Galvanic Corrosion of bolts


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Trad climber
Upstate NY
Topic Author's Original Post - Aug 15, 2006 - 07:14pm PT
I've heard that mixing Stainless Steel hangers with non-SS bolts could present a problem in some situations. Anybody know about this?
T Moses

Trad climber
Paso Robles
Aug 15, 2006 - 07:28pm PT
More specifically:

Edit: I would like more information on this one also. Anybody have any more in depth info?

Trad climber
Upstate NY
Topic Author's Reply - Aug 15, 2006 - 08:01pm PT
Even in dry climates, climbers should use stainless steel bolts and hangers. It is also important not to pair stainless with non-stainless metals (i.e. stainless hangers with non-stainless bolts, etc.) in wet areas. This miss-match accelerates corrosion and can be avoided by painting hangers with numerous coats of primer or by using Fixe or Metolius pre-painted hangers. Better yet, always use stainless steel bolts AND pre-camouflaged hangers appropriate for your area (plain stainless steel is camouflaged for most good granite). While non-stainless bolts will last for some time in dry climates, much rusting occurs even in desert locations like Owens River Gorge, where those maintaining anchors observe significant rusting inside the bolt hole on routes only a few years old."

I've read most of the articles on Greg's site before and found them to be really interesting. I'm looking for climbers that have first hand experience with this kind of corrosion, and what they discovered (like time frames for the reaction to occur, was silicon used to help slow the process and did it seem to work, how wet of an environment, etc.)

Trad climber
the south
Aug 15, 2006 - 10:30pm PT
The worst possible combination if I recall correctly is aluminum and stainless steel in a salt water environment. this makes a battery charging station in effect, and corrosion is rapid.

You can find a table for the potential differences between metals, used to be called galvanics I think, if you look around. Metals that have similar electro-potentials are not going to corrode each other as quickly as those with very different EP.

Considering that pourous rock like sandstone can have a lot of salts and those salts dissolve in water, you don't have to figure too hard to see a problem.

There used to ba a very good discussion of this very problem on the net somewhere, but I don't have the link any more. It was not the safe climbing people. An engineer interested in such things and I discussed it on the SCC site a few years ago, and then we found that web page dedicated to what we were talking about.

caver sites might be where we found the best info, cause cavers for one deal with wet bolt situations a lot, and they also used to use aluminum hangers, DOH!

I think also Ed Leeper knows a bit about this stuff, you could ask him.


Trad climber
Hong Kong & Wales
Aug 15, 2006 - 11:46pm PT
I've had a few SS bolts with SS hangers rust (inland/compact sub-tropical granite) within only 2 months... how the heck is that so? Although, it is usually always as humid as a granny's panties...

I've been coming to the conclusion that maybe the washer I put on them were non-SS and so have been reacting... these were regular Rawl/Powerbolt 5 piece, is it possible the washer isn't SS, atleast where I'm getting them from?

Trad climber
one pass away from the big ditch
Aug 16, 2006 - 12:09am PT
I've had batches of 90s Rawl bolts that were stainless shafts, but non stainless washers- straight from the store

on other occasions when the sleeves have fallen off in a box of a bunch of bolts I've mixmatched by mistake the stainless for non stainless washers.

it could happen if you haven't learned to recognize

Trad climber
Mountain View, CA
Aug 16, 2006 - 01:19am PT
I have placed hundreds of SS and non-SS Rawl/Powers bolts, here are some of my observations.

The washers on the non-SS bolts suck, especially the old Rawl models. These particular washers rusted incredibly quickly, but the bolt and sleeve looked good when removed and inspected. Lately, I have been buying bulk SS washers to replace the non-SS washers which come with the non-SS bolts.

About galvinic corrosion, this does not seem to be a problem at the areas I frequent such as Yosemite, Pinnacles National Monument and the Boulder, CO Front Range. I have removed non-SS bolts with SS hangers I have placed and while there may be some surface rust there is nothing which appears to be even closr to critical.

Recently, I removed some Rawls which have been in a water streak for over 10 years and though the washers looked horrible, the bolts had only minimal surface rust.

Obviously, galvinic corrosion can happen, but I think in the majority of the climbing areas this is not a problem. Clearly, seaside crags are an exception.

Brian in SLC

Social climber
Salt Lake City, UT
Aug 16, 2006 - 12:35pm PT
I've noticed similar. Pulled a number of bolts here in Big Cottonwood and in American Fork Canyon that were around 14 years old. No significant mass loss due to corrosion. No enhanced corrosion between the shaft of the bolt, washer, or the stainless hanger.

There were SMC stainless hangers in combo with Rawl (Powerbolt) grade 5 bolts.

