SS304 and SS316 are both austenitic stainless steel pipes under ASTM A312; SS316 contains 2 to 3 percent molybdenum that SS304 lacks, giving substantially better chloride-pitting and crevice-corrosion resistance for marine, dairy CIP and chloride-bearing service. Tensile and yield are nearly identical and SS316 carries a 30 to 40 percent cost premium worth it only when chlorides are present.
SS304 vs SS316 — composition and properties
| Attribute | SS304 / 304L | SS316 / 316L |
|---|---|---|
| Chromium % | 18.0 – 20.0 | 16.0 – 18.0 |
| Nickel % | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum % | None (trace only) | 2.0 – 3.0 |
| Carbon max (standard) | 0.080 % (0.030 % for 304L) | 0.080 % (0.030 % for 316L) |
| Tensile strength min | 515 MPa (75 ksi) | 515 MPa (75 ksi) |
| Yield strength min | 205 MPa (30 ksi) | 205 MPa (30 ksi) |
| Magnetic in anneal | No (austenitic) | No (austenitic) |
| Chloride pitting | Poor (< 200 ppm Cl⁻) | Good (up to ~1000 ppm Cl⁻ ambient) |
| Marine atmosphere | Not recommended | Recommended baseline |
| Cost premium | Baseline | +30-40% over SS304 |
| Primary applications | Food, pharma, decorative, neutral-pH chemical | Marine, dairy CIP, brewery, sterile pharma, chloride service |
The molybdenum difference — what 2 to 3 percent buys
Molybdenum in austenitic stainless stabilises the passive chromium-oxide film against chloride attack. SS304 in chloride-bearing service (above roughly 200 ppm Cl⁻ at ambient, lower at elevated temperature) develops pinhole pitting and, under tensile stress, chloride stress-corrosion cracking. SS316 with 2 to 3 percent Mo extends safe service to roughly 1000 ppm Cl⁻ at ambient and gives meaningful protection in marine atmosphere, dairy CIP wash, brewery clean-in-place chemistry and brine handling. The pitting-resistance equivalent number (PREN = Cr + 3.3 × Mo + 16 × N) rises from about 19 for SS304 to about 26 for SS316.
When to choose SS304
If the service is neutral-pH water, food handling without salt brines, pharma WFI loops in soft-water plants, non-chloride chemical lines, decorative architectural railings or general-purpose stainless utility, SS304 is the right pick. The molybdenum-free chemistry costs 30 to 40 percent less per kg than SS316 and the corrosion performance is identical in chloride-free service. For pure water, sugar syrup, edible oil, vegetable processing and most cosmetic / pharma feedstock, SS304 (or SS304L for welded lines) is the industry default.
When to choose SS316
Move to SS316 when chlorides enter the service envelope. Coastal installations within about 5 km of seawater (the salt-laden atmosphere alone justifies the upgrade), dairy and brewery CIP lines, sterile-pharma loops with chloride-bearing buffer salts, marine deck piping, brackish-water and brine handling, and most pharmaceutical product-contact loops above 25 NB. The cost premium is real but the failure cost from a chloride-attack leak in a sterile or food-grade loop is many multiples higher.
304L vs 316L — low-carbon variants for welded service
Welding austenitic stainless can sensitise the heat-affected zone — chromium combines with carbon to form chromium carbides at grain boundaries, locally depleting the chromium that the passive film needs and leaving the weld zone vulnerable to intergranular corrosion. The L-grades (304L, 316L) cap carbon at 0.030 percent versus the standard 0.080 percent, suppressing carbide precipitation and protecting the weld zone. For any welded stainless line above about 25 NB that will see corrosive service, specify the L-grade — the cost difference is small and the welding insurance is real. Many mills now supply “dual-grade” 304/304L and 316/316L material that meets both specs simultaneously.
FAQ — SS304 vs SS316 procurement
What is the difference between SS304 and SS316 stainless steel pipe?
Is SS316 always better than SS304?
Are SS304 and SS316 magnetic?
What is the difference between SS304 and SS304L, SS316 and SS316L?
When should I specify SS316 for marine or coastal service?
Related pages
Updated: