You need to find out the minimum{/b] radius that the pipe will bend under its own weight without overstress.
Bending_Stress = Bending_Moment / section_modulus
Set Maximum bending stress = the max allowed longitudinal stress
and calculate the max bending moment.
Be sure you limit the maximum bending stress to the yield stress.
Calculate moment of intertia, I,
find E, Young's modulus
curvature = M/EI = d2y/d2x
from that curvature you can calculate the minimum radius it can bend to while still avoiding overstress.
Hold that radius as a minimum and it doesn't matter how it is deformed, by it's own weight, or by any kind of bending during the lowering operation, it simply cannot be overstressed by bending.
If it ain't broke, don't fix it. If it's not safe ... make it that way.