UNS N08020 · ASTM A351 CN7M · API 598
Alloy 20 Valves for Sulfuric Acid, Sulfate, and Raffinate Service
Supreme Valves supplies Alloy 20 valves for sulfuric acid, sulfate-bearing process liquor, and copper raffinate circuits. Cast bodies are ASTM A351 Grade CN7M (UNS N08020). Gate, globe, ball, and dual-plate wafer check valves ship with EN 10204 3.1 material certificates and API 598 hydrostatic tests. US buyers receive DAP delivery and a proforma invoice in US dollars.
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Short answer: Specify Alloy 20 (CN7M) when the fluid is sulfuric acid or raffinate and SS316 has a short life. Use a dual-plate wafer check valve on raffinate pump discharge. Use a gate valve for isolation and a globe valve for throttling on acid dilution and transfer lines.
Where Alloy 20 valves are specified
- Sulfuric acid valves — concentrated acid near 93–98%, dilution headers, and the 20–40% range where SS316 corrodes quickly.
- Raffinate valves — copper heap-leach and SX-EW return acid that also carries chlorides and silica fines. Utah, Arizona, and Nevada mines are the main US demand.
- Sulfate service — copper sulfate and similar sulfate liquors produced with sulfuric acid. The corrosion driver is the acid and chlorides, so the valve material is still Alloy 20, not a separate “sulfate alloy.”
- Fertilizer acid lines — phosphoric acid plants that consume sulfuric acid, including the Tampa Bay corridor.
Alloy 20 vs SS316 vs Hastelloy for acid and raffinate
| Service | SS316 CF8M | Alloy 20 CN7M |
|---|---|---|
| Sulfuric acid, about 20–40% | Rapid corrosion | Usual specification |
| Sulfuric acid, about 93–98% | Unsuitable | Usual specification |
| Raffinate (dilute acid, chlorides, fines) | Pitting in months | Standard leach-circuit material |
| Chloride plus hot acid beyond Alloy 20 limits | Fails | Review Hastelloy C276 |
Send concentration, temperature, chlorides, and solids with the RFQ. Alloy 20 is the economic choice for most sulfuric and raffinate lines. Hastelloy is justified only when the corrosion data says CN7M is outside its window.
Valve type by duty
- Alloy 20 dual-plate wafer check valve — raffinate and sulfuric pump discharge. API 594, Class 150 or 300, spring-assisted non-slam closure. Body, discs, and seat rings in CN7M. Hinge pins ASTM B462. Spring Inconel X-750.
- Alloy 20 gate and globe valves — isolation and control on acid transfer and dilution. API 600 / API 603 / API 623, ASME B16.5 flanges.
- Alloy 20 check valves — swing and wafer options when the piping spec is not dual-plate.
Proven US supply
A US equipment buyer took NPS 2 in and NPS 4 in Class 150 dual-plate wafer check valves in full Alloy 20 for sulfuric acid 97% and dilution service. Delivery was DAP to Saint George, Utah, with air freight into Las Vegas. The same construction is quoted for Houston sulfuric units, Tampa fertilizer plants, and raffinate headers in Arizona and Nevada.
Read the Utah delivery case study · USA Alloy 20 supply pages
What to send for a quote
- Valve type, NPS, and class (150 or 300).
- Fluid: sulfuric acid percent, raffinate, or sulfate liquor, plus temperature and chlorides if known.
- Quantity and US delivery city.
- Documents required: EN 10204 3.1 and API 598 are standard.
Questions buyers ask
What valve material is used for sulfuric acid and raffinate?
Alloy 20, cast as CN7M. SS316 is the material that gets replaced after it fails.
What is a raffinate valve?
The check or isolation valve on the acidic solution pumped back over a copper leach pad. Dual-plate Alloy 20 wafer checks are the usual pump-discharge valve.
Do you ship Alloy 20 valves to the United States?
Yes. Proforma invoices are in USD. Typical lead time for cast CN7M valves is 8–10 weeks. DAP air freight can be included in the unit price.
Sulfuric acid service guide · Raffinate pump-discharge checks · Buying from India into the USA