Gray Cast iron VS Ductile iron | Eng-Tips

PAM,

The only set of rules that should concern you is the design code that governs your installation.

Both ASME B31.1 and B31.3 put limitations on use of cast iron in toxic, flammable and steam service. Limitations imposed typically are in the form of pressure/temperature maxima or inclusion only in non-shock service.

If a material is deemed suitable for service (by the piping code) and the component is design rated for that combination of temperature and pressure, then you should be able to use it. Valve manufacturers have excellent experience with succesful and non-successful installations and are usually happy to share it with a customer..

MJC The Iron body is not wetted as it is fully insulated by the teflon lining. So there is no discussion on the chemical properties.
Why should you consider cast iron. It will not save you money. The standard for any valve manufacturer is ductile.

My advise, stick to the standard material configuration.

ood luck !
Ed

Valves 14"–24" shall be resilient wedge gate valves, of a non-rising stem design and rated for 250 psig cold water working pressure. All cast ferrous components shall be ductile iron, ASTM A536. Valves 14"–24" shall meet or exceed all applicable requirements of AWWA C515. The words “Ductile Iron” or “D.I.” shall be cast on the valve. The wedge shall be ductile iron fully encapsulated with EPDM rubber.

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The wedge shall be symmetrical and seal equally well with flow in either direction. Wedge guides shall be equipped with male guide covers. The use of auxiliary bronze rollers and plow-style shoes are not acceptable. The wedge nut shall be independent of the wedge and held in place on three sides by the wedge to prevent possible misalignment. Valves shall be Certified to NSF/ANSI/CAN 61 and NSF/ANSI/CAN 372.

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Bolting materials shall be 304 stainless steel unless otherwise specified. Bolts may have either regular square or hexagonal shaped heads with dimensions conforming to ANSI B18.2.1. Metric size socket head cap screws are not allowed. The operating nut shall be constructed of ductile iron. All gaskets shall be pressure-energized O-Ring type seals. Stem shall be sealed by three O-Rings. O-Rings set in a cartridge shall not be allowed. The valve shall have thrust washers located with (1) above and (1) below the thrust collar to assist operation of the valve. All internal and external surfaces of the valve body and bonnet shall have an epoxy coating, complying with ANSI/AWWA C550.

Valves shall be AMERICAN’s Series resilient wedge gate valve.

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