Induced Currents in Pipelines
Induced Currents in Pipelines
(OP)
We have many miles of gas transmission and distribution pipelines that share right of ways with electrical T&D lines. My concern is with induced currents on the pipelines caused by faults on the electrical lines and specifically, the shock hazards that personnel could be exposed to at regulating and metering stations. All of the pipelines are cathodically protected. I'm mainly interested in how others in the industry are addressing this problem. Do they perform grounding studies and calculate current contributions from each line? Do they use polarization replacement cells? Are there any papers written on the subject? Also, are they any organizations or groups of electrical engineers in the natural gas or pipeline industry? I haven't found anything in NACE or AGA.






RE: Induced Currents in Pipelines
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Alan
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"It's always fun to do the impossible." - Walt Disney
RE: Induced Currents in Pipelines
RE: Induced Currents in Pipelines
RE: Induced Currents in Pipelines
RE: Induced Currents in Pipelines
There are hundreds of papers written on the subject. I would refer you to IEEE and also to NACE (national association of Corrosion engineers).
Polarization replacement cells are a pretty old technology. Dairyland Industries makes a nice product called a DC decoupling device which allows AC currents to be grounded while blocking DC current (for cathodic protection). You could also install a zinc ribbon anode system which can be directly connected to the pipeline (may require some extra CP studies especially if your using an impressed current system).
I used to perform these studies and they are a good way to cover yourself from liability...but I've also seen the trial and error method...install a bunch of zinc ribbon, measure your voltage, then if you need more, dig another trench.
RE: Induced Currents in Pipelines
Bill
RE: Induced Currents in Pipelines
I think I understand your issue a lot better now. To estimate the voltage ratings for your PRC's at the station is going to be difficult especially considering that these are older existing pipelines. The main reason is the resistivity of the coatings (for new FBE usually assume 1,000,000 Ohm*ft2 vs. Old Coal Tar could be only 100,000 Ohm*ft2 or less).
The usual thinking is that older (lower resitivity) coating provide an easier path for current to leave the pipeline. So you would have a lower voltage at the pipeline station. However, you would probably have to hire someone to do a thorough analysis because it's all based on geometry of the lines and how many pipelines...among many other things.
A good reference is from NACE Corrosion 2003, Paper #03698 entitled: Estimating AC Mitigation Requirements for Pipelines installed in High Voltage AC Corridors: Fault Conditions.
Hope this helps.
-Eamon
RE: Induced Currents in Pipelines
Niall
Niall Molloy
Power Engineer - Railway Systems
Mott Macdonald