive system provides three-dimensional imaging of biotic and abiotic materials. The Zeiss Versa is part of the Institutes of Energy and the Environment’s core facilities, specifically the Center for Quantitative Imaging (CQI).
“The Zeiss team has been instrumental in helping us use X-ray computed tomography to quantify corrosion rates associated with our simulated exposure tests,” Hall said. “The instrument allowed us to nondestructively track how the base metal and oxide layer changed with increasing exposure time and contamination levels.”
Sara Mueller is CQI’s research technologist who is running the project samples on the Zeiss. She said this project demonstrates the power of computed tomography technologies.
According to Mueller, divergent materials absorb different amounts of X-ray. The difference in photon counts detected by the camera allows researchers to see different density materials as part of the same sample, in this case the oxides and the base metals.
“The Zeiss allows researchers to ask, ‘what's inside?’ at a resolution that was previously only visible by cutting a sample and using other technology, such as a scanning electron microscope,” she said. “Cutting a sample introduces its own variation that we do not have in computed tomography. Additionally, we can track the same sample over time and across treatments as the researchers did in this study.”
Mueller added that beyond metals, CQI can measure small animal brain regions, embryonic bone, individual fibers, pores and cracks that would otherwise be invisible.
“With the right size and density of sample, we can achieve a resolution of about 300 nanometers, which allows us to begin to visualize micron-sized features,” she said. “To put that into perspective, that's examining features less than 1% of the width of human hair. We are discovering features we didn't even realize to ask questions about. It's really exciting.”