English: Inconel springs for check valves. Valves and are generally made of plastic or steel, the latter being the most widely used in chemical and petrochemical applications. Steel grades range from the most common type, namely carbon steel, with standard stainless steel being the second most common. Stainless steel alloys, which include nickel or copper are used in applications that require higher corrosion or heat resistance. In such cases, the most commonly used valve configurations -- ball valves, gate valves, check valves, globe valves and butterfly valves -- are often forged or cast as duplex valves, super duplex valves, alloy 20 valves, monel valves, inconel valves, incoloy valves and 254 SMO valves (6Mo valves). Titanium valves are also used in some highly corrosive applications. Titanium is not a stainless steel alloy.