Key Differences Between AL-6XN® and C-22®

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Environments with high temperatures, low pH, and aggressive chemicals require a material that exhibits a high corrosion resistance, which traditional stainless steel alloys fail to attain. The unique properties and quick availability of super-austenitic stainless steel alloys AL-6XN® and Hastelloy® C-22® make them both favorable for highly corrosive environments, but they still have some important differences.

Both AL-6XN® alloy and Hastelloy® C-22® have a face-centered cubic lattice structure and contain chromium, molybdenum, and nickel as the major ingredients for providing corrosion resistance. However, C-22 has a higher quantity of these elements, which gives it better resistance to chlorides, mineral acids, and high-temperature oxidation. The chromium adds resistance to pitting, stress corrosion cracking, and crevice corrosion. The molybdenum provides greater resistance against reducing media such as hydrochloric, formic, and phosphorous acid mediums. The nickel better resists attacks from chlorides and other halides. Both AL-6XN and C-22 are materials that can withstand very corrosive environments, but they each have material design limitations and application restrictions.

AL-6XN was originally developed for seawater applications, but it is also an excellent material for food and beverage products such as sports drinks, ketchup, soy, barbecue, salsa, and other product that eats away at regular materials. AL-6XN is also found to resist corrosive attacks from various personal care products such as deodorant and hair care products. AL-6XN is usually the best choice for corrosion resistance regarding applications that require excellent formability, strength, and weldability that is not achievable by any conventional stainless steel alloy.

C-22 is designed to tolerate extremely corrosive environments. The advantage of this material is that it can withstand both oxidizing and reducing acids at high temperatures exhibiting high resistance to localized corrosion. C-22 has been used in chemical, food, beverage, and pharmaceutical industries where high temperatures and high concentrations are needed. Some of the processes use extremely high concentrations of chlorides at high temperatures. C-22 works effectively in these aggressive conditions.

However, every material has a threshold limit. AL-6XN will not hold well after reaching its threshold. So, it is beneficial to opt for C-22 beyond this limit.

AL-6XN is a cost-effective alternative to 316L for higher corrosion resistance and strength. It is considerably less expensive when compared to C-22, and yet it provides a comparable level of corrosion resistance.

AL-6XN and C-22 are readily available in forms such as tube, pipe, sheet, plate, bar, billet, and forgings from which components such as fittings, valves, fasteners, and castings can be obtained. Many sanitary piping components made from AL-6XN alloy are readily available.

“AL-6XN” is a registered trademark of ATI Properties, Inc., licensed to Allegheny Ludlum Corp.

“Hastelloy” and “C-22” are registered trademarks of Haynes International.

Expert Bio

Yogini Dhopade

Yogini Dhopade has three degrees, speaks four languages, and has traveled to ten different countries across the world. She has an unmatchable passion for metals and spends her time at CSI managing everything related to corrosion-resistant alloys.