High Voltage Cabling Trench Over Buried Gas Pipeline 2

[MrMechanik]

Hi Everybody,
Is there any limitation on cabling HV line (230kV) in a trench over a buried natural gas pipeline?
Any reference to standard (or credible article) will be highly appreciated.
Regards,

 

[BigInch]

No public standard that I'm aware of. Are you crossing perpendicular, or running parallel?

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[zdas04]

That is one key question, another is how much separation will you be able to get.

David

 

[BigInch]

Frankly I don't think I'd let them anywhere on the RoW going parallel and I would probably put it in a concrete crossing box culvert for the entire width of the RoW going perpendicular... under the pipeline, well under.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[zdas04]

"Letting them" is an iffy proposition in many jurisdictions. For example, in New Mexico they do not allow exclusive ROW. There are quite a few places in this county where a dozen or more pipes run parallel in a corridor. If I want to come in and lay a high voltage line in that corridor (on public land), the BLM or the state would look favorably on the application compared to an application that created new disturbance. The dozen pipeline owners also in the corridor would not even be consulted. They wouldn't know of my intentions until I made a "One Call" and they were notified that I would be digging near their line. If they show up for line locating and say "I'm not going to let you run that high voltage power line parallel to my line at all" I would just laugh at them. If they said "you have to be 60 ft from my line" I'd just laugh at them. If they wanted to talk about what can be done to minimize adverse impacts, we could have a conversation. That is just because I'm a nice guy. I've known folks that would flip you the bird if you said anything to them.

David

 

[BigInch]

That's the problem with using public corridors. But then again, maybe less problems overall.

However I wouldn't think that safety issues would be ignored when placing utilities in those corridors either.

How's the induction current near 230 kVA UG lines running parallel?

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Have you ever talked to someone from the BLM? They are not hired for their technical expertise. Every now and then someone with real ability slips in, but they are shunned by their peers and don't last long. Typically the questions stop at "the price of the ROW is $___/rod, make your check payable to ___".

There was a thread here a few weeks ago on induction current, I can't remember what the title was, but there was some information in it that I hadn't seen before.

David

 

[BigInch]

Oh no. Bad memories. Pinter Reservoir Gas Plant just north east of Evanston. Plant placed in error (by others) on uncontrolled fill with subterrainian melting ice pack and moving 1" towards south east and 1" down per month. Had to unbolt the scrubbers from the foundation to let the pipe hold them up while we filled in the valley downslope. BLM land. North Dakota pipeline RoW for Northern Natural and in
Colorado, south of Lamar on the BLM Comanche Grassland, and in Kansas BLM Cimarron Grassland. Ya, I remember those guys. I know your pain. Don't forget that BLM also runs the offshore lease lands. Texas was independent and of the land they kept inside the state lines when joining up, that's all theirs. They gave the BLM Colorado, New Mexico and half of Utah and I think Oklahoma so that they would leave the Texans alone. The BLM later gave OK. to the Indians, then took it back.

I mentioned the part about the farmers getting some voltage off their parallel fence lines in that thread and not storing pipes N-S. Otherwise there was no usable info there, as I recall. I would expect that UG cables might get some insulation effect from earth covering, but I really don't know how much, if any. Induction, something to think about until the EE guy shows up.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Small world. I spent a bit of time at Painter when it was under construction.

David

 

[MrMechanik]

Thanks David and BigInch, a lot for your responses. Actually duw to Client RECENT requirement, we are going to lay a 16" U/G natural gas who feeds from north to south a power plant and the power output should goes by a surface trench (230kV) from east to a western 400kV substation. So the crossing is perpendicular. My question is: is there any minimum vertical spacing requirement between them?

 

[BigInch]

The minimum spacing from pipe to foreign structure is often only 12" by the B31.8 code, but that may be insufficient in some cases where loads are above the pipe. Its doubtful that the box and cable will weigh enough to be a concern, but there may be other safety issues. A perpendicular boxed crossing of the cable through the entire RoW width above the pipeline, installing the pipe below its normal clearance, would probably be the best method. Mark the pipeline route very well in the area using warning signs and place red concrete plates 12 to 24" above the pipe.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[MrMechanik]

I've found following link regarding induction of cabling on buried pipeline:

http://www.matcor.com/images/graphics/PGTImprovingACmitigationMarch2009.pdf

The guys in above article describe a method for mitigation of AC induced current on buried pipeline. In our case the buried gas pipeline shall have an earthing system (for corrosion). Is that enough for local induced current which was discussed in the article?
It should be added that buried pipeline is also wrapped.

 

[BigInch]

Typical earthing for corrosion prevention neutralizes voltages between pipe and earth, which in my understanding, may not be sufficient to neutralize local voltages between adjacent cables and pipe, but my understandings in this area is extremely limited.

When paralleling AG HV transmission lines, various clearance distances are maintained depending on voltage levels, plus direct bonding between pipe and towers is often employed.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[brimmer]

As far as earthing system being enough to dissipate AC, depends on how much AC might be induced on the pipeline, and how big the earthing system is, you really can’t answer that question without going into the details. You would have to complete some form of AC modeling to find out. Normally if crossing perpendicular, steady state AC induction is not an issue, especially if underground line is in a non-conductive conduit. You will have to find out where the power line has grounding, as AC could be induced during a fault if any of their grounding is close enough.

Wrapping will actually not help for dissipating AC but allow the AC to be moved farther on pipelines (obviously helps protects against corrosion and any potential AC induced corrosion, certainly keep it on).