Inconel 740H Introduction

Precipitation
Strengthened Alloy

Nickel

Chromium

Cobalt

Corrosion
Resistance

85

Mechanical
Behavior

92

Purity

83

Overview

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As the world’s demand for electrical power increases, governments also demand that emissions be strictly controlled to minimize the greenhouse effects of society’s carbon footprint. Despite that situation, coal, oil and gas continue to be the major fuels for power generation facilities. While nuclear, gas turbine, solar and wind generation are expected to increase, coal is still predicted to fuel 37% of the world’s electrical generating capacity in 2035.1 Thus, there is a strong impetus for development of cleaner, more efficient power generation. The efficiency of fossil fuel-fired boilers increases with operating temperature and pressure. There have been progressive increases in these conditions for boiler design culminating in advanced ultra-supercritical (A-USC) technology. A-USC boilers are expected to offer levels of generation efficiency over 50%(HHV) and their operation is such that carbon-base emissions can be readily collected and sequestered.

Programs to develop A-USC capability are currently active around the world. Since A-USC plants will operate at higher temperatures (700° to 760°C) and pressures (up to 35 MPa), nickel-base superalloys are required to meet the rigors of strength and corrosion resistance. INCONEL® alloy 740H® was developed specifically to operate under these demanding service conditions.

INCONEL alloy 740H is a nickel-base, precipitation hardenable superalloy that offers a unique combination of high strength and creep resistance at elevated temperatures along with resistance to coal ash corrosion. The alloy was originally targeted for use as A-USC boiler tubes in the superheater sections of these plants but was then adapted for application as a material for the steam headers to which the boiler tubes are connected. A-USC boiler tubes are conventional sizes [typically 1.5 to 3 inch (38 to 76 mm) outside diameter]. Main steam header pipe sizes occupy a much larger size range, with outer diameter greater than 12 inches (305 mm) and wall thickness likely exceeding 1.5 inches (38 mm). Seamless steam reheat piping, at up to 30 inch (760 mm) outer diameter, is also a feasible product line with INCONEL alloy 740H.

Corrosion Resistance

With its high content of chromium, alloy 740H offers excellent resistance to corrosion at elevated temperatures. This is especially important for boiler tubes as they are exposed to fireside corrosion on the exterior and steamside corrosion on the interior. Alloy 740H has been extensively evaluated under both sets of conditions.

Physical Properties

Mechanical Properties