Are cast-iron fittings and Class 150 fittings permitted in clean agent systems?

• A. Yes
• B. No
• C. Only cast-iron
• D. Only Class 150

Answer: (B)

Material compatibility and system pressure govern what fittings can be used in clean agent systems. Clean agent piping must be made from materials that won’t react with or be corroded by the agent, and fittings must be able to withstand the system’s design pressure.

Cast-iron fittings are not suitable because iron can be attacked by some clean agents and the material’s properties don’t consistently meet the reliability and corrosion resistance needed for these systems. In practice, materials such as steel, stainless steel, or approved copper alloys, and certain compatible plastics, are used instead because they’re proven to hold up under the agent and the operating pressures.

Class 150 fittings carry a nominal working pressure of about 150 psi, which is often not enough for clean agent systems that operate at higher pressures to distribute the agent effectively. Using fittings rated only to 150 psi would risk failure under normal design conditions.

So, neither cast-iron fittings nor Class 150 fittings are permitted. Acceptable choices are materials and fittings that are compatible with the chosen clean agent and rated for the system’s design pressures, as specified by the applicable standards and manufacturers.