Fill pipe for flammable liquid storage tank

[Eric1230]

I got a question from an operator that I couldn't answer adequately. On flammable storage tanks where the fill tube extends to the bottom of the tank, a hole is put near the top of the tube to prevent siphoning. Since there would be some material coming out of this hole when filling is there a potential for static buildup?

 

[sshep]

This is just my memory and opinion. The fill tube is not only used to avoid the splash filling that would cause static, it insures that the feed and the bulk liquid are electrically bonded. Besides the fact that practically no flow will come out the siphon break anyway, once the drops hit the liquid the charge is dissipated.

best wishes,
sshep

 

[dcasto]

There should be no potential to allow a static charge to jump or arc the way you describe it. In real life a plant interconnected the pipeing between tanks one time with PE pipe so the tanks ended up witha potential betweem. The results were not pleasent. Make sure the fill pipe and tank have a bond between them.

 

[MJCronin]

Eric,

I have been involved with bulk storage tanks for many years and have seen many tanks equipped with a "dip tube" for filling.

Yes, there will be some small escape of liquid from the vent hole during filling. But the benefit of the vent hole (also called the siphon breaker) outweighs any other minot buildup of charge that it may incur.

Most importantly, understand if you have a liquid with a high potential to build up a charge and ensure that you are using metallic pipe and that the piping and tank all have grounds that are in good shape. I have seen many plants where the tank/skid grounding cable is missing or has been eroded away.

In my opinion all tanks should have two functioning grounds

Eric, specifically what liquids are you dealing with ?

-MJC

 

[Eric1230]

The liquids used range from high conductivity alcohols to low conductivity monomers. I have worked with bulk storage of flammable liquids for about 15 years and have designed & installed many tanks. I put in a siphon break on all tanks as a standard feature and have never thought twice about it.
In a recent meeting about converting a tank for use with flammables, I brought up the need for a fill tube & a siphon break. One of the maintenance guys says, how about the liquid coming out of the hole, aren't you free-falling it? Considering our emphasis on safety telling him it shouldn't be a problem just didn't seem right. I looked in the codes & there's no mention any where of a siphon break. Everybody puts one in but I have a feeling that answer won't quite satisfy him. What do I tell him & our EHS manager?

 

[dcasto]

Surface Tension. The liquid will dribble down the side of the line.

 

[BenThayer]

it has always been understanding that the other reason to have the fill tube is to minimize the vapor / liquid contacting.

if the tank has a nitrogen pad/depad or CBV, this minizes the amount of solvent vapors expelled when filling the tank since it will be mostly nitrogen or air leaving the tank.

and i agree the anti-siphon hole is needed.