304 vs 316 Stainless Steel Pipe
Same minimum strength, nearly the same pressure rating, different corrosion behaviour. What the molybdenum buys, and why the L grade question matters more than the 304-versus-316 one.
- Key difference
- 316 adds 2–3% molybdenum
- Chloride pitting
- 316 markedly better
- Cost premium
- 316 roughly 20–30% over 304
- Strength
- Identical specified minimums
- B16.5 group
- 304 is Group 2.1, 316 is Group 2.2
Short answer. 304 and 316 have the same specified minimum strength at room temperature, but ASME B16.5 puts them in different material groups: 304 in Group 2.1 and 316 in Group 2.2. Their flange ratings are equal at 100 °F and 316 rates higher when hot, by up to 25 psig in Class 300 at 850 °F. The main difference is chemistry: 316 contains 2–3% molybdenum, which markedly improves resistance to chloride pitting and crevice corrosion. Use 304 for clean, dry and non-chloride service; use 316 wherever chlorides, seawater, or aggressive process chemistry are present.
Molybdenum is the whole story
Both are austenitic 18-8 type stainless steels — roughly 18% chromium, 8–10% nickel — relying on a passive chromium oxide film for corrosion resistance. Chloride ions attack that film locally and start pits. Molybdenum stabilises the film against exactly that attack, which is why 316 survives coastal atmospheres, brackish water and chloride-bearing process streams that pit 304.
Neither grade is immune to chloride stress corrosion cracking, which is a different mechanism and remains the characteristic failure mode of austenitic stainless above about 140 °F in chloride service. Where that is the risk, the answer is a duplex grade such as 2205, not a step from 304 to 316.
| Specification | Form | Tensile min | Yield min | Typical temperature range | Notes |
|---|---|---|---|---|---|
| ASTM A312 TP304 | Pipe | 75 ksi | 30 ksi | -425 to 1500 °F | General-purpose austenitic stainless. Sensitises if welded and held at 800-1500 °F. |
| ASTM A312 TP304L | Pipe | 70 ksi | 25 ksi | -425 to 800 °F | Low-carbon 304 for welded assemblies; resists weld decay. |
| ASTM A312 TP316 | Pipe | 75 ksi | 30 ksi | -425 to 1500 °F | Adds 2-3% molybdenum for chloride pitting resistance. |
| ASTM A312 TP316L | Pipe | 70 ksi | 25 ksi | -425 to 850 °F | Low-carbon 316. The default stainless for welded chemical process piping. |
| ASTM A790 S31803 | Pipe | 90 ksi | 65 ksi | -60 to 600 °F | Duplex, commonly sold as 2205 (strictly, 2205 is UNS S32205, at 95/65 ksi). Roughly twice the yield of 316L with far better chloride SCC resistance. |
Strengths are specified minimums in ksi. 1 ksi = 1000 psi = 6.895 MPa.
The L grades matter more than 304 vs 316
Holding an austenitic stainless between roughly 800 and 1500 °F — which welding does, either side of the bead — precipitates chromium carbides at the grain boundaries and strips those boundaries of the chromium that was protecting them. The result is intergranular attack alongside the weld, called sensitisation or weld decay. The low-carbon L grades hold carbon low enough that there is little to precipitate.
For welded piping the practical default is 316L, which is why it is the most commonly stocked stainless pipe grade. The cost of the L grade is a lower allowable stress — B16.5 puts the L grades in Group 2.3, below both 304 and 316:
| Temperature | Class 300 Group 2.1 (304) | Class 300 Group 2.2 (316) | 316 against 304 | Class 300 Group 2.3 (304L, 316L) |
|---|---|---|---|---|
| 100 °F | 720 psig | 720 psig | 0% | 600 psig |
| 200 °F | 600 psig | 620 psig | +3% | 510 psig |
| 300 °F | 540 psig | 560 psig | +4% | 455 psig |
| 400 °F | 495 psig | 515 psig | +4% | 420 psig |
| 500 °F | 465 psig | 480 psig | +3% | 395 psig |
| 600 °F | 440 psig | 450 psig | +2% | 370 psig |
| 650 °F | 430 psig | 440 psig | +2% | 365 psig |
| 700 °F | 420 psig | 435 psig | +4% | 360 psig |
| 750 °F | 415 psig | 425 psig | +2% | 355 psig |
| 800 °F | 405 psig | 420 psig | +4% | 345 psig |
| 850 °F | 395 psig | 420 psig | +6% | 340 psig |
Group 2.1 covers F304 and F304H; Group 2.2 covers F316, F316H and F317; Group 2.3 covers the L grades, with no B16.5 rating published above 850 °F and 304L limited to 800 °F.
Choose 304 / 304L when
- The service is clean water, steam condensate, food or pharmaceutical without chlorides
- The environment is dry and inland
- Cost matters and the corrosion case does not demand moly
- Cryogenic service — both grades are tough to −425 °F
- Nitric acid and other oxidising acids, where 304 is actually the better choice
Choose 316 / 316L when
- Chlorides are present in any concentration worth measuring
- The plant is coastal or marine
- The service is a process chemical, sour, or reducing
- The line handles seawater, brine, or treated effluent
- The pipe is insulated — chlorides concentrate under insulation as moisture evaporates
A note on cost
316 typically runs 20–30% above 304 for the same item, and the premium tracks the nickel and molybdenum markets rather than staying fixed. On a large project the difference is real money — but a chloride pitting failure in a process line costs more than the entire material premium, so the corrosion case should decide this and not the budget.
See also: carbon steel vs stainless · 5S vs 10S · B36.19M stainless · material grades.
Common questions
What is the main difference between 304 and 316 stainless?
316 contains 2–3% molybdenum, which substantially improves resistance to chloride pitting and crevice corrosion. Specified minimum strength is the same; flange pressure ratings are equal at 100 °F and slightly higher for 316 when hot.
Is 316 stainless stronger than 304?
Not at room temperature: both A312 TP304 and TP316 specify 75 ksi tensile and 30 ksi yield minimum. When hot, 316 keeps its strength a little better, which is why B16.5 puts it in Group 2.2 and rates a Class 300 flange at 450 psig at 600 °F against 440 psig for 304 in Group 2.1.
Should I use 316 or 316L?
316L for anything welded, which is nearly all piping. The low carbon prevents sensitisation at the weld. The cost is a slightly lower allowable stress, since B16.5 puts the L grades in Group 2.3.
Will 316 stainless resist seawater?
Better than 304, but not indefinitely. In stagnant or crevice conditions 316 still pits in seawater. Continuous seawater service normally calls for a duplex, super-duplex or 6-moly grade.
Does 316 prevent chloride stress corrosion cracking?
No. Both 304 and 316 are susceptible above roughly 140 °F in chloride service. Duplex grades such as 2205 are the usual answer where SCC is the governing risk.