Pipeline Isolation joints 1

[elylrc]

My pipeline comes above grade in a plant. Between the overbend and the pig trap I have an isolation joint. Does the isolation joint require a spark gap protector ?

 

[SJones]

NACE SP0286 would suggest that a device is required for lightning protection at least.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[BigInch]

Stray currents and induced currents can also get quite high in a populated or otherwise electrically active region.

It is also a bit more common to make the trap/launcher integral to the pipeline with isolation between trap/launcher and plant, even though all extraneous connections from the trap/launcher to the plant must be isolated thereafter. Design, installation and inspection, not to mention future operation, of the trap/launcher is often more convenient when included in the pipeline, rather than the plant and maintenance managers don't get confused about who's budget cleaning the pipeline falls under.... IMO.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[elylrc]

We're talking about lightning here. It is standard practice to isolate what is below grade from that which is above so the pipeline CP is isolated.

 

[BigInch]

You wern't talking about lighting until Steve mentioned it, nor should you restrict it to lighting. Simply flowing products within the pipeline can build up hi static Voltages.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[elylrc]

I purposely did not mention anything to get an unbiased opinion. I am not sure that I understand how static in a product would be mitigated by a spark gap protector. Perhaps you can enlighten me.

 

[BigInch]

The flowing product imparts the charge to the pipe, so it could be convenient to block that charge from traveling into an aircraft fueling terminal where static inhibitor was about to be added, for example.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[elylrc]

But isn't that the job of the isolation joint? Besides steel is a conductor not a capacitor like A1, so wouldn't the static just move with the product? I know Shell blew up some AI tanks at SFO due to static at the discharge nozzle inside the tank, but that was before they used additives to mitigate static.

 

[BigInch]

Yes it is the job of the isolation joint.

Anything is a capacitor until it is in a discharge process, ie. steel in a sense is just a very bad capacitor. When charged quickly by lightning, or slowly by product, if the steel is isolated, it can hold charge for awhile. Its a matter of time.

As the product is moving, some charge is given off and some is picked up to balance whatever it is in contact with at the moment. Product at one point can have a different charge from another point. Charge will be leaked as product moves across the isolation joint as well, if the product is a good conductor, then leakage is faster.

"Jet fuel" without antistatic additive and vapor pressure depressents is still basically just a form of kerosene. Antistatic additives degrade with shearing forces, so they are administered just before the actual fueling point.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[elylrc]

Hey, thanks for all your time and help.