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When using weathering steel (COR-TEN) on a project, what sort of bolts should I be using?

I have yet to see fixings made of weather steel; presumably because the way it uses a sacrificial layer to form a protective rust coating makes it unsuitable for precision applications (such as bolt threads; maintaining the structural area, etc.).

I am also aware that mixing different metals; even various steel alloys, can lead to accelerated corrosion due to anodic/cathodic behaviour.

So what type of bolts should be specified with weathering steel?

thomasmichaelwallace
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4 Answers4

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For structural applications (in the US), the most common bolt for weathering steel is ASTM A 325 Type 3.

Type 1 is a plain steel bolt that can be galvanized, but in this situation the zinc in the galvanizing will quickly be used trying to protect the rest of the structure.

Update for British bolts

Interestingly, the only option for UK seems to be to get these same bolts in metric (M24) size. References:

hazzey
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WR grade bolts are available in the UK in 1/4 inch imperial size HSFG (when imported from America) and also in M24 TCB's, both of which are used regularly in bridge steelwork in the UK.

user1515
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Re-iterating some of above as manufacturer I can advise that Weathering Steel TCBs are generally available in M24 diameter only, with the following lengths: 70, 80, 90, 100, 105, 110, 120, 125, 130, 140, 150, 160, 170, 180, 190, 200, 220, and 240 mm.

CSK & alternative diameters can be manufactured bespoke - dependant on quantity. Galv / Zinc Flake / GK Coatings in WS structures are susceptible to bi-metallic corrosion.

Wasabi
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Arnie Glausiusz
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I assumed you'd use normal bolts, but use a nylon washer to electrically insulate the bolt from the weathering steel (in order to avoid bi-metallic corrosion).

AndyT
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