Inconel® 725 is used where high strength and strong corrosion resistance are needed together in demanding environments. Applications include oil and gas equipment, naval and marine components, aerospace, pollution control and chemical processing.

Inconel 725 (Alloy 725, UNS N07725) is practically identical in composition to Inconel 625 (Alloy 625, UNS N06625, 2.4856), so the two share very similar corrosion resistance and physical properties. The difference is strength: Alloy 725 is significantly stronger because it benefits from precipitation strengthening.

How it gains its strength

Inconel 625 was found to develop increased strength on heat treatment, and small additions of titanium enhance the effect. These additions encourage microscopic precipitates to form during an extended heat treatment, effectively doubling the yield strength compared with Inconel 625. Because Inconel 725 gains its strength by heat treatment rather than cold working, its ductility and toughness stay high. The smallest diameters are therefore most used for fasteners, with slightly larger sizes used for complementary fixings. We carry an extensive stock of Alloy 725 from 1" (25.4mm) to 4" (101.6mm) diameter, with larger diameters available to order.

Marine and naval components

High strength and resistance to seawater corrosion make Inconel 725 a good candidate for marine components in naval and submarine systems. With a pitting resistance equivalent number (PREN) greater than 45, it provides high resistance to pitting and crevice corrosion. It can be considered an upgrade for Monel® K-500 (Alloy K-500, 2.4375), long used in marine construction. Monel K-500 has been used with less corrosion-resistant metals by the US Navy and others, with cathodic protection extending the life of the alloy steels. Occasional failures of Alloy K-500 items have been linked to hydrogen embrittlement and to accelerated corrosion from galvanic interaction with more noble metals. Inconel 725 removes that risk and adds strength and toughness. It has been used for shafts controlling glide planes and other exposed structural elements.

Oilfield applications

Inconel 725 is an improvement over Inconel 718 and Monel K-500 for selected oilfield applications. Hydrogen sulphide, carbon dioxide and chlorides at high pressures and temperatures create extremely corrosive conditions in sour wells. With its greater corrosion resistance, Inconel 725 is widely used for tubing hangers, mandrels and receptacles, though these are typically forged components rather than machined from our bar stock.

Alloy 725 is included within NACE MR0175/ISO 15156-3, API 6A and API 6ACRA.