We have done exactly this quite a few times. I suspect he saw a
repair job on large, heavy copper water line. We have used two
rosebuds (there is your 4" diameter flame) to get the moisture out
of the line. To get the copper up to solder temperature we
certainly do use oxy acetylene on 4" heavy wall copper. A B
bottle will work, but I think you would be hard pressed with a
typical propane torch.
The OP is talking about soldering light weight 2" and I agree that
soldering dry thinwall pipe is quite doable with a good propane
torch.

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"SQLit" wrote in message
...

"Ken" wrote in message
oups.com...
We are in the middle of renovating a kitchen and bathroom.
House was
built in 1925, and kitchen pantry was converted to a bathroom
I'm
guessing in the 1950's. Current plumbing vent for the bathroom
is 2"
copper run on the exterior wall of the house. This vent will
be moved
into the wall cavity. (Already have the walls ripped out and
holes in
top plates drilled.) Hired plumber will be doing most of the
work.

I'd like to reuse the current copper vent pipe inside the wall.
I have
no sound reasons for wanting to reuse the pipe other than I
just like
the idea of reusing old materials rather than always buying
new, even
if it adds to the cost of the job. We'll be asking the plumber
about
this, and I anticipate that his answer will be that it is way
easier
and cheaper to just run new PVC inside the wall than trying to
clean up
the pipe enough to sweat new couplings on as sections of the
pipe are
stuffed up the wall cavity.

Also, current waste pipe for the toilet is 3" (I think) copper.
This
had to be cut in one place as part of the renovation, so it
would only
take one coupling to reconnect the existing waste line to the
new
stuff.

So my question is, how hard is it to sweat a 2"+ diameter
copper pipe?
I've done plenty of 1/2" and 3/4", so I know how easy it is to
do that,
but does it become exponentially more difficult to sweat larger
diameters? Is the plumber going to run screaming from our
house if we
ask him to do this? I assume he will want to just rip
everything out
and re-run PVC, so should we let him do this?

Thanks for any insight anyone can give me.

Ken

With a big "turbo torch" it is done daily. The average plumber
may not have
such a tool. Never seen one at a rental yard.

Last one I saw the flame end was 4 inches in diameter and they
used dual
gasses. Oxy and Acetylene. Took a skilled journeyman about 30
minutes a
joint. No flammable materials anywhere near.

Since this is for a vent I would think about a "no hub"
connection.