HDPE pipe location 1

[AMedhat]

Dear all,
Here`s the issue,

A contracting company was installing a huge vacuum sewage network about 100Km,the pipe/fitting material is HDPE.
After the company finished installation they had a problem to finish the As-Built drawings for the pipe line profile.
They seek a device or a technique to confirm the precise location and accurate depth of all fittings with error of not more than 2cm.

We decided to use an electro-magnetic pipe locator
But the access points to the lines to insert a tracer wire or a sonde transmitter are about 1Km from each other
So,
1) we chose to insert a copper cable inside the pipeline every 1Km as a tracer wire.
2) Insert additional separate sonde transmitter attached to a rope to control its position by pulling the rope from the end of the pipeline.

I appreciate any advice regarding to the following:
1)attaching the sonde to a rope (not to a fiber glass rod as usual max. 200m)
2)Using ground penetrating radar instead of the electro-magnetic method.
3) any other advice from your side.

Thanks and regards,
AMedhat

 

[zdas04]

You didn't say the diameter of the pipe. The density of HDPE is similar to dirt, so ground penetrating radar has a really hard time seeing HDPE. Sometimes you get lucky and see the void in the center of the pipe, but not always. Your chances are better if the pipe is above about 12 inches nominal, smaller than that is really hard to see on GPR. Another thing that is needed is moisture. I live in a high desert with very dry sandy soil, GPR couldn't find a buried locomotive here. I've seen them used in Florida and they can clearly see a coin under 2 m of earth. GPR is great technology where it works, but there are so many places where it doesn't work.

If I had this task I would look at running a smart pig through the network. This will probably require you to install temporary launchers and receivers, and the pig runs are not cheep, but all of the other options are pretty much sure to fail. A smart pig can give you a contour of elevations, locations of fittings, and bad welds. Nothing else will give you any of those things with any confidence.

When I'm building non-metallic lines I pay for a survey team to give me precise date before backfilling (I also put tracer tape in the ditch). Turns out to be cheaper in the end.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[bimr]

Your project does not sound like it is doable.

These pipes are probably 2-3-Inch diameter and you will never achieve 2 cm accuracy with a wire inside of the pipe because the wire may not always be located at the same depth inside of the pipe. Don't see a need for that kind of accuracy anyway since the pipes should be installed just under the frost depth. Not sure that it is possible to pull in 1 km of wire.

The best option is probably taping a wire to the outside of the vacuum pipe. I would also ask for some relief on the 2 cm accuracy.

 

[AMedhat]

Thank you zdas04 and bimr,

The pipe diameter differs betwen DN100-300,
Material is HDPE,
soil is a sandy desert,
We can reach the pipe at a point every 1km
We already can insert a wire & a separate rope inside the pipeline along 1km
We are planning to use the wire as a tracing wire and in parallel, attach the sond to one end of the rope and pull it from the other side of the pipe
I want to ask about:
1) the ability of attaching the sonde to a rope?
2) would the sonde signal interfere with the cable signal in case of each has a different frequency(512Hz, 116KHz)?
3) Would the sonde signal of high frequency about (116KHz)energize the wire and cause reading error?

Thanks for all and regards,
Ahmed

 

[bimr]

Why bother with the sonde? One would think that it is more practical to put a signal on the wire and then detect the depth along the wire.

With a moving sonde, it will be difficult to pinpoint the location while the sonde is moving, especially with the accuracy that you desire.

http://www.radiodetection.com/doclib/RDTheoryManual_complