GRADE PROFILE
316L stainless steel — 1.4404 / X2CrNiMo17-12-2
316L is 304L with 2 to 2.5% molybdenum added. That single difference in composition lifts the PREN from 19 to 25 and opens up the moderately chlorinated media that 304L cannot handle. It is the most ordered grade in industrial piping — and the most frequently over-specified.
- Austenitic
- PREN 24–26
- Cost index 130
- Welded · Seamless · Heat exchanger
- Ø 6 to 610 mm
When to choose it
Wherever chlorides are present and stay moderate. Process piping in chemicals and pharmaceuticals, food processing where cleaning cycles introduce chlorine, heat exchangers on industrial water, sanitary networks. This is where molybdenum earns its price: it stabilises the passive film in conditions where a 304L film breaks down locally and a pit starts.
316L also makes sense when the grade is not really the issue but the installation is mixed. On an existing 316L network, dropping to 304L for one section creates a dissimilar-metal couple and a discontinuity in the certificate trail, for a saving nobody will notice on the accounts.
The L suffix is not cosmetic. At 0.030% carbon maximum, the grade resists chromium carbide precipitation at grain boundaries as a weld cools. On site-welded piping, with no possibility of heat treatment after assembly, that is what prevents intergranular corrosion next to the weld.
When not to choose it
In seawater. A PREN of 25 sits far below the 40 commonly required for that service, and 316L pits within months. This is the most frequent and most expensive specification error in this range: duplex 2205 or super duplex 2507 are the grades for that job, not 316L.
In concentrated chlorides at temperature, for the same reason. Above roughly 60 °C, temperature lowers the chloride threshold the grade tolerates, and water that passed in winter no longer passes in summer. Chloride stress corrosion cracking is the other failure mode of austenitics in these conditions, and it is brutal: cracking with no visible loss of metal.
In hydrochloric acid, at any concentration and any temperature. No austenitic stainless holds that medium; it is the domain of nickel alloys, C-276 in particular.
And finally, with no chlorides at all. On a fresh water network, a structure, a support or non-chlorinated food processing, 316L costs 30% more than 304L for identical service. Molybdenum is only worth paying for when it works.
Composition
| Element | % |
|---|---|
| C | ≤ 0.03 |
| Cr | 16.5–18.5 |
| Ni | 10–13 |
| Mo | 2–2.5 |
| Mn | ≤ 2 |
| Si | ≤ 1 |
| P | ≤ 0.045 |
| S | ≤ 0.015 |
| N | ≤ 0.11 |
Mechanical properties
We only publish mechanical properties tied to a specific standard and product form — welded tube, seamless tube and bar do not share the same values, and the gap routinely exceeds 30%. The figures that apply to your specification appear on the material certificate; ask us at enquiry stage.
Designations and standards
| Reference | Designation |
|---|---|
| EN (numeric) | 1.4404 |
| EN (symbolic) | X2CrNiMo17-12-2 |
| ASTM / AISI | 316L |
| UNS | S31603 |
| JIS | SUS316L |
| AFNOR | — |
Tube product standards :
- EN 10216-5
- EN 10217-7
- ASTM A312
- ASTM A213
- ASTM A249
- ASTM A270
Availability
Welded, seamless and heat exchanger tube, Ø 6 to 610 mm, plus fittings, flanges and bar. Partner stock or mill depending on the size and quantity: no restriction in principle, we source against the requirement. EN 10204 3.1 material certificates supplied with the goods.
Related grades
- 304L (1.4307) — the same grade without molybdenum, 30% cheaper. Worth comparing every time before ordering 316L: with no chlorides in the medium, 304L is the answer.
- 1.4435 — a 316L with higher molybdenum and nickel (PREN 26 to 28), carrying the same AISI and UNS without being interchangeable.
- Duplex 2205 (1.4462) — the step up when chlorides exceed what 316L can hold — PREN 35, and close to double the yield strength, which often allows a thinner wall.
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Frequently asked questions
- 316L or 304L — how do I decide?
- On the presence of chlorides, and nothing else. With none, 304L gives the same service for around 30% less. With chlorides, even moderate ones, 304L pits and the 316L premium is the cheaper of the two options. Everything else — weldability, fabrication, appearance — is equivalent.
- Are 1.4404 and 1.4435 the same thing?
- No, and it is an expensive trap: both carry AISI 316L and UNS S31603. 1.4435 has 2.5 to 3% molybdenum against 2 to 2.5%, and 12.5 to 15% nickel against 10 to 13%. Some pharmaceutical specifications call for it explicitly, particularly on delta ferrite content. If your specification says 1.4435, a 1.4404 is not compliant — even where the certificate reads "316L".
- Is 316L suitable for seawater?
- No. Its PREN of 25 is far below the threshold of 40 commonly required for seawater. That is the domain of duplex 2205, super duplex 2507, 254 SMO or copper-nickel depending on flow velocity and temperature.
- What does the L in 316L mean?
- Carbon limited to 0.030% instead of 0.08% for standard 316. It reduces the risk of chromium carbide precipitation as a weld cools, and therefore of intergranular corrosion. On piping welded without post-weld heat treatment, this is the version to specify.