“Stainless steel doesn’t rust” is only half true. By the sea even good stainless steel can pick up brown stains if the wrong grade is chosen or it is poorly finished. The difference between 304 and 316 is the first thing to know.
How they differ
| AISI 304 (1.4301) | AISI 316 (1.4401 / 1.4404) | |
|---|---|---|
| Chromium | about 18% | 16–18% |
| Nickel | 8–10.5% | 10–14% |
| Molybdenum | none | 2–3% |
| Resistance to chlorides (salt) | moderate | high |
| Material price | lower | noticeably higher |
The key difference is molybdenum. It is what resists the pitting corrosion caused by chlorides in sea water. By eye, 304 and 316 look the same.
When 304 is enough
- indoors: stair railings, handrails in the house, kitchens;
- outdoors away from the sea, where rain regularly washes the surface.
When you need 316
- balconies, terraces and pool railings on the coast;
- anything facing the sea or within reach of spray;
- sheltered outdoor parts — under eaves rain does not wash the salt off, so it builds up.
By the sea, 304 usually develops brown staining (so-called tea staining) after the first winter. It is not corrosion through the metal, but it has to be cleaned and it looks poor.
What matters besides the grade
- Surface finish. The smoother the surface, the less salt it holds. By the sea a polished or fine-brushed finish is better than a coarse one.
- Weld treatment. After welding, the weld and the area around it must be cleaned and passivated. Heat tint is the first place rust appears.
- Clean workshop practice. Stainless must never be ground with the same disc or brush as mild steel — iron particles stick to the surface and rust.
- Matching fixings. Screws, brackets and anchors should be the same grade as the railing.
Looking after stainless steel by the sea
Rinse the railing with fresh water a few times a year and wipe it with a soft cloth. Remove stains with a stainless cleaner, never with wire brushes or abrasive pads. Wash sheltered areas more often.
If the railing should be coloured rather than bright, the other route is mild steel with hot-dip galvanising and powder coating. We make 304 and 316 stainless railings to measure — see railings and handrails or send an enquiry through our contact page.
