How difficult to remove header pipe from 90 240

I have a 90 240 with 100K miles and I need to replace the header pipe.
That's the pipe between the exhaust manifold and the catalytic
converter. Where I live we have real winter and hot summer. The car
is quite rusted, but works like a new one.

Given it has never been unscrewed, I'm concerned about breaking the
bolts from the exhaust manifold.

The nuts are copper, btw. (At least the new ones I got).

Any advice as to the best method/tools/technique to use to achieve
that while minimizing the risk of damaging the exhaust manifold.

In case you wonder, rust has perforated holes in the header pipe and I
do need to change it.

Thank you

 

At work we use the "hot wrench" (the acetylene powered one), but a
good plumber's torch works too. Get the nuts HOT (glowing orange with
the big torch, or as hot as the little one can manage), then socket on,
air-impact on reverse, and blaaap!

In the absence of air tools, a tight fitting socket, extension and longish
ratchet should suffice. As well as the heat, you may want to soak the nuts
(with Liquid Wrench, WD40, PB Blaster, whatever you've got) for a day or
two beforehand to help break the rust bond.

 

you may have missed the important point in all that. hot metal
expands. you want to heat the nut & keep the bolt cooler. this will
loosen the "rust seal". be careful! WD40 is light oil & keroscene. can
we say flame hazard? if this doesn't work, acetylene is great, but
mapp gas is easier to come by. even a Dremel tool w/ diamond bits will
work. i'm worried about copper nuts on base metal bolts. where i live
the dielectric effect would kill that connection quite quickly. bon
chance!

 

I just use a propane turbotorch, mapp gas works better though. It's a
bit of a tight fit for impact sockets, I just use a ratchet or a box end
wrench. Usually after a bit of heat they come right off.

 

Thanks to all for your answers. I'll keep you posted on the outcome.
Might be a few days before I find the time to do it.