The stainless steel grade you specify decides how long your filter survives in service — and whether it quietly contaminates your product with rust before it fails. For most filter mesh parts the choice comes down to two families: 304 and 316/316L. Get it right the first time and the part lasts its full design life. Get it wrong and you are re-ordering in months. Here is how we help customers choose.
First, why grade matters more for mesh than for solid parts
Filter mesh is made from very thin wire — often 0.02–0.5 mm in diameter. A solid stainless bracket can afford to lose a few microns of surface to corrosion; a 0.05 mm filter wire cannot. Once corrosion starts to eat a fine wire, the opening size drifts, particles break loose, and the rating you specified no longer holds. That is why grade selection deserves more attention in filtration than in general fabrication.
304: the general-purpose workhorse
SS 304 (18% chromium, 8% nickel — the classic “18/8”) offers good strength, excellent formability and solid corrosion resistance at the lowest cost. It is the right default for:
- Dry filtration, air and gas
- General liquids that are not acidic or salty
- Indoor equipment and machinery
- Applications where chlorides and aggressive chemicals are absent
304L is the low-carbon version. It resists carbide precipitation (“sensitisation”) in the heat-affected zone, so we prefer it when a 304 part is welded — for example a welded disc ring or a light cylinder seam.
316 / 316L: corrosion resistance where it matters
The key difference is molybdenum. 316 adds roughly 2–3% Mo, which sharply improves resistance to chlorides, acids and pitting. Choose 316/316L for:
- Marine environments and seawater
- Chemical and pharmaceutical processing
- Food and beverage contact
- Any wet, salty or corrosive medium
316L (low carbon, ≤0.03% C) further resists corrosion in and around welds, so it is our default for welded assemblies — cylinders, baskets and multilayer sintered packs — where a plain 316 weld seam could become the first point of attack.
The numbers behind the choice: PREN
Engineers who want one number to compare pitting resistance use the Pitting Resistance Equivalent Number:
PREN = %Cr + 3.3 × %Mo + 16 × %N
| Grade | Cr | Mo | Approx. PREN | Plain-language pitting resistance |
|---|---|---|---|---|
| 304 / 304L | ~18% | 0% | ~18–20 | Good in clean, dry, low-chloride duty |
| 316 / 316L | ~16–18% | ~2–3% | ~24–28 | Much stronger against chlorides & acids |
A higher PREN means the steel tolerates more chloride before pitting begins. The jump from ~19 to ~25 is exactly why 316 survives where 304 slowly pits.
A quick decision guide
| Your service condition | Recommended grade |
|---|---|
| Dry, indoor, general use | 304 |
| Welded part, otherwise mild duty | 304L |
| Wet, outdoor, mild chemicals | 316 |
| Chlorides, acids, seawater, welded parts | 316L |
| Food, pharma, high-purity | 316 / 316L |
Cost vs. lifetime — the calculation we run with customers
316L typically costs 30–50% more than 304 in mesh form. That premium looks large on a quote and small over a service life. In a genuinely corrosive duty, 316L often lasts several times longer and — just as important — avoids product contamination from rust particles shedding off a corroding 304 screen. When the medium is wet, salty or acidic, the upgrade almost always pays for itself. When it is dry and clean, paying for 316 is money left on the table.
A worked example. A customer specified 304 filter discs for a coastal water-treatment skid to save cost. The salt-laden air pitted the fine wires within a season and fines began passing downstream. Re-tooling in 316L cost about 40% more per disc but ended the replacements and the contamination complaints. The “cheaper” grade had been the expensive choice.
Common mistakes we help customers avoid
- Speccing 304 for a “mild” chemical that contains chlorides. Even dilute chlorides pit 304. Check the medium, not just the industry.
- Using plain 316 for a welded basket. The weld zone can sensitise — 316L is the safer default for anything welded.
- Assuming higher grade = higher rating. Grade controls corrosion life, not filtration fineness. Your mesh count / micron rating sets the rating; grade sets how long that rating survives.
How we back the grade you choose
Whatever grade you specify, we provide material test reports (MTRs) for the stainless we supply, so the certificate reflects the material actually in your part — see our Quality & Certifications page. If you are unsure, tell us the medium, temperature and environment, and we will recommend the grade and document it.
This grade choice applies across every form we make — filter discs, cylinders and tubes, cartridges and strainer baskets. If you are still weighing woven against a bonded pack, our guide on woven vs. sintered mesh pairs naturally with this one.
Not sure which grade your duty needs? Send us the medium, temperature and environment, and we will recommend the right material — and quote within 24 hours.