What is the difference between SS 304 and SS 316?

316 contains 2-3% molybdenum and 304 contains none. Molybdenum improves resistance to chloride pitting corrosion. 316 also has slightly less chromium than 304 (16-18% against 18-20%), trading chromium for molybdenum.

Should I use 304 or 316 for coastal or marine applications?

Use 316. Airborne salt reaches well inland, and 304 in coastal exposure commonly shows tea-staining within a year or two.

Is 316 better than 304 for high temperature service?

No. For sustained high temperature the relevant grades are 321, 347H and 310S. Choosing 316 for heat resistance is a common mis-specification.

Should I specify 304L or 316L instead?

If the component will be welded, yes. The low-carbon L grades suppress chromium carbide precipitation at the weld zone, which otherwise leaves it vulnerable to corrosion. For welded fabrication in corrosive service the real choice is usually 304L versus 316L.

SS 304 vs SS 316: Which Grade Do You Need?

The short answer. If the material will meet chlorides — salt air, seawater, brine, swimming pools, de-icing salt, many process chemicals — specify 316. If it will not, 304 will almost certainly do the job for materially less money. Everything below is the reasoning behind that rule and the cases where it breaks down.

The one difference that matters: molybdenum

304 and 316 are both austenitic 18/8-type stainless steels and are similar in strength, formability and weldability. The meaningful difference is that 316 contains 2–3% molybdenum and 304 contains none.

Chloride ions attack the passive chromium-oxide layer that makes stainless steel stainless. They do it locally, producing pitting — small deep holes rather than general thinning. A pit can perforate a pipe wall while the surrounding surface still looks perfect, which is what makes chloride attack dangerous: it fails without warning. Molybdenum substantially improves the passive layer's ability to resist that local breakdown and to repair itself.

Note that 316 has slightly less chromium than 304 (16–18% against 18–20%). 316 is not simply "more alloyed". It trades a little chromium for molybdenum, and in chloride service that trade is strongly worth making.

Composition and PREN tables are being prepared. Numeric data is awaiting verification against the current edition of ASTM A312 before publication. Contact us for grade data in the meantime.

Where each one belongs

Specify 304 when

The environment is indoor, dry, or fresh water
Food and beverage processing without salt or acidic brines
Architectural and structural work away from the coast
General fabrication, frames, handrails, equipment housings
Budget matters and chlorides genuinely are not present

Specify 316 when

Marine, coastal or offshore installations
Seawater, brine, or chlorinated water
Chemical and pharmaceutical process lines
Pulp and paper, dyeing, and acidic process chemistries
Exterior architecture within a few kilometres of the sea
Anywhere a failure would be expensive or dangerous to reach

Four things that catch people out

1. Coastal air counts as chloride exposure

Airborne salt reaches well inland. Balustrades and cladding in 304 within sight of the sea commonly show tea-staining — brown surface rust — within a year or two. It is usually cosmetic rather than structural, but on architectural work the client will regard it as a failure.

2. If it will be welded, consider the L grades

Welding heats the parent metal through a range where chromium carbides form at grain boundaries, locally depleting chromium and leaving the weld zone vulnerable — sensitisation. The low-carbon variants 304L and 316L cap carbon to suppress it. For welded fabrication in corrosive service, the real choice is usually 304L versus 316L rather than 304 versus 316.

3. 316 is not the high-temperature answer

For sustained high-temperature service the relevant grades are 321 (titanium-stabilised), 347H (niobium-stabilised, with controlled carbon for creep strength) and 310S (high chromium and nickel for oxidation resistance). Reaching for 316 because it is "the better grade" is a common and expensive mis-spec.

4. Neither grade is immune to chloride SCC

Austenitic stainless steels are susceptible to chloride stress corrosion cracking above roughly 60 °C under tensile stress. 316 is somewhat better than 304, but not immune. Where hot chlorides and stress occur together, the answer is usually a duplex grade rather than either of these. Tell us the service conditions and we will say so rather than sell you 316 and hope.

Cost

316 carries a consistent premium over 304, driven by molybdenum and a higher nickel content, and the gap moves with alloy surcharges rather than staying fixed. Specifying 316 where 304 would serve is a real and recurring waste; specifying 304 where 316 is needed is far more expensive once replacement and downtime are counted. Ask us for both prices against your actual sizes and we will quote them side by side.

Not sure which one your application needs?

Tell us what the material will be exposed to — the medium, temperature, whether it will be welded, and whether chlorides are present — and we will tell you which grade fits, including when the answer is neither of these two.

Ask our technical team