Seawater desalination pumps operate in the most corrosive commercial fluid service on the planet. A pump that handles fresh water reliably will pit and leak within months in seawater. An RFQ that does not specify corrosion-resistant materials, high-pressure testing, and seawater-grade mechanical seals will produce a quote that fails in service.
This checklist covers the pump-specific RFQ points that are unique to desalination — not the general pump procurement steps that apply to every industry.
Seawater's Three Pump-Killing Properties
Before comparing pump quotes, understand what seawater does to pump materials. The RFQ must address all three:
Chloride-induced pitting. Seawater contains ~35,000 ppm chloride. Standard 316L stainless steel will pit within months in seawater, especially at weld heat-affected zones. The wetted parts must be duplex stainless steel (2205) or super duplex (2507) for high-pressure service, or bronze/duplex for lower-pressure intake service.
Biofouling and marine growth. Seawater intake structures grow mussels, barnacles, and algae. Pumps that sit idle for weeks will have impeller passages clogged. The pump should have accessible casing drains and preferably a non-stick coating on the impeller.
High dissolved solids and scaling. RO brine reject has twice the salinity of intake seawater. Pumps handling brine operate at even higher chloride concentrations. Material selection for brine pumps is more demanding than for intake pumps.
By Pump Type: What the RFQ Must Specify
A desalination plant has three distinct pump groups, each with different RFQ requirements.
High-Pressure RO Feed Pumps
This is the most critical pump in the plant. It runs 24/7 at 60–80 bar discharge pressure. Failure means full plant shutdown.
| RFQ Item | Requirement |
|---|---|
| Design pressure | 1.25x operating pressure (safety margin for membrane fouling) |
| Material | Super duplex (2507) or duplex (2205) wetted parts; cast or fabricated |
| Mechanical seal | Double mechanical seal with barrier fluid; Plan 53B for hazardous service |
| Minimum flow | Specify minimum recirculation flow to protect membrane and pump |
| Testing | Hydrotest at 1.5x design pressure; performance test at operating point |
| Efficiency | Specify target efficiency at BEP; ask for pump efficiency curve |
For large plants, the high-pressure RO feed pump is typically a multistage centrifugal pump in vertical or horizontal arrangement. Confirm whether the supplier offers energy recovery device (ERD) integration or whether you will source the ERD separately.
Seawater Intake Pumps
Intake pumps sit at the ocean front, pumping raw seawater through screens and filters to the pretreatment system. They operate at low head (10–30 m) but high flow (thousands of m³/h).
| RFQ Item | Requirement |
|---|---|
| Flow | Plant capacity + 15% overload margin |
| Material | Duplex stainless or bronze impeller; cast iron casing with non-metallic lining |
| Seal | Single mechanical seal with seawater flush; or submersible motor |
| Screening | Confirm whether pump includes suction strainer or if separate |
| Submergence | Specify minimum submergence depth to avoid vortex and air entrainment |
For deep seawater intake, vertical turbine pumps are the standard arrangement. See our vertical turbine pump range for deep-well and intake applications.
Booster and Circulation Pumps
These include pretreatment booster pumps, cartridge filter feed pumps, and post-treatment permeate pumps. They are lower pressure (2–10 bar) and less critical than RO feed pumps, but still handle treated seawater or permeate.
Material for booster pumps: 316L is acceptable for permeate (already desalinated water), but duplex is safer for any brine or concentrate handling. Do not assume that "stainless steel" is enough — ask whether it is 304, 316L, or duplex.
Material Specification: What to Ask For
"Stainless steel" is not a specification. The RFQ must name the exact grade. Here is the standard material selection matrix for desalination service:
| Component | Standard Material | Upgrade Option | Avoid |
|---|---|---|---|
| Casing (high pressure) | Duplex 2205 cast | Super duplex 2507 | 316L (pits in seawater) |
| Impeller | Duplex 2205 | Super duplex 2507 or Ni-hard (for abrasion) | Cast iron (rusts) |
| Shaft | Duplex 2205 | Super duplex 2507 | Carbon steel (corrodes) |
| Bolting | Duplex | Super duplex or Alloy K-500 | 316 (galvanic corrosion) |
| Seal faces | Silicon carbide / SiC | Tungsten carbide | Carbon / ceramic (wears fast in seawater) |
| Gaskets | EPDM | Viton or FFKM for chemical compatibility | Natural rubber (degrades in seawater) |
For plants in corrosive coastal environments with high humidity, also specify external coating on the pump casing and baseplate — epoxy or polyurethane coating on carbon steel external surfaces prevents atmospheric corrosion.
Testing and Documentation for Desalination Pumps
Desalination pumps require more testing than standard industrial pumps. Verify the RFQ specifies:
Hydrostatic shell test: 1.5x design pressure for 30 minutes. No weeping at casing joints or gaskets.
Performance test on water: Run at rated flow and head. Record flow, head, current, vibration. Acceptance: flow within ±5%, head within ±3%, vibration below ISO 10816 Grade A.
Salt spray test (optional but recommended): 48 hours salt spray on wetted material test coupons. Pass criteria: no pitting, no rust on machined surfaces.
Material mill certificates (EN 10204 3.1): Required for all wetted metal parts. The certificate must show actual chemical composition and mechanical properties, not just "meets ASTM A890 4A".
Common Desalination RFQ Mistakes
Mistake 1: Specifying 316L for seawater wetted parts. 316L looks identical to duplex but has much lower chloride pitting resistance. In seawater service, 316L will pit at welds within 6–12 months. The cost premium for duplex is 20–30% of pump price — cheap compared to a pump replacement after one year.
Mistake 2: No ERD integration specification. Energy recovery devices reduce desalination energy use by 40–60%. If the RFQ does not specify whether the RO pump must interface with an ERD (e.g., Pelton wheel, isobaric chamber), the supplier may quote a standard pump that cannot be retrofitted with ERD later.
Mistake 3: Ignoring brine side. Everyone specifies the high-pressure RO feed pump. The brine disposal pump — handling concentrated brine at higher chloride levels — gets less attention but fails just as often. Specify material for brine service separately from intake water.
Mistake 4: No suction condition data. Intake pump performance depends on water level variation (tide), screen pressure drop, and suction piping losses. If the RFQ does not specify maximum and minimum suction water level, the supplier sizes the pump for average conditions — it will lose prime at low tide.
For pump selection and performance verification, use the pump power calculator before issuing the RFQ. For seawater material compatibility, the material corrosion guide lists standard wetted material performance.
Once your operating data and material specifications are complete, submit your desalination pump RFQ for quotation with performance curves and test reports.