Desalination Plant Pipe Material Selection Guide
Desalination plants combine high chloride concentrations, elevated temperatures, and high operating pressures. Material selection directly impacts plant reliability, maintenance costs, and 25+ year service life.
Desalination Process Zones
| Process Zone | Chloride Environment | Recommended Material | PREN Required |
|---|---|---|---|
| Seawater Intake | Seawater, ambient temp | Duplex 2205 | ≥ 35 |
| Pre-treatment / Filtration | Filtered seawater | 316L / Duplex 2205 | ≥ 26 |
| RO High-Pressure Feed (60-80 bar) | Seawater, 60-80 bar, 20-30°C | Super Duplex 2507 | ≥ 40 |
| RO Permeate (Fresh Water) | TDS ≤ 500 ppm | 316L | ≥ 26 |
| Brine Discharge | 60,000+ ppm TDS, concentrated | Super Duplex 2507 / 254 SMO | ≥ 40 |
| MED / MSF Evaporator | Hot brine, 70-110°C | Super Duplex 2507 / Titanium Gr.2 | ≥ 40 |
| Chemical Dosing | Acids, anti-scalants, chlorine | Alloy 825 / Hastelloy C-276 | ≥ 45 |
Why Super Duplex for RO High-Pressure?
SWRO plants operate at 60-80 bar on the membrane feed side. At these pressures, 316L requires very thick walls — uneconomical and difficult to fabricate. Super duplex 2507 (yield strength 550 MPa vs 316L's 170 MPa) allows significantly thinner walls, reducing pipe weight by 50-60%. This saves material cost, welding time, and structural support requirements.
550 MPa
Super Duplex 2507 Yield Strength
50-60%
Weight Reduction vs 316L
PREN ≥ 40
Critical for Brine & Hot Seawater
316L in Desalination: Know the Limits
316L is acceptable for: permeate (fresh water) lines, low-pressure pre-treatment piping at ambient temperature, and non-critical utility lines. Never use 316L for: brine discharge lines, RO high-pressure feed, or any service above 30°C with chloride concentrations exceeding 1,000 ppm. Crevice corrosion under gaskets and deposits is the primary failure mode — 316L has zero crevice corrosion resistance in seawater above 25°C.
Related Resources
Duplex 2205
PREN 35
Super Duplex 2507
PREN 42
Desalination Industry
Solutions & Projects
SWRO Case Study
UAE Mega Plant
Frequently Asked Questions
What materials are used for desalination piping (SWRO, MSF, MED)?
Desalination piping sees high chlorides (about 19,000 ppm) plus oxygen, temperature, and biofouling. Standard: duplex 2205 (PREN about 35) for most seawater lines; super duplex 2507 (PREN about 40–42) for higher velocity, hot spots, and high-pressure RO feed; 904L or 6Mo (254SMO) for acidic or organic-rich streams; CuNi 90/10 for low-velocity intake, brine, and condenser tubes where biofouling resistance helps. TOKO TECH supplies 2205 and 2507 pipe, fittings, and flanges with PMI and seawater-service MTCs for SWRO, MSF, and MED plants.
Why specify duplex or super duplex for seawater desalination?
Seawater demands high pitting and crevice resistance. Duplex 2205 (PREN about 35) resists chlorides to a critical pitting temperature around 60–70°C; super duplex 2507 (PREN about 40–42, at least 25% Cr, 3.5% Mo, 0.25% N) extends that to about 80°C and higher velocities. Their strength also lets walls thin, saving weight on skids and offshore modules. TOKO TECH stocks both as pipe, butt-weld fittings, and flanges with EN 10204 3.1 and PMI of Cr, Mo, and N.
Where is CuNi 90/10 used in desalination plants?
CuNi 90/10 (C70600) is valued in desalination for natural biofouling resistance and tolerance of turbulent, aerated seawater at low-to-moderate velocity (below about 3 m/s to avoid erosion-corrosion). It is used for intake screening, low-pressure brine, and condenser tubes rather than high-pressure RO feed. It does not need chlorination for fouling control but is softer and costlier per MPa than duplex. TOKO TECH supplies CuNi 90/10 pipe and tube with certification for seawater service where its antifouling edge matters.
How do chlorination and dechlorination affect desalination materials?
Desalination chlorinates intake water (0.5–1 mg/L free Cl2) to control biofouling, then dechlorinates (SO2 or MB) before RO membranes. Materials must survive alternating oxidizing, chlorinated, and dechlorinated conditions. Duplex, super duplex, and 904L handle both; CuNi tolerates chlorination better than stainless but avoid high residuals. TOKO TECH specifies grades that remain passive across the chlorination and dechlorination swing so membranes and pipes are not compromised.
What is the crevice corrosion risk in desalination piping?
Crevice corrosion is the top failure mode in desalination — under deposits, gaskets, flange faces, and at tube or tubesheet joints. Require high PREN (at least 32 for 2205, at least 40 for 2507), smooth finishes, and proper gasket and flange design with controlled crevices. Avoid carbon steel and low-alloy in seawater wetting. TOKO TECH supplies crevice-resistant duplex and advises flange-face finish and gasket type to minimize crevice sites in SWRO and MSF or MED trains.
What PREN is required for seawater desalination service?
As a rule, seawater service should use PREN at least 32; for warm (above 25°C), high-velocity, or high-chloride concentration points specify PREN at least 40 (super duplex 2507 or 6Mo). MSF and MED operate hotter than SWRO, pushing toward 2507 in hot brine; SWRO high-pressure feed also favors 2507. TOKO TECH verifies actual Cr plus 3.3Mo plus 16N chemistry by PMI and reports measured PREN so designers meet the plant's corrosion envelope.