Material choice decides the service life of every valve body. It also drives 40 to 60 percent of the piece price. Many buyers default to stainless everywhere and overpay. Others pick carbon steel and replace parts too early. This guide compares the three most common valve body casting materials so you can match grade to duty.
WCB carbon steel: the workhorse for neutral media
ASTM A216 WCB is the default for water, steam, oil and gas up to roughly 425 degrees C. It offers high strength at the lowest cost, and it welds easily for repairs. However, it rusts in wet corrosive service. Therefore, WCB suits power plants, HVAC and general process lines with inhibitors or clean media.
CF8M stainless: the standard for corrosive media
CF8M, the cast equivalent of 316, handles acids, seawater splash and food media. Its molybdenum content resists pitting that defeats plain 304 castings. Keep in mind two buying points. First, specify solution annealing after casting, or sensitization can reduce corrosion resistance at welds. Second, CF8M costs about 1.8 to 2.2 times WCB per kilogram, so use it where corrosion is real.
Duplex 2205: strength plus chloride resistance
Duplex 2205 delivers about twice the yield strength of CF8M and far better pitting resistance. Consequently, thinner walls are possible, which offsets part of its premium price. It shines in seawater cooling, desalination and chloride process lines. One caution applies: duplex needs tight ferrite control during heat treatment, so buy only from foundries that measure it. Our knife gate valve body casting page shows a typical duplex specification in practice.
Quick comparison
| Property | WCB | CF8M | Duplex 2205 |
|---|---|---|---|
| Relative cost per kg | 1.0 | 1.8-2.2 | 2.5-3.0 |
| Max service temp | 425 C | 300 C | 280 C |
| Chloride resistance | Poor | Good | Excellent |
| Yield strength | Medium | Medium | High |
Common buyer mistakes
- Specifying 316 everywhere because the last project used it, even for clean water duty.
- Ordering duplex without requiring ferrite testing on the certificate.
- Ignoring body cavity design, which often costs more than the alloy upgrade.
Frequently asked questions
Which material for seawater valves?
Duplex 2205 or nickel aluminium bronze for wetted parts. CF8M survives splash zones but pits under immersion.
Can I upgrade from WCB to CF8M without redesign?
Usually yes, because CF8M castings keep similar strength. Check pressure class and flange ratings with your engineer.
Our engineers review media, temperature and pressure class before quoting. Browse the valve and pipe casting category and send your specification for a material recommendation.