The Pacific Northwest National Laboratory (PNNL) (Richland, Washington, USA) is currently conducting validation research on cold spray technology, which represents the newest addition to PNNL’s suite of solid phase processing (SPP) tools. Laboratory officials believe cold spray offers the potential to repair hydroelectric dam turbines without the melting associated with traditional repair methods.
SPP is described as a disruptive approach to metals manufacturing that can be better, cheaper, and greener than traditional melt-based methods.
According to PNNL, almost every U.S. state uses hydropower for electricity. Over time, though, the force of the water causes cavitation—typically pits and cracks—on the surface of turbines. That amounts to high repair costs and lost revenue for dam operators, who must shut down the turbines to repair them, often by arc welding. The problem is that the heat from welding melts and degrades the metal, causing the turbine to incur cavitation damage at an increasing rate.
One potential solution, according to PNNL, is cold spray, which sprays tiny metal particles onto the turbine’s damaged area at supersonic speeds, with no melting involved. The particles impact the surface hard enough to form a bond, producing materials and coatings with superior hardness, wear resistance, and corrosion resistance.
PNNL has taken receipt of a cold spray system developed by VRC Metal Systems (Box Elder, South Dakota, USA), and it is considered that company’s most current technology. The cold spray process makes turbine blades much more resistant to damage over arc welding approaches, according to laboratory testing performed to American Society for Testing and Materials standards. PNNL is now actively working with hydropower collaborators toward an initial field application of the technology to validate those testing results.
“We have economic data that enabled us to conclude that once cold spray technology is established for hydro repairs, it will significantly reduce downtime and repair frequency due to resistance to cavitation erosion,” says Chris Smith, mechanical engineer at PNNL. “It also gives dams the flexibility to time needed repairs, for example, during times of drought.”
The team is also looking into using cold spray to create solutions for other energy sector areas. For example, they have investigated using it for the repair and mitigation of corrosion damage in nuclear waste storage canisters.
Beyond repair, PNNL notes that cold spray can also be used as an additive manufacturing process. Because the metal particles do not melt, there is potential to create new alloy systems that are otherwise incompatible in melt-based processes.
Source: PNNL, www.pnnl.gov.