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  1. #1
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    Is this corrosion? [alloy dropouts]

    This on a carbon frame with alloy drop-outs, the paint has turned "coarse" for lack of a better word, although it's well anchored.

    Hopefully the shots are clear enough, I had trouble getting good ones, click to enlarge:





    What do you think?

  2. #2
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    Quote Originally Posted by oct3 View Post
    This on a carbon frame with alloy drop-outs, the paint has turned "coarse" for lack of a better word, although it's well anchored.

    Hopefully the shots are clear enough, I had trouble getting good ones, click to enlarge

    What do you think?
    Most likely that is a result of corrosion of the . Blistering or bubbling of paint over aluminum alloys is one sign of corrosion of the underling aluminum. Blistering / bubbling can be caused by other mechanisms, but over aluminum alloys corrosion is one of the more common causes. Since it's an aluminum alloy part bonded to a carbon part the possibility of galvanic corrosion is a concern.

    It appears in the photos that the blistering is limited to the dropout and the dropout adapter that is also probably aluminum alloy and bonded to the seatstay. The primary immediate concern would be loss of adhesion between the carbon stays and the adapter in the seatstay or dropout in the chainstay.

  3. #3
    wim
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    I wouldn't worry too much about the paint feel or appearance. Many bikes have unpainted alloy screw tabs and dropouts and they seem to do just fine. If you don't like the looks, carefully take the paint off.

  4. #4
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    Quote Originally Posted by wim View Post
    I wouldn't worry too much about the paint feel or appearance. Many bikes have unpainted alloy screw tabs and dropouts and they seem to do just fine. If you don't like the looks, carefully take the paint off.
    If it were just surface corrosion of the alloy (oxidation), I wouldn't be concerned either. But if is from galvanic corrosion between the alloy and the carbon frame, then I would be very concerned.

  5. #5
    wim
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    Quote Originally Posted by ibericb View Post
    If it were just surface corrosion of the alloy (oxidation), I wouldn't be concerned either. But if is from galvanic corrosion between the alloy and the carbon frame, then I would be very concerned.
    Well, another reason to get rid of that paint and see what's going on if you're the worrying type. Chances are that the screw tab and the chainstay end of the dropout are plugged 'n glued into frame, so there's a thick layer of glue between the alloy and the carbon. He'll know if the dropout pulls loose and can have it repaired then. But it's a long stretch from a few harmless paint bubbles to a dropout coming out. Were it my bike, I'd do nothing more than just watch it.
    Last edited by wim; 01-19-2015 at 09:00 AM.

  6. #6
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    Quote Originally Posted by wim View Post
    Well, another reason to get rid of that paint and see what's going on if you're the worrying type. Chances are that the screw tab and the chainstay end of the dropout are plugged 'n glued into frame, so there's a thick layer of glue between the alloy and the carbon. He'll know if the dropout pulls loose and can have it repaired then. But it's a long stretch from a few harmless paint bubbles to a dropout coming out. Were it my bike, I'd do nothing more than just watch it.
    That's about all you can do. If galvanic corrosion is the problem, it's a non-trivial repair. The challenge is insulating the alloy insert from the carbon fiber composite. The paint blistering is harmless. It's the corrosion underneath and it's cause that may not be so harmless. In the meantime about all anyone can do is watch it closely, and if either the dropout in the chainstay or the adapter in the seatstay separates, then find a carbon frame repair expert. Several of the big names in carbon frame repair (e.g. Calfee) won't even touch a debonded aluminum alloy dropout in a carbon frame. Some others will.

    We had a lengthy discussion /debate about an alloy adapter that had pulled out of a carbon frame seatsay a couple of months ago here.

  7. #7
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    I don't see what we're worrying about. I don't even look at my dropouts except when the bike is getting it's yearly overhaul and inspection. And then I don't look at them as close as these photos make them.

    Are they straight and solid, good to go. But that's just me.
    Too old to ride plastic

  8. #8
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    Quote Originally Posted by velodog View Post
    I don't see what we're worrying about. I don't even look at my dropouts except when the bike is getting it's yearly overhaul and inspection. And then I don't look at them as close as these photos make them.

    Are they straight and solid, good to go. But that's just me.
    Do you have a carbon frame with bonded Al dropouts? You're signature says "Too old to ride plastic", so I'm guessing no. Al parts bonded to carbon in frames has been a problem for some manufacturers.

