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- Cast Iron & Ductile Iron
Cast Iron & Ductile Iron
The economic body grade for large-diameter water and HVAC valves. Strong, castable at large bore, and entirely the wrong material for hydrocarbon fire-exposed service unless it has been fire-safe tested.
Ductile iron (spheroidal graphite, GJS) has a specified minimum tensile of 400 MPa and meaningful elongation, which is what separates it from grey cast iron. It is the standard body grade for large-diameter wafer and lug butterfly valves, gate valves on water transmission, and check valves on clean water duty.
Grey cast iron (GJL) is still specified in some legacy water and HVAC classes, with a much lower tensile and no meaningful ductility. We supply it only where the piping class explicitly requires it; our default recommendation on new water work is ductile iron.
The boundary condition is fire exposure. Ductile iron loses strength rapidly above about 350 °C and has no meaningful fire-safe performance unless the valve has been tested. On hydrocarbon service, specify carbon steel or stainless — not ductile iron with a note.
For water service the seat material matters more than the body. EPDM handles potable water and chlorinated supplies; NBR handles oils; PTFE handles aggressive media. Tell us the medium and the chlorination level and we will specify the seat, not the other way round.
Key properties
| Property | Value |
|---|---|
| Specified min tensile (GJS-400) | 400 MPa |
| Elongation | ≥ 12 % typically |
| Structure | Spheroidal graphite |
| Corrosion allowance | Epoxy or fusion-bonded coating available |
| Fire-safe | Not applicable without specific testing |
| Potable water | EPDM seats with WRAS / NSF options |
Where you meet this grade
Send the piping class, not the part number
We check the dimensions, the material and the standard before we price — which is the part that decides whether the valve actually fits. RFQ answered within one working day.