Matching valve body material to application

By "Apollo" Valves
February 12, 2018

Most valves are available with bodies made of bronze, brass, cast iron, or steel. Their appearance and cost vary, but those should never be the main concerns when deciding which to use. The most important aspect is the nature of the application. An inexpensive valve could be a costly choice if it fails in service.

Matching valve body to application takes an understanding of material properties and service conditions. We'll review those here and discuss the implications for how and where each material should be used.

APPLICATION FACTORS

The most important are as follows:

Pressure

High pressure can cause a valve body to fail, but it's not always obvious when this is a risk. In high-rise buildings, for example, water pressures at ground level can exceed 600 psi.

Temperature

Metals lose strength at higher temperatures, which reduces the ability of a valve body to handle high pressure. A low carbon steel valve body good for 285 psi at 100°F can only accommodate 50 psi at 900°F.

Shock and vibration

Vibration can be a problem in some fluid systems. Pumps may be the cause, but a second and potentially more damaging cause is water hammer. The shock waves this sends through a system can crack more brittle materials.

Media

Corrosion is another potential hazard. While some fluids are benign, others can cause extensive corrosion. For instance, the piping and valves used in dairies to handle warm milk also must contend with hot caustic cleaning chemicals.

MATERIAL SELECTION

Bronze

Recognizable by its gold tint, this copper-tin alloy is easily cast and machined and has good corrosion resistance. It's not expensive, which makes it a popular choice, but it loses strength at elevated temperatures. Bronze is typically used in water supply applications when the line diameter is under 3”.

Brass

Reddish-gold in hue, this copper-zinc alloy is easily cast and machined. It's often preferred over bronze for use with potable water because it has a lower lead content. In low-flow applications, brass is susceptible to “de-zincification,” where zinc is gradually removed from the alloy.

Cast iron

Black or dark gray in appearance and readily cast and machined, cast iron is limited to temperatures and pressures below 450°F and 300 psi. As a hard but brittle material, it is not suitable for applications where vibration is likely.

Steel

Steel can be forged (which makes for very high-integrity valve bodies) or cast. It's very strong, so it works well in high-pressure applications, and it welds readily. Stainless steel has excellent corrosion resistance, making it ideal in chemical systems.

BOTTOM LINE

Material cost and performance vary widely. Always select valve body materials based on the application needs.

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