Underground Transition piece locate

[JaeBo]

Hi Everyone,
Looking for some creative ideas for locating an underground 10" to 12" transition piece on a sour gas pipeline that is unpiggable. I'd prefer not opening up the line for a tethered tool or taking it out of service. I'm looking for as built records, old hands that were around at the time of construction, but not much is turning up. My thoughts were to hire a dowser to locate the transition and then bring in the hydrovac. Any other ideas? Any thoughts or experience with using dowsers for this kind of thing?
Thanks!

 

[DLite30]

Ground penetrating radar?

 

[StoneCold]

JaeBo
You can locate the line by Dousing but you won't be able to locate the transition. Dousing looks at the impact a large metal object has on the magnetic field of the earth, the size transtion will not show up. What about looking at how many feet of each size of pipe were ordered for the project and calculating the transition general area from that?
The radar might work if it is not buried too deep. I don't have any idea what "too deep" is before you ask.

Goodluck
StoneCold

 

[rconner]

This is probably a stupid or impractical suggestion as I have no experience with such, but if you know for sure the diameter and wall thicknesses of both lines (that I assume but do not know are welded steel), and furthermore if you have some sort of access to electrically contact a bare or bonded spot on pipeline at two points some distance 'LTotal' apart (that someone is pretty sure are some distance on either side of i.e. straddle the reducer), it may be worth a stab to measure the electrical resistance of the line between the two bond points and call it 'RTotal'? It may then be possible with the known electrical resistance of steel to calculate the theoretical unit resistances of both sizes of pipes say 'R10' and 'R12', to then determine a length 'L10' of 10" pipe and a length of 'L12' of 12" pipe that would equal that total resistance solvable with two equations and two unknowns? [It may be even better if it is possible to measure a short length resistance somehow of the actual 10" and 12" pipes if any portions of both sizes of pipes are exposed/accessible somewhere to get a better idea of working unit resistance. Maybe very small or even vacuum excavations could be used to establish bond points?]

(R10)(L10) + R12(L12) = RTotal , and L10 + L12 = LTotal

 

[MikeHalloran]

I'm rather intrigued by the electrical resistance method, but not real hopeful.

When all else fails, I suggest a shovel and a binary search.



Mike Halloran
Pembroke Pines, FL, USA

 

[SNORGY]

Is the line or are the lines not licensed by some regulatory body or other? Does the line cross other lines, roads, rails or utilities? From the crossing agreements that ought to be in place, one might be able to locate what line size is where, thereby narrowing down where the transition is.

I sure like rconner's idea as well.

 

[JaeBo]

Wow, thanks everyone, lots of interesting ideas. I'll see if there are any records from the 60's on the material and crossings. That will get us a bit closer then look into the other suggestions. Looked into GPR and the pipe is too deep to detect the 2" OD change