I know of no standard that limits that off hand. You obviously can't have your weld inside the tangent point of the bend for fit up and ovality problems.
So, I am assuming you are using an induction bender in which case once you are outside of the tangent point you are essentially, for all practical purposes, outside of the heat affected zone of the material?
But you need to take a close look at the bending sections and welding section of whatever code you are working to.
In the old hot slab bending days when I was faced with this in the past we qualified a weld procedure in which the weldment was subjected to a normalize heat treatment with a temper consistent with our PWHT (which is essentially the heat regime being imposed in hot bending) becasue if the weld was performed prior to bending it definately was inside the HAZ.

The heated part of a Hot Induced Bend is normally to be heat treated and mechanically tested to qualify the hot induced bend procedure. With my experience in offshore pipeline, there is no minimum distance requirements between a weld and heated part. you can even weld the connection between pipe to hot induced bend without tangent ends (tangent ends cut out after bending).

Regards,
Noel

There are situtations, like internal stiffeners in a tubelike structure, where you'd pretty much have to weld right on a bend.  So it can't be forbidden, I'd think.

Hg