It's not necessary for the material to be ferrous to do magnetic testing.
All it has to be is conductive. You can induce currents into the metal by
means of an electric field (and yes, it can have circulation ie it is
magnetic). The discontinuities in the induced current (due to cracks) will
cause a net increase in the responsive magnetic field (even though it is not
magnetic material - think - copper wire produces magnetic fields but it is
non ferrous) or changes in the E field on the surface of the metal. There
are films responsive to E fields, these can be used on the metal surface or
you can use small electric field probes.

You can even use the old standby of iron filings if you know what to look
for. I prefer RCS measurements to look for cracks.

Amen!



wrote in message
ps.com...
The cracks shown in that link are exactly like the ones I found in my
20 yr old rigging. The cracks in mine were very difficult to find
until I used fine sandpaper. They were all on the lower swaged end.
Most of the cracks were under small brown stains that were the result
of the stainless in the crack becoming non-stainless and rusting. They
required a 10X magnifier to find. At work, I ground the fittings away
to see how deep they went and they went through the entire fitting. I
even used dye penetrant with no luck. I replaced all the rigging and
lifelines last year.
NOW, although thefittings and wire and rod are stainless, stainless can
be slightly ferromagnetic and can be tested via flux leakage methods (I
used to do magnetic NDT research). Furthermore, the area around a
fatigue crack is less stainless and more ferromagnetic than the bulk
material. This may allow testing via mag particle inspection
(so-called magnafluxing). It is entirely that nobody has done this
because they simply assumed that teh stainless material wouldnt allow
this to work. Unfortunately, I threw the old rigging away so I cannot
try this.