Cast iron or steel gate valve: choosing the body material
The body material sets a gate valve’s pressure and temperature limits, its behaviour under impact and frost, and its price. Mistakes are dangerous: grey iron on high-pressure steam can fracture. These are the practical rules.
TAZ Engineering Team · · 6 min
Grey cast iron
The lowest-cost material, easy to cast and corrosion-resistant in water, but brittle in tension, bending and impact. Used for water and low-energy steam, typically up to PN 16 and moderate temperatures, indoors or in chambers without frost risk.
Ductile iron
Spheroidal-graphite iron is stronger and more ductile than grey iron and tolerates moderate impact and bending. Modern resilient-seated water gate valves (for example 30ch39r) and butterfly valves are made from it, with fusion-bonded epoxy coating for drinking water.
Carbon steel
Cast carbon steel (25L, WCB) is standard for steam, high-temperature hot water, crude oil, oil products and gas. It is ductile, weldable and suited to high pressure. Gate valves 30s41nzh and 30s15nzh are rated up to 425 °C. Outdoor service in cold climates calls for low-temperature steels such as LCB or 09G2S.
Stainless steel
Austenitic grades such as 12Kh18N9TL, CF8 and CF8M are used for corrosive media, food and chemical plants and cryogenic service. They cost considerably more, so they are chosen for water only when there is a specific reason.
Short rules
Gas, flammable liquids and high-energy steam: steel only. Outdoor installation with frost risk: steel or ductile iron, never grey iron. Cold water in chambers and buildings: cast iron. Corrosive media: stainless steel. Send the medium, PN, temperature and location and TAZ will propose body and trim materials.
Checklist
- medium
- PN
- temperature range
- indoor or outdoor
- pipe loads
- drinking-water requirements
- corrosiveness