On 6/1/2020 12:40 AM, Jeff Liebermann wrote:
On Sun, 31 May 2020 13:14:54 -0500, AMuzi wrote:

http://www.yellowjersey.org/photosfr...t/failspok.jpg

2004 chinese Trek low end hybrid with low miles. Rider (est
120lb) says she took it out for the first time this year
and during first ride, spokes failed and wheel rubbed the brake.

The front wheel, fork, brake, handlebar are severely
corroded, perhaps from being parked in a garage with the
front closest to a car's daily salt splashes. 8 spokes
missing or broken. Spokes failed in the middle, not the
heads. A dozen or so green nipples are covered in white
efflorescence near the rim (assume these were at the bottom
when parked). The other nipples are dingy nickel.

Spokes do not respond to a magnet. Being 'stainless' or
'inox' doesn't mean a steel will not corrode, it just
succumbs more slowly.

I know you said that the spoke corroded in the middle, but by any
chance were they corroded where the spokes cross over and touch other
spokes? One problem with stainless is that it can be both anodic and
cathodic to itself:
https://yarchive.net/metal/galvanic_corrosion.html
...remember that sometimes the above rules must be
bent a little for other reasons, and that corrosion
can be far more complex than just galvanic corrosion.
Look at the stainless steels for example. Most can
be both cathodic and anodic to themselves! Corrosion
while immersed in sea water can be quite different
than corrosion from exposure to pollutants in the
atmosphere.

In other words, two pieces of stainless steel will develop a
sufficient potential between them to produce galvanic corrosion. In
the galvanic table in the above URL, note that chromium-nickel-iron
appears twice, once as "active" and again as "passive" with quite a
large gap in potential between them. I may have seen this while
working on marine radios, but did not bother to investigate. In your
photo, the upper spoke did not break perpendicular to the axis of the
spoke, but rather broke lengthwise, as I would expect if the spoke
were under tension or torsion. However, the perpendicular breaks on
the other spokes seem to indicate bending, not tension. My guess(tm)
is that the wheel already had some broken spokes before the owner took
the bicycle for a ride.

The white powder(?) kinda looks like aluminum oxide, which is what I
would expect if something made from aluminum were leaned against the
spokes in a electrolytic (salt) atmosphere. Possibly contact with
another bicycle, aluminum rim, frame, rack, floor pump, aluminum bike
stand, aluminum bike rack, etc?

I'm doing quite a bit of guessing based on only one photo. If you
still have the remaining spokes, try match up pairs of several broken
spokes in a photo. I suspect I can extract some more guesswork from
how the spokes broke. I'm especially interested if they broke where
the spokes crossed over each other.




The spokes failed about 1/3 from the rim not at the cross (a
known issue but not applicable here). Yes, the aluminum rim
and the brass nipples appear to have been galvanically engaged.

The shiny spots seem to be from riding with spokes flappng
around and striking each other and the fork.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971