Galvanic Corrosion on Aluminum Insert with Carbon Seatpost

[RyanH]

I went to swap seatpost collars on my Litespeed and had a terrible time getting the seatpost out. This has happened before on probably all of my Litespeeds. They use aluminum inserts and assessing my post, there's galvanic corrosion. I always prep my seatpost with Finish Line but that seems to not be sufficient to prevent corrosion. Has anyone had any luck with other solutions?

Edit: Changed title after researching further.

[RyanH]

To answer my own question, I found this from Craig Calfee:

Dear Lennard,
Thankfully! An opportunity to dispel the myth that one shouldn’t greasea carbon post!I don’t know where the myth started, but carbon composites are not affectedby grease. Our advice is simple: If the seatpost fits tight,grease it. If it slips, de-grease it. As has been known formany years, when aluminum and carbon fiber contact each other, galvaniccorrosion can start. That is why Calfee uses a fiberglass sleeveas a seat tube shim. Aluminum seat tube (or sleeve) and a carbonpost will result in corrosion of the frame and possible seizure of thepost within the frame. A carbon sleeve on an aluminum post will resultin corrosion of the post. Salty environments accelerate this corrosion.Anodizing merely slows it down. About the only common chemical thatwill hurt carbon fiber is paint remover (which attacks the resin betweenthe fibers). But there are many solvents that will dull a nice paintjob.
Craig Calfee

[Valbrona]

Grease is for lubrication.

If you need to use an anti-seize compound on a seatpost, well then use the stuff that comes in a spray can. Like the stuff that Loctite do.

[djwalker]

I have always had the same problem just in reverse- an aluminum seat post with a carbon frame. Solution- match the frame and seatpost materials. In your case use an aluminum seatpost. Every other option (grease, anti-seize) just slightly slows the inevitable. I sweat a lot which makes things even worse. No matter what I do an AL seatpost in a carbon frame looks horrible in only a few months. So, your choices are an AL seatpost or a new frame if you want to eliminate the problem. Personally, I would get a nice Thomson AL post or something like that and then not worry about it.

[pdlpsher1]

What's an aluminum insert doing in a titanium frame? The Litesoeed I had has no insert.

I just acquired a new titanium bike. I just bought a carbon seatpost. I hope titanium and carbon will be OK.


Sent from my iPhone using Tapatalk

[sungod]

it'll be ok, in practice ti and carbon have similar galvanic potential, they are are both at the 'noble' end of the table

corrosion occurs when you get a bigger difference in galvanic potential

al has a much more negative gp, it is less noble so it is the one that gets corroded

[mattr]

What's an aluminum insert doing in a titanium frame?

Making the ID of the tube suitable for fitting a seatpost?

All 3 (4 maybe?) of my Ti frames have had an insert.

But i've always used grip paste or grease, so while they may start to discolour/corrode. No jamming.

[youngs_modulus]

Grease is for lubrication.

No; grease is not just for lubrication. Grease is generally an insulator, but dielectric grease (made from silicone) is an even better insulator. If you must join a carbon part to an aluminum part, dielectric grease will help inhibit galvanic corrosion. In fact, many carbon "assembly pastes" are made from silicone grease (plus grit, most likely aluminum oxide or silica) precisely because it's better than hydrocarbon greases at inhibiting galvanic corrosion.

If you need to use an anti-seize compound on a seatpost <snip>

I think you've misunderstood the problem here. The OP is (correctly) concerned less about a semi-stuck seatpost and more about galvanic corrosion between his seatpost and frame insert, which could eventually cause catastrophic failure in his post.

Anti-seize is pretty conductive for a grease-based compound and would accelerate any galvanic corrosion, especially in the presence of a little sweat (an electrolyte in the carbon/aluminum battery the OP was riding).

"Carbon paste" is mostly grease, yet it increases friction. Anti-seize would accelerate the process that caused the OP's seatpost to (partially) seize. So grease can increase friction and anti-seize can cause seizing. All generalizations are false.

[Dilbert]

Below is a table of galvanic potential for stuff in sea water ( I cant find one for sweat ) . For a cell to form, there has to be:
electrolite
Galvanic potential in the order of 0.5V (AFIK)

Graphite/carbon is at +0.2, and aluminium alloy between -0.8 tot -1.0. That gives a potential of 1 to 1.2, which is enough
for a cell with a carbon cathode and alu anode.

[bikemaniack]

Use grip paste,will work fine.

