Boilers

DOE work leads to superalloys that stand up to power plant cycling
DOE work leads to superalloys that stand up to power plant cycling

A six-year project backed by the U.S. Department of Energy and involving Energy Industries of Ohio Inc. and other partners has led to the manufacture of commercial-scale nickel superalloy components that are needed to enable higher-efficiency thermal power plants.

The Advanced Ultra-Supercritical (AUSC) Component Testing (ComTest) Project aimed to fabricate full commercial-scale components to enable plants to operate with greater efficiency and at conditions of up to 1,400 degrees Fahrenheit and steam or supercritical carbon dioxide pressures of at least 3,500 pounds per square inch. At higher efficiency levels, fossil-fueled power plants generate electricity using less fuel and produce fewer emissions.

The $27.7 million project included $20 million in DOE funding led by the National Energy Technology Laboratory. The most recent phase focused on developing a U.S. supply chain of commercial AUSC components made of nickel-based alloys.

Nickel superalloy ingot producers, foundries, forging, pipe extrusion and bending fabricators and research centers in 15 states participated in the project. The aim was to design and build AUSC components from nickel superalloys and other advanced alloys for reliable operation under both steady-state and varying-load operating conditions.

To make room for greater amounts of wind and solar power on the electric grid, conventional generating units must ramp down and ramp up or stop and start electricity-generating operations more frequently. During cycling, boiler tubes, superheaters and other plant components undergo large temperature and pressure stresses. The AUSC components developed through ComTest are expected to withstand cycling for operating lifespans of at least 30 years.

Two nickel superalloys used in the project were approved by the American Society of Mechanical Engineers (ASME) for use in boilers and pressure vessels. 

In 2021, the new nickel-based superalloy Haynes International H282, developed by Haynes International and tested as part of the ComTest project, received ASME approval for use in boilers, fired heaters, pressure vessels and other key components.

The new superalloy may also be suited for other high-temperature structural applications, especially those in aero and industrial gas turbine engines. The superalloy offers a combination of creep strength (the tendency of materials to deform permanently under persistent mechanical stresses), thermal stability, weldability and fabricability typically not found in currently available commercial alloys.

One final ComTest project was a successful effort by Scot Forge to forge, machine and apply final heat treatment to a thick-wall pipe fitting manufactured with Inconel Alloy 740H, a nickel-based superalloy that offers a combination of high strength and creep resistance at elevated temperatures along with resistance to coal ash corrosion.

Special Metals Inc., the developer of Inconel 740H, provided the ingot for the wye fitting. Inconel Alloy 740H was the other nickel superalloy approved by ASME for use in power plant boilers and pressure vessels.

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