316/316L Stainless Steel Flanges
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316L flanges – when molybdenum matters
1.4404 (AISI 316L), X2CrNiMo17-12-2, is an austenitic stainless steel with 2–2.5% molybdenum and low carbon. Molybdenum raises resistance to pitting and crevice corrosion in chlorides, while low carbon protects the heat-affected zone against intergranular corrosion after welding. That is why 316L flanges are specified for chloride-bearing water, brines, food and chemical media and CIP cleaning systems. Most flanges in this category are dual-certified 1.4401 / 1.4404 (316 / 316L) and meet the requirements of both grades.
Chemical composition of 1.4404 / 316L
| Grade | C | Cr | Ni | Mo |
|---|---|---|---|---|
| 1.4404 / 316L | ≤ 0.030 | 16.5–18.5 | 10.0–13.0 | 2.0–2.5 |
| 1.4301 / 304 (for comparison) | ≤ 0.07 | 17.5–19.5 | 8.0–10.5 | – |
Values in wt. % per EN 10088. Equivalents: 1.4404 = X2CrNiMo17-12-2 = AISI 316L = UNS S31603; forgings per ASTM A182 – F316L.
Types, sizes and pressure ratings
The category covers forged flanges in three designs: slip-on plate flanges from DN15 to DN300, weld neck flanges from DN15 to DN250 and blind flanges from DN15 to DN150, matching pipe from 21.3 to 323.9 mm OD. Pressure ratings are PN6, PN10, PN16 and PN40 per EN 1092-1. The DN/PN pair sets the bolt circle and the number of bolt holes, so both must match the mating flange. Allowable working pressure drops as temperature rises – for hot service, check it in the tables of the standard.
Installation and welding
A weld neck flange is joined to the pipe with a butt weld, which makes it the most reliable option under higher pressure, vibration and fluctuating temperature. A plate flange slips over the pipe and is fillet-welded, which is sufficient for low-pressure systems. 316L welds well by TIG or MIG, usually with 316L filler metal. Heat tint and scale must be removed by pickling or pickling paste, since this is where pitting most often starts.
Pipe and fittings in the same grade
To go with 316L flanges, choose 316L / 1.4404 pipe & tube and 316L / 1.4404 elbows. For higher service temperatures, see 316Ti / 1.4571 flanges; for chloride-free media, 304 / 1.4301 flanges will do. All flange types are in the Flanges category.