Best alloys for use in chemical media
Today a large range of materials are used in broad spectrum of aggressive chemicals. As chemicals and their properties vary on a large level, it is tough to select a suitable material for a specific chemical application. Commonly used materials in chemical applications are:
316 stainless steel- An alloy of iron, carbon, nickel and chromium, this non-magnetic stainless steel has higher ductility than SS400. Austenitic in structure, stainless steel 316 has supreme corrosion resistance to diverse chemicals. It is not sensitive to stress corrosion cracking or remains intact to heat processing. This steel is commonly used in pump heads, check valves, balls and other wetted components.
Hastelloy C: A Ni-Cr-Mo alloy that has supreme resistance to a wide range of chemical process conditions including strong oxidizers like sodium hypochlorite and ferric chloride. Hastelloy C prevents corrosion in nitric, hydrochloric and sulfuric acids at medium temperatures. It is usually used as spring material in check valves of non-metallic pumps. The grades of Hastelloy C used in pump components – hastelloy C276 bar and C22 bar that slightly differ in chemical compatibility.
Incoloy alloys 800, 800H, 800HT are high nickel-iron base alloys and are resistant to diverse aqueous media, they are primarily used for oxidation and carburization resistance and high strength at elevated points.
Nickel-Chromium-Molybdenum alloys such as Inconel alloy 625 are widely used in oxidizing and reducing media as they prevent corrosion and heat damages. They offer a combination of high temperature strength and resistance to halogen attack, oxidation and carburization that makes alloy 625 a popular material for chemical and petrochemical process equipments for use in vigorous, high temperature conditions. Other nickel based alloys offer supreme resistance to acids, salts and a large spectrum of other materials occurred in chemical processing. They are also resistant to chloride ion SCC.
High molybdenum alloys are used in highly contaminated sulfuric acids with halides. They are also used in presence of sulfuric acid during the development of other chemicals for example phosphoric acid, hydrofluoric acid, titanium dioxide, ammonium sulfate and in refining of nickel and copper ores.
Incoloy 825 offers excellent performance in sulfuric and phosphoric acid applications. Although suitably resistant to hydrochloric acid, this alloy is sensitive to pitting and crevice attack in stagnant unaerated solutions.
Hastelloy G-30 is particularly resistant to sulfuric acid and contaminated phosphoric acid and can withstand reducing and oxidizing conditions. It offers good welability and overall good corrosion resistance even in weld heat affected regions.
Nickel-Copper Alloys– The corrosion behavior of nickel-copper alloys as that of pure nickel is excellent in reducing conditions and can be adjusted by aeration and oxidizing chemicals. Monel 400 possesses excellent resistance to halogen acids and compounds specifically hydrofluoric acid and hot gases containing fluorine or hydrogen fluoride.
Pure Nickel has significant contribution in applications involving alkaline media such as sodium hydroxide for a large range of temperature and concentrations. They are also resistant to corrosion by high temperature halogens, reducing salts and other oxidizing halides and foods.