Galanic corrosion opinions/wisdom appreciated ....

I have heard that galvanic corrosion can compromise the strength of bolts and that "regular" steel degrades if miss-matched with SS …. a pic from The Eaglet (Franconia Notch New Hampshire) shows a mostly shiny SS hanger with a rusted bolt ….  should I worry about the strength of this  bolt, and others that look like it  ???

Jim Titt will chime in but I believe the answer is simply that the bolt itself is rusting as expected. The SS hanger does not make it necessarily worse...which means you have to use your own judgment as to when the bolt is too rusty to trust (and hopefully you will replace it). Just because they are dissimilar metals does not mean that galvanic action is contributing significantly, the rust just is what it is and a stainless hanger is virtually always a better choice regardless of the bolt material AFAIK.

Ian Dibbs wrote: I have heard that galvanic corrosion can compromise the strength of bolts and that "regular" steel degrades if miss-matched with SS …. a pic from The Eaglet (Franconia Notch New Hampshire) shows a mostly shiny SS hanger with a rusted bolt ….  should I worry about the strength of this  bolt, and others that look like it  ???

Galvanic corrosion is mostly a myth in the climbing world.  Yes galvanic corrosion does exist, but it can only happen when there is an electrolyte present between the two dissimilar metals to allow the transfer of electrons to occur.  Now depending on the location, there could be an electrolyte present for much of the time (think wet environment where water gets trapped in the bolt hole), but galvanic corrosion isn't somehow worse than normal corrosion, it just speeds up the corrosion process.  A bolt that is corroded without the assistance of the galvanic process is not somehow better than a similarly corroded bolt where a galvanic reaction was occuring (as your post seems to imply).  So the take away is this, in a wet environment, yes galvanic corrosion will take place and make it so that the bolt will need to be replaced more frequently, but it is no worse than a similarly corroded bolt on a non-stainless hanger where no galvanic corrosion took place.  As far as dry desert climates are concerned, galvanic corrosion is really not even a concern (though there are many climbers who will act like they are experts on the topic and spew about the dangers of galvanic corrosion in dry climates until they are blue in the face).   

The solution is sacrificial anodes at every bolt. 

i mostly agree with ken's comment, but i think what he is saying about galvanic corrosion not being worse is maybe misleading.  i think what he is saying is that if you have 2 sets of dis-similar bolt/hangers that have equal amounts of corrosion, it doesn't matter if one of them is suffering from galvanic corrosion - they are both corroding.  however, if you have 2 sets of bolt/hangers, one in a dry evironment the other in a wet environment, i would think the total corrosion would be worse in the wet environment for a given length of time.  i would think that anything that speeds up a corrosion process would generally be worse than otherwise.

Jared Chrysostom wrote: The solution is sacrificial anodes at every bolt. 

10 pound discs of magnesium are next years piton d'or!

slim wrote:

10 pound discs of magnesium are next years piton d'or!

im voting for zinc...

slim wrote: i mostly agree with ken's comment, but i think what he is saying about galvanic corrosion not being worse is maybe misleading.  i think what he is saying is that if you have 2 sets of dis-similar bolt/hangers that have equal amounts of corrosion, it doesn't matter if one of them is suffering from galvanic corrosion - they are both corroding.  however, if you have 2 sets of bolt/hangers, one in a dry evironment the other in a wet environment, i would think the total corrosion would be worse in the wet environment for a given length of time.  i would think that anything that speeds up a corrosion process would generally be worse than otherwise.

Correct Slim, sorry if I wasn't clear on that point.  Obviously, in a wet environment, you don't want to mix metals because yes it will speed up the overall corrosion process.

Problems with galvanic corrosion will be more often seen with more highly dissimilar metals coming in contact with each other. For example using stainless steel hardware in an aluminum part. add a catalyst like sea water and you essentially have created a battery. And the aluminum will corrode at a more accelerated rate.

However in the case of your stainless clip and the bolt. It depends how moist of an enviroment it is in as well as minerals prevalent in the rock it is in. 
 Assuming the washer bolt and nut are the same material. Essentially you have 4 metals together.
Stainless hanger
Carbon steel bolt
The spreader on the end of ththe bolt
And the zinc coating.

Zinc will go first and it appears it has.Not knowing the material of the spreader holding the bolt in place is the gamble. Because if it scores less on the galvanic scale than the steel bolt you have no way of knowing its condition other than removing it or falling on it and reporting back.
I say it looks bomber. Trust it and climb on. 

slim wrote:

10 pound discs of magnesium are next years piton d'or!

Look at Mr Fancypants with his expensive magnesium!  Us plebs will stick with zinc.

Jared Chrysostom wrote: The solution is sacrificial anodes at every bolt. 

I posted about this years ago. It is a bit depressing that the climbing industry hasn't gotten on board with this. The marine and storage tank industries figured this out decades ago.

Gunkiemike wrote:

I posted about this years ago. It is a bit depressing that the climbing industry hasn't gotten on board with this. The marine and storage tank industries figured this out decades ago.

Or just follow EN959 which says all parts must be the same material

Jim Titt wrote:

Or just follow EN959 which says all parts must be the same material

What about an impressed current cathodic protection system? 

The real issue, of course, is that when the exposed part of the bolt is rusted you've got no way to know how bad is the portion in the hole.  Judgment, and perhaps some knowledge (like the date of the FA..."how old is this thing" can help, but this only goes so far.

Galvanic corrosion (i.e. a faster corrosion) is a real issue in two situations I know of: 1) Near an ocean. Salt is horrible, especially is there are "micro cracks" (in the hanger, usually arond the bolt's nut) that the salt can get into.  and 2) when there's a real difference in the contact metals, as is the case with some home-made aluminum hangers combined with carbon-steel bolts, even if originally zinc plated.