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For a decade the old Melbourne site sold 316 as “the standard marine grade” and immediately warned that it is not fully resistant to seawater. That warning is the most honest sentence in the stainless trade. “Marine grade” is a nickname. It is not a certificate, not a coating, and not a promise that a polish will stay bright on a pier.
In an Australian warehouse, marine grade almost always means 316 or 316L. Sometimes a salesperson means a 316 fastener (A4). Sometimes they mean a marketing adjective on a barbecue. Your job is to write the number. This journal is an editorial shop, not a merchant. It will not quote a live price and it will not pretend a nickname is a warranty.
The grades and alloys hub sits behind this essay. The marine, balustrade and outdoors hub is where the same nickname walks onto a building.
What 316 does, and what it does not
Molybdenum helps 316 resist pitting in chlorides compared with 304. That is why 304 versus 316 in Australia tells you to pay for 316 on a coastal post. Atlas Steels grade data lists the usual 2% molybdenum band; ASSDA’s public notes treat 316 as the architectural outdoor austenitic, not as armour plate. It is also why tea staining still happens on 316: surface corrosion can bloom as brown stains in a salt-laden film, especially on a rough or horizontal face that never gets washed.
Seawater immersion is a different duty. Warm, aerated, creviced seawater is where 316 fittings pit, gall and disappoint. Boat yards move to 2205 duplex, 6-mo super-austenitics, or non-stainless hardware for some jobs. Read duplex versus 316 if the metal will live wet.
316L is the low-carbon version you should name if the job is welded. Sensitisation in the heat-affected zone is a real mechanism; the L suffix is not decoration. Filler should match — see welding 304 and 316.
Chemistry under the nickname
“Marine grade” does not appear as a UNS number. 316 is UNS S31600 (EN 1.4401); 316L is S31603 (EN 1.4404). Chromium still builds the passive film. Nickel keeps the austenitic structure. Molybdenum raises pitting resistance in chlorides. That is the entire chemical claim hiding inside the sales word.
| Phrase on a docket | What you should hear | What you should write |
|---|---|---|
| Marine grade | Probably 316, maybe a vibe | 316 or 316L, product form, finish |
| Marine grade 304 | A contradiction | Refuse it |
| Marine grade polished tube | Incomplete | 316L, grit or finish, OD × wall |
| A4 / A4-70 | Fastener chemistry aligned with 316 | A4-70 (or the specified class) |
| Duplex marine | A different family | UNS or EN number, not a nickname |
430 is never marine grade. A magnet-hard “marine post” is a documentation failure, not a ferritic success.
Design is part of the grade
A 316 tube with a carbon-steel core, a trapped gasket, or an A2 screw is not a marine assembly. A2 versus A4 fasteners is the cheapest way to undo a good alloy choice. A base plate that ponds water is a crevice you installed on purpose. A grind that left heat tint is a place the passive film is already thin.
Passivate after fabrication — passivation after stainless fabrication is the chemical reset, not a polish. Specify a finish you can wash; finishes 2B, No. 4, BA, No. 8 explains why a mirror is a maintenance contract. Give water a way off the metal. Then write a care note — coastal stainless steel care — into the handover, not into a brochure nobody reads.
Australian coastal chlorides are not a Sydney-only problem. Surf towns, river mouths, and any balcony that sees salt-laden wind share the same film. Inland dry towns are a different specification. The postcode belongs on the order.
Australian places that abuse the nickname
- Surf-club hardware sold as marine grade 304.
- Pool fences in 316 with carbon swarf from a site cut.
- Boat trailers that mix zinc, aluminium and 316 without thinking about galvanic couples.
- Barbecue lids specified in 304 because the lid “isn’t structural,” then parked five streets from the beach.
- “Marine grade” glass standoffs with unlabelled screws from a mixed tin.
The old custom-cut counter in Melbourne at least named 304, 316 and 430. It did not invent a fourth alloy called marine. Keep that habit. Pool and marine fittings live in harder water than air; outdoor kitchens live outside even when the brochure shows a still day.
Failure modes
Tea staining on genuine 316. The alloy is correct. The face holds salt. The client photographs rust. Wash, drain, and stop promising a mirror.
304 renamed. The magnet will not catch this. Identify the grade with paper, a stamp, or a chemical test.
Crevice pitting under a base plate or gasket. Design, not alloy shopping, is the fix. A thicker wall does not drain a cup.
Weld line weaker than the tube. 308 filler on a 316 rail, or heat tint left as a brown rainbow. Dress, match filler, passivate.
Fastener first. A2 screws in a 316 post. The brown dots start at the holes. That is a specification miss, not fate.
Immersion surprise. A 316 fitting left in warm seawater, creviced, uninspected. Boat builders already moved on. A balcony specification does not license a shaft in a pump.
Write the specification, not the vibe
“Marine grade, polished, 50.8 tube” is not a specification. “316L, 320-grit polish, 50.8 × 1.5 mm, A4 fasteners, passivated, coastal balcony, drained base” is. If a merchant can only say marine grade, ask them to print 316 on the docket. If they cannot, you are buying a story.
Name the environment: coastal balcony, pool surround, splash zone, or immersed. Those are different duties. Name the product form: tube, sheet, bar, fastener. Name the finish you can actually maintain. For a 316 balustrade the barrier design is a separate legal job — this journal will not stamp a building.
How to order
- Write 316 or 316L, not marine grade.
- Write the finish and the thickness or wall.
- Write A4 for fasteners on the same job.
- Ask for a mill certificate and a heat number.
- State coastal, pool, or immersed so the fabricator does not treat it like a café bench.
- Require passivation after welding and a wash note at handover.
If the duty is a food room that also sits on the coast, read food-grade stainless in Australia as well. Chlorinated washdown plus salt air is two chloride sources, not one adjective.