Question on dissimilar metals

[Skywagon]

I need to install some new zerks on an aluminum device exposed to salt water. I can’t let the zerks corrode or become hard to remove… long story. 
 

would it be appropriate to use some copper slip or thread anti-seize, or should I just go zerk to aluminum. I’m not sure what metal zerks are anyway. 
 

Thanks

 

[Hosstage]

I would definitely use an anti-seize compound. I'm assuming the zerk is steel of some sort, very unlikely aluminum. It would likely gall even if not exposed to salt water. Zinc coating can help prevent galling, but the salt water adds another corrosive element to the process.

[Joe Frickin' Friday]

When you put two metals together in salt water, the galvanic series tells you which metal will be protected and which will be sacrificed:

 

https://en.wikipedia.org/wiki/Galvanic_series

 

Whichever metal is more "noble" is protected, and whichever metal is less noble is the one that's going to be sacrificed.  Note that zinc is way down at the sacrificial end of the list, which is why it's great for protecting steel in a saltwater environment: the steel gets protected, and the zinc gets slowly eroded away.  

 

Looking at that list, copper is more noble than aluminum.  Put the two together in seawater, and the aluminum is likely to come out second best.  

 

Same is true for an unlubed steel zerk screwed into aluminum: the aluminum will suffer to protect the steel.

 

I see that Loctite makes a marine-grade anti-seize compound that doesn't include any metals:

https://next.henkel-adhesives.com/us/en/products/industrial-lubricants/central-pdp.html/loctite-lb-8023/BP000568.html

 

Comically, the first ingredient they list is graphite.  While technically not a metal, it is the absolute most noble thing in the galvanic series.  I guess maybe there's just not much of it in there?  Anyway, if Loctite says it's suitable for use in seawater, then it's probably a good choice.

 

[Skywagon]

Thanks all. I’ll look for the anti-seize Mitch mentions. Yep familiar with Zinc on aluminum as just replaced $300 worth… annual event, but have never changes the zerks. 

[BamaJohn]

Perhaps a dumb question but....is it possible to only install the zerks when lubing and remove them the rest of the time?  

[TSConver]

Zerks are likely pot metal with a cheap chrome plating. Personally I would just screw them in with some grease.

[Skywagon]

20 minutes ago, BamaJohn said:

Perhaps a dumb question but....is it possible to only install the zerks when lubing and remove them the rest of the time?  

 

Perhaps, but would have to plug the hole with another kind of bolt or water would get in.  I only have to change these out every 2-3 years from corrosion.  The main ask on the question was in hopes I would never break one off which would require major surgery due to lack of access....  It would be kind of like replacing an alternator on our wetheads....

[Hosstage]

If that's the case, it might be worth it to pull them out every year, inspect, and decide to re-install or replace them.

[Skywagon]

Thanks all....I ordered enough zerks from the mfg of the unit I am working with to change them once a year for the next 3 years...after that....I probably won't give a hoot.  I found the Loctite product Mitch pointed out.  It must be made by BMW as it is quite expensive...but...should arrive tomorrow.

[Lowndes]

David, put a magnet on the zerks.  I'd bet they are steel.

[realshelby]

Another thumbs up for the Loctite product. Their stuff will do what it claims it will do. Probably a LOT less messy than Anti-sieze too!

[Lowndes]

David, one other thing, PTFE plumbers pipe tape works VERY WELL on threads in "adverse conditions" like lawnmower blade bolts and shotgun choke tubes.  I doubt it would be an electrical insulation to prevent the galvanic action but the alu is the more reactive metal anyway.

 

Also, you can get the little plastic snap-on covers for the zerks on amazone: