7472 G Family G G3 and G30

Alloy G was a development from alloy F, an alloy of similar composition, but with addition of about 2% copper. This addition of copper significantly improved the corrosion resistance in both sulfuric and phosphoric acid environments. Alloy G, developed in the 1960s, had excellent corrosion resistance in the as-welded condition and could handle the corrosive effects of both oxidizing and reducing agents. The alloy exhibited resistance to mixed acids, fluorsilicic acid, sulfate compounds, concentrated nitric acid, flue gases of coal-fired power plants, and hydrofluoric acid. Due to its higher nickel and molybdenum content over alloy 825, the alloy is essentially immune to chloride stress corrosion cracking and has significantly superior localized corrosion resistance. This alloy has been widely used in industries similar to those using alloy 825 as mentioned before, with the added advantage of improved corrosion resistance. However, this alloy is now obsolete and has been replaced by alloy G-3.

Alloy G-3 is an improved version of alloy G, having similar excellent corrosion resistance characteristics, but greater resistance to HAZ attack and with better weldability. Due to its lower carbon content, the alloy offers slower kinetics of carbide precipitation and its slightly higher molybdenum content provides for superior localized corrosion resistance. Alloy G-3 has replaced alloy G in almost all the industrial applications to date and alloy 825 in many applications, where better localized corrosion resistance is needed.

Alloy G-30 is a modification of the G-3 alloy with significantly increased chromium content and a lower molybdenum content. The alloy shows excellent resistance in commercial phosphoric acids as well as many complex and mixed acid environments of nitric/hydrochloric and nitric/hydrofluoric acids. The alloy has good resistance in sulfuric acid also. Some typical applications of alloy G-30 have been in phosphoric acid service, mixed acid service, nuclear fuel reprocessing, components in pickling operations, petrochemicals, agrichemicals manufacture (fertilizers, insecticides, pesticides, herbicides), and mining industries.

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