Zinc plated va stainless steel, anchors chains and quick links

Since there seems to be a fair amount of metals knowledge in this forum, maybe I could ask about the specific electrode potential between stainless steel and zinc, and between SS and carbon steel, once the zinc is gone.

To my knowledge, the only really powerful galvanic corrosion that's been noted in climbing hardware has been between steel bolts and aluminum hangers - famous case at Index, WA, I believe. Maybe one of you experts could interpret some numbers from the galvanic charts, indicate which metal gets sacrificed (never the stainless steel, correct?), and give some real-world examples of how powerful the galvanic corrosion can be.

Also, RE SS's passivation layer (mostly chromium oxide) not being replaced in the oxygen-poor environment underwater, why, then, is there plenty of oxygen to rust the iron? In other words, why can iron oxide form, but not chromium oxide?

Also, what kind of corrosion was observed in the stainless bolts whose holes filled with water?

Jeff, there's all kinds of surface effects going on with corroding metals that makes it a lot more difficult to predict how "bad" a particular metal pair will be, compared to just looking up the metals' relative oxidation potentials. Aluminum is a nice, quirky example: from the tables it looks reactive as hell - our biners should self destruct every season - but it is usually protected by a tight oxide surface layer. Probably analogous to the oxide(s) that passivate stainless steel (but that's getting beyond my level of familiarity, so I'll shut up at this point).

My next sport route's gonna be all 24K gold and platinum hardware.

Morgan Patterson wrote: Agreed Disagree. Maybe in UT desert its not but, along the east coast of this country, this is horrible advice and simply wrong. We have moist humid climates and mixing metals is a time bomb and should never be done.

No Morgan, the plated steel bolt is the time bomb and will be regardless of whether metals are mixed or not. Even on the east coast mixing metals won't significantly change the lifespan of the anchor. The corrosion is going to start wherever the zinc plating is compromised, will the zinc plating be compromised by galvanic corrosion? Yes of course, but the zinc plating will be compromised long before that just by placing the bolt, so it will be rusting away without the assistance of galvanic potential between the two metals long before the zinc plating is sacrificed in the galvanic process.

Gunkiemike wrote: As a chemist and climber, I wish everyone in this endless "mixed metals" discussion would become familiar with the sacrificial anode concept. It could be developed and used to a significant benefit. And it's not at all new; it's what "plated steel" refers to, after all. The outboard boat motor and underground fuel storage tank industries figured this out a long time ago.

This makes me think we should be attaching some kinda sacrificial anode-washer type thing that's totally not structural - just part of the circuit, easily replaced year to year.

Consensus from a few other sources is that regular corrosion rate of a plated bolt is going to beat out any SS-on-plated-bolt effects by a fair margin, it seems.

Are we comfortable agreeing with this?

kennoyce wrote: No Morgan, the plated steel bolt is the time bomb and will be regardless of whether metals are mixed or not. Even on the east coast mixing metals won't significantly change the lifespan of the anchor. The corrosion is going to start wherever the zinc plating is compromised, will the zinc plating be compromised by galvanic corrosion? Yes of course, but the zinc plating will be compromised long before that just by placing the bolt, so it will be rusting away without the assistance of galvanic potential between the two metals long before the zinc plating is sacrificed in the galvanic process.

I get what you're saying... but from everything I've read and discussed with folks ss hanger on ps bolt will rust out quicker than just PS bolt and hanger. All the major climbing organizations advise against it. I'm not engineer or a chemist (i think ur an engineer if my memory servers) but I've seen mixed metal bolts in wet cliffs and they are DRAMATICALLY more rusted than non mixed ones in the same area. I believe the mixed metals speeds up the process.

Ken Chase wrote: This makes me think we should be attaching some kinda sacrificial anode-washer type thing that's totally not structural - just part of the circuit, easily replaced year to year. Consensus from a few other sources is that regular corrosion rate of a plated bolt is going to beat out any SS-on-plated-bolt effects by a fair margin, it seems. Are we comfortable agreeing with this?

Zinc washer...

Morgan Patterson wrote: I get what you're saying... but from everything I've read and discussed with folks ss hanger on ps bolt will rust out quicker than just PS bolt and hanger. All the major climbing organizations advise against it. I'm not engineer or a chemist (i think ur an engineer if my memory servers) but I've seen mixed metal bolts in wet cliffs and they are DRAMATICALLY more rusted than non mixed ones in the same area. I believe the mixed metals speeds up the process.

Two questions for you:

1. Were the non-mixed bolts that you've seen a stainless hanger on a stainless bolt, or were they a plated hanger on a plated bolt? Obviously the stainless on stainless will rust much less than a plated on plated or a stainless on plated.

