"the line is no heavier now than when it was installed"

Yes, beyond a doubt. And it's a HR line, so even if the insulation got waterlogged it will dry out.

But the question you need to answer is, "Is the line heaveier than the line that was analyzed?" Mill tolerances on the wall of seam welded pipe is pretty tight compared to extruded pipe (see the applicable ASTM spec, and the plate spec it references for details), but even 1/16" on your pipe is 3%. If there is no vertical control point in the riser, or if the control point has failed, this is more than enough to cause a bunch of constants to bottom out.

Also, adding supports without a lot of analysis could raise hell with your nozzle loads. You'll need to do a lot of analysis to consider what has happened to the HR nozzles on the turbine, and what might then happen if you attempt to return the HR line to its design elevations.

Finally, you need to check to make sure that the sag has not created a low point within the system, else the potential puddling problem noted above by John Breen could have bowed the line.

All in all, a rather fine mess. Good luck!