Valves in a pipeline network are akin to gates of a besieged castle.
They must remain tightly shut to stop the media while opening swiftly for the right proportion to pass. While doing this, they must endure not just the pressure from the flow of media but also the attacks from elements of nature.
The performance and service life of the valve depends upon an important basic factor: Its material composition.
Key material properties to consider in valves
Material strength
Good tensile strength is essential for operations under high pressure. When they originated in the 18th century, iron valves were used in most cases. However, later brass, bronze-iron and steel valves became more popular along with other high alloy valves. Today, steel and high alloy valves are used in high-pressure applications while cast iron valves are reserved for low-pressure applications.
Resistance to corrosion
A media with strong chemical properties could cause serious corrosion damage within the valve. A strong acidic media can cause deep damage and deformities even within steel valves. Due to this, valves used in chemical industry are made of corrosion resistant alloys such as molybdenum and chromium alloy combined with other elements.
Important metals used in metallic valves
Cast iron
It is a mixture of iron, carbon, some amount of silicone, and has good temperature tolerance. It is also the most economical metal to use for valves. Cast iron is unsuitable for high-pressure operations because of tensile strength.
Bronze
Bronze is an original metal alloy of tin, copper, lead, and zinc. Bronze valves are generally used for low to medium pressure applications, and in places where high corrosion resistance is needed such as the marine industry.
Brass
Brass is an alloy made primarily of copper and zinc. It displays high corrosion resistance and malleability. However, it breaks down when exposed to high amounts of chlorine. Brass valves are typically used as shut off valve in natural gas lines and in drinking water pipelines.
Ductile iron
Ductile iron is an alloy of iron, graphite, and also contains small quantities of magnesium. Nodule-shaped graphite in this alloy gives it higher ductility, but its temperature tolerance stands lower than cast iron. Ductile iron’s chemical composition makes it costlier than cast iron. It is typically used in oil, steam, water, and gas applications.
Stainless steel
Stainless steel is an iron alloy mixed with chromium and nickel. It is more resistant to leaks. Stainless steel has a higher temperature tolerance and durability than brass. Stainless steel valves that contain iron, nickel and molybdenum display high resistance to corrosion. Such valves are often used in marine & chemical applications.
Carbon steel
Carbon steel is an isotropic material capable of performance in a wide range of temperatures and pressures. Because of this, carbon steel is used in industries such as petrochemicals refineries and oil fields. These valves have a wide application range.
Non metal materials
Graphite
Graphite delivers excellent performance in rugged service conditions and high temperatures.
Teflon
Teflon has a lower temperature tolerance than graphite, but delivers considerably low friction. Teflon can be combined with other materials such as graphite to improve its temperature tolerance. Teflon is used to make valve seats. However, in tougher conditions, elastomers such as PEEK and TFM are used for valve seats.
Conclusion
Materials used for valves have been evolving ever since valves were first put to use. Factors such as costs, and changing requirements have led to numerous new alloys being used in valves. Throughout the evolution of valves, achieving the right balance between cost, quality, and performance has been the key. IPC has been working to help its clients achieve that balance by meeting the demand for quality valves in the shortest possible lead time. To know more, write to us at evalve@ipcvalves.com