My understanding is the rust layer prevents further oxidation, so the reaction stops.
But if that layer is disturbed, away she all starts again.
We did some industrial buildings using exposed columns back in the day.
Ended up blasting/painting them after endless complaints from anyone who brushed against a columns.
Does not have to be a flaky rust surface, but I believe an oxidised surface which can be pretty tough.. The extra cost over normal steel is negligible..
I have seen cattle crates made out of corten and there is no denying how much longer they last compared to normal steel... It is just a pity the corten thickness range is so limited... We had to go for 6mm thick.... 3mm would have been too thin for putting heavy loads like tractors on the tray... Neighbour used aluminium in their truck and bowed the tray between the supports when putting their tractor on it... Plus I would not be surprised if aluminium has galvanic corrosion issues if not properly installed with anodes...
From previous experience, steel fabricated lightly constructed items tie themselves in knots as soon as they hit the hot tank.
All the welding stresses relieve with disastrous results.
Plus you'd be pressed to find anyone with a tank big enough to do it in one hit, double dipping always looks crook.
For the same end result, I'd use a blast then hot zinc metal spraying.
Such a big area of plate though, it will cost.
Jeffo,The reason I mentioned it, Is. I know of a couple of fairly new rigid Stock Trucks with Hot dipped Galvanized Trays, One has an Aluminium Floor in It, Not too sure about the other one.
The points you raise make sense, though.
From memory the trays were done in Albury, as they have a Vat big enough to do it in one go.
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