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Monel cannot be directly replaced with 316 duplex steel because the corrosion resistance of the two is significantly different. Especially in environments containing hydrofluoric acid, strong alkali or high concentrations of chloride, 316L or duplex steel cannot replace the corrosion resistance of Monel. Monel alloy (such as Monel 400) is a nickel-copper alloy that is extremely resistant to hydrofluoric acid, alkali, seawater and a variety of corrosive media, and is often used in extreme corrosive conditions. Although 316L stainless steel is better than 304, it is only suitable for weak acid, weak alkali and general environments containing chloride ions. It is prone to pitting corrosion and stress corrosion cracking under strong reducing or high concentration harsh conditions. Although duplex stainless steel (such as S32205) has high strength and good resistance to chloride stress corrosion, it may still fail in low pH, high chlorine, and high temperature environments. There have been cases showing that it was damaged due to underscale corrosion due to ammonium chloride deposition in the overhead condenser of a refinery. If you need to replace Monel, it is recommended to consider: High-molybdenum austenitic stainless steel (such as 904L, 6Mo alloy) Hastelloy (such as C-276) Corrosion rate test verification based on specific media In terms of cost, although duplex steel is lower than Monel, improper selection will lead to frequent maintenance and replacement, which will increase the overall cost.