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Thread Protection on Galvanising.

Thread Protection on Galvanising.

(OP)
We have to drill and tap lots of M8 threaded holes in Galvanised steel RSJ beams to fix some open flooring panels to the top of it .
The fixings being used are M8 A4 Stainless steel bolts and we want to apply something to the tapped hole prior to fitting the bolts to stop the tapped hole from rusting .
The installation will be typically outside in a water treatment facility , it will be out of the water but exposed to the elements .
We know you could in theory use Galvifroid spray on each tapped hole to add back in protection but this can look unsightly and wondered if there was a better paste or sealant we could use to try and seal the thread.
Any help would be appreciated .

Regards Chris

RE: Thread Protection on Galvanising.

If your beams are mild and your fasteners are stainless, your anode/cathode area ratio is in the right direction to minimize corrosion. To eliminate it completely you have a few options-

1) Switch to zinc-coated fasteners to reduce the magnitude of the galvanic couple. High quality zinc dichromate fasteners can give very good corrosion performance.

2) Switch from tapped connections to bolted connections, with barrier tape or plastic washers (no metal-to-metal contact, eliminate the galvanic couple)

3) Coat the threads and washer contact area with a sealant, as you have already described. Eck or Galvifroid are both available in cans, so that you can brush it on for a neater appearance. Depending on the loads on the fastener, the thread contact pressure *may* squeeze out some or all of a liquid coating, allowing metal-to-metal contact.

RE: Thread Protection on Galvanising.

As alternative choice to the above comment, go for Ceramic, Xylan or Fluorocarbon coating on the bolting.

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