No single published standard covers “filter housings for seawater desalination.” What buyers actually work with is a stack of requirements:
The decision that goes wrong most often is the material. A housing marked SS316L is stainless, yet the membrane manufacturer’s own guidance places 316L at the minimum tier for low-salinity service, not at the level it recommends for seawater. This guide shows how to build a defensible specification, where stainless steel housings fit around a desalination plant, and what to include in an RFQ.
In practice, a desalination housing specification combines five layers, and each layer has a different owner:
If treated permeate will be used as drinking water, the owner’s specification may also require drinking-water-contact certification for wetted components. Confirm that requirement at tender stage rather than after fabrication.
The housing exists to hold the cartridge filter that protects the high-pressure pump and membranes. According to DuPont’s FilmTec Reverse Osmosis Membranes Technical Manual, a cartridge filter with an absolute pore size below 10 µm is the suggested minimum pretreatment for every RO system, and 5 µm absolute is recommended. The same manual advises 1–3 µm absolute where colloidal silica or metal silicates create a fouling risk.
That guidance translates into housing requirements:
Cartridge media is also part of the specification. The manual recommends a synthetic, non-degradable material such as nylon or polypropylene, and it does not recommend backflushable filters as the final safety filter.
SS316L is a sensible default for many industrial liquids, but seawater is a different exposure. The DuPont manual treats pitting and crevice corrosion as the main risk and ties its recommendations to the salinity of the concentrate stream:
Seawater feed and brine both sit well above that 7,000 ppm line, so they fall in the higher-alloy tier. The manual’s explicit scope is piping and fittings. Applying the same logic to a filter housing is an engineering inference, but a reasonable one. A housing has a gasket seat, a closure joint, bolted or clamped flanges and stagnant pockets: the same crevice geometry the manual flags.
An illustrative example (hypothetical, not a customer case). A tender sheet asks for “SS316L filter housing, 5 µm cartridges” for the feed to a seawater RO train. A bidder quotes a polished 316L vessel at a competitive price. The unit passes inspection, but nobody matched it to the chloride level at the gasket seat. The buyer saved on unit price and took on a corrosion and replacement risk. Lowest purchase price and lowest lifecycle cost are different things here.
The conclusion is narrow: stainless steel is not wrong, but “stainless” is not a specification. The grade must be named, and it must match the exposure.
The table is qualitative. It does not rank materials by measured corrosion data, which varies by grade, fabrication and operating conditions.
| Material option | Where it is typically considered | Main strength | Main watch-out | Verify with supplier |
|---|---|---|---|---|
| SS304 | Non-chloride utilities, air, general process liquids | Widely available, economical | Not a choice for chloride-bearing seawater service | Exact exposure; is it truly chloride-free? |
| SS316L | Low-salinity duties, cleaning skids, chemical solution filtration | Low-carbon grade suited to welded fabrication | Named by DuPont as the minimum, not the seawater grade | Chloride level, temperature, crevice locations |
| 6% Mo stainless (such as 254 SMO) and similar higher alloys | Seawater-wetted housings and fittings | Named by DuPont for crevice locations in high-TDS service | Higher material cost; fewer fabricators | Grade, mill certificates, weld procedure |
| FRP / GRP | Seawater feed cartridge housings | Non-metallic, so no pitting mechanism | Pressure and temperature limits; shell design basis | Design pressure, manufacturing standard, flange and nozzle design |
| Thermoplastics (PP, PVC, PVDF) | Small or low-pressure housings | Non-metallic | Mechanical and temperature limits | Rated pressure at operating temperature |
Housing material is a project-specific choice. Pore Filtration’s RO protection page notes that plastic, GRP and stainless steel housings are all available, with the choice depending on the raw water source. That is a manufacturer statement rather than an independent standard, but it matches the broader picture: no single material wins in every position.
A desalination plant has many filtration points beyond the seawater feed. Several suit SS304/316L better than the seawater cartridge position does.
| Duty in the plant | Stainless housing fit | What to verify |
|---|---|---|
| Seawater-wetted RO feed cartridge filter | Only with a grade matched to seawater (see above) | Named alloy for every wetted part |
| Cleaning-in-place (CIP) cartridge filter | Good candidate. DuPont’s CIP schematic lists SS as one housing option, alongside PVC and FRP | Cleaning pH range, temperature, chloride in make-up water |
| Chemical solution filtration before dosing | Often suitable for non-seawater liquids | Chemical compatibility of metal and seals |
| Compressed air and gas lines | Suitable where the gas is clean and dry | Rating, media, connection size |
| Plant steam utilities | Suitable for steam duty | Pressure, temperature, element material |
The DuPont manual shows a CIP cartridge filter as 5–10 micron polypropylene with a PVC, FRP or SS housing. It says cleaning solutions can range from pH 1 to 13, so non-corroding materials are needed throughout the cleaning system. It also recommends that a sodium bisulfite solution used for dechlorination be filtered through a separate cartridge before injection into the RO feed. Both are natural jobs for compact stainless cartridge housings, provided the chemistry is checked.
