KOSA Filtration · Material Selection
316L vs 304 Sanitary Stainless: Which Grade to Specify
316L vs 304 sanitary stainless: the molybdenum and low-carbon difference, when 316L (UNS S31603) is required for pharma/food/marine duty, and the standards (ASTM A270/A269, EN 10217-7) KOSA supplies to.
Key Takeaways
- 316L adds 2–3% molybdenum over 304 — that single element is what gives pitting and crevice corrosion resistance in chloride and acidic duty.
- L = low carbon (C ≤ 0.030%): prevents weld-zone sensitization (chromium carbide precipitation) so hygienic lines stay corrosion-resistant after orbital welding.
- For pharma, food, dairy, beverage and marine service, 316L (UNS S31603) is the specified grade; 304 is generally limited to non-corrosive, ambient duty.
What 316L and 304 are
Both are austenitic stainless steels used for sanitary tubing, fittings and vessels. The difference is chemistry: 316L carries molybdenum and tighter low-carbon control; 304 does not.
Composition at a glance
| Element | 304 / 304L | 316L (UNS S31603) |
|---|---|---|
| Chromium (Cr) | 18.0–20.0% | 16.0–18.0% |
| Nickel (Ni) | 8.0–10.5% | 10.0–14.0% |
| Molybdenum (Mo) | — (0%) | 2.0–3.0% |
| Carbon (C), max | 0.030% (304L) | 0.030% |
Why the molybdenum matters
Molybdenum raises resistance to pitting and crevice corrosion — the failure modes that dominate in chloride-bearing process streams (brine, CIP acids, seawater, some food acids). 304 has no molybdenum, so once chloride concentration or temperature rises, its passive film breaks down far sooner. In WFI, CIP/SIP and product contact, that margin is what keeps a line from rusting from the inside.
Why "L" (low carbon) matters for welding
At 500–800°C during welding, carbon in normal 316 can precipitate chromium carbides at grain boundaries — "sensitization" — starving the grain of chromium and creating a corrosion-prone zone next to the weld. Holding carbon at C ≤ 0.030% (the "L" grade) suppresses this, so hygienic 316L lines welded by orbital TIG keep their corrosion resistance without a post-weld solution anneal. This is why ASME BPE and most pharma specifications call for 316L, not 316.
When to specify 316L vs 304
| Service | Recommended grade | Reason |
|---|---|---|
| Pharmaceutical / WFI / SIP | 316L | Chloride + CIP acids; weld integrity (ASME BPE) |
| Food / dairy / beverage | 316L | Cleanability, mild acids, regulatory preference |
| Marine / outdoor washdown | 316L | Seawater chloride resistance |
| Ambient, non-corrosive, dry air | 304 (acceptable) | Cost saving where no chloride/acid |
Grade choice is an acceptance criterion, not a default. State the alloy, standard and surface finish on the spec, and request mill certificates (EN 10204 3.1) with the batch.
Standards KOSA supplies to
Sanitary 316L tube, fittings and valves are typically ordered to ASTM A270 / A269, EN 10217-7, BS 4825, with electropolished Ra 0.25–0.8 µm for high-purity duty. KOSA stocks and fabricates 316L sanitary lines and can supply orbital-welded spools with a surface-finish report.
Need a 316L sanitary line quoted?
Send KOSA your alloy, size, Ra and standard — we return a matched schedule and certification package.
Request a quoteRelated: Electropolished 316L pipe · ASME BPE vs 3-A standards · Technical bulletins
Frequently asked questions
Is 316L better than 304 for sanitary service?
For anything chloride- or acid-bearing (pharma, food, dairy, marine, CIP), yes: 316L's 2–3% molybdenum gives pitting/crevice corrosion resistance 304 lacks. 304 is fine only for ambient, non-corrosive, dry duty.
Can 304 be used in pharmaceutical lines?
Generally no for product/WFI contact. Pharma and ASME BPE service specify 316L (C ≤ 0.030%) so welds stay corrosion-resistant after orbital welding. 304 is reserved for non-corrosive auxiliary duty.
What does the 'L' (low carbon) mean?
L = low carbon, max 0.030%. It prevents weld-zone sensitization (chromium carbide precipitation at 500–800°C), keeping the grain corrosion-resistant without post-weld anneal — essential for hygienic welded lines.
Authoritative references
- ASTM A270 / A269 — seamless austenitic stainless sanitary tubing
- ASME BPE — Bioprocessing Equipment
- 3-A Sanitary Standards
Request a Quote from KOSA
Tell us about your 316L stainless piping, filtration, valve or heat-exchanger requirements. The responsible KOSA specialist will get back to you with a quotation and technical proposal.