WHAT TYPE OF ALLOY IS KNOWN AS HASTELLOY?

The registered name Hastelloy derives from the company name Haynes Stellite Alloys, which in 1920 developed the nickel alloy Hastelloy B, used 50 years later in the Viking I and II spacecraft that reached Mars. Hastelloy C was subsequently developed and has found widespread use in the chemical process, petrochemical, pharmaceutical, and energy industries.

Hastelloy X emerged as a high-temperature superalloy of great importance in the aviation engine industry. It was later surpassed by the Haynes 188 and Haynes 230 alloys.

One of the drawbacks of Hastelloy C that slowed its expansion in the marketplace was the need to subject welded components to post-weld heat treatment in order to restore the corrosion resistance lost during the welding process. This problem was solved by the Hastelloy C-276 variant, which features incredibly low carbon and silicon levels achievable through an argon-oxygen decarburization process. This ensures that the weld heat-affected zone exhibits corrosion resistance comparable to that of the base metal.

During the 1970s and 1980s, Hastelloy C-22 emerged with superior corrosion resistance, along with Hastelloy G-30 for the agrochemical, biopharmaceutical, and other aggressive process industries. More recent additions include Hastelloy B-3, C-2000, and D-205 alloys.

Today, many nickel-chromium-molybdenum alloys are used for various applications in the chemical and petrochemical industries. The following are some of the most relevant references and industrial applications.

THE MOST COMMON HASTELLOY ALLOYS.

Corrosion-resistant: B-2, B-3, C-4, C-22, C-276, C-2000, D-205, G-3, G-30, G-50, H-9M, and N

High-temperature resistant: S, W, and X

Corrosion-erosion resistant: Ultimet

Erosion resistant: 6B

Hastelloy B-2 Alloy. Nickel-molybdenum based alloy with excellent resistance to hydrochloric acid at all temperatures and concentrations. It also resists hydrogen chloride, sulfuric acid, hydrofluoric acid, acetic acid, and pure phosphoric acid. It exhibits excellent resistance to stress corrosion cracking and intergranular corrosion in weld heat-affected zones due to the absence of carbide precipitation upon heating. It can be used in the as-welded condition without post-weld heat treatment. Not recommended in the presence of ferric or cupric salts, where corrosion fatigue may occur.

Hastelloy C-4 Alloy. Nickel-chromium-molybdenum based alloy with excellent thermal stability at elevated temperatures (650–1038 °C). It offers excellent resistance to stress corrosion cracking and oxidizing atmospheres up to 1038 °C.

It resists mineral acids, solvents, dry chlorine, formic acid, acetic anhydride and acetic acid, brines, and seawater. It can be used in the as-welded condition without post-weld heat treatment.

Hastelloy C-22 Alloy. Nickel-chromium-molybdenum-tungsten based alloy with corrosion resistance superior to that of Hastelloy C-276 and C-4.

It offers excellent resistance to pitting corrosion, crevice corrosion, and stress corrosion cracking. It provides outstanding resistance to strongly oxidizing aqueous media, mixtures of nitric acid or other oxidizing agents with chlorides, as well as wet chlorine. It resists both reducing and oxidizing media, making it applicable to a wide variety of processes.

Hastelloy C-276 Alloy. Nickel-chromium-molybdenum-tungsten based alloy with versatile resistance to both general and localized corrosion (pitting and stress corrosion cracking). Excellent resistance to reducing and oxidizing media.

It resists ferric and cupric chlorides, wet chlorine, hypochlorite, chlorine dioxide, acetic anhydride and acetic acid, formic acid, brine, and seawater. It also resists sulfur-bearing compounds. Highly fabricable, it requires no post-weld heat treatment. Only hot-forged components require heat treatment at 1121 °C.

Hastelloy G-30 Alloy. High-chromium nickel-based alloy with excellent resistance to phosphoric acid and corrosive mixtures of oxidizing acids such as nitric/hydrochloric, nitric/hydrofluoric, and sulfuric acid. Its outstanding resistance to intergranular precipitation allows it to be used in the as-welded condition without post-weld heat treatment.

Hastelloy H-9M Alloy. Nickel alloy specifically designed for outstanding resistance to crevice corrosion and pitting in acidic chloride-fluoride mixtures. It is also resistant to stress corrosion cracking in general and, in particular, to that induced by hydrogen/hydrogen sulfide environments.