An alloy highly resistant to sulphuric acid
Incoloy 82517th April 2020
Incoloy® 825 (UNS N08825/W.Nr. 2.4858) is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium.
The Incoloy family of alloys are all based upon a nickel-iron-chromium base composition, but with a varying number of additional alloying elements. They were originally developed and produced by the Special Metals Corporation group of companies, which includes the former Wiggins business in Hereford, UK, that pioneered new alloys for use in Sir Frank Whittle’s original jet engine. They are designed for excellent corrosion resistance as well as strength at high temperatures; with specific alloys created to resist attack by particular chemicals.
The Incoloy trademark, registered to Huntingdon Alloys Corporation (‘Special Metals Corporation’) has been in commercial use since the 1950s, but many of the grades are now produced by other manufacturers. For instance, Sandvik manufactures a version of Incoloy 825 under their trademark Sanicro®41, whilst Bohler (Voest Alpine) manufacture L314.
The very first Incoloy alloy in the market was Incoloy 800, launched in 1949. At that time, nickel was in relatively short supply. Therefore, this lower-nickel alloy met the need for cost-competitive alloys able to retain its strength and resist oxidation and high-temperature corrosion, making it well-suited to furnace components and equipment, petrochemical items and protective sheathing for electrical heating elements.
Incoloy 825 was brought to the market in 1952, building upon Incoloy 800 in order to better resist sulphuric acid. Copper additions are well-known to improve resistance to reducing environments, such as sulphuric acid. This property is also exploited in Ferralium 255 (containing 2% copper additions) and the much more highly alloyed Alloy 20 (3-4% copper) to great effect. Although the nickel content is lower than the likes of Inconel 625 and Inconel 718, it is still sufficient to impart resistance to stress corrosion cracking (SCC) in chloride-containing environments. The increased chromium content ensures good resistance to oxidising environments such as nitric acid, whilst the molybdenum additions are well-known to improve pitting corrosion resistance.
The mechanical properties of Inconel 825 are relatively constant from very low temperatures (considered cryogenic i.e. -150degC) up to 540degC (100degF). Above this temperature, there is the possibility of undesirable microstructural phase changes that significantly reduce impact toughness and elongation.
Langley Alloys carries a significant stock of Alloy 825 solid bar, from ¾” up to 10” in a large number of incremental sizes. In addition, we also carry some bespoke sizes of hollow bar or tube for specific customer applications, as well as using our in-house deep hole borer to offer one-offs and specific sizes of bored bar. Popular applications currently served by our customers include valve components, thermowells and sensors, fasteners and also some downhole tooling which make use of its non-magnetic properties.
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Incoloy and Inconel are trademarks of the Special Metals Corporation group of companies.
Sanicro is a trademark of Sandvik Intellectual Property AB.
Ferralium is a trademark of Langley Alloys Ltd.New Guide to Duplex and Super Duplex Stainless SteelsInconel 718