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.
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.