In article ews.net,
"Doctor Drivel" writes:

Cap up one end, fill with fine sand, cap the other end. Bend over suitable
structure to make the curve. This could be you knee or two metal rollers.
First anneal it. Where the curve is to be heat the copper to cherry red
then quench in water. This makes it more pliable. You will need a
substantial blow lamp to anneal it. You could try it cold first, it may
work. When making the bend, do not make sharp pulls, Gentlly move up and
down the bend pulling a small amount at a time.

I've done this to bend 28mm copper, for which I don't have
a proper pipe bender. However, your annealing process is for
wrong metal. Copper is annealed at 700-800C (can be done as
low as just over 400C, but you have to hold it at that
temperature for a long time). There is no state change on
cooling copper, so quenching is not required -- you can cool
it over as long a period as you like. The annealing process
for copper is reversed by flexing and vibration, not by slow
cooling. If you quench it just for ease of handling, watch
out for being burned by steam and boiling water spraying out.

For the sand, make sure it's dry or you'll have difficulty
getting it out of the pipe afterwards. Even so, I sucked a
large cotten wool ball through the pipe with a vacuum cleaner
several times to remove as much sand residue as possible (this
was a gas pipe, so I don't want sand getting into the boiler).
A sand bag makes a good bending former. Do not try to bend
near the end of the pipe -- saw any excess off afterwards.

For 22mm pipe rather than 28mm, I would however use a bending
spring for this purpose. You should still anneal the pipe
before bending it though.

--
Andrew Gabriel