How do I prevent static elec. in plastic tanks

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dean belcher

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How would I bond 2 plastic tank used for the storage of methanol to prevent static electricity build-up from either the filling of the tanks, to when a person should touch the tanks and static electricity should occur. The tanks are placed on a concrete floor. One is 2000 gal. the other is 3000 gal. Both are plumbed together with SCH 80 pvc and each have stainless steel bungs for the opening.
 
I have read dozens of articles on static control processes during product transfer in industrial facilities. There are ways for mitigation of the static discharges. Do some reasearch and perform a web search. You will find plenty of articles.
 
Bryan,
There are ways for mitigation of the static discharges.
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There are very few solutions for controling static caused by liquid transfer when the transfer system is non-conductive.
Don
 
dean belcher said:
How would I bond 2 plastic tank used for the storage of methanol to prevent static electricity build-up from either the filling of the tanks, to when a person should touch the tanks and static electricity should occur. The tanks are placed on a concrete floor. One is 2000 gal. the other is 3000 gal. Both are plumbed together with SCH 80 pvc and each have stainless steel bungs for the opening.
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The answer is you were supposed to buy tanks that were made of conductive plastic. Yes, there is such a thing. Yes, they are pricey.

I am surprised the bungs are SS. You would think aluminum for its non-sparking nature.

The fill nozzle would be aluminum bonded to the bung.

You could buy some conductive cloth and roll around the outside of the tanks. Then bond the bung and cloth to ground. Best place to bond to is the rebar in the concrete floor.

For static control you do not necessarily need a lot of current carrying capacity.

Incidentally, this is not a trivial thing to do, and I have only outlined it, not designed it. Best bet is to get someone intimately familiar with such things to design it.

You might find that all you really need is a humidifier.
 
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Bob,
While the conductive cloth may prevent people from being shocked it may not prevent the staic spark caused explosion. The static charge can build up in the liquid itself and can jump to a grounded object causing a spark. I think the only way to prevent that is to have the liquid in contact with conductive materials to bleed off the charge before it gets to the point that you can have a spark. As you said this is not easy to do. There have been cases of static build up in grounded steel jet fuel lines if the transfer rate was too high.

Don
 
don_resqcapt19 said:
Bob,
While the conductive cloth may prevent people from being shocked it may not prevent the staic spark caused explosion. The static charge can build up in the liquid itself and can jump to a grounded object causing a spark. I think the only way to prevent that is to have the liquid in contact with conductive materials to bleed off the charge before it gets to the point that you can have a spark. As you said this is not easy to do. There have been cases of static build up in grounded steel jet fuel lines if the transfer rate was too high.

Don
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as I pointed out, the thoughts i put forth were not a design so much as an outline of things that could be done to reduce the risk of static generated sparks.

i am a little surprised that static could build up in a grounded pipe like that, although after thinking about it, I have seen some very odd designs for reducing static generation inside piping systems.
 
So is the answer for affectively eliminating the static charge in the tanks,to bond the SS bungs on the bottom tank to the central grounding electrode conductor or do I run a wire into the tank also
 
Dean, you are looking for a step 1-2-3 method to comply with. Several experienced members have stated that this static control is fairly involved. And this is not really a NEC/NFPA 70 issue, its answer is found in a different NFPA standard.
 
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