Material Selection for Floating Ball Valves: The Impact of Pressure And Bore Size on Stainless Steel And Cast Iron Valves

Understanding Floating Ball Valves

Floating ball valves are designed with a floating ball mechanism that allows the ball to move slightly within the valve body. This movement helps maintain contact with the seals, providing better sealing performance and compensating for any misalignment in the piping system. These valves are commonly used in applications requiring high reliability and tight shutoff, such as in the oil and gas, chemical, and water treatment industries.

Key Components of Floating Ball Valves

• Valve Body: The main structure that houses all internal components.

• Floating Ball: The spherical element that controls the flow of fluid. It can move slightly within the valve body to maintain contact with the seals.

• Seats: The sealing elements that provide a tight seal against the ball.

• Stem: The component that connects the ball to the external actuator or handle.

• Flanges: The connection points that allow the valve to be bolted to the piping system.

aterial Options for Floating Ball Valves

Stainless Steel

Stainless steel is a popular choice for floating ball valves due to its excellent corrosion resistance, strength, and durability. Common grades used include:

• 304 Stainless Steel: Offers good corrosion resistance and is suitable for a wide range of applications. However, it may not be ideal for highly corrosive environments.

• 316 Stainless Steel: Provides superior corrosion resistance compared to 304, especially in marine environments and applications involving chlorides.

• 316L Stainless Steel: A low-carbon version of 316, which reduces the risk of carbide precipitation during welding, making it suitable for high-temperature applications.

Cast Steel

Cast steel is another common material used for floating ball valves, particularly in applications requiring high strength and durability. Cast steel valves are known for their robustness and ability to withstand high pressures. Common types include:

• Carbon Steel (WCB): Suitable for applications up to 650°F (343°C) and pressures up to 2,000 psi (138 bar). Carbon steel is known for its strength and cost-effectiveness.

• Alloy Steel (ASTM A350 LF2): Provides better low-temperature toughness and is suitable for applications up to 800°F (427°C) and pressures up to 2,500 psi (172 bar).

Impact of Pressure on Material Selection

Low-Pressure Applications (Up to 150 psi)

• Stainless Steel: Suitable for low-pressure applications, especially where corrosion resistance is a priority. Grades like 304 and 316 are commonly used.

• Cast Steel: Carbon steel (WCB) is a cost-effective option for low-pressure applications, providing sufficient strength and durability.

High-Pressure Applications (Above 150 psi)

• Stainless Steel: For high-pressure applications, 316L stainless steel is often preferred due to its superior strength and corrosion resistance. It can handle pressures up to 2,000 psi (138 bar) and temperatures up to 800°F (427°C).

• Cast Steel: Alloy steel (ASTM A350 LF2) is ideal for high-pressure applications, providing robust performance and the ability to withstand pressures up to 2,500 psi (172 bar) and temperatures up to 800°F (427°C).

Impact of Bore Size on Material Selection

Small Bore Sizes (Up to 2 inches)

• Stainless Steel: Suitable for small bore sizes, especially in applications requiring high corrosion resistance. The lighter weight and ease of installation make stainless steel an attractive option.

• Cast Steel: For small bore sizes, carbon steel (WCB) can be used, providing sufficient strength and durability at a lower cost.

Large Bore Sizes (Above 2 inches)

• Stainless Steel: For large bore sizes, 316L stainless steel is often used due to its high strength and corrosion resistance. It can handle larger flow volumes and higher pressures.

• Cast Steel: Alloy steel (ASTM A350 LF2) is preferred for large bore sizes, providing robust performance and the ability to withstand high pressures and temperatures.

Comparison of Stainless Steel and Cast Steel Floating Ball Valves