Under-base Gas purge function in Double Containment LPG Storage Tank

[Rasyid30]

Hello,
In most of above ground LPG/LNG Double Containment storage tank, have been provided with piping extending under the tank base (in the sand layer/insulation layer) through the annular space and exhausted to atmosphere. I am trying to find in the multiple threads to get some clear information about this, but still not getting the detail.
Some doubt is here :
1. what the purpose and main function of this facility ?
2. Should we purging IN by inert gas or just vented OUT to atmosphere?
3. Any chance Hydrocarbon from product slipped in to this pipeline ?

Thanks in advance

 

[LittleInch]

Needs a drawing or sketch as this doesn't make sense.

All depends on whether the double skin is just here to hold in / keep dry the insulation or be true double containment

Sometimes these tubes are to stop ground freezing or insert heating cables or just detect any leakage.

But the description you give is very vague and hence difficult to be specific.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Most likely there is perlite insulation powder in this annular space - usually purged through with N2 and kept under very light positive pressure to keep out moisture laden air.

There may be more details in API625 on this for double containment tanks in cryogenic service.

 

[Rasyid30]

Sorry for slow response.
The sketch is attached and marked in red color.