Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Super Duplex 2507 in Desalination Plants
Super Duplex 2507 (UNS S32750 / EN 1.4410) is a workhorse alloy in modern desalination plants where chloride concentration in concentrate (brine) reaches 60,000 to 80,000 ppm and process temperatures climb above ambient. PREN above 41 and a critical pitting temperature above 50 degrees Celsius per ASTM G48 Method E let 2507 handle multi-stage flash (MSF) brine recirculation, multi-effect distillation (MED) shells and tubes, and reverse-osmosis (RO) high-pressure trains where 316L pits within months and 6Mo austenitic carries a price premium that programme economics often cannot absorb.
TorqBolt supplies 2507 pipe, fittings, flanges, fasteners, plate, and forgings to desalination EPCs and operators globally. Material is dual certified to ASTM A790 / A815 / A182 F53 / A1082 with EN 10204 Type 3.1 mill test certificates as standard, Type 3.2 third-party-witnessed available where the project specification calls for it.
Why Super Duplex 2507 in Desalination
Desalination loads sit at the intersection of three corrosion drivers: high chloride, elevated temperature, and dissolved oxygen. Material selection criteria:
- Chloride pitting and crevice resistance in brine concentrates (PREN, CPT). 2507 holds CPT above 50 degrees Celsius per ASTM G48 Method E.
- Resistance to chloride stress corrosion cracking in hot brine. The duplex microstructure is far more resistant than austenitic 304L / 316L, both of which crack readily in hot chloride.
- Erosion-corrosion limit at high-velocity brine return lines. 2507 tolerates continuous service to about 6 m/s.
- Fatigue and pressure capacity at RO design pressures. 2507 minimum yield is 550 MPa, roughly twice that of 316L, which lets designers reduce wall thickness on high-pressure RO piping.
- Cost vs 6Mo / titanium. Where chloride and temperature combination is acceptable for 2507, the alloy avoids the 25 to 40 percent premium of 6Mo austenitics and the 60+ percent premium of grade 2 titanium.
Super Duplex 2507 Desalination Design Data
| Parameter | Value | Reference |
|---|---|---|
| PREN | 41 to 43 | Cr + 3.3 times Mo + 16 times N |
| CPT (ASTM G48 Method E) | Greater than 50 degrees Celsius | ASTM G48-11 |
| MSF top brine temperature | Up to about 110 degrees Celsius | Typical MSF cycle |
| MED shell-side temperature | 60 to 70 degrees Celsius (top effect) | Typical MED cycle |
| RO high-pressure side | Up to about 70 bar (1015 psi) for seawater RO | SWRO membrane housings |
| Brine chloride at concentrate | 60,000 to 80,000 ppm | Typical SWRO recovery 40 to 50 percent |
| Maximum continuous service temperature | 250 degrees Celsius (sigma-phase risk above 300) | NORSOK M-630 |
| Hardness limit (sour, where applicable) | 28 HRC max | NACE MR0175 / ISO 15156-3 |
Where Super Duplex 2507 Is Specified in Desalination
- MSF brine recirculation piping handling top brine at up to 110 degrees Celsius. 2507 replaces 316L (which pits under chloride and oxygen) and is competitive with 904L below the 6Mo CPT line.
- MSF heat-rejection section tubes and tubesheets where brine and seawater meet. 2507 forged tubesheets and welded tubes are specified to ASTM A789 / A815.
- MED evaporator shells and falling-film tubes on the brine side. Process temperatures and chloride combine in a band well-suited to 2507.
- RO high-pressure feed piping on the membrane side, typically 50 to 70 bar. The high yield strength of 2507 lets designers cut wall thickness vs 316L.
- RO membrane pressure-vessel end-closures and connector hardware in 2507 forgings.
- RO concentrate (brine reject) piping handling the most concentrated chloride stream in the plant. 2507 is the standard pick where temperature stays below about 45 degrees Celsius.
- Energy recovery device (Pelton turbine, isobaric ERD) housings and connecting piping.
- Brine outfall manifolds and dilution diffusers in subsea installations.
- Pre-treatment and dosing skid manifolds exposed to coagulant chemistry, FeCl3, and seawater simultaneously.
Super Duplex 2507 vs Competing Alloys in Desalination
| Alloy | PREN | CPT (G48 E) | Cost Index | Desalination Verdict |
|---|---|---|---|---|
| 316L (austenitic) | ~25 | About 15 degrees Celsius | 1.0 | Pits under brine; only acceptable in cold low-chloride streams |
| 904L (austenitic) | ~35 | About 35 degrees Celsius | 1.6 to 1.8 | Marginal for SWRO brine; better in MED low-temp effects |
| 2205 duplex | 34 to 38 | About 30 degrees Celsius | 1.5 to 1.8 | Good for low-temperature seawater intake; insufficient for hot brine |
| Super Duplex 2507 | 41 to 43 | Above 50 degrees Celsius | 2.0 to 2.5 | Standard pick for SWRO high-pressure, MSF, MED brine duties below 60 degrees Celsius brine temp |
| 6Mo (254 SMO, AL6XN) | 43 to 45 | About 60 degrees Celsius | 2.5 to 3.0 | Used where brine temperature pushes past the 2507 envelope |
| Titanium grade 2 | Not pitting-controlled | Effectively immune | 3.5 to 4.5 | Reserved for hot brine condensers and MSF heat input sections |
Super Duplex 2507 Installation Notes for Desalination
- Welding per NORSOK M-601 with filler ER2594 (overmatching) for brine duty; heat input 0.5 to 2.5 kJ per millimetre, interpass below 150 degrees Celsius. See welding procedure.
