Corrosion-resistant alloy

Citation

(2002), "Corrosion-resistant alloy", Anti-Corrosion Methods and Materials, Vol. 49 No. 5. https://doi.org/10.1108/acmm.2002.12849ead.011

Corrosion-resistant alloy

Corrosion-resistant alloyKeywords: Corrosion resistance, Alloys

Allegheny Technologies Incorporated reports the introduction of a corrosion-resistant alloy, Allcorr (UNS N06610). This fully austenitic, non-age hardenable nickel base alloy is designed to withstand highly corrosive environments.

The alloy, originally designed at Allvac, an Allegheny Technologies company, for use in the "sour" oil and gas industry, was reportedly found to be extremely corrosion-resistant to a wide variety of corrosive environments. Allcorr corrosion resistance, coupled with its good strength, ductility and toughness, makes it a candidate for a wide variety of applications.

Allcorr alloy is described as a nickel base alloy containing about 31 per cent chromium, 11 per cent molybdenum, and 2 per cent tungsten. The very high chromium content is said to allow the alloy to be exposed to very highly oxidising environments without degradation. The molybdenum and tungsten help to resist high chloride environments and low pH conditions. An extensive corrosion-testing program performed by an independent laboratory compared a variety of corrosion-resistant alloys in selected environments. These environments included pure acids, organics, mixed acids, and various salt solutions.

The results are said to show the Allcorr material to have superior corrosion resistance to a higher number of environments than any of the other nickel base alloys compared (C-276, 625, G3, C4, B2, 600 and 825). Allcorr alloy was reportedly found to perform well in certain environments where zirconium does not, such as ferric or cupric chlorides. Allcorr material was even found to have corrosion resistance comparable with tantalum in specific environments such as salts, certain oxides and organics, and sulphates.

Other published corrosion studies are believed to echo these findings, with Allcorr alloy reportedly outperforming 625 and C-276 in numerous acid environments, including dilute nitric with small amounts of HCI, or HF and lower concentrations of formic acid over a range of temperatures.

Allcorr alloy, like many of the nickel base materials tested in both cited studies, would not be recommended for high temperature, low concentration HCI service.

Mechanical and physical properties

Allcorr alloy also claims good mechanical properties; with a typical room temperature yield strength around 50Ksi (345Mpa) and elongation above 50 per cent. Typical impact properties exceed 240ft-lb (325 joules) at room temperature. The alloy is easily cold-worked, similar to other austenitic alloys, to enhance mechanical strength. The alloy was cold-worked up to 70 per cent without any loss of corrosion properties. Physical properties, such as density, thermal expansion, and thermal conductivity, are available upon request.

Allcorr material is stated to be covered by a full range of ASTM "B" specifications as well as being qualified in NACE MR-01-75 up to 35Rc hardness.

Further details are available from: Allegheny Ludlum. Tel: +1 724 226 6231.