Don,
You will find that the wrinkle bends whould be limited to 15 degrees each.
To do a 90 you should have six wrinkles. I first stumbled on to this
procedure in an old Union Carbide gas welding textbook. The procedure works
with any size pipe and if you follow the 15 degree rule there is no
appreciable reduction in cross sectional area so fluids are not restricted.
On really big pipe a com-a-long is needed to maintain bending force as you
heat the pie section.
As you mention cooling off after each heat is necessary so that you can
locate the wrinkle accurately.
Randy

"Don Foreman" wrote in message
...
http://users.goldengate.net/~dforeman/conduit/

Field-expedient tight bends in EMT for making stuff. Not pretty, but
it works.