Can or cant horizontal piping be considered self draining

[Process2108]

I have a system of water flowing from and steam traced and insulted header, to a bare vertical run (~10 ft), turning 90 degrees to a bare horizontal pipe (~3ft), ending to an open ended bare nozzle pointed vertically.
The water is used to cool discarded material before being disposed of, so flow is opened only for a few minutes after each drop.
There's great debate as to whether the drop leg can be considered self draining or not, and whether it would freeze in winter time.
Does anybody has experience with a system like this?
Can an open ended horizontal pipe be considered self draining?

 

[MikeHalloran]

If it doesn't have noticeable slope, it's not really self-draining.

If it's not heat-traced, it will freeze anyway.



Mike Halloran
Pembroke Pines, FL, USA

 

[pennpiper]

The size of the pipe has an influence on this puzzle.

Example:
#1). 12"NPS may not be a problem

#2). 1/2"NPS is potentially a problem

 

[BigInch]

An open-ended horizontal pipe would certainly self drain, however the extent to which it would drain and the rate that it would drain would be a subject for debate, as would whether such would satisfy your practical needs to do so effectively and in a timely manner.

Practicality would suggest that the pipe have some nominal slope, so that draining could continue without the need for a driving head of liquid behind the flow, which would obviously leave small amounts of liquid behind the flow when the liquid head behind was no longer sufficient to drive liquid ahead of it forward. In other words, a flat surface can't drain completely.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[Duwe6]

Additionally, the allowable span of pipe takes into account deflection -- the typical allowable spans of welded pipe allow for a vertical deflection "droop" of up to 1/2-inch. So it depends what the draining requirement is.

For freeze protection, horizontal pipe is considered self-draining. There will be much less than 10% liquid remaining.

For line-breaks, horizontal pipe is NOT self-draining. There will be a small ammount of retained liquid in the center of every support-to-support span.

 

[cvg]

won't the vertical nozzle at the end prevent it from fully draining?