Galvanic corrosion around valve hole of aluminium rim?

[PpPete]

Rim is a Kinlin XR-31RTS, spokes CX-Ray, brass nipples, valves are Effetto Mariposa Caffeelatex (as is the sealant ).

After a year my tubeless set up above was not holding pressure, despite more than adequate amounts of sealant and no obvious holes in the tyre. Finally stripped it down, removed valve and rim-tape to see if I could find a cause.
On the tube facing side, the valve hole was a jagged mess, far from round - certainly too big to seal with the tapered valve seat.
The valve stem (which I think is some sort of brass) had quite bit of corrosion deposit around it, so I'm guessing some sort of galvanic effect, But there was no obvious corrosion around the spoke nipples which are also brass, so I'm not sure.
I've never seen this before, and the only thing different to what I've done previously (on H+ SON Archetype rims) was not to put rim tape over the valve hole (which then has to be pierced anyway).
Anyone have similar experience? or knowledge of how the KLM41 alloy that Kinin boast about differs from others/

 

[fossyant]

The valve is probably not brass then

 

[Yellow Saddle]

Rim is a Kinlin XR-31RTS, spokes CX-Ray, brass nipples, valves are Effetto Mariposa Caffeelatex (as is the sealant ).

After a year my tubeless set up above was not holding pressure, despite more than adequate amounts of sealant and no obvious holes in the tyre. Finally stripped it down, removed valve and rim-tape to see if I could find a cause.
On the tube facing side, the valve hole was a jagged mess, far from round - certainly too big to seal with the tapered valve seat.
The valve stem (which I think is some sort of brass) had quite bit of corrosion deposit around it, so I'm guessing some sort of galvanic effect, But there was no obvious corrosion around the spoke nipples which are also brass, so I'm not sure.
I've never seen this before, and the only thing different to what I've done previously (on H+ SON Archetype rims) was not to put rim tape over the valve hole (which then has to be pierced anyway).
Anyone have similar experience? or knowledge of how the KLM41 alloy that Kinin boast about differs from others/

Does the sealant have ammonia in? Usually if it contains latex, ammonia is added to the solution to prevent the latex from decomposing (it is plant juice and easily rots). Ammonia solution in water has a pH of almost 12 - very alkaline. Aluminium is easily corroded by caustic solutions.

 

[Cycleops]

Just give me a good old inner tube.

 

[PpPete]

Just give me a good old inner tube.

Well, I ran it with an inner tube for a while - but given the size of the whole I was always scared of an explosive deflation:

Does the sealant have ammonia in? Usually if it contains latex, ammonia is added to the solution to prevent the latex from decomposing (it is plant juice and easily rots). Ammonia solution in water has a pH of almost 12 - very alkaline. Aluminium is easily corroded by caustic solutions.

Sealant bottle says it contains no ammonia.

The valve is probably not brass then

Must be some kind of copper alloy in it somewhere as the part of threaded area of the valve had a green colouration.

I've bought some aluminium valves for the replacement rim....

 

[silva]

Lol that's not a hole that's a cave.
Galvanic corrosion should stop itself in a hole if things stay into position, since it requires an electrical conductive path, and dissolved material = conducting material gone and thus remaining material farther from the other pole - abit like how a glowing bulb ends, a bright flash due to material melting and a spark over the length the voltage can bridge in the gas, and then nothing.
Has to have been a shotgun, or that Yellow Saddle scenario.

 

[Rickshaw Phil]

Hells bells! I think it is safe to say that rim is scrap.

A good chance to practice relacing a wheel?

 

[Ming the Merciless]

I use Kinlin rims in tubeless mode. I cover hole with rim tape. Not seen this occur with over 4 years use.

 

[Ajax Bay]

put rim tape over the valve hole (which then has to be pierced

Yup, I guess this is the lesson identified (or good practice supported by a reason).
With an aside of realising the differing pH of sealants may have consequences and that if a tyre is losing air faster than 'normal' after a few pump ups, worth checking to determine the reason without further delay.

 

[Ian H]

The instructions I follow say to wrap the room tape all the way round, at least once. Then pierce, don't cut, at the valve hole and push the valve through.

 

[PpPete]

The instructions I follow say to wrap the room tape all the way round, at least once. Then pierce, don't cut, at the valve hole and push the valve through.

This is indeed what I shall always be doing in the future.