Re[2]: Magnaflux

["Dunst, Mordecai" <mdunst@smtplink.coh.org>]

Hi Mordy!     

1)  If an important piece of metal is "cracked-checked" and is found
     to be "o.k.". 
     
      What is the certainty that it really is "o.k."?

It depends what type of material and how it is checked.  Magnetic particle
and penetrant testing are for the most part only surface checks.  Other NDT
methods such as ultrasonic inspection or x-ray are sub-surface checks.  But
remember, most cracks do start at the surface and propagate inward, so the
first two techniques I mentioned are usually sufficient.
     
     2)  If an old cast (porous) aluminum piece is broken and needed 
     re-welding..
     
      Would it need to be heated hot enough to burn out and rid it of oil 
     that it accumulated over the years..?

This is good practice prior to welding any porous material.  But remember,
when you heat oil in an air atmosphere it forms a deposit that may not be so
easy to remove.  The best solution is to replace the broken part.

Hope this helps....

Chuck
(way too much materials knowledge)