Quick Answer
A valve body is a pressure vessel with flow paths — its casting must be sound, its material must survive the media, and its specification must say both explicitly. The material ladder runs from WCB carbon steel (water, steam, oil) through CF8M stainless (chemicals, chlorides) up to CN7M and duplex grades (acids, brines). Process-wise: investment casting for bodies up to ~50 kg needing smooth passages, sand casting for larger sizes. The three requirements that prevent most disputes: named grade with certificates, NDT class on critical zones, and a shell/seat pressure test protocol.
Material Selection by Media
| Service | First-choice grade | Notes |
|---|---|---|
| Water, steam, air, oil (−29 to 425°C) | WCB / WCC (A216) | The global default; see our WCB guide |
| Cold climate / low temperature | LCB / LCC (A352) | Charpy-tested at −46°C |
| Chlorides, food CIP, marine | CF8M (A351) | Cast 316; CF3M if welded |
| Sulfuric / phosphoric acid | CN7M | Alloy 20 class |
| Brines + abrasion, desalination | CD4MCu duplex | 2× yield of CF8M |
| High temperature (>425°C) | WC6 / WC9 (A217) | Chrome-moly creep grades |
Casting Process: Investment vs Sand for Valve Bodies
- Investment casting: smooth internal flow paths (better Cv, less turbulence), thin uniform walls, near-net flange faces — the standard for control valves, instrument valves and stainless bodies to roughly DN150
- Sand casting: gate, globe and check bodies above ~50 kg, iron and carbon steel classes, where machining defines all sealing surfaces anyway
The Specification Package That Prevents Disputes
- Material: spec + grade + heat treatment condition, per-heat chemistry and mechanicals
- Pressure boundary NDT: RT or UT on gate/riser zones per severity class; MPI (carbon steel) or DPT (stainless) on machined sealing faces — method-to-material logic is in our NDT methods guide
- Pressure test: shell test at 1.5× rated pressure, seat test per API 598 / ISO 5208 class — state duration and acceptable leakage class
- Weld repair policy: allowed zones, qualified procedures, re-heat-treatment and re-NDT after repair — agree it before the first pour, not after the first defect
- Marking and traceability: heat number cast or stamped on the body per MSS SP-25
Common Failure Points to Design Against
- Shrinkage at the neck-to-body junction — the thickest section; riser design and RT sampling target it
- Porosity on machined seat pockets — machining opens subsurface gas; DPT after machining catches it before assembly
- Distortion of flange faces in heat treatment — machining after treatment, never before, for critical flatness
YCUMETAL casts valve bodies and trim in WCB/WCC, CF8/CF8M and higher alloys with in-house CNC machining of flanges, seats and stem bores, plus hydro testing and documented quality assurance.
FAQ
Cast or forged valve body?
Castings dominate up to large sizes for geometry freedom and price; forged bodies rule small-bore high-pressure classes (API 602). Above ~DN50 at moderate pressure classes, casting is the economic answer.
What surface finish should flow passages have?
Investment-cast passages arrive at Ra 3.2–6.3 µm — typically used as-cast. Sand-cast passages are rougher; specify only if your Cv calculation cares.
Which pressure class can cast bodies reach?
With the right grade and NDT class, cast steel bodies serve through ASME Class 600–1500 routinely; above that, forging economics take over.