Start with the service
Before choosing a material, write down four things: the media, the pressure, the temperature and any corrosive content such as chlorides, ammonia or acids. The material follows from those.
The common grades
| Grade | Material | Good for | Avoid |
|---|---|---|---|
| ASTM A126 Cl.B | Grey cast iron | Water, air, low-pressure utilities | Steam above low pressure, shock and water hammer |
| ASTM A536 | Ductile iron | Water, firefighting, HVAC | Hydrocarbon and high-temperature service |
| ASTM A216 WCB | Cast carbon steel | Oil, gas, steam, hydrocarbons | Corrosive and chloride-rich media |
| ASTM A105 | Forged carbon steel | Small bore (typically 2" and under), high pressure | Large sizes, corrosive service |
| ASTM A352 LCC | Low-temperature carbon steel | Sub-zero service | Corrosive service |
| ASTM A351 CF8M | Cast stainless 316 | Chemicals, pharma and food, mild chlorides | Hot concentrated chlorides |
| CW617N | Brass | Water, air, light oils | Seawater, ammonia |
Carbon steel: the workhorse
WCB castings and A105 forgings cover most oil, gas, steam and water service at moderate temperatures. They are strong, weldable and economical, but they rust in wet, oxygenated or corrosive media.
Stainless steel: for corrosion and cleanliness
CF8 is the cast equivalent of 304 and CF8M of 316. The molybdenum in CF8M improves resistance to chlorides, which is why it is the usual starting point for chemical, pharmaceutical and food lines. Stainless is resistant, not immune: hot concentrated chlorides can still cause pitting, and severe service may need duplex or higher alloys.
Cast iron and brass: utility service
Cast iron and ductile iron valves are economical for water and air. Brass is common in small threaded valves. Brass should not be used in seawater, where zinc leaches out, or in ammonia service, where it can crack under stress.
Do not forget the trim and seals
The body is only part of the valve. Seats, stem, packing and gaskets must suit the same media and temperature. A stainless body with the wrong seat material will still fail.
