SS 904L vs 316L: when is 904L worth the extra cost?
316L (PREN ≈ 24) is the standard molybdenum stainless for chloride-bearing water, food, pharma and general chemical service. 904L (PREN ≈ 35) adds far more nickel, more molybdenum and copper: choose it for dilute sulphuric and phosphoric acid, warm chlorides and where 316L has suffered pitting or stress-corrosion cracking. It costs significantly more because of its nickel and molybdenum.
Chemistry side by side
| Element | 316L (S31603) | 904L (N08904) |
|---|---|---|
| Chromium | As specified | As specified |
| Nickel | As specified | As specified |
| Molybdenum | As specified | As specified |
| Copper | — | As specified |
| Carbon | As specified | As specified |
| PREN (approx.) | ≈ 24 | ≈ 35 |
Under technical review for TDS. Numerical specification requirements are published only after the applicable current standard edition has been verified.
Governing specification: ASTM A240.
Side by side: composition and pitting resistance
Corrosion: where the difference shows
Sulphuric acid. 904L was developed for dilute sulphuric acid; its copper and high nickel keep corrosion rates low in concentrations and temperatures where 316L corrodes quickly.
Chlorides. With about 25% nickel and high molybdenum, 904L resists pitting, crevice corrosion and chloride stress-corrosion cracking much better than 316L — useful in warm brackish and chloride-bearing cooling water.
Where 316L is enough. Potable and process water with modest chlorides, food and dairy, pharmaceutical utilities and most atmospheric service.
Strength and physical properties
| Minimum property (plate, A240) | 316L | 904L |
|---|---|---|
| Tensile strength | As specified | As specified |
| Yield strength 0.2% | As specified | As specified |
| Elongation | As specified | As specified |
| Density | 8.0 g/cm³ | 7.95 g/cm³ |
| Magnetic | No (annealed) | No (annealed) |
Under technical review for TDS. Numerical specification requirements are published only after the applicable current standard edition has been verified.
Standards for each product
Welding
Both weld readily. 904L is fully austenitic and more sensitive to hot cracking, so it is welded with low heat input, low interpass temperature and matching ER385 filler; for severe chloride service ERNiCrMo-3 is often used instead.
A simple rule
- Water, food, pharma and mild chemicals: 316L.
- Dilute sulphuric or phosphoric acid, warm chlorides, 316L has pitted: 904L.
- Chloride stress-corrosion cracking with high strength needed: consider duplex 2205.
- Acid plus chlorides or H₂S beyond 904L: Alloy 825.