- Pickling and passivation after fabrication: 20 percent nitric plus 5 percent HF, then citric or nitric passivation. Carbon-steel tool contamination during fab causes pitting initiation in service.
- Crevice management at gasketed flanges. Spiral-wound CG gaskets with PTFE or graphite fill minimise crevice geometry vs flat-sheet rubber.
- RO high-pressure flanges sized to ASME B16.5 Class 600 or 900 depending on operating pressure. 2507 weld-neck flanges to ASTM A182 F53.
- Hydrotest with low-chloride water (less than 30 ppm chloride) and complete drain plus dry-out within 24 hours of test. Stagnant high-chloride hydrotest water is the most common cause of pre-commissioning pitting.
- Bolting per ASTM A1082 / API 20F in matching S32750. PTFE thread lubricant on assembly.
Recommended TorqBolt 2507 Products for Desalination
- 2507 pipe: ASTM A790 seamless and welded for brine and RO high-pressure lines
- 2507 fittings: ASTM A815 WP-S32750 buttweld elbows, tees, reducers
- 2507 flanges: ASTM A182 F53 weld neck and blind for RO trains
- 2507 stud bolts: ASTM A1082 / API 20F for pressure-vessel and flange connections
- 2507 heavy hex nuts: ASTM A1082 in matching S32750 chemistry
- 2507 flat washers: UNS S32750 chemistry
- 2507 bar and forgings: ASTM A479 / A182 F53 for tubesheets and end-closures
Related Application Pages
- Seawater applications: sea-chest, fire-water, lift systems
- Marine and offshore: subsea hardware, christmas trees
- FGD: wet flue gas desulfurization
- Chemical processing: dilute HCl, H2SO4, HF service
- NACE MR0175 compliance: sour-service rules
Super Duplex 2507 Desalination FAQ
Why is Super Duplex 2507 used in SWRO high-pressure piping instead of 316L?
Two reasons. First, brine on the concentrate side reaches 60,000 to 80,000 ppm chloride, which sits well above the pitting threshold of 316L (PREN around 25). Second, 2507 yield strength is roughly twice that of 316L, which lets designers cut wall thickness and reduce installed cost on Class 600 / 900 RO pipework.
Is Super Duplex 2507 suitable for MSF top brine at 110 degrees Celsius?
2507 is acceptable for MSF brine recirculation up to about 110 degrees Celsius if dissolved oxygen is controlled and chloride does not climb beyond design assumptions. Where the operator runs higher temperatures or higher recovery ratios, 6Mo or titanium should be evaluated on a stage-by-stage basis. NORSOK M-630 limits continuous service to 250 degrees Celsius; sigma-phase risk above 300 degrees Celsius is the long-term ceiling.
What is the maximum design pressure for 2507 RO high-pressure piping?
SWRO trains typically operate at 60 to 70 bar (about 870 to 1015 psi) on the membrane side. ASME B31.3 design with ASTM A790 pipe and A182 F53 flanges to Class 600 or Class 900 covers the standard pressure envelope. Energy recovery devices (Pelton, isobaric ERD) reduce parasitic load but do not change the pipework rating.
How does 2507 compare against 6Mo (254 SMO) for brine service?
6Mo has slightly higher PREN (43 to 45 vs 41 to 43) and higher CPT (about 60 vs 50 degrees Celsius), and it costs 25 to 50 percent more. For SWRO brine at ambient to warm temperature, 2507 delivers equivalent service life at lower installed cost. 6Mo is preferred where brine temperature exceeds 50 degrees Celsius or where chloride is concentrated above 80,000 ppm.
Can 2507 be used in MED falling-film evaporator tubes?
Yes, in the lower-temperature effects where shell-side temperature stays below 70 degrees Celsius. Top-effect MED tubes are commonly aluminium brass, copper-nickel, or titanium where heat-transfer coefficient drives the choice. 2507 is most useful in the brine-distribution piping and pump trims rather than the heat-transfer surface itself.
What welding filler is correct for 2507 in desalination service?
ER2594 (overmatching, slightly higher PREN than the base) per AWS A5.9 is the standard pick. ER2553 (matching) is acceptable for less aggressive duty. Heat input 0.5 to 2.5 kJ per millimetre, interpass below 150 degrees Celsius. Argon plus 2 to 5 percent nitrogen shielding for GTAW root pass to maintain austenite balance in the weld metal.
What hydrotest precaution applies to 2507 in desalination plants?
Use low-chloride hydrotest water (below 30 ppm chloride per ASTM A380), drain completely within 24 hours, and dry the system. Stagnant high-chloride hydrotest water against unpassivated weld surfaces is the most common cause of pre-commissioning pitting in 2507 systems. Where low-chloride water is unavailable, dose with sodium nitrate (per NACE SP0298) to suppress pitting during the test.
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