The difference between 304 and 316L comes down to one element: 316L contains 2–3% molybdenum (Mo). Molybdenum's role is resistance to pitting and crevice corrosion, so this judgment line is essentially not about "whether to choose better" but about "whether there is chlorine in the medium."
One-Sentence Judgment
When in contact with chloride-containing media (seawater, brine, sodium hypochlorite, hydrochloric acid mist, food sauces) or when the temperature is persistently above 60℃ and chloride ions > 200 ppm, use 316L. For pure water, atmosphere, dry indoor environments, and general food contact, 304 is sufficient.
Three Common Misjudgments
- "Use 316L near the coast" is too coarse: 316L is only necessary within 5 km of the sea where salt accumulates on the surface (sea-facing facades, railings); inland factories using 304 for ten years show no rust.
- For welded structures, prefer 304L over 304: 304 precipitates chromium carbides 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 will fail first: under flange gaskets, where brackets meet the plate surface, even in atmospheric environments, chloride concentration can cause pitting. Eliminating crevices structurally (continuous welding, adding drainage holes) is more effective than upgrading the grade.
| Condition | Recommendation | Notes |
|---|---|---|
| Indoor dry, decorative parts | 304 | Cost priority; 2B / HL surface both acceptable |
| Food contact, dairy, beer | 316L | Cleaners contain chlorine; 304 will show pitting |
| Coastal curtain walls, railings | 316L | Surface requires regular rinsing; otherwise salt accumulation sites corrode first |
| Chemical media, chlorine >200 ppm | 2205 | PREN ≈ 34; 316L about 25 |
| High-temperature flue gas, desulfurization | 316L / 2205 | Dew point condensate pH can be as low as 2–3 |
How to view cost: 316L is about 30–40% more expensive than 304 (molybdenum and nickel). The cost of one unplanned shutdown and replacement usually far exceeds the price difference of the entire batch of material — so in situations where chlorine may be present, we recommend 316L by default and write the basis for the judgment in the quotation remarks, rather than letting the customer guess.
If you need to confirm the operating 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 standards.
