Bill Freeman wrote:

Paul,

I have 750 hrs on my "prototype" carbon steel exhaust
on my LE.  Originally planned to replace it in 50 hrs or so,
with SS, expecting failure.  The only failure so far has been where
I wrapped it locally with fiberfrax (ceramic felt) and aluminum
foil retained with a wrap of safety wire.  This portion of the
pipe failed thru exfoliation and cracking in about 60-70 hrs.
I had put this on to protect the nearby rudder cable from heat.

I cut out the severely damaged section and verified that altho
the covered area was perhaps 0.005" thick in spots, the adjacent
uncovered pipe was full thickness or about 0.060".  I welded
in a replacement and have put 9 more years and 650+ hrs since
the fix without any obvious deterioration.  I have removed the
exhaust pipes several times and they seem sound in every way
except for a moderate "rusty" exterior, MUCH less than a
typical cast iron auto exhaust manifold.

I would stay away from wrapping the exterior of a carbon steel
exhaust pipe.  I assume that I locally overheated the pipe, altho
the possiblity exists that the fiberfrax somehow chemically
interacted with the steel at high temps.

Bill

Looks like everything else; "There is no free lunch!"
You want quality you need to pay for it and go SS or Inconel on
a rotary.

Paul
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