Alloy 20 Check Valve — CN7M Dual Plate Wafer | Sulphuric Acid Service
Alloy 20 (UNS N08020 / ASTM A351 CN7M) dual-plate wafer check valve for sulphuric acid, phosphoric acid, hydrochloric acid, and chloride service. Class 150, sizes 1½–24 inch, metal-to-metal seat. Manufacturer India. DAP/DDP export USA, Gulf countries.
Alloy 20 (commercially known as Carpenter 20, UNS N08020) is a nickel-iron-chromium-molybdenum-copper austenitic stainless alloy specifically engineered to resist sulphuric acid corrosion. The 3–4% copper content and 2–3% molybdenum content provide substantially better resistance to hot concentrated sulphuric acid than standard 316 stainless steel or Hastelloy C276 in certain acid concentration ranges. The cast equivalent designation is ASTM A351 CN7M (also written Alloy 20 Cb3). A dual-plate wafer check valve in CN7M with a metal-to-metal seat is the standard selection for acid plant pump discharge lines, absorption tower drain lines, and other corrosive process streams where elastomeric seat materials are unsuitable. Supreme Valves India manufactures and exports Alloy 20 check valves to sulphuric acid producers, fertiliser companies, and chemical process EPC contractors in India, the USA (DAP delivery to Saint George, Utah and other locations), and the Gulf countries.
Technical Specifications
Chemical Compatibility of Alloy 20
Alloy 20 (CN7M) provides outstanding corrosion resistance in: sulphuric acid (10–98% concentration range, especially above 60%); phosphoric acid; hydrochloric acid (dilute); nitric acid (oxidising); mixed acid streams; chloride-containing environments; and many organic acids. The copper content suppresses corrosion in hot concentrated sulphuric acid in a way that 316 stainless cannot match. Alloy 20 is not recommended for halide-reducing environments or oxidising halide service where Hastelloy C276 or Titanium should be considered.
Applications
- Sulphuric acid plant absorption and drying tower drain and transfer lines
- Oleum (fuming sulphuric acid) handling in fertiliser and mining chemical plants
- Phosphoric acid production and distribution pipelines
- Chlor-alkali spent acid and HCl handling
- Electroplating acid rinse and recovery systems
- Pulp and paper bleaching (chlorine dioxide, dilute H2SO4)
- Reference export project: DAP delivery to sulphuric acid plant, Saint George, Utah, USA
Related Products
Also see: Alloy 20 Valves Overview, PTFE Lined Butterfly Valve, Dual Plate Check Valve.
Frequently Asked Questions
Should a metal-to-metal or soft seat be used for sulphuric acid service?
For concentrated sulphuric acid (above approximately 93% H2SO4), metal-to-metal seating in Alloy 20 is preferred because elastomers (PTFE, EPDM, Viton) are attacked by concentrated acid at elevated temperatures. A metal-seated Alloy 20 check valve maintains seating integrity at temperatures up to 150°C and across the full acid concentration range. For dilute sulphuric acid (below 93%) at ambient temperature, a PTFE seat option provides bubble-tight shut-off with lower leakage rates.
What are the pressure-temperature limits for an Alloy 20 CN7M Class 150 check valve?
Per ASME B16.34 for Group 2.3 (CN7M / Alloy 20), the Class 150 rating at room temperature is 270 psi (18.6 bar). At 100°C the rating is approximately 230 psi (15.9 bar), and at 150°C approximately 205 psi (14.1 bar). These ratings are suitable for most sulphuric acid plant and chemical process operating conditions.
How do I specify an Alloy 20 check valve for ordering?
The minimum information required is: (1) Body material — CN7M (ASTM A351) casting; (2) Valve type — dual plate wafer check; (3) Size in inches or DN; (4) Pressure class (Class 150 standard); (5) Face-to-face per API 594 / MSS SP-125; (6) Seat type — metal-to-metal or PTFE; (7) Process fluid details (acid type, concentration, temperature); (8) Required certifications — EN 10204 Type 3.1 or 3.2. Share this information with us to receive a complete technical and commercial offer.
Need Alloy 20 Check Valves for Acid Service?
Share your process data (acid type, concentration, temperature, pressure, size) and we will provide material confirmation, a technical datasheet, and a competitive quotation. We supply DAP to USA, DDP within India, and FOB for Gulf export.