High strength bolt coating ASTM A490 & A354BD

[NewENG102]

I know typically high strength bolts are not to be zinc galvanized due to hydrogen embitterment, what coating options can be used to prevent rusting due to weather?

Typically these bolts are to be plain/black finish. Which means no coating, maybe a slight dip in oil.
I have some of these plain finish bolts which are showing sign of rust, what options do I have to prevent further rust?

 

[EdStainless]

There are metallic coatings like ASTMB994 (a Ni-Co alloy) that work well.
There are also the fluropolymer coatings that work well also.

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P.E. Metallurgy, Plymouth Tube

 

[Screwman1]

You can also use mechanical zinc or one of the dip spin (Magni, Doerken) type of finishes. Lots of options.

 

[NewENG102]

Great- Thank you both for your answers.

 

[UcfSE]

I spec Dacromet or Geomet usually.

 

[Billybaru]

Suggest reading ASTM F3125, which covers the "A490" structural bolts, especially Annex A1 as this lists acceptable coatings for this grade of bolt. Both mechanical zinc and hot-dip galvanized coatings are not permitted on A490 bolts. ASTM A354 is not as restrictive on coatings. Note 1 - ASTM F3125 was first published in 2015 and combines all the structural bolting standards (such as A490). Note 2 - Dacromet is no longer available in most, if not all countries, due to environmental reasons (contained Hexavalent Chromium). Believe NOF Metal Coatings no longer produces the Dacromet coating chemicals.