2. Did you see the condition of the bolt inside the hole (i.e. were you replacing the bolt to get a view of the whole thing)? The reason I ask is that from the outside of the hole, a stainless hanger on a plated bolt will make the plated bolt look a lot worse due to the galvanic process between the bolt head and the hanger which will cause the bolt head to rust more quickly than on a non-mixed plated on plated combo. This doesn't mean that the lifespan of the bolt has changed though, because the worst corrosion should still be taking place inside the hole where you can't see it at the same rate as the mixed combo, and the corrosion inside the hole should be worse than the corrosion on the bolt head. In fact, this is a good reason for mixing metals, because on non mixed bolts you may not have any external indication of the corrosion that is taking place inside the hole, whereas with the mixed metals you will also get the exterior corrosion to help you know when to replace the bolt.

As with everything, there are always exceptions, but in general, the corrosion is going to begin with an area of the bolt inside the hole where the zinc plating has been compromised during the installation of the bolt, and will progress more rapidly inside the hole than on the bolt head where the galvanic corrosion would be occurring.

Morgan Patterson wrote: Disagree. Maybe in UT desert its not but, along the east coast of this country, this is horrible advice and simply wrong. We have moist humid climates and mixing metals is a time bomb and should never be done.

I agree with your disagree. There is no shortage of examples showing corrosion issues when plated and stainless are mixed. I've seen more examples than I can count, and there are hundreds on Google.















Some of those photos were taken from common climbing areas like the RRG. Now, would some of those bolts corroded without mixing the metals? Probably, but mixing them certainly dident help, and in several photos it's dead obvious.

Wow those are some pictures.

So in replacing hangers, it's terribly bad to mix metals? How do you replace a missing hanger not knowing what the target is? Should we be carrying all PS hangers now so they remain the visible sacrificial anode in the system that can be replaced (vs invisible corrosion inside the hole) - and if you do meet a PS bolt at least you're not mixing metals.

So is the official position now to carry PS hangers? Or throw in a zinc washer as sacrificial anode? I dont even know where to find PS hangers, here in Canada MEC (~REI in USA) has 3-4 types of hangers but they're all SS304.

(And what's the scoop on Aluminum leaver biners on PS or SS hangers? What does that cause?)

Ken Chase wrote:Wow those are some pictures. So in replacing hangers, it's terribly bad to mix metals? How do you replace a missing hanger not knowing what the target is? Should we be carrying all PS hangers now so they remain the visible sacrificial anode in the system that can be replaced (vs invisible corrosion inside the hole) - and if you do meet a PS bolt at least you're not mixing metals. So is the official position now to carry PS hangers? Or throw in a zinc washer as sacrificial anode? I dont even know where to find PS hangers, here in Canada MEC (~REI in USA) has 3-4 types of hangers but they're all SS304. (And what's the scoop on Aluminum leaver biners on PS or SS hangers? What does that cause?)

The seriousness of the issue would depend on the area. If you're mixing metals in the desert where the area sees an inch of rain a year, it's probably not going to be a problem. If you're mixing metals in an area where bolts do show corrosion overtime, it's more of a problem. I would say the best judging standard would be to say if the area is moist enough to show corrosion on bolts overtime, the correct solution is to use all stainless steel bolts and hangers. If the area is so dry that you get little to no corrosion over the course of several years, then mixing hangers/ bolt material is not that critical. If you want to be sure, just use stainless bolts, problem solved. As is always, look at what other developers are doing in the area and examine bolts on the oldest routes in the area for a clue.

Leaving AL leaver biners on stainless hangers is not a problem in most environments. If used in a marine area, the AL biner will suffer from a quite serious form of corrosion called exfoliation corrosion, but putting the biner on a AL hanger instead of a SS hanger wont stop that.

My question was not so much about 'what do I do when equipping a route' - obviously Im going to use all 304 at least (standard in my area of Southern Ontario limestone escarpment climbing - and if its in a darkened seep line, maybe haul out my few pieces of 316 I've got).

This is more when you find a missing hanger - does screwing on a SS hanger and nut now accelerate the corrosion drastically because you didnt know it was a PS bolt? What do I carry as spares on my 'missing gear' biner (got 2 nuts and a hanger on it now, and a small wrench)? A zinc-plated washer if I only have SS hangers and nuts?

Ken Chase wrote:My question was not so much about 'what do I do when equipping a route' - obviously Im going to use all 304 at least (standard in my area of Southern Ontario limestone escarpment climbing - and if its in a darkened seep line, maybe haul out my few pieces of 316 I've got). This is more when you find a missing hanger - does screwing on a SS hanger and nut now accelerate the corrosion drastically because you didnt know it was a PS bolt? What do I carry as spares on my biner+wrench set? A zinc-plated washer if I only have SS hangers and nuts?

