STATIC BUILDUP/GROUNDING PROBLEM

[sensiblesteve]

I am in a debate with a co-worker about the static bulid-up / grounding of a metalic portable tote.
The product is extremly flammable, and has a very low MIE (min. ignition energy).
He feels that simply using an isolated plate in contact with the flowing product, in the following configuration: coupler- gasket- ballvalve- gasket- grouning plate- gasket- delivery pipe from tote body, will create a grounding of the product that will eliminate the need for grounding the unit or linking of the isolated components.
If that is correct discharge of the product onto the ground would not require grounding of any sort.
I am of the opinion that the components themselve are charged and that its the movement/flow that creates the charge and by simply grounding the flowing product will not eliminate the danger.
Could someone please offer up an opinion/advise or a reference that will either prove or disprove this theory.

 

[MintJulep]

It would seem to me that "ground" is less important that ensuring that everything is at the same potential.

 

[sensiblesteve]

Yes, but I don't think the above set up will do this.
Let me explain, what he wants to do is simply use an isolsted plate in contact with the flowing product that has a conductive strap attached from one of the tote legs to the plate. He is claiming that by equalizing the product with the tote that all other components [see the above valve train discription],will also balance out.
I say the product is in contact with the tote already and all this will do is equal out the plate that the strap is attached to. A balanced "zero/grounded" potential is what I am trying to achieve and I feel that "linking" all isolated member in the "train" is still needed to eliminate static buildup.

 

[jistre]

Look up grounding and bonding of tanker trucks for ideas on how the chemical industry avoids "energetic events" due to static discharge while offloading volatile material. It should be similar to what you'd need, just on a larger scale.

If I remember right, the idea is to ground everything to bring them all to the same potential, then make sure everything's bonded together to keep them at the same potential.

Like I said, the chemical industry knows all about preventing explosions when moving volatile stuff from one location to another.

 

[tygerdawg]

National Fire Protection Assocation NFPA defines what is proper on this in their standard on storing & using flammable liquids. Can't remember what the exact standard number is, but I had to put straps on everything once and sink copper ground rods into the earth. You can purchase the standard for nominal cost and settle this discussion quickly.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[IRstuff]

You NEED to ground EVERYTHING, including yourself! You've listed 3 gaskets. Are your gaskets metallic? If not, you need to add grounding straps to each isolated piece that is not otherwise grounded. Don't forget that the operator is probably the biggest potential ESD source in the area.

You should be wearing an ESD wriststrap that's properly configured and grounded when doing the transfer operation. Ideally, you should also be wearing an ESD labcoat that has embedded wires to minimize any clothing ESD impacts.

TTFN

FAQ731-376

 

[JJPellin]

I would offer one more word of caution. Even if everything is grounded, there can be problems depending on the properties of the fluid. Do some research on loading facility problems when loading diesel fuel or gasoline. We had such an event at our refinery a few years ago. The loading equipment was grounded, the truck was grounded, everything was grounded and there was still an event. In the end, after much analysis, we determined that the conductivity of our fuels allowed for a buildup of static potential that could result in an event. We now inject a chemical in tiny amounts to increase the conductivity of our fuel. This is not my area of responsibility, but there maybe product specification requirements for conductivity enacted since then. I believe that all of this was related to the loading of diesel. But, there is a chance that my memory could be wrong and it could involve gasoline.

Johnny Pellin

 

[hacksaw]

External gounding is only part of the solution. If the fluid velocities are high enough you get charging (indeed even arcing) within the process environment. This may not be eliminated by internal grounding fixtures. The conductivity of the fluid is the issue, and the "charging" rate i.e. fluid velocity.

 

[Compositepro]

The NFPA codes can be read on-line but not printed.