Is Alloy 20 required for sulfuric acid check valves?

For many concentrated and hot dilute sulfuric acid duties, Alloy 20 (UNS N08020 / CN7M) outperforms SS316. Confirm concentration, temperature, and velocity with corrosion data before finalising MOC.

What size Alloy 20 dual plate check valves are commonly stocked?

Supreme Valves lists ready stock in 2 inch (DN50) and 4 inch (DN100) Class 150 wafer dual plate Alloy 20 check valves. Other sizes are manufactured to order.

Alloy 20 Dual Plate Check Valve for Sulfuric Acid Service

Technical guide · Supreme Valves India · September 2026

Plant and EPC buyers searching for an Alloy 20 dual plate check valve usually need a short-pattern non-return valve that survives sulfuric acid where austenitic stainless steel fails. This article covers material choice, dual-plate vs swing check, and how to write a clear RFQ.

Product page: Alloy 20 Dual Plate Check Valve — MOC, API 594 / API 598 specs, and ready stock in 2 inch and 4 inch Class 150.

Why Alloy 20 (CN7M / N08020)

Alloy 20 is a nickel-chromium-molybdenum-copper austenitic alloy. Cast valve bodies are typically ASTM A351 CN7M; wrought parts follow UNS N08020 (ASTM B462 / B473). Copper in the alloy improves sulfuric acid resistance across a wide concentration range. For acid plant pump discharge, dilution lines, and copper leach raffinate, Alloy 20 is a standard MOC when SS316 shows pitting or high corrosion rates.

Dual plate wafer check vs swing check

A dual plate (dual disc) wafer check uses two spring-assisted plates in a short API 594-style body that bolts between flanges. Benefits in acid service:

Short face-to-face — less piping stress and easier retrofit
Spring-assisted closure — less slam and water hammer on pump trip
Lower weight than a same-size swing check

Swing checks remain correct on some horizontal large-bore lines. If the datasheet says dual plate / dual disc / wafer check, specify full Alloy 20 wetted parts (body, plates, hinge pins, seats) and an Inconel spring for acid duty.

Standards to put on the PO

Design / face-to-face: API 594 wafer dual-plate practice
Test: API 598 shell and seat
Flanges: ASME B16.5 Class 150 (or as per piping class)
Material certs: EN 10204 3.1; PMI optional but recommended for Alloy 20

Sizes that move fastest

Enquiry volume concentrates on 2 inch and 4 inch Class 150 wafer dual plate Alloy 20 checks for skids and headers. Supreme Valves currently holds ready stock in these two sizes. Other NPS and Class 300 / 600 are built to order.

RFQ checklist

NPS / DN and quantity
Class and flange standard
H2SO4 concentration, temperature, solids
Metal seat or stellited facing
Delivery location / Incoterms
ITP: hydro, PMI, third-party witness

Send the checklist to info@supremevalves.in or open the Alloy 20 dual plate check valve product page to enquire.