Body materials: cast iron, ductile iron, carbon steel, stainless, bronze

Grey cast iron is the original valve body material and remains common in general water, HVAC and non-critical process service. EN-GJL-250 (the equivalent of BS Grade 250 or ASTM Class 30) offers adequate strength for typical PN10 and PN16 applications at temperatures up to approximately 200–250°C.

Cast iron is brittle: it does not deform before fracture under overload or impact, which makes it unsuitable for services where water hammer, surge or freeze risk is present. It is also vulnerable to graphitic corrosion in certain water chemistries, where the iron matrix corrodes while the graphite flakes remain — the valve looks intact but has no structural strength.

The cost advantage of cast iron over ductile iron is modest at smaller sizes and negligible at larger bores. In most new-build specifications, ductile iron is now preferred even where cast iron would be acceptable by standard.

Ductile iron (spheroidal graphite cast iron, EN-GJS-500 or ASTM Grade 65-45-12) offers significantly better mechanical properties than grey cast iron: higher tensile strength, and critically, the ability to deform plastically before fracture. It is resistant to water hammer and freeze damage that would crack a grey iron body.

Ductile iron is the standard body material for water and wastewater valves, fire protection systems, HVAC, and general industrial service. It is compatible with potable water (with appropriate epoxy lining), seawater (with coating and cathodic protection), and a wide range of industrial fluids.

Pressure ratings to PN40 are achievable in ductile iron for smaller bores; large-bore ductile iron valves are typically rated to PN25 or PN16. The material handles temperatures from below freezing to approximately 350°C.

Carbon steel ASTM A216 Grade WCB is the standard body material for industrial process valves, oil and gas applications, and high-pressure services where grey or ductile iron would not achieve the required pressure-temperature rating. WCB offers high tensile strength, good weldability, and pressure-temperature ratings to Class 600 and above depending on design.

Carbon steel is susceptible to general corrosion in aqueous environments without coating or cathodic protection. It is not suitable for seawater, strong acid or alkali service without special lining or alloy overlays. In water service, carbon steel valves require internal epoxy or rubber lining.

Low-temperature carbon steel applications (below approximately −20°C) require impact-tested material to ASTM A352 Grade LCB or equivalent, because standard WCB becomes brittle at sub-zero temperatures. Always specify the minimum design temperature when ordering valves for cold service.

ASTM A351 Grade CF8M is the cast equivalent of wrought 316 stainless steel (18% chromium, 10% nickel, 2–3% molybdenum). The molybdenum addition dramatically improves resistance to pitting and crevice corrosion in chloride environments compared to CF8 (Grade 304). CF8M is the standard for chemical process, food and beverage, pharmaceutical, and marine applications where broad corrosion resistance is required.

Stainless steel is not universally corrosion-resistant. Chloride concentrations above approximately 200 ppm at elevated temperature can initiate pitting or stress corrosion cracking in CF8M. Highly concentrated sulphuric acid, hydrochloric acid and certain reducing acids will attack 316 stainless. For severe chemical service, consult a corrosion engineer.

CF8 (Grade 304) is a lower-cost alternative for applications where the molybdenum addition of CF8M is not required — notably fresh water and food service without significant chloride exposure.

Bronze CC491K (gunmetal, formerly known as LG2 or BS 1400 LG2) is a tin-copper-zinc-lead alloy with excellent corrosion resistance in seawater, brackish water, and most water service applications. It is the standard body material for marine valves, water service fittings and small-bore valves across many industries.

Bronze is not suitable for ammonia, acetylene or other media that attack copper alloys. It is also not cost-competitive at larger bore sizes where the material cost per kilogram and casting weight both increase steeply — above DN100 or DN150, ductile iron or stainless steel are generally preferred.

Dezincification (selective leaching of zinc from brass alloys) is a concern in aggressive water, but gunmetal CC491K with its high tin and lead content is highly resistant to dezincification compared to standard brass. For drinking water service, verify that the specific alloy meets the applicable WRAS or national standard for potable water contact.