Sulfurous acid is normally of very corrosive nature . The solutions of sulfurous acid and calcium bisulfate utilized to prepare sulfite paper pulp are also of extremely attacking nature in the dilute solutions like exist in spent cooking liquor or in the paper itself. The corrosion resistance is superior and significant magnitude of Monel alloy is utilized for pulp washers, thickeners and screens in the sulfite pulp mills.The contents of sulfurous acid that produce in the condensed moisture from the flue gases through heating device and smelting processes may significantly increase corrosion.

In the smoking-scrubbing systems where the magnitude of sulfurous acid is kept low and where chance for oxidation to the nominally corrosive sulfurous acid occurs, Monel alloy 400 is commonly useful and is one of strong and malleable metals useful for these operations.

Hydrochloric Acid: Monel alloy 400 is one of alloys that may be utilized to deal with hydrochloric acid. The corrosion rate in solutions of 10% contents at room temperatures has been observed to be less than 10 mpy. Normally at room temperature, concentrations below 20% in unaerated solutions and in 10% aerated solutions should not be exceeded. In the several processes where HCl is produced as a result of hydrolysis of chlorides or chlorinated solvents, contents are normally lower than 0.5%.

Monel alloy 400 can adhere in these content percentages effectively at temperatures about 400oF. In the air-saturated HCl above room temperatures, the applications are normally bounded to contents below 3 to 4%. If the oxidizing salts are available in any but very nominal percentages, the corrosion can be considerably accelerated. Monel alloy 400 offers better resistance to corrosion by chlorinated solvents even at the boiling temperatures and is utilized for dry cleaning device and solvent distillation and reclamation units.

Hydrofluoric Acid: Monel alloy 400 is an excellent metallic material for hydrofluoric acid operation. Aeration or the availability of oxidizing salts increases corrosion rate but in the unaerated acid it offers resistance to all content percentages up to boiling point. Monel alloy 400 is commonly utilized in the production and filtration of hydrofluoric acid. It is broadly utilized for crucial components like bubble caps or valves and piping that are in contact with the running acid.

Phosphoric Acid or Skydrall – Monel alloy 400 offers excellent resistance to pure acid. The stainless steel grade 316offers generally equal or superior performance than alloy 400 in dealing with phosphoric acid.

Nitric or Nitrous acid:The stainless steels are good material.

Organic Acids: Monel alloy 400 offers significant resistance to corrosion due to the entire types of organic acids. Since with other non-oxidizing acids, aeration and temperature normally increase corrosion. Alloy 400 offers good resistance to glacial acetic acid. Monel alloy 400 has been utilized for distillation of fatty acids at temperatures about 500oF.

Alkalies: Monel alloy 400 offers efficient performance in handling most of the alkalies. It offers resistance to corrosion due to caustic soda across the entire concentration range. Alloy 400 offers resistance to anhydrous ammonia and to ammonium hydroxide solutions of about 3% concentration.

Salts : With the dissolution of salt in water, the conductivity of water increases and hence enables it to carry more corrosion current. The galvanic effects are enhanced.Monel alloy 400 is not subjected to stress corrosion cracking inthe chloride salts and it offers superior resistance to the whole non-oxidizing halides.

1.       Neutral and Alkaline Salts like chlorides, carbonates, sulfates, nitrates and acetates have minor effect on Monel alloy 400.

2.       Acid salts: Monel alloy 400 offers significant resistance to solutions of acid salts like zinc chlorides, ammonium sulfate and ammonium chloride.

3.       Oxidizing salts: Monel alloy 400 is not good resistant to oxidizing acids and salts like ferric chloride, ferric sulfate, cupric chloride, stannic chloride, mercuric chloride and silver nitrate excluding the highly dilute solutions. it implies to the acids including chromates,dichromates, nitrates, peroxides and other oxidizing compounds excluding the few particular situations that include acid tanning and textile solutions of chromates where glucose or other organic materials may be present producing the hindering effect.

4.       Oxidizing alkaline salts: Hypochlorites are the sole common alkaline salts that are completely corrosive. Monel alloy 400 is utilized in contact with alkaline peroxide bleaching solutions.

Mercury: Monel alloy 400 offers resistance to amalgamation by mercury at moderate temperatures.

Monel alloy 400 is used in the marine operations including valves, pumps, tanks, instrumentation. Water processing-deaerater heaters, heat exchangers, instruments and process, sour gas, food and beverage lines.