Drain pipe design 1

[simplemath2]

I am assigned to design a spill way for LNG tank. It is to drain LNG in case flange failure. While sizing the vertical drain piping, I was told to use self-venting design which limites froude # <0.3.

My questions are:

1. If design for full flow(froude # =0.8), is it acceptable? what bad will happen?
2. Is that necessary to design for self venting for this never or once in the tank lifetime scenario? The reason is the cost difference betw 12" and 20" SS pipe.

Thank in advance.

 

[simplemath2]

Any general practice in sizing drain piping is highly appreciated.

 

[katmar]

The recommendations you will find for designing drains are MOST unlikely to apply to LNG. Where do you want to drain the LNG to? How will you deal with flashing? Usually containment is more of a concern than draining it away. I am reluctant to give any recommendations on how to design such a drain without understanding the purpose of the design. The drains from tank spillways are normally for draining rainwater, and not for the product contained in the tanks.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[mbt22]

As Katmar says, something sounds odd here. Is this to limit pool fires in the event of a spill?

Taking it at face value that you want to drain LNG. If the line isn't self venting the vapourising LNG would most likely vapour-lock the line, or at least massively restrict the flow.

As for whether it's necessary to design for a rare event, if you need this as mitigation for equipment failure, you need it to work.

Matt