Special Alloy Valves
Duplex and super duplex stainless steels contain both ferritic and austenitic phases. Compared with 316 stainless steel, they offer much higher resistance to pitting and stress corrosion cracking and about twice the yield strength, which makes them well suited to seawater, brine and chloride-bearing process lines.
Overview
Duplex (F51 / cast 4A) is preferred for general chloride service, and super duplex (F53, F55 / cast 5A, 6A) for more aggressive environments such as seawater and offshore. Because heat treatment and weld control are critical, ferrite content measurement and ASTM G48 pitting corrosion testing can be added to the quality plan. For a material comparison, see the table on our stainless steel valves page.
Technical specifications
| Forged materials | A182 F51 (2205), F53 (2507), F55 |
|---|---|
| Cast materials | ASTM A995 4A, 5A, 6A |
| Valve types | Ball, gate, globe, check, butterfly |
| Quality control | 100% PMI, ferrite measurement, ASTM G48, EN 10204 3.1 / 3.2 |
| Applications | Seawater, brine, chloride process, offshore, desalination |
Key features
- High resistance to chloride corrosion
- High strength, thinner walls
- Quality verified by ferrite and corrosion testing
Alloy and material program
Body, bonnet and internal parts can be produced as castings or forgings in the alloys below. Material is selected by fluid, concentration, temperature and chloride content; for alloy materials, 100% PMI and EN 10204 3.1 certificates are standard.
| Alloy group | Cast (ASTM) | Forged / bar (UNS) | Typical service |
|---|---|---|---|
| Duplex stainless | A995 4A (CD3MN) | A182 F51 (S31803), F60 (S32205) | Chloride-bearing water, sour service; seawater depending on conditions |
| Super duplex | A995 5A (CE3MN), 6A (CD3MWCuN) | A182 F53 (S32750), F55 (S32760) | Seawater, high chloride, pressurized lines |
| Super austenitic | A351 CK3MCuN (6Mo) | S31254 (6Mo), N08904 (904L) | Seawater, chloride-bearing process fluids |
| Alloy 20 | A351 CN7M | B462 N08020 | Sulfuric acid |
| Ni-Cu (Monel 400 / K-500) | A494 M35-1 | N04400, N05500 | Hydrofluoric acid, seawater, brine solutions |
| Ni-Cr-Mo (Inconel 625) | A494 CW6MC | N06625 | High temperature, chloride and acid mixtures |
| Ni-Mo-Cr (Hastelloy C-276 / C-22) | A494 CW12MW, CX2MW | N10276, N06022 | Wet chlorine, hypochlorite, mixed acids |
| Ni-Fe-Cr (Incoloy 800H / 825) | n/a | N08810, N08825 | High temperature, phosphoric and sulfuric acid |
| Pure nickel | n/a | Ni 200 / 201 (N02200 / N02201) | Caustic (NaOH) service |
| Titanium | B367 (Gr. C-2, C-3, C-5, C-12) | Gr. 2, 3, 5, 7, 12 (B381 / B348) | Seawater, chlorinated media, oxidizing acids |
| Zirconium | n/a | Zr 702, 705 | Hot acids (e.g. acetic and formic acid processes) |
| Nickel-aluminum bronze | B148 C95800 | n/a | Seawater, shipboard systems |
Documentation and testing
On industrial projects the documentation package matters as much as the valve. We confirm the certificate and test scope for every line item at quotation stage:
- EN 10204 3.1 material certificates for pressure-retaining and wetted parts, traceable by heat number
- EN 10204 3.2 with third-party inspection, on request
- Pressure test reports to API 598 or EN 12266-1: shell, seat and, where specified, gas tests
- Fire-test certificates (API 607 / ISO 10497) for fire-safe type-tested designs
- PMI reports for alloy and stainless materials
- Dimensional, visual and coating inspection records
- PED 2014/68/EU CE declaration for equipment within its scope
- NACE MR0175 / ISO 15156 compliance statement for sour (H₂S) service
Technical datasheet
Frequently Asked Questions
What is the difference between duplex and super duplex?
Super duplex contains more chromium, molybdenum and nitrogen; its pitting resistance equivalent number (PREN) is above 40. It is therefore more reliable than duplex in aggressive chloride environments such as seawater.
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