So, if there is a galvanic effect between these zinc plated bolts/washers and a stainless hanger, I've not observed it visually. Bolt would be the donor. No more corrosion than down lower on the shaft, and, just surface rust.

-Brian in SLC

Sport climber
White Salmon, WA
Aug 16, 2006 - 03:54pm PT
So the powerbolts (aka Rawl) I have gotten in the past have a D stamped on the hex-end. Does this perhaps indicate it is stainless? If not, how does one tell? Thanks.
Hardman Knott

Gym climber
Muir Woods National Monument, Mill Valley, Ca
Aug 16, 2006 - 04:59pm PT
There was a route at Mickey's Beach which had 1/2" carbon-steel bolts with SS hangers.

Here's one of the bolts, with one of the newly installed titanium "glue-ins" below:

And here's a closer view of the old bolt:

I figured this would be a simple bolt to chop, but was utterly stunned by
the amount of back-and-forth blows it (and the others) withstood before
the bolt finally sheared. We're talking a 2 1/2 lb sledge, with full-force blows.
It was like 10 minutes per bolt. I had to rest several times because my arm
was getting really tired! But nobody climbed that route for years because
they looked like you wouldn't want to hang from them, let alone take falls...

To answer the question that the OP posed, I wouldn't worry too much about adverse
interaction; what could possibly be worse than this? Keep in mind that SCC* is a separate
issue altogether, and the usual precautions should still be taken in places where SCC is an issue.

*Stress Corrosion Cracking; see this article for more info:

Big Wall climber
Bay Area, CA
Aug 16, 2006 - 05:20pm PT
pcousar: the 'D' is a length stamp. It tells how long the bolt is. If I remember correctly (unlikely), D is 3.5 or 4" long?

The problem with stainless steel is that if it can't get oxygen (or even worse, chlorine is around) is that it corrodes without obvious signs, and will often corrode deep within the steel without it being visible.

carbon steel isn't susceptible to deep crevice corrosion like stainless, and it's corrosion generally follows the standard 'get very rusty, convert iron to rust' process. This takes time in any climate to remove any signifigant amounts of metal (though it can start showing surface rust very quickly).

Assuming the design of the bolt requires signifigant metal loss before it becomes weak (not always the case), even signifigant corrosion won't weaken the bolt to a dangerous level, and as noted people are VERY hesistant to use a rusty bolt - even if it is still probably pretty strong.

A stainless bolt in the same case will often look nearly new, until it snaps (which can happen with very little force) - lots of reports of this happening in thailand with bolts only a few years old.

Normal stainless steels should never be used where Chlorine (a component of salt), and stress (most climbing bolts are pre-stressed as part of the design - aka 5 piece powers bolts, fixe stud bolts, etc) are present.

People give carbon steel a bad rap, but honestly it is a far more predictable and better understood material than SS. As long as the bolt can be replaced when obviously rusty, and the rust is not a major visible eyesore, there is no reason not to use them.

Hardman Knott

Gym climber
Muir Woods National Monument, Mill Valley, Ca
Aug 16, 2006 - 05:37pm PT
Lazide wrote:

A stainless bolt in the same case will often look nearly new, until it snaps (which can happen with very little force) - lots of reports of this happening in thailand with bolts only a few years old.

Great post. Just wanted to point out that there was an instance where a SCC-affected SS bolt failed under body-weight, and that bolt was reported to be only 18 months old...

Social climber
Aug 16, 2006 - 06:06pm PT
Another factor with stainless steel is the suspectibility to "stress corrosion cracking". Under certain environmental corrosive conditions micro cracks develop that can lead to sudden failure of SS bolts. The stainless stell may look OK to the naked eye but could be a time bomb.

This mechanism is possible with all metals but especially problematic with aluminum and stainless steel. I think titanium for sea cliffs and carbon steel for relatively less corrosive environments makes good sense.

Some Links:
Hardman Knott

Gym climber
Muir Woods National Monument, Mill Valley, Ca
Aug 16, 2006 - 07:22pm PT
Dingus Milktoast snidely wrote:

Any more insight you can share would be useful, as would understanding your metalurgical background?

I got yer "metalurgical"(sic) background right here, pal...

I beat the fuçk out of numerous six-year old 1/2" carbon steel bolts (with SS hangers)
which were splashed heavily every day with salt water at a low-tide crag, and yet it took
a Herculean effort on each of those bolts––with a sledge––to get them to finally break.

Why worry about metallurgical background when you have compelling real-world data?

Big Wall climber
Bay Area, CA
Aug 16, 2006 - 07:40pm PT
Specific mentions -

Especially check out how stainless steel corrodes.

I spent over 2 weeks researching various grades of stainless steel (304, 316, AL6-XN, etc) availability, failure modes, etc. This was about 1 1/2 years ago, and was specifically related to bolting.

