Neoprene and Nylon insulating washers for galvanic corrosion

[yahoo123]

Does anybody know how strong neoprene and nylon washers are? What if I need to torque them beyond snug-tight (e.g. pretension or slip-critical connections)?

Can these washers handle the stress? Does anybody know what their strength properties are?

I would like to use these to seperate SS bolts from aluminum or galvanized steel members.

Thanks

 

[MintJulep]

Don't use them on a joint that you want to stay tight.

 

[dimjim]

You want washers with mechanical properties greater than the bolts. Plastics will not do it.

 

[CoryPad]

You either need to use similar materials for all joint members, or use a metallic insert in the polymeric washers. That way, the insert takes the preload and the polymer insulates. However, sealing performance would be very important. All in all, it usually makes sense just to use similar materials for the fasteners and clamped members.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SJones]

Research NEMA LI-1 Grade G10 or Grade G11 materials for insulating washers (and maybe sleeves if you can't prevent contact further down the thread), along with use of metallic washers over the non-metallics against the bearing surface of the bolts.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[gr2vessels]

yahoo123,
There is a number of companies specialised in supplying insulating washers, sleeves, gaskets, etc..Check out one of the many sites, refer below:

http://www.farwestcorrosion.com/fwst/insulate/psi12.htm

cheers,
gr2vessels

 

[Metalguy]

Is this app. in submerged sea water, etc? Sounds like your anode/cathode ratio is fine, so you may not have a problem w/o insulating items.

Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling

 

[yahoo123]

Does it make a difference if it is submerged? IF it is submerged does it even help by isolating the materials since current will conduct through water?

 

[MarkAJohn]

I don't know what your application is, but I would be surprised if there is much (if any) test data on Slip-critical connections made with dis-similar materials. Pre-tensioned connections, on the other hand, may not need to be pre-qualifed.

MJ

 

[gr2vessels]

yahoo123,
The flange and bolting insulators are non-metallic electric insulators, but they can take large compressive stresses, typically associated with flange bolting stresses. The washers supplied come usually with precise torquing instructions. Ah, by the way, those are not made of rubber. The rubbes washers are used for water taps. As far as the galvanic corrosion in submerged sea water concerns, the insulators will interrupt the galvanic circuit between the metallic parts and the water will become a passive component in the circuit. No more galvanic corrosion issues. I would rather be concerned with the suitability of SS bolts in marine submerged environment and also the galvanised components as subjected to direct corrosion, rather than galvanic corrosion of dissimilar materials.
If you refer to structural bolting outside a wet marine environment, the insulator washers and sleeves are still your best option, as those washers can take loads associated with class 1500# flanges without problems...
cheers,
gr2vessels