The manufacturing innovation being developed by EPRI can produce valve bodies and other components in near-net-shape form, accelerating fabrication, improving inspectability, and reducing life-cycle costs.

Valve bodies, pump housings, piping elbows, and many other large and complex power plant components are commonly fabricated using metal casting processes similar to those first applied more than 50 years ago. After casting, extensive machining is typically required to prepare components for service duty. Once installed, components often are difficult to inspect due to a complex cast microstructure. EPRI's Technology Innovation Program is leading collaborative development of powder metallurgy fabrication as an alternative to casting that promises to significantly decrease rework and improve inspectability, reducing both costs and risks.

Powder metallurgy fabrication methods were initially developed for aerospace and other specialty components, which are commonly much smaller than those designed for power plant applications. The multi-stage powder metallurgy fabrication process begins with component design, alloy specification, and mold construction. After a metallic powder with desired composition is produced via gas atomization manufacturing, the mold is loaded, degassed under vacuum, and sealed. Hot isostatic processing is then applied for high-temperature, high-pressure consolidation of the powder into a solid with homogenous microstructure.

Primary advantages include the following:

• Efficiency . By producing near-net-shape components, powder metallurgy reduces material waste and minimizes the need for machining and cleanup.
• Inspectability and Weldability . Powder metallurgy results in a uniform, homogenous microstructure that eases inspectability (for both detection and sizing) and also enhances weldability.
• Optimization . Powder metallurgy allows materials composition and amount to be specified and optimized on a component-by-component basis, reducing waste and facilitating the use of new alloys.

In 2009, EPRI demonstrated the feasibility of powder metallurgy by using an austenitic (316L) stainless steel powder to produce a 12-inch-diameter valve body in near-net-shape form. The component incorporated intricate features, required no finish machining, offered exceptional toughness, a 15% improvement in mechanical performance, and superior inspectability relative to conventional cast stainless steel components.

Subsequently, valve bodies have been produced from multiple heats of 316L stainless steel, a creep-strength-enhanced ferritic steel (Grade 91), and nickel-based alloy (Inconel 625), representing a broad cross-section of materials used in nuclear, conventional coal, and ultrasupercritical coal plant applications. Detailed testing is under way to verify inspectability and to generate the property and performance data required to support an ASME code case permitting use of powder metallurgy and hot isostatic processing for fabrication of large pressure-retaining components. Weldability also is being evaluated as part of the overall data package for ASME.

EPRI expects a code package for 316L stainless steel to be submitted to ASME in 2011, with other alloys to follow in 2012. Pending process qualification, an in-plant testing and demonstration program for large-scale valves fabricated using powder metallurgy is scheduled for late 2012 or early 2013, and commercial manufacturing could begin as early as 2013.

For more information, contact David Gandy at 704.595.2695 or davgandy@epri.com.