ASTM A790 2507 Duplex Stainless Steel Pipe For Water Desalinisation
ASTM A790 UNS S32750 / 2507 Duplex Stainless Steel Pipe for Water Desalination
ASTM A790 2507 duplex stainless steel pipe is a super duplex pipe product specified for seamless and straight-seam welded ferritic/austenitic stainless steel pipe used in corrosive service, especially where chloride-induced pitting, crevice corrosion, and stress corrosion cracking are design concerns. For seawater desalination, UNS S32750 is one of the most proven material choices for high-pressure piping, reverse osmosis skids, seawater transfer lines, and heat-exchanger service because it combines a high PREN level, minimum 0.2% proof strength of 550 MPa, and strong resistance in aggressive chloride-bearing media.
Specifications
| Item | Description |
|---|---|
| Material | Super duplex stainless steel pipe |
| Grade | UNS S32750 / 1.4410 / 2507 |
| Standard | ASTM A790 / ASME SA790 |
| Manufacturing | Seamless or straight-seam welded pipe |
| Outside Diameter | Custom production; seamless tube/pipe commonly supplied up to 260 mm OD |
| Wall Thickness | Customized to schedule / pressure class / project drawing |
| Length | 1-12 m, custom cut lengths available |
| Tolerance | According to ASTM A790 purchase specification and agreed dimensional standard |
| Straightness | Mill standard or project-specific requirement |
| Surface Condition | Solution annealed, white pickled, or bright annealed |
| Heat Treatment | Solution annealed and rapidly cooled |
| Typical Desalination Service | SWRO high-pressure piping, seawater transport pipe, RO pressure-vessel piping, heat-exchanger tubing |
Main Features
- High localized corrosion resistance in chloride media
SAF 2507 has a nominal chemistry of about 25% Cr, 4% Mo, and 0.3% N, and Alleima reports a minimum PRE value of 42.5 for seamless tubes, placing it firmly in the super duplex class for severe seawater duty. - High strength for pressure-bearing desalination lines
In the solution-annealed condition, tube and pipe up to 20 mm wall thickness have minimum yield strength 550 MPa, minimum 1.0% proof strength 640 MPa, tensile strength 800-1000 MPa, and minimum elongation 25%. - Strong resistance to chloride stress corrosion cracking
ASTM A790 itself emphasizes corrosive service with particular attention to SCC, while duplex/super duplex grades are widely selected where austenitic grades are vulnerable in chloride-rich systems. - Suitable for seawater reverse osmosis systems
ISSF’s desalination guidance notes that super duplex stainless steel is used in high-pressure piping on the seawater reverse osmosis side because it resists the severe corrosivity of seawater together with the required operating pressure. Alleima also lists desalination plants, pressure vessels for RO units, seawater transport pipe, and heat exchanger tubing among typical SAF 2507 applications. - Good fabrication and weldability when properly controlled
IMOA’s fabrication guidance notes duplex grades require controlled fabrication practice, especially heat input and post-fabrication metallurgical balance, which is critical for maintaining corrosion performance in desalination assemblies.
Our Advantages
1) Concern: “Will the pipe resist pitting and crevice corrosion in warm seawater and brine?”
Yes. The key engineering basis is the super duplex chemistry itself. SAF 2507 has a minimum PRE value of 42.5 for seamless tubes, and duplex guidance from the Nickel Institute identifies super duplex grades with PRE around 40 or higher as commonly selected for seawater-exposed and other severe chloride applications.
2) Concern: “Will it handle RO system pressure without forcing excessive wall thickness?”
Yes. UNS S32750 offers minimum 550 MPa yield strength and 800-1000 MPa tensile strength in tube/pipe form, which gives designers much more mechanical margin than standard austenitic stainless steels and often supports lighter, more compact pressure piping designs.
3) Concern: “Is 2507 actually used in desalination service, or only described that way in theory?”
It is used in real desalination duty. ISSF states super duplex stainless is used in SWRO high-pressure piping, and Alleima explicitly lists reverse osmosis pressure vessels, seawater transport tube/pipe, and desalination plant service for SAF 2507.
Execution Standards
| Standard System | Relevant Standard | Brief Description |
|---|---|---|
| ASTM / ASME | ASTM A790 / ASME SA790 | Seamless and welded ferritic/austenitic stainless steel pipe for corrosive service, especially SCC-sensitive duty |
| EN | EN 10216-5 / EN 10217-7 | Seamless / welded stainless steel tubes for pressure purposes; widely used for duplex stainless piping in Europe |
| GOST | GOST 9941 / GOST 9940 | Corrosion-resistant stainless seamless pipes, cold- and hot-deformed supply routes |
| JIS | JIS G3459 | Stainless steel pipes for corrosion-resistant, low-temperature, elevated-temperature and similar piping service |
| GB | GB/T 14976 | Seamless stainless steel pipes for fluid transport |
Application Field
Seawater reverse osmosis high-pressure piping spool
A typical single-product application is the high-pressure piping spool between the RO high-pressure pump discharge and the membrane pressure-vessel header, where the pipe must withstand chloride-rich seawater, elevated pressure, and long-term corrosion-fatigue risk. ISSF and Alleima both identify this type of SWRO duty as a core use case for super duplex stainless steel.
Chemical Composition
The table below gives representative chemistry for five commonly referenced duplex and super duplex grades used for comparison in procurement and engineering selection. Values are nominal or standard-grade ranges from the cited grade datasheets.
| Grade | UNS / EN | Cr (%) | Ni (%) | Mo (%) | N (%) | Mn (%) | Cu (%) | W (%) | C max (%) | Notes |
|---|---|---|---|---|---|---|---|---|---|---|
| LDX 2101 | S32101 / 1.4162 | 21.0-22.0 | 1.35-1.70 | 0.10-0.80 | 0.20-0.25 | 4.0-6.0 | 0.10-0.80 | — | 0.040 | Lean duplex |
| 2304 | S32304 / 1.4362 | 22.5 | 4.5 | 0.3 | 0.1 | ≤2.0 | 0.3 | — | 0.030 | Lean/standard duplex |
| 2205 | S32205 / 1.4462 | 22 | 5 | 3.2 | 0.18 | ≤2.0 | — | — | 0.030 | Standard duplex |
| 2507 | S32750 / 1.4410 | 25 | 7 | 4 | 0.3 | ≤1.2 | — | — | 0.030 | Super duplex |
| ZERON 100 / F55 | S32760 / 1.4501 | 24.0-26.0 | 6.0-8.0 | 3.0-4.0 | 0.20-0.30 | ≤1.0 | 0.50-1.00 | 0.50-1.00 | 0.030 | Super duplex with Cu + W |
Mechanical Properties
| Grade | UNS | 0.2% Yield Strength | Tensile Strength | Elongation | Hardness |
|---|---|---|---|---|---|
| LDX 2101 | S32101 | ≥65 ksi / 450 MPa | ≥94 ksi / 648 MPa | ≥30% | 290 HB max |
| 2304 | S32304 | ≥400 MPa | 630-820 MPa | ≥25% | 30 HRC max |
| 2205 | S32205 | ≥485 MPa | 680-880 MPa | ≥25% | 28 HRC max |
| 2507 | S32750 | ≥550 MPa | 800-1000 MPa | ≥25% | 32 HRC max |
| ZERON 100 / F55 | S32760 | ≥550 MPa | 800-1000 MPa | ≥20% | 230 HB max |
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