plate gonna break?

[Dave Nereson]

    Tried to tune a 1964 Wurlitzer spinet today that I've tuned many times,
but the treble just wouldn't hold.  Tuning pin torque was good -- not even
marginally loose.   A4 was only a couple beats flat, so I did a pitch raise,
overshooting by a beat or so.  Then started over to fine tune and the treble
was still way flat.  So I pitch raised just the treble, then went back to
fine tune and the treble was still way flat.  So I raised it again,
overpulling more than usual. Still way flat. Raised it again. Still quite
flat. In the middle of this 4th (!!) treble pitch raise, I remembered that
the last time a piano behaved like this, a strut was giving way and the
plate broke.  So now I'm getting nervous and looking for signs of the plate
pulling away from the back, or the pinblock separating, and I'm inspecting
the plate for any hairline cracks.  Nothing apparent.  But I'm afraid to go
on.  The middle of the piano is staying in tune, but after 4 or 5 pitch
raises in the treble, it's still not holding.  Again, pin torque is good.
    So I give up and tell the owner I'm having a hard time with it and leery
of going on for fear something might be giving way.  He then informs me that
a few days ago the washing machine overflowed, flooding that area of the
house quite seriously.  But they started mopping up within 20 minutes, then
called some outfit (plumbers?), who brought in a heavy duty commercial
dehumidifier, which had been running now for three days (mainly to dry out
the carpet, I guess).
    Well, OK, maybe that's why the weird behavior.  The last two times I
tuned it were both in the summer, and this is winter, so it's normal that it
would be somewhat flat, and the big dehumidifier should make it go even
flatter.  But it should make the whole piano go flat, and by quite a bit,
not just 2 beats.  And it shouldn't cause the treble section to not hold
pitch even after 4 or 5 pitch raises.  I don't know what to do now.  I'm
afraid to raise it any more.  I could just tune it to a lower pitch -- the
owner doesn't absolutely need it at A 440.
    Is there any way to detect (besides X-ray) if there's a crack in the
plate that's not visually apparent?  I tried tapping lightly around the
plate with a small hammer, like brakemen on trains used to do to detect
cracked wheels, but discovered of course that the plate doesn't ring like
steel -- I knew that, but in wary, cautious, nervous moments, you try
anything that might give you some information.
     We chose to wait a week or two until the house climate is back to
normal, then see what the pitch of the piano does.  But what would you do?
Go ahead and raise it and if it breaks, it breaks?  Tune it to a lower
pitch?  Tell him the plate might be ready to crack and he should buy another
piano?  Quit the business & leave town so you don't have to deal with it?
                                                                            
 --David Nereson, RPT, Denver