[djwalker]

Use grip paste,will work fine.

My experience is that NO it won't work fine. I used grip paste and cleaned and replaced it every few months and the seatpost still looked like it had been through a war. Same result with grease. I have ruined more seatposts than I can count. Only by taking the galvanic potential into account did the problem go away.

[Calnago]

I am using this now for parts that don't get removed often and where I want to prevent oxidation, galvanic corrosion, etc.

For parts where I don't want slippage I'll still use carbon assembly compound. I'll use it on alloy parts as well where slippage could be a factor. So, stem to steertube, bars to stem, seatposts... ill generally use this. But you need to be especially diligent about maintenance where different metals contact and stay put. Threaded bottom brackets in particular I've always used a healthy coat of copper based antiseize compound but lately I've been trying out the Morgan Blue Aquaproof Paste too, as it's so much cleaner to work with. And for seatpost going into a titanium or aluminum seattube I'm a little more diligent about regular checkups etc. Pull it, clean it, put it back. Doesn't take long but it's not fun when you find those parts seized together. I've never had it happen to any of my bikes because I'm aware of it, unfortunately through having to remove, or attempt to remove, them form other bikes.

[youngs_modulus]

I strongly suspect that Morgan Blue Waterproof Paste is just silicone grease. All of the claims Morgan Blue makes on its web site are also true of silicone grease. It also looks exactly like silicone grease.

Plus, 200 ML of "waterproof paste" goes for about $26 online, but you can buy about the same amount of thick silicone grease all day long for $5-$8.

Calnago, you imply you're using Morgan Blue's product in place of antiseize for threaded parts. If that's what you're actually doing, be careful. Silicone grease won't prevent galling of similar metals. For example, threading titanium into titanium (or stainless into stainless) galls heavily and can seize, which is essentially the same thing. Silicone grease doesn't prevent galling. Morgan Blue doesn't claim to prevent it either.

Mllions of dollars have been sunk into R&D to come up with a non-anti-seize grease that can prevent galling. The aerospace industry has a few compounds, but they are eye-wateringly expensive. DuPont Krytox, for example, has some anti-seize properties and costs $175.00 (US) for an 8-ounce tube.

But Calnago has a point that conventional anti-seize is incredibly messy to work with. I've had very good luck with copper-based anti-seize tape:

https://www.lawsonproducts.com/Lawson/C ... e/98663.lp

[kode54]

I am using this now for parts that don't get removed often and where I want to prevent oxidation, galvanic corrosion, etc.

For parts where I don't want slippage I'll still use carbon assembly compound. I'll use it on alloy parts as well where slippage could be a factor. So, stem to steertube, bars to stem, seatposts... ill generally use this. But you need to be especially diligent about maintenance where different metals contact and stay put. Threaded bottom brackets in particular I've always used a healthy coat of copper based antiseize compound but lately I've been trying out the Morgan Blue Aquaproof Paste too, as it's so much cleaner to work with. And for seatpost going into a titanium or aluminum seattube I'm a little more diligent about regular checkups etc. Pull it, clean it, put it back. Doesn't take long but it's not fun when you find those parts seized together. I've never had it happen to any of my bikes because I'm aware of it, unfortunately through having to remove, or attempt to remove, them form other bikes.

i started using MB aqua-roof as well...in places that i'm concerned about water/rust. seems to block more water as it is super sticky.

[kode54]

To answer my own question, I found this from Craig Calfee:

Dear Lennard,
Thankfully! An opportunity to dispel the myth that one shouldn’t greasea carbon post!I don’t know where the myth started, but carbon composites are not affectedby grease. Our advice is simple: If the seatpost fits tight,grease it. If it slips, de-grease it. As has been known formany years, when aluminum and carbon fiber contact each other, galvaniccorrosion can start. That is why Calfee uses a fiberglass sleeveas a seat tube shim. Aluminum seat tube (or sleeve) and a carbonpost will result in corrosion of the frame and possible seizure of thepost within the frame. A carbon sleeve on an aluminum post will resultin corrosion of the post. Salty environments accelerate this corrosion.Anodizing merely slows it down. About the only common chemical thatwill hurt carbon fiber is paint remover (which attacks the resin betweenthe fibers). But there are many solvents that will dull a nice paintjob.
Craig Calfee

Ryan,

so tell me how you got the seat post out. i have a carbon post in a Litespeed Ghisallo and its seized in there like yours was. TIA