  9. #9
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    Quote Originally Posted by ibericb View Post
    Do you have a carbon frame with bonded Al dropouts? You're signature says "Too old to ride plastic", so I'm guessing no. Al parts bonded to carbon in frames has been a problem for some manufacturers.
    As a matter of fact I do, it's just been relegated to a bare frame hanging on a hook. I put somewhere in the neighborhood of 12,000 miles on that bike before I realized it wasn't for me. I treated it just like my steel bikes and never had an issue that caused me to think that it was somehow compromised because of the materials that it was built with.

    The only problem that I had was the screw that joined the seat stay to the dropout got a bit loose, so I snugged it up and all was good.

    I'm not trying to be a dick here, but all these posts by owners of carbon frames fretting over every little scratch, pimple or discoloration just make me shake my head. They're tools, meant to be ridden, and ridden hard. They're used in races like Paris Roubaix and the Tour of Flanders and usually make it all the way to the finish line.

    If these owners have so little confidence in these frames, there are plenty of aluminum, steel or titanium frames to choose from.
    Too old to ride plastic

  10. #10
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    I got your point. I don't fret over mine either, but it's newer. The bonding of Al parts to carbon was problematic for a number of producers in their early carbon fame experience. When it's done properly it shouldn't be an issue, at all. But it has been in the past.

    If it were my bike and I just happened to notice that blistering paint, I'd be concerned for the reasons I previously stated. I'd try to identify the cause / problem, and if it was galvanic corrosion on an older bike, I'd chalk it up to experience and retire the bike. But that's me. That wouldn't dissuade me from buying a newer model carbon frame from a reputable manufacturer.

  11. #11
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    Quote Originally Posted by ibericb View Post
    If it were just surface corrosion of the alloy (oxidation), I wouldn't be concerned either. But if is from galvanic corrosion between the alloy and the carbon frame, then I would be very concerned.
    Assuming the paint was smooth before and is bubbled now, then it almost certainly is aluminum corrosion underneath the paint.

  12. #12
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    Quote Originally Posted by Kerry Irons View Post
    Assuming the paint was smooth before and is bubbled now, then it almost certainly is aluminum corrosion underneath the paint.
    The real issue/question is the kind of and cause for the corrosion.

    There are two basic options:
    - remove the paint, prep and treat the Al surface, and then refinish as if it were crack/crevice or filiform corrosion, hoping there is nothing more significant;
    - monitor, wait and see what happens.

    To my mind, the first option is the prudent one. The thing to watch closely are the joints between the Al dropout inserts and the carbon frame elements.

  13. #13
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    OP here, thanks guys for all the replies.

    The paint was indeed smooth, although I'm not sure 'bubbled' is quite the appropriate word there? there are no pockets of air under the paint, the surface being hard and resisting the pressure of my fingernail.

    I feel ibericb might be right about galvanic corrosion: the lower side (facing the pavement) of the dropout is still smooth (or smoother).

    On the left side, there is a little 'coarseness' on the adapter, but the dropout itself is smooth. I can take pictures of that side too, if it's useful.

    The bike is not terribly old: it's been assembled in 2011 and bought by me in 2013, ridden mostly in fair weather and has ~19,000 km. The model however dates back to 2006 or 2007, can't say for sure in which year this specific frame has been manufactured.

    Both the bike and the frame are still under warranty (the bike's is about to expire though), and I talked to the shop and have been told to take it in for an inspection, although the bike will have to be shipped off to a service center.

    I am wondering what's generally the response manufacturers have when confronted with this type of damage?

  14. #14
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    Quote Originally Posted by oct3 View Post
    ...

    Both the bike and the frame are still under warranty (the bike's is about to expire though), and I talked to the shop and have been told to take it in for an inspection, although the bike will have to be shipped off to a service center.

    I am wondering what's generally the response manufacturers have when confronted with this type of damage?
    Good!

    Galvanic corrosion of Al dropouts and adapter, or worse between carbon tubes and Al lugs in the early bonded frames, was not that unusual in the early years for about every OEM. It was something new for them, and about every one of them had to go through the experience. In current models it should be a rather rare occurrence for any quality brand.

    Response varies by OEM. If it's one of the reputable one,s and there is no sign of an "external force", it should be covered so long as your warranty is still valid. The real issue is how they deal with it - repair or new frame.

