Static Bonding Across Piping Flanges - Chem/Petrochem/Refining

[bazak]

I have seen in the past where people apply separate bonding conductors across metal piping flange connections. I believe this to be a practice brought forth by the concerns of static discharge in hazardous areas.

Does anyone have experience with this (especially with application in the chemical/petrochem/refining industries)?

What criteria is used to size the jumper wire? Is it typical to use flange tabs, star washers, etc? Are there any standards that encourage this (I have reviewed NEC, NFPA 77, API RP 2003, IEEE Green and have not found any specific suggestions for install).

Thanks!
bazak

 

[Kiribanda]

bazak,
This is my perspective.Please feel free to correct me if I am wrong.

Once there was a concept that some petroleum fluids specially AVTAR,kerosene and naptha accumulate static charges on the pipe surface when they are pumped through metalic pipe lines.Therefore,the lines were interconnected and bonded to the refinery grounding system to avoid any flashovers due to difference in potentials.Eventhough there is no strong evidence to support that concept in the present day,still the practice is continued assuming the pipe lines are extreneous conductive parts.I donot see any harm in continuing this practice due to two reasons.Firstly,grounding & bonding is always better than nothing and secondly most of these pipe racks are overhead and any grounding & bonding would ground any static charges built up due to indirect lightning strikes neraby.If my memory is correct,this grounding practice was mentioned in IP code (UK).Also there was no any equation given to size the grounding wire.But 25 sq mm(#4 AWG) was widely used.

 

[waross]

In the Canadian Electrical Code the minimum size of grounding conductor that may be run unprotected (by conduit, armor or other means) is #6 AWG. It must be of copper. I expect that this would be the absolute minimum subject to other factors.
I saw an installation where refined lube oil picked up severe static charges in a filter. The static did not discharge completely in over 100 feet of piping following the filter. The operators would see discharge arcs inside the oil when looking down into a truck tanks that were being loaded.
There was an incident involving a tank that had residual traces of gasoline from the previous load. One man dead and a truck and trailer melted down.
A cone of stainless steel rods was installed downstream of the filter and was found to be effective in discharging the static charges.
This line did not have insulated joints. When you consider the number of metal to metal current paths provided by the flange bolts of a flanged connection, grounding seems superfluous.
However clamped joints may benefit from grounding jumpers.
I have installed jumpers on pipe with cathodic protected to ensure continuity. one accepted method of connection is Cad-Welding. See Erico.com

See also;

http://www.erico.com/public/library/fep/LT0398.pdf

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[controlnovice]

You can find some information in these documents, not about bonding size, but the recommendations on why/when you need the bonding across flanges or in piping:

NFPA 77
NFPA 654
API 2003
British Standard: BS5958-1 and BS5958-2

Basically, the recommendation is that the resistance to ground at any point of the system not be greater than 10x6 ohms to effectively dissipate static. So, if you can do that without bonding, great.

We bond our powder handling system piping due to some interpretation of the British Standards. In it is stated the same 10x6 ohms is adequate, but then it goes on to state that, in general, piping is usually somewhere tied to ground for electrical grounding at a resistance commonly lower than 10 ohms.

So, there is a section that states something to the effect of, "well, since electrical grounding is 10 ohms, we'll just make our recommendation at 10ohms..."

But there is a huge difference between electrical grounding and static electricity discharge/relaxation.

Unfortunately for us, our EHS dept took the 10 ohms. We spent over 7 digits (US$) to comply. There are 5000 bonds in our plant just for powder handling piping.

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