Lines in 2 D & 3D loop

For safety reasons I think a Flare Header would always be restricted to single plane self draining 2D loop. However, almost any other commodity could, under the right circumstances have a 2D or a 3D Loop.
Keep in mind a 2D loop does not always mean "flat plane". It could be vertical up or vertical down. I have seen both and have used both. I used 2D vertical loop for pipe lines that were on sleepers (close to the ground) and needed to allow for expansion and cross a road. The loop rose up on one side of the road and down on the other side of the road. Two elevated pipe supports held the loop up. 2D loops are also hung vertically down under an elevated pipe rack or above an elevated pipe rack.
Except for flare gas lines the commodity makes no difference in whether you use a 2D or 3D.

Images of Piping Loops: www.google.com/search?q=Piping+Loop+Imag...sAQ&biw=1024&bih=645
Seniors can u please list out (service wise) preferred configuration for the 2D & 3D loops.

All Steam lines can and will form Condensate.
Example: Consider a plant with three levels of Steam ( High, Medium and Low pressure)
- Condensate from the steam traps on the High Pressure Steam system should be routed to the nearest point on the Medium Pressure Steam system.
- Condensate from the steam traps on the Medium Pressure Steam System should be routed to the nearest point on the Low Pressure Steam system.
- Condensate from Low Pressure Steam system is just hot water. The lines from the steam traps should be routed to the Low Pressure Condensate Collection header. The individual lines and headers for this Condensate system should not be insulated and if it is maintained at the proper pressure it will not "flash" and vaporize. It will be the same as any other warm water line.
So, I say, no it does not need to be sloped or free draining to the collection vessel.