    Hope you come back and let us know what answer you get, and how thy treat you.
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  15. #15
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    Here I am, the bike is supposedly ready for pick up. The manufacturer has a reputation to replace everything at the drop of a hat, but it took a little more than two weeks for the bike to come back, and last time I ordered a spare part the wait was considerably longer.

    It's not impossible they had a replacement frame on hand but I'm not overly optimistic since that model has been phased out: expecting to hear someone tell me it's all my fault.

  16. #16
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    Looking forward to hearing how this is resolved.
    "When man invented the bicycle he reached the peak of his attainments."
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  17. #17
    rooky tour rider
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    My elemental knowledge isn't what it used to be when still in college so bear with me,
    but why don't they switch the dropouts out for steel or titanium ones?
    Weight difference should only be some grams and costs should be more or less the same for such a small part (except maybe Ti).

    Or is galvanic corrosion even more present in a Ti/carbon mix for instance?

  18. #18
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    Nope - Ti is a great combination. It's what Calfee does with C-fiber frames. I have no clue why others don't do the same, other than cost.
    "When man invented the bicycle he reached the peak of his attainments."
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  19. #19
    Done
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    I'll be curious to hear what the manufacturer says.

    My belated guess is that it might be more of a paint issue than a galvanic corrosion issue. Some finishes are more porous than others, especially with how they handle salt or sweat. I've learned the hard way with my own bikes just how corrosive human sweat can be on a finish. The fact that the OP says that it is not as corroded on the bottom of the dropout/joint makes me think that it might be caused by something sitting on the paint coming from above. Like sweat. Or it could be that the primer isn't compatible with the alloy used for the dropout/connector.

    I've got a bike from 2003 with carbon seat stays (Columbus Carve) that, like yours, are bonded with an alloy connector plugged into each end (and bolted to a titanium frame). The joint is unpainted and looks fine. No fuzz, no corrosion. Which proves absolutely nothing with respect to this particular bike...

    EDIT:

    Found this - pretty interesting

    Carbon Fiber Q & A

    Q: On your web site you have indicated that aluminum and carbon fibre react so as to cause cathodic corrosion. Is this also the case with steel or cromoly steel and carbon fibre?

    A: Yes, it is a problem with steels as well as with aluminum alloys. The easy solution is to prevent contact. One way to do this is to include a single light ply of fiberglass in the layup as an electrical insulator between the metal and carbon. Trek did this with their bonded aluminum lug carbon tube bikes. Specialized did too, and Kestrel uses small patches of fiberglass in the fork and frame where metal parts attach. Aerospace structures do the same. See NASA's document TM-584C, CORROSION CONTROL AND TREATMENT MANUAL.
    Last edited by Gregory Taylor; 02-20-2015 at 07:35 AM.
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  20. #20
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    So do you have the answer yet? Inquiring minds want to know
    "When man invented the bicycle he reached the peak of his attainments."
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    Never use your face as a brake pad.
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  21. #21
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    Actually I did, but completely forgot about posting a follow-up, until now! So, fashionably late:

    The frame was replaced under warranty.

    Now, two years have passed, and during today's maintenance, I found out the right drop-out is bubbling up again: I haven't noticed so far because the corrosion has, for the time being, only affected the inside of the drop-out, facing the cassette.

    I'm wondering whether the issue may not be specific to the two frames I was given, and there is a greater problem with manufacturing instead.

  22. #22
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    Carbon fiber is relatively highly reactive with other materials, including aluminum. If there isn't some sort of insulator between the carbon and the aluminum, you'll get the corrosion you see.

    Typically, manufacturers will do things such as insert a Kevlar sleeve over the dropout end which plugs into the tube or use some other method to insulate the dropout from the tube.

    I'm inclined to think the problem lies there with your frame.

  23. #23
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    Yup, assuming the frame were to be replaced again, I am inclined to think, too, the problem will resurface in two years time.

    A newer iteration has the same geometry and basic features but a host of changes, including full carbon drop-outs.

    I'm planning to ask to talk to a higher-up, whether they will agree to the swap remains to be seen, what else can I do anyway?

  24. #24
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    What is the brand & model of the frame?

  25. #25
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    I avoid to ever say in public because, as much I believe at a theoretical level in the idea that other people are riding this specific bike somewhere, I never actually saw one on the road! Wish it were so anonymous as a Pinarello

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