The difference between 304 and 316L comes down to one element: 316L contains 2–3% molybdenum (Mo). Molybdenum resists pitting and crevice corrosion, so the real question is not "do we want something better" but "is there chloride in the medium".
One-line decision
Use 316L when in contact with chloride-containing media (seawater, brine, sodium hypochlorite, hydrochloric acid mist, food sauces) or when the temperature stays above 60℃ with chloride > 200 ppm. For pure water, atmosphere, dry interiors and general food contact, 304 is sufficient.
Three common misjudgements
- "Use 316L on the coast" is too crude: 316L is only necessary within 5 km of the sea where salt accumulates on the surface (sea-facing facades, railings); inland plants using 304 show no rust for ten years.
- For welded structures prefer 304L over 304: in 304, chromium carbide precipitates in the weld heat-affected zone, causing chromium depletion; 304L (C ≤ 0.03%) largely avoids this. This point is more often overlooked than "304 or 316L".
- 304 in crevices fails first: under flange gaskets, where brackets meet the sheet surface, even atmospheric conditions can cause pitting through chloride concentration. Eliminating crevices structurally (continuous welding, drain holes) is more effective than upgrading the grade.
| Condition | Recommendation | Notes |
|---|---|---|
| Indoor dry, decorative parts | 304 | Cost first; 2B / HL finish both fine |
| Food contact, dairy, beer | 316L | Cleaners contain chlorine; 304 will show pitting |
| Coastal curtain walls, railings | 316L | Surface needs regular rinsing, otherwise salt deposits corrode first |
| Chemical media, chloride >200 ppm | 2205 | PREN ≈ 34, 316L about 25 |
| High-temperature flue gas, desulphurization | 316L / 2205 | Dew-point condensate pH can drop to 2–3 |
How to view cost: 316L costs about 30–40% more than 304 (molybdenum and nickel). The cost of one unplanned shutdown and replacement usually far exceeds the price difference of the whole batch — so where chloride is possible, we recommend 316L by default and write the basis for the decision in the quotation remarks, rather than letting the customer guess.
If you need to confirm the service conditions, tell us the four points: medium composition, temperature, whether welded, and whether crevices exist; we can directly give a grade recommendation and the corresponding acceptance standard.