For a cleaning skid or a small dosing line, a CUNO-style single-cartridge stainless steel housing is a typical format. Its product page lists SS304 or SS316L, 10–40 inch cartridges with DOE, 222 or 226 connections, ratings from 0.1 to 200 µm, and limits of 10 bar and 120°C. Where a compact, metal alternative to a polymer Big Blue unit is wanted, the 20-inch Big Blue-style stainless steel housing lists a quick-clamp closure and threaded ports. Its page names the material only as “stainless steel,” so ask which grade is supplied.
When one cartridge cannot carry the flow, a multi-cartridge stainless steel housing combines 3, 5, 7, 11 or 19 cartridges in one vessel. The listed limits are 10 bar and 90°C, so check the temperature ceiling against warm cleaning cycles.
Bag housings are macrofiltration devices. They suit coarse prefiltration of utility and chemical liquids, not the final 5 µm absolute protection step in front of an RO train. Lyfilter’s single-bag formats differ mainly in how liquid reaches the bag and how the cover opens:
Bag ratings are often quoted as nominal, while RO feed protection is specified in absolute terms. Ask which one the datasheet gives.
Sites with steam or compressed air systems have separate duties. A process steam filter housing uses sintered or pleated stainless steel elements and lists limits of 10 bar and 150°C. A T-type stainless steel gas filter housing is a single-cartridge format for compressed air, nitrogen and compatible process gases. These are plant-utility items, not part of the seawater path.
None of the Lyfilter product pages above mention seawater or desalination service. They describe SS304 or SS316L general-industrial housings. Treat them as candidates for the duties in the table, and ask the supplier in writing about any seawater-wetted position.
The cartridge filter sits upstream of the feed pump. The DuPont manual describes feedwater flowing through the cartridge filter to the feed pump, so the housing sees the low-pressure side of the plant. Ten-bar designs may therefore be adequate, but confirm the maximum pressure the supply or booster pump can produce, including shutoff and surge conditions.
Check these items on the datasheet:
Corrosion performance depends on how a vessel is built as much as on the grade. The DuPont manual lists practices that apply directly to housings:
Polishing and electropolishing, which appear as finish options on many housing pages, are separate from passivation. Confirm which is included. Exterior corrosion matters too. The manual notes humid, saline atmospheres and says coatings and regular maintenance can generally control it.
Ask for the paperwork your project requires, typically material certificates, welding records, pressure-test records and dimensional drawings. Define the required set at RFQ stage.
An accurate quotation needs process data as well as dimensions:
Before awarding an order, confirm the following in writing:
Send the completed data to the supplier through the quote form on the relevant product page. Ask for any limitation in seawater service before the purchase order.
No single standard dictates it. Specifications combine the membrane supplier’s feed requirements, corrosion-resistant materials guidance, a pressure-vessel design code set by the project, and chemical compatibility. The owner’s or EPC contractor’s specification usually determines which codes and certificates apply.
DuPont lists 316L as the minimum for pipe systems where concentrate TDS is below 7,000 ppm. For higher-salinity streams it recommends 904L and 254 SMO-type alloys at crevices. Seawater is above that level, so 316L needs written justification from the supplier.
DuPont recommends 5 µm absolute, with a suggested minimum of below 10 µm absolute for every RO system. Where colloidal silica or metal silicates threaten fouling, 1–3 µm absolute is recommended. Confirm the final rating against your membrane supplier’s warranty requirements.
Replace them before differential pressure reaches the permitted limit, and at least every 3 months, per the DuPont manual. If replacement is needed more often than every 1–3 months, the manual says that usually indicates a pretreatment problem rather than a cartridge problem.
Neither is universally better. FRP avoids metallic pitting but has pressure and temperature limits. Stainless steel works only if the alloy matches seawater exposure. Compare design pressure, temperature, alloy grade, documentation and maintenance access for your specific position.
Generally no. Bag housings suit coarse prefiltration. The final protection step before RO is usually a cartridge filter rated 5 µm absolute, per DuPont’s guidance. A bag housing may sit upstream, but check whether its rating is nominal or absolute.
