what is this corrosion?

[Ron Nossaman]

>The first piano tech on the scene pronounced it a write-off.
-----------------------
>However, for some reason, a second
>technician was called out about a week or so later.

The second tech was called out because the first tech didn't report what
the claims adjuster (interesting title, don't you think?) wanted to hear.
The second tech evaluated the piano based on what he thought he saw. It
could happen to any of us, and probably has. No real lost points for the
second tech, other than an unfortunately overly optimistic diagnosis.



>Now, four years later, corrosion is rampant, but in an odd way.  The new
>strings and pins are fine. The speaking lengths of all the strings are fine.
>Only on some sections where the strings cross  the understring felt is
>there rust.  All the coils are rusted, but it almost looks to me like the
>plating on the old tuning pins is rusting, not the coils themselves. There
>is also rust on the INSIDE of the brass agraffe holes and at the bases of
>the agraffes.

With the extreme humidity level that everything was exposed to without
actually getting wet, it was effectively gotten wet anyway. The understring
felt absorbed enough humidity, and retained it, long enough to rust the
strings resting on it. This probably happened immediately, but it wasn't
visible because it was on the bottom side of the string. The same thing
happened inside the coils, where the restricted air circulation kept the
high humidity trapped long enough to get the rust started. Again, it wasn't
visible under the coils. Same thing, but to a lesser degree, with where the
strings go through the agraffes.



>on the agraffes where the
>strings passing thru the holes have worn the brass plating thin.  Perhaps
>the rust appearing at the base of the agraffes is where the threads
>underneath the agraffes are not solid brass, but plated steel.

I'm not aware of such a thing as a brass plated steel agraffe. Are you
sure? I've never seen one that wasn't solid brass. 



>Would a reasonable repair be to clean off the rust, and spray lacquer on the
>tuning pins and coils and agraffes?  Would that hurt anything?

I wouldn't, since you can only clean what you can reach, but can't get to
the source. I think the only realistic choices are ignore or rebuild. It
seems that the first tech was right.



>Could there have been something corrosive that eats plating sitting in the
>sprinkler pipes?  I think residential fire sprinkler systems use PVC pipe,
>not galvanized steel ones.

Not that I'm aware of. Firemen used to (still do?) put a detergent in the
water reservoirs in their trucks as a wetting agent - to aid penetration by
lowering surface tension. That, and the heat, steam, and water pressure,
pretty much guarantees that highly corrosive combustion products are forced
to the bone in every item in the house. In this case, there wasn't a fire,
so there's no heat, steam, combustion products, or high pressure stream.
Just water is bad enough. 



>  I have been asked to give a second
>opinion in this case, but I have never seen anything like it.  How about you
>guys?
>
>Carol Beigel

Once, when a new piano was left overnight in a broken down truck. Lots of
slushy melting snow, night temperature slightly below freezing, and warming
quickly in the early morning. Very high humidity warm air contacting
interior metal parts still considerably below the dew point in temperature
had about the same effect, but it showed up in a couple of weeks. I
restrung the piano.


Ron N