Carry a magnet and check the bolt.

Brian in SLC wrote: Carry a magnet and check the bolt.

That's actually brilliant. But then I have to decide what im doing about the missing hanger once I know - is it just "add the PS washer" or "don't"? In which case just always adding a PS washer isnt so bad - a rusty washer wont ruin your life -- or can the corrosion 'bleed' onto the stainless and corrode it too?

I followed other people's advice in ensuring I got a stainless hammer for my equipping as getting flakes of steel onto a SS bolt will start a corrosion circuit or something - wouldn't this be the same (worse, with everything tightened down with nice surface area contact) -- zinc plating would accelerate corrosion on SS gear too?

Ken Chase wrote:But then I have to decide what im doing about the missing hanger once I know - is it just "add the PS washer" or "don't"? In which case just always adding a PS washer isnt so bad - a rusty washer wont ruin your life -- or can the corrosion 'bleed' onto the stainless and corrode it too? I followed other people's advice in ensuring I got a stainless hammer for my equipping as getting flakes of steel onto a SS bolt will start a corrosion circuit or something - wouldn't this be the same (worse, with everything tightened down with nice surface area contact) -- zinc plating would accelerate corrosion on SS gear too?

Ontario is fairly humid and wet? I'd probably consider replacing the bolt as a priority.

20 kN wrote: I agree with your disagree. There is no shortage of examples showing corrosion issues when plated and stainless are mixed. I've seen more examples than I can count, and there are hundreds on Google. Some of those photos were taken from common climbing areas like the RRG. Now, would some of those bolts corroded without mixing the metals? Probably, but mixing them certainly dident help, and in several photos it's dead obvious.

Sayer, I generally agree with you, but out of the pictures you posted of actual climbing bolts, only one of them even appears to possibly have a galvanic contribution to the corrosion (the SMC hanger on the rawl bolt). The rest appear to all suffer from uniform corrosion, and even the one with a galvanic contribution as seen by the severity of the corrosion right at the bolt head/hanger interface, the bolt will most likely fail due to corrosion of the threaded area first just due to having less material in that area to begin with. I stand by my point, the life of those bolts was not shortened in any appreciable way by the galvanic corrosion process.

Brian in SLC wrote: Ontario is fairly humid and wet? I'd probably consider replacing the bolt as a priority.

Yep, this is the way to go, if you need to replace a missing hanger on a plated bolt, just replace the bolt as well.

kennoyce wrote: Yep, this is the way to go, if you need to replace a missing hanger on a plated bolt, just replace the bolt as well.

That's not so simple. While I have the gear and knowledge to replace bolts, many others dont and I frequently encounter bolts without hangers (perhaps least 3-5 times a season). Once that happens, that's it, have to pound in the bolt and drill a new hole? Over 50 years that's going to cause a lot of holes, and in marginal rock sometimes the best placement has already been used (on one rebolting we ended up adding an extra bolt and moving all the bolts about 3-4 feet to find good rock again).

If a PS washer would act as sacrificial anode in such a case, then it seems easy enough for people to carry a hanger, PS washer and a nut and small wrench (like the hex punchouts on my nuttool) with them (vs a drill and hammer set, do you carry those everywhere?).

Question is, does adding PS anywhere to a SS system increase SS's corrosion? I am wondering why people use SS hammers on SS bolts then...

(Ontario has humid summers, isnt a jungle but sometimes feels like one, and there is seepage for long periods on some routes after spring melt and rain...)

Ken Chase wrote: Question is, does adding PS anywhere to a SS system increase SS's corrosion? I am wondering why people use SS hammers on SS bolts then... (Ontario has humid summers, isnt a jungle but sometimes feels like one, and there is seepage for long periods on some routes after spring melt and rain...)

Yes, it can, basically, if the protective layer on the stainless is damaged somehow and then iron is deposited in the damaged area it can be a point for corrosion to begin. This is exactly why you should use a stainless hammer when placing stainless bolts, hammering the bolt damages the protective layer and a non-stainless hammer can then deposit iron on the damaged area as you place the bolt.

Also, with the right methods, most bolts can be removed so that the hole can be reused so that you don't have to swiss cheese the rock to replace a bolt. look up gregger man's posts for some great information on bolt replacement.

What the heck is this?!

"Stainless and zinc plated"

amazon.com/SE-Hook-Quick-2x…

How's that even work?

Ken Chase wrote:What the heck is this?! "Stainless and zinc plated" amazon.com/SE-Hook-Quick-2x… How's that even work?

It sounds like it's exactly what it says it is, stainless steel plated with zinc. It doesn't give the type of stainless though, so who knows exactly what's under the zinc plating.