Galvanic Corrosion

[larryinnewyork]

Hello all,

I hope this is in the right section.

Question about "Galvanic Corrosion".

I have a 1977 Ariens Snow Thrower.

I have it all apart and am taking the time to replace all the
Bronze Bushings and Ball Bearings.
And doing a total paint job (using brush).

At first, I wanted to replace alot of the 'steel' nuts & bolts with Stainless.

Question: In using the stainless fasteners,
how worried should I be about "galvanic corrosion".

Example:
Cast Iron Gear Box with S.S. Drain / Fill Plugs
Sheet Metal with S.S. nuts & bolts

In the future, the stainless would be nice,
but not at the cost of unnecessary corrosion.

I have been reading about galvanic corrosion on the net.

Just thought I'd see what your experences & opinions are.

Thank you for any assistance.

Larry / Buffalo, New York

 

[Chris142]

Coat the threads with grease or antisieze?

 

[NHGUY]

I would use regular bolts.The little bit of corrosion you get will keep them from loosening with all the vibration coming out of that Tecumseh engine.

 

[doitmyself]

I have applications at work that say I should be getting galvanic corrosion according to the galvanic charts, yet it is not happening. One example are aluminum greenhouse cooling pad systems with stainless fasteners. This is a wet environment and the aluminum should be corroding where it contacts the stainless, but it is not.

Likewise, the charts show that mild sheet steel will corrode when fastened with stainless. I just can't figure how these charts play out in the real world.

You could use galvanized fasteners, but they are only grade 2. I'm not sure if they are available below 1/4". Here's an example: http://www.nutty.com/Galvanized-Fasteners_c_12.html

Or, you could step up to grade 5 zinc coated fasteners. The ones I get seem to resist corrosion a bit better than the gypo chinese grade 2 available everywhere. But, this might just be a bias of mine vs. fact. The fact that they are harder steel might make them hold up better regarding thread breakdown from rust...just a guess.

Good luck.

 

[Gabe]

Galvanization is just coating the steel with zinc. Zinc oxides but doesn't rust.

It should be fine for another 30 years...

 

[tom slick]

On the galvanic chart, stainless steel is much further from brass, bronze, aluminum, and cast iron than mild alloy steels. That means SS it is more likely to corrode in contact with those bushings etc. It also has a tendency to gall.

 

[dwcopple]

our Montego has it. The hood and trunk are aluminum panels but the structure/supports are steel and the paint is bubbling because of it. Facepalm for Ford.

 

[Donald]

I need to replace a bolt on my boat trailer. The fender is painted steel, this attachment frame piece is aluminum, a bracket to hold a clearance light is steel and the bolt needs to carry the ground for the light. Its a 3/8" and surprising HD does not go up that high in stainless. I will try a local hardware store.

The old bolt was electroplated steel.

 

[FXjohn]

you can't go wrong with stainless steel fasteners. use them

 

[tom slick]

You can certainly go wrong with stainless steel fasteners in certain applications.

From Fastenal (industrial fastener supplier):
http://www.fastenal.com/content/feds/pdf/Article - Corrosion.pdf
Quote:
If brass and aluminum plates are connected by a passivated 304 stainless steel bolt, both the brass and the aluminum will corrode severely where they touch the stainless steel because they are much more anodic than stainless steel. The aluminum plate will corrode more heavily due to it being more anodic to stainless steel than brass is. The aluminum will also corrode where its exposed surface contacts the brass plate because brass is more cathodic.


Stainless is okay when used with other metals that are on the Cathodic side of the galvanic chart but bad news when used with aluminum, brass, copper which is on the Anodic side of the galvanic chart.

 

[doitmyself]

Tom,

How does one explain the first paragraph in my post above.....aluminum and stainless (304) in a constantly damp/wet environment?


Maybe the p.h. (7.8) and high mineral content of the water is affecting the galvanic action??

It doesn't make sense.

 

[Doog]

Originally Posted By: larryinnewyork

Example:
Cast Iron Gear Box with S.S. Drain / Fill Plugs
Sheet Metal with S.S. nuts & bolts



I would use brass drain/fill plugs

 

[tom slick]

Originally Posted By: doitmyself
Tom,

How does one explain the first paragraph in my post above.....aluminum and stainless (304) in a constantly damp/wet environment?


Maybe the p.h. (7.8) and high mineral content of the water is affecting the galvanic action??

It doesn't make sense.


Are there any anodes in the system? Zinc or Magnesium?

 

[GMBoy]

My first experience with this was back in 1994 when I purchased my new 1994 Corvette. I bought a set of fancy valve stem caps with the Corvette logo on them and put them on my tires. It wasn't 1 month and I went to check my tire pressure (my low tire light came on) and NONE of the caps would come off! They were fused on, I chewed up one valve stem with vise grips trying to get the cap off. I had to go to Discount Tire and they replaced the stems in all 4 wheels. They had to cut the stems.

 

[doitmyself]

Originally Posted By: tom slick
Are there any anodes in the system? Zinc or Magnesium?



No.

 

[larryinnewyork]

Hello all,

I appreciate all the comments.

What I think I will do is:
1) Continue to learn about Galvanic Corrosion.
2) When reassembling the SnowThrower, I will use NON Stainless
but atleast 'zinc plated'.
3) For the Chute & Deflector, where the metal is 1/16 thick"
I will use S.S. and observe it for corrosion.

I'm trying to take very good care of this SnowThrower, as most
people on here take care of their cars.

I thank everyone for responding.
As most people try to get the most out of what they own (repairing)
perhaps more people will be aware of this (and not just Engineers).

Happy Memorial Day.

Larry / Buffalo

 

[FXjohn]

I don't use brass hardware much. I've never seen a problem using stainless on aluminum in real use.