304 is by FAR the most prevalent SS grade (I checked with Fixe and Metolius, and they confirmed their hangers are 304, and fixe confirmed everything else they make is also 304, including bolts) .

It is possible to get 316 bolts (5 pieces, forged marine grade eye bolts, or cut threaded rod), but they are either prohibitively expensive or difficult to locate for the most part.

304 stainless is widely known to be unsuitable for marine enviroments (from what I have read) when loads are present, and is often not used even when loads aren't present due to signifigant pitting and strength loss.

Stainless steel stays 'stainless' due to oxidation of the chromium in the metal. The produced chromium oxide protects the metal underneath and stops further corrosion. (just like aluminum oxide and aluminum).

When chlorine is present, or when oxygen is not present, this layer never forms (or in the worse case, can't reform when a small scratch happens) and corrosion occurs. Once a pit (even microscopic) forms, a naturally low oxygen enviroment is created, and corrosion inside the pit continues.

The wikipedia article on stainless has an excellent writeup of the many corrosion forms of stainless (of which the one I outlined is just one).

Other than extensive research on my own, I have no metalurgical credentials.

The research I have done however has convinced me that in most cases, carbon steel is much more predictable than SS and hence usually safer (it is usually pretty obvious when it is signifigantly corroded and weakened).

It is possible (but unlikely) for instance that when pounding a stainless steel bolt into a tight hole in granite, and then sealing with a washer (included on many of the fixe stud bolts), that an oxygenless enviroment coupled with exposed stainless steel (not yet reacted with oxygen, and so unprotected) could result in signifigant corrosion and weakening.

And how would you know?

Compounding the (possible) problem is people sealing around the bolt when placing bolts (I've seen people use silicone cauking, which contains a pretty strong acid).

Honestly I'm just amazed we don't see MORE problems considering the wacky things some people do!

Edit: As long as the bolt is COMPLETELY removeable and can be replaced with something else in the same hole, I think things are ok.

Stud style bolts are not a good thing in the long run, I feel.
Hardman Knott

Gym climber
Muir Woods National Monument, Mill Valley, Ca
Aug 16, 2006 - 08:33pm PT
Mr Milktoast, I realized I was being hyperbolic even as I typed my blistering retort,
but there seems to be a part of me that longs for the good ol' days of rec.climbing.

I'm sure you understand...

Big Wall climber
Bay Area, CA
Aug 16, 2006 - 08:37pm PT
I should also note that 316 is better re: corrosion than 304, BUT is still not even remotely suitable for use in high chloride (i.e. sea) installations. All 3xx series SS should be considered unsuitable for marine use, ESPECIALLY when coupled with warm temps.

There are some forms of stainless that should be just fine for the temp ranges, but they are pretty exotic and hella expensive - seems like a better bet to just use the titanium glue-ins.
Wes Allen

Boulder climber
Aug 16, 2006 - 08:40pm PT
Old style stud bolt, replaced in the rrg a couple months ago, had probably been in the rock for 10+ years:

Very, very slight torque force to break it. I have replaced a few, and have helped to replace a bunch of bolts in the red, and generally speaking, it is really hard to tell how strong they are just by looking at them. The bolt in the photos was easy to spot as bad, but others have looked bad, yet I couldn't twist them off with full body wieght, and I am not a little guy. The next worst bolt that I help replace, was at the crux of a very well traveled and fallen on sport route. From the outside it looked as good as the others, but it broke really easy. And it had been holding falls (including me) right up to the day it was replaced.

We have been using, and continue to use non-ss powers, and they work well. We used some dynobolt golds, but those seemed to have issues with coming loose, unless you really cranked them down. Maybe a problem with the softer sandstone?

I thought the link to the BD blog in the rope breaking thread was good, as farther down the page, there are some interesting things about what worn gear breaks at, and what kind of force the ave. sport fall creates.
Greg Barnes

Aug 16, 2006 - 08:45pm PT
I agree strongly with lazide - stud bolts, even stainless, are not removable. From a rebolting point of view, eventually they'll need to be replaced. Better to use carbon steel 5-pieces than stainless studs (about the same price). Totally lame to use non-stainless studs.

In some spots in Europe, you'll have an old rusty self-drill sleeve (with rust stains draining from it), then 6" away a old broken-off stud bolt (with rust stains), then 6" away a new glue-in. Ugly! Let's try to avoid that over here.

FYI for hand-drilling folks - a few months ago Powers came out with a shorter version of the 3/8" Power Bolt (aka Rawl 5-piece). No blue sleeve, about 1/4" shorter. Some folks who use stud bolts do it because the hole is about 1/4"-1/3" shorter for those - now you can get shorter 5-pieces (or I guess now "4-pieces"!).

hither and yon
Aug 16, 2006 - 08:46pm PT

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