Grades 304 and 316 are the two most widely used austenitic stainless steels in piping. They look identical and have similar strength, but the difference in chemistry makes a real difference in service.
The key difference: molybdenum
304 is the classic 18/8 stainless steel, with about 18% chromium and 8% nickel. 316 has slightly less chromium (16–18%), more nickel (10–14%) and, most importantly, 2–3% molybdenum. Molybdenum greatly improves resistance to pitting and crevice corrosion in chloride environments such as seawater, brackish cooling water and many chemical processes.
One way to compare pitting resistance is the PREN (Pitting Resistance Equivalent Number). 304 sits at around 18–20 and 316 at around 23–25.
What the "L" means
304L and 316L are low-carbon versions, with carbon held to 0.03% maximum. Lower carbon reduces chromium carbide formation during welding (sensitisation), which protects the weld zone from intergranular corrosion. That is why L grades, or dual-certified 304/304L and 316/316L, are the norm for welded piping. Our IGC (intergranular corrosion) test checks exactly this property.
Common ASTM specifications
| Forged flanges & fittings | ASTM A182 F304 / F304L, F316 / F316L |
|---|---|
| Buttweld fittings | ASTM A403 WP304 / WP304L, WP316 / WP316L |
| Pipe | ASTM A312 TP304 / TP304L, TP316 / TP316L |
How to choose
- Choose 304/304L for fresh water, food and beverage, general process and indoor or mild atmospheric service, where it offers good value.
- Choose 316/316L for chlorides, coastal and marine exposure, chemical and pharmaceutical plants, and wherever pitting is a risk.
- Look beyond 316 to duplex or super duplex when chloride levels, temperature or strength requirements exceed what 316 can handle.
Not sure which grade your line needs? Our team can help you compare options and verify grade with PMI testing before dispatch.
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