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 Post subject: Is this corrosion?
PostPosted: Thu Aug 14, 2014 7:54 pm 
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Joined: Sun Aug 03, 2014 1:00 pm
Posts: 11
Hello all,
My frame is now 8-9 years old although it was ridden for much less than this, and I always had the problem that after a ride in the rain, the water would somehow be trapped in the frame. It is a bit annoying but I just remove the seat post and turn the frame upside down for a couple of minutes and its OK again.

Today I realise that there is something funny going on below my bottom bracket. Here is a picture:
Image

Could this be related to the water issue? Is this corrosion? At first I thought that they didn't sand the welds properly, but thats not the case, the bubbly parts are quite soft. Any idea what this could be, and how I could treat it? In case it is important, the frame is aluminium lugs with carbon tubing, and the bottom bracket is aluminium.

Also I wonder if this outer cable piece was meant to be like that or if the mechanic that transferred the components from my old frame back then was creative and blocked some water draining hole with it for some reason... Have you seen any other bike having something like that?

Best,
Lightweenie


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 Post subject: Is this corrosion?
Posted: Thu Aug 14, 2014 7:54 pm 


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 Post subject: Re: Is this corrosion?
PostPosted: Thu Aug 14, 2014 8:57 pm 
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Joined: Fri Dec 24, 2010 9:37 pm
Posts: 558
Location: it's raining, it must be uk
could be that water has got in, when aluminium corrodes the product occupies more volume, which'd explain the bubbling

if it's only on the surface it should be ok, i'd use a fine abrasive to remove the blistered paint and corrosion (which'll probably be white and crunchy) then recoat the exposed area


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 Post subject: Re: Is this corrosion?
PostPosted: Thu Aug 14, 2014 9:52 pm 
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Joined: Tue May 23, 2006 4:33 am
Posts: 731
Are those carbon chain stays? Carbon has to be sealed completely from aluminum or the epoxy can start corroding the metal quite significantly. It's a manufacturing defect, not a use issue, and this was common in frames from around this period. It's caused by the very caustic nature of carbon resin when it isn't insulated from the aluminum.

I ask because the drain hole seems open, you don't have corrosion coming out from it, and the corrosion seems to originate from joints in the bottom bracket. It's an awful lot of corrosion given how limited it is, which makes me think it could be epoxy corrosion at points where the aluminum wasn't completely sealed off. The area closer to the bottom bracket itself seems to originate not from the inside of the bottom bracket but from the hole for the cable run. When that hole was drilled, it could have violated the barrier between carbon and aluminum, and thus allowed corrosion to start. The corrosion at the back (closest to the wheel) is where the join of the aluminum and the carbon may not have been sealed and thus corrosion started.


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 Post subject: Re: Is this corrosion?
PostPosted: Thu Aug 14, 2014 10:01 pm 
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Joined: Sun Aug 03, 2014 1:00 pm
Posts: 11
@11.4 This sounds very worrisome, but looking at my picture again, it makes a lot of sense. Yes they are carbon chain stays. However you say that the drain hole is open, I think you refer to the hole to which the cable guide was screwed at.

@sungod removing the paint and corrosion should be easy, but what worries is how to recoat the area? (assuming that it is only a surface thing, because if 11.4 is right I probably need a new frame)


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 Post subject: Re: Is this corrosion?
PostPosted: Thu Aug 14, 2014 10:28 pm 
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Joined: Fri Jan 03, 2014 7:37 am
Posts: 173
i wouldn't worry personally. just looks like some moisture/contamination got under the paint or it wasn't prepped well in the first place. i have an old carbon/alloy lugged trek that i ride in the winter that has developed a similar issue, all i did was scrape the offending paint off to make sure the joints were OK and there wasn't anything crazy going on. everything was fine and i still ride it worry free.

if i were you id remove the offending paint. maybe hit it with some laquer or clear. but its aluminum so even if you leave it raw its not really going to corrode into oblivion


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 2:35 am 
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Joined: Tue May 23, 2006 4:33 am
Posts: 731
Scrape the paint off and if the corrosion is originating at the carbon to aluminum interface, you have corrosion from the resin. There is nothing you can do to refinish or stop it. You may choose to keep riding until the frame breaks, if it ultimately does. But this happened when the frame was glued together and nothing will fix it. You have a reasonable case for asking the manufacturer to at least give you some partial settlement. I presume it's out of warranty, though some carbon frames have 10 year or lifetime warranties. There's definitely a new frame in your future.

Btw, I was referring to the hole centered in the BB that wasn't a source of corrosion. The corrosion comes from the hole drilled to accommodate the front shifter cable.


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 1:23 pm 
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Joined: Sun Aug 03, 2014 1:00 pm
Posts: 11
11.4 wrote:
Btw, I was referring to the hole centered in the BB that wasn't a source of corrosion. The corrosion comes from the hole drilled to accommodate the front shifter cable.


Yes, I also refer to this hole. This hole is threaded, and there is normally a screw in there that holds the cable guide in place (the guide can be seen on the top of the picture along the cables). When the guide is in place, the hole is totally blocked, so there seems to be no real drain-hole in the frame.

In any case, since it is not necessary to repaint aluminum, I will scrape the paint off, see how deep the corrosion goes, and report back. I will probably get around to this early next week.

One last question, how dangerous can a bottom bracket failure be? Since there should not be too many forces on the bb during descending, I am only worried about failure while sprinting - but perhaps I forget something. In any case will look into the warranty issue (it is a merida frame) and/or look at new frames, in parallel.


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 2:01 pm 
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Joined: Wed Sep 20, 2006 1:03 am
Posts: 296
Location: Phoenix, AZ
11.4 wrote:
Carbon has to be sealed completely from aluminum or the epoxy can start corroding the metal quite significantly. It's a manufacturing defect, not a use issue, and this was common in frames from around this period. It's caused by the very caustic nature of carbon resin when it isn't insulated from the aluminum.

Carbon/aluminum corrosion is absolutely a real thing, but this is not quite how it works. The resin isn't particularly caustic, although I wouldn't mainline the stuff. The problem is that when you put carbon next to aluminum, you've created a battery. When carbon and aluminum swap electrons, the aluminum corrodes and the bond between the two fails.

As 11.4 notes, this was a problem on early (late '80s-early '90s) carbon frames. If you look at the old Giant Cadex frames, you'll see that the aluminum bottom bracket shells are hard anodized. The anodization is an excellent electrical insulator and prevents galvanic corrosion with the adjacent carbon.

Here's a more detailed explanation from http://www.boeing.com/commercial/aeroma ... rrosn.html :

Quote:
For example, graphite fibers, which are used to reinforce some plastic structure, present a particularly challenging galvanic corrosion combination. The fibers are good electrical conductors and they produce a large galvanic potential with the aluminum alloys used in airplane structure. The only practical, effective method of preventing corrosion is to keep moisture from simultaneously contacting aluminum structure and carbon fibers by finishing, sealing, using durable isolating materials such as fiberglass, and providing drainage.

You can scrape the paint off and see what's under there, sure. Corroded (oxidized) aluminum typically looks white and powdery.

In my opinion, your frame is so recent and made by such an experienced manufacturer of carbon-bonded-to-aluminum frames (Merida) that galvanic corrosion is an unlikely culprit. Furthermore, there's lots of corrosion far from the carbon stays; galvanic corrosion would start at the carbon/aluminum interface and radiate outward.

Many alloys of aluminum corrode like crazy in the presence of salt water. If you rode this bike in the winter and didn't rinse off all the road brine, I'd expect to see corrosion like this. If this is a non-galvanic corrosion issue, it's really not a manufacturing defect, so I wouldn't expect Merida to warranty the frame.

But there's a fair chance that your frame is structurally sound and just needs to have the corrosion removed with, say, a wire brush. Structural integrity is impossible to assess without putting hands on the frame. If I were you, I'd take it to a shop I trusted for an opinion.

Speaking of trusting shops, why on earth are you running the cables without a guide? They will certainly abrade your paint and provide a great place for new corrosion to start.

Cheers,

Jason


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 2:46 pm 
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Joined: Sun Aug 03, 2014 1:00 pm
Posts: 11
Thanks a lot for the information Jason.

Indeed I do ride the bike during both winter and summer. Since I am moving to a new country every couple of years, I try to keep my belongings to the bare minimum, which means only one bicycle that has to be ridden summer and winter. Also I don't have access to a hose to rinse off the bike after every ride - if it was a very wet ride I usually do some cleaning in the bathtub, else I just park the bike as is. So salty water would be another possible explanation. I had not thought of that :).

Also, as I mentioned in a previous post, I am running the cables with a guide! You can see the guide is pushed a bit along the cables to the top of the picture. I just unscrewed it to check how the paint looks beneath it, and to make for a clearer picture.

One thing confuses me a bit: you say that "abraded paint provides a great place for new corrosion" which contradicts what was mentioned earlier in the thread that aluminium does not need paint. So what is the case?

Best,
Lightweenie


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 2:49 pm 
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Joined: Thu Oct 26, 2006 8:54 pm
Posts: 382
Location: USA
@youngs_modulus: look at his photo carefully... he isn't running it without a cable guide, he just removed the screw and slid the guide up the down tube to fully expose the BB for the photo.

_________________
Enjoying my Funk


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 6:01 pm 
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Joined: Wed Sep 20, 2006 1:03 am
Posts: 296
Location: Phoenix, AZ
Now I see the guide. Sorry I missed that.

Lightweenie wrote:
[snip] if it was a very wet ride I usually do some cleaning in the bathtub, else I just park the bike as is. So salty water would be another possible explanation. I had not thought of that :).

It's the salty water, an electrolyte, that you have to watch out for. Standard rainwater isn't a big deal. So salted winter roads and rides in coastal areas are the things to watch out for.

Lightweenie wrote:
One thing confuses me a bit: you say that "abraded paint provides a great place for new corrosion" which contradicts what was mentioned earlier in the thread that aluminium does not need paint. So what is the case?

11.4 was right insofar as aluminum is corrosion resistant under most conditions. But obviously you're riding in conditions under which aluminum corrodes. So I'd paint or clearcoat over the areas you strip.

Aluminum pitting seems to be the primary form of corrosion on your bike, but dissimilar metals (like a stainless steel cable and aluminum) can induce corrosion as well. Small gaps between parts (e.g., your cables and bottom bracket shell) are also nucleation sites for corrosion; this is sometimes called crevice corrosion.

The link below has a wealth of useful information regarding aluminum corrosion.

http://www.aluminiumdesign.net/design-s ... esistance/


Cheers,

Jason


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 6:05 pm 
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Joined: Tue May 23, 2006 4:33 am
Posts: 731
youngs_modulus wrote:
11.4 wrote:
Carbon has to be sealed completely from aluminum or the epoxy can start corroding the metal quite significantly. It's a manufacturing defect, not a use issue, and this was common in frames from around this period. It's caused by the very caustic nature of carbon resin when it isn't insulated from the aluminum.

Carbon/aluminum corrosion is absolutely a real thing, but this is not quite how it works. The resin isn't particularly caustic, although I wouldn't mainline the stuff. The problem is that when you put carbon next to aluminum, you've created a battery. When carbon and aluminum swap electrons, the aluminum corrodes and the bond between the two fails.

As 11.4 notes, this was a problem on early (late '80s-early '90s) carbon frames. If you look at the old Giant Cadex frames, you'll see that the aluminum bottom bracket shells are hard anodized. The anodization is an excellent electrical insulator and prevents galvanic corrosion with the adjacent carbon.

Here's a more detailed explanation from http://www.boeing.com/commercial/aeroma ... rrosn.html :

Quote:
For example, graphite fibers, which are used to reinforce some plastic structure, present a particularly challenging galvanic corrosion combination. The fibers are good electrical conductors and they produce a large galvanic potential with the aluminum alloys used in airplane structure. The only practical, effective method of preventing corrosion is to keep moisture from simultaneously contacting aluminum structure and carbon fibers by finishing, sealing, using durable isolating materials such as fiberglass, and providing drainage.

You can scrape the paint off and see what's under there, sure. Corroded (oxidized) aluminum typically looks white and powdery.

