Static in FRP

[Corrosiondoc]

We manufacture FRP over the road tankers and customer has a question about static charge and how to dissipate during loading or unloading. There is a carbon fiber conductive layer but not sure how to address this problem in a practical manner.

Thanks for the help.

 

[berkshire]

On FRP aircraft fuel tanks, a conductive mesh layer is placed in as the second layer, or a grid of copper tape is laid on the outside of the finished tank depending on the manufacturer.
The common feature to both methods, is that the conductive layer is bonded to the filler neck, and to ground,( earth.) so that any charge is dissipated as it builds.
B.E.

 

[Corrosiondoc]

Berkshire, you see in the attachement how large the unit is. It has a core construction I have attached a pic of that cross section in this message. Can you be more specific on the details of how to do this in this application? Would the carbon fiber veil be what you consider a conductive mesh.....it is conductive and can bond to the discharge flange and wrap the outside of the flange with the CF material and then how to get it to ground? Could attach copper tape to the outside of the flange as well and then how to get this to ground from here? Not sure if can ground to the chassis? Thanks for your help.

 

[Compositepro]

You want to make the inside surface of the tank slightly conductive. It does not have to be every square inch, however. A carbon veil will work if it is not too deeply imbedded in resin. You can also use carbon black as a filler in epoxy. Then there has to be a conductive path out of the tank to ground. Metal tapes will work but you need to be aware of corrosion problems that may develop, especially in contact with carbon.

Charge separation develops due to fluid molecules separating from surfaces in pipes and tanks. But charged fluid molecules are attacted to grounded surfaces. So the amount of charge is a balance between charge creation and charge dissipation. Without grounded surfaces in the tank, the tank becomes a big capacitor. Grounded surfaces on the outside of the tank will significantly increase capacitance.

Simply having a grounded pipe dipping into the fluid will improve static dissipation.

 

[berkshire]

corrosion doc
If I read your cross section correctly. The carbon layer is in the outermost skin of the tank. You can use that as your conductive layer. A grid of stainless steel or bronze mesh with a contact pin welded to it, bedded down tight to the carbon fiber and covered with resin will give you a means of connecting a ground cable.
With that balsa core there, you would need to connect the inner and outer skins with a conductive layer at some point or you will be making a capacitor inside the tank.
I hope this helps.
B.E.

 

[Corrosiondoc]

The carbon layer would be on the top and exposed to the liquid. We can put an additional carbon layer anywhere within the laminate. Are you saying its better to put the second layer on the outside skin to totally encapsulate the laminate including the balsa or just on the outside of the balsa? Please see the modified cross section....the layers are marked A-D. Where would you place the second layer?

thanks again

 

[berkshire]

Corrosiondoc (Materials)
OK I misread your layup section. Your existing carbon veil is inside the tank next to the liquid.I was thinking of a second layer of carbon to get a conductive layer next to the liquid.You already have the conductive layer where it is needed.Now you just need a conductive path from that layer out of the tank and to ground.

If you have an area where there is no balsa core, like an inspection hole, then a few layers of carbon cloth or veil and or resin loaded with carbon black, in that area, will get you a conductive path to the outside of the tank where you can fit a grounding clamp or strap.
B.E.