304 is fine for normal atmosphere and fresh water; 316L adds molybdenum for clearly better chloride pitting resistance. Use PREN, then check welding and cost.
The first question in choosing 304 or 316L is not price but the chloride level and temperature of the service environment.
PREN (pitting resistance equivalent number) is commonly written as PREN = Cr + 3.3Mo + 16N. Typical 304 grades sit around 18–20, 316L around 24–26; a higher PREN means better pitting resistance.
Practical guidance:
• Indoor, normal atmosphere, fresh water and food contact: 304 is usually sufficient.
• Coastal atmosphere, chloride-containing cleaners, pool areas and chemical media: prefer 316L.
• High chloride with elevated temperature, or crevices: evaluate 2205, 904L or 6% Mo super-austenitic grades.
Two reminders:
1) Molybdenum improves corrosion resistance, but surface condition matters for deep-drawn or highly polished parts.
2) Both grades need controlled heat input when welded; 316L's low carbon reduces intergranular corrosion risk but is not a substitute for solution annealing.
When requesting a quote, state the medium, temperature, chloride content and whether the part is welded — that is more useful than a grade name alone.