In my opinion, your frame is so recent and made by such an experienced manufacturer of carbon-bonded-to-aluminum frames (Merida) that galvanic corrosion is an unlikely culprit. Furthermore, there's lots of corrosion far from the carbon stays; galvanic corrosion would start at the carbon/aluminum interface and radiate outward.

Many alloys of aluminum corrode like crazy in the presence of salt water. If you rode this bike in the winter and didn't rinse off all the road brine, I'd expect to see corrosion like this. If this is a non-galvanic corrosion issue, it's really not a manufacturing defect, so I wouldn't expect Merida to warranty the frame.

But there's a fair chance that your frame is structurally sound and just needs to have the corrosion removed with, say, a wire brush. Structural integrity is impossible to assess without putting hands on the frame. If I were you, I'd take it to a shop I trusted for an opinion.

Speaking of trusting shops, why on earth are you running the cables without a guide? They will certainly abrade your paint and provide a great place for new corrosion to start.

Cheers,

Jason


We had a team sponsorship with BMC and had two frames in 2006 that had this problem. BMC did insulate the components, but on smaller frames, they had to mill the faces of the head lugs so they could fit them onto a very short head tube. That milling removed the insulative coating and allowed the head lugs to corrode. These were the last generation of the BMCs with aluminum lugs, but it's in the same time period as the OP's frame. It's not that the insulation isn't applied, it's that the builder then does something (in this case, potentially the hole for the front shifter cable) that violates the insulation.


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 Post subject: Re: Is this corrosion?
PostPosted: Fri Aug 15, 2014 6:12 pm 
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Joined: Wed Sep 20, 2006 1:03 am
Posts: 296
Location: Phoenix, AZ
To be honest, it sounds like BMC screwed up. In 2006, this had been a solved problem in the bike industry for more than a decade. If BMC was milling off the insulation they applied, they just messed up. Why did they mill these head tube lugs in the first place? Were these custom frames that somehow used stock lugs?

At any rate, there's no issue with "caustic resin."

That's not to say galvanic corrosion never happens on bike parts anymore. Just a few years ago, ENVE was shipping carbon rims with alloy nipples. The alloy nipples corroded, naturally, so now ENVE uses their own (rather nifty) brass nipple.


Edit: fixed typo


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 Post subject: Re: Is this corrosion?
PostPosted: Sat Aug 16, 2014 3:31 am 
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Joined: Tue May 23, 2006 4:33 am
Posts: 731
youngs_modulus wrote:
To be honest, it sounds like BMC screwed up. In 2006, this had been a solved problem in the bike industry for more than a decade. If BMC was milling off the insulation they applied, they just messed up. Why did they mill these head tube lugs in the first place? Were these custom frames that somehow used stock lugs?

At any rate, there's no issue with "caustic resin."

That's not to say galvanic corrosion never happens on bike parts anymore. Just a few years ago, ENVE was shipping carbon rims with alloy nipples. The alloy nipples corroded, naturally, so now ENVE uses their own (rather nifty) brass nipple.


Edit: fixed typo



That's my point. They screwed up. They used a standard pair of head lugs on all their frames but on their two smallest sizes they had to remove part of each lug (the edges that faced each other when mounted on the head tube) because the head tube was so short. In the case of the OP's bottom bracket, it looked like the same might have happened here -- the frame was assembled and then the hole for the front shifter cable was drilled and finished. That would have led to the same problem.

I agree this is an electrolytic issue. I used the term caustic loosely because I've never been able to convince people that carbon fiber and a metal can create a battery -- even though the next generation of batteries will be just that.


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 Post subject: Re: Is this corrosion?
Posted: Sat Aug 16, 2014 3:31 am 


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 Post subject: Re: Is this corrosion?
PostPosted: Mon Aug 18, 2014 6:35 pm 
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Joined: Sun Aug 03, 2014 1:00 pm
Posts: 11
Hello again,

I removed the paint and there was some sort of compressed yellowish/white powder beneath it. It is quite strange and I don't know what it was. Here are some pictures:

Image
Image

Now the frame looks like this:
Image
Image

I am quite happy that it seems intact, I really like this frame and I think I can keep riding it at least a year longer. However I have no idea what product to use to seal this part off again. Any suggestions?


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