Prevent rainwater in vent pipes

[pukka111]

I have a small problem in my plant with vent lines. The current design has the tip of the pipe slightly angled (45 deg) to prevent rain water entering the main system. But this is not sufficient and it is important for the system to remain dry. I am tempted to increase the angle to a full 90deg or place a shroud over it but I am concern about dispersion issues. Has anyone dealt with this before??

Point to note, these vent lines are used occasionally, say once every two months.

 

[jamesbanda]

You could use a simple rain trap in the line?

 

[pennpiper]

I recommend That you leave the vent pipe pointed straight up. The end of the pipe may be straight cut or 45 deg angle cut, it makes no matter. At the bottom of the vent pipe, in the horizontal portion after the PSV drill a "weep" hole in the bottom of the line. In this way any rain water will drain out and not cause back-pressure problems.
If there is a concern about vapors purging out the "weep" hole during a major relief then connect a drain line to the "weep" hole and run it to a safe location.

 

[dcasto]

They make waterproof vent covers that slip over the ends to keep rain out. They ar made of fabric so they do not add any pressure. They come in bright yellow, orange or other colors.

 

[zdas04]

I've used the "drill a weep hole" technique many times. Recently I was asked to do a mechanical inspection for Electrical Area Class and the National Code specifically addresses these weep holes - the hole counts the same as the open ended pipe and must be at least 10 ft from any electrical equipment that isn't Div 1. We replaced a bunch of vent pipes to get rid of the weep holes.

A better answer seems to be the poly "socks" that people are putting over the pipes these days. It only takes a couple of oz dP to launch them and once they're gone they don't create any dispersion issues (like the hinged caps can). If you can't find the cap after a launch, they're not very expensive.

David

 

[pukka111]

Thank you all for your posts. I considered the weeping hole as well but dismissed it as I was concerned about the presence of flammable vapours.
I would like to review the use of these ‘poly covers’. Does anyone the technical name for these??


Many thanks again.

 

[pleckner]

Review this conversation:

http://www.cheresources.com/invision/lofiversion/index.php/t501.html

You can also review the conversation at this thread on this website:

thread292-168893

 

[chief]

Why not just fit a 'gooseneck' on the end of the vent. This can be welded to the end or a clamp-on arrangement. A gooseneck is a 180 degree turn on the pipe vent end., so there is no ingress of rain. A fine metal screen, similar to a pot scourer can be incorporated to act as a spark arrestor. This is a common arrangement on fuel and chemical tanks.

Offshore Engineering&Design

 

[Latexman]

Most chemicals need to be dispersed UP into the air so as to not affect us folks on the ground. A gooseneck does the opposite.

Good luck,
Latexman

 

[zdas04]

The goosneck arrangement is fine for atmospheric tanks. If they develop any pressure in them, then they'll likely blow up anyway so you don't have to be worried about a high velocity vent/PSV event. They are a really bad idea for a vent/PSV on a pressurized line.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[Leclerc]

Consider a vent stack tip arrangement as follows:
A larger diameter end section of some length fits over the tip and is fixed and located concentrically with the vent by at least three space bars to leave an annular space between vent stack and new tip.

Any rainfall that is not exactly vertical will impinge on the inner wall of this end section, run down and then drip down the outer wall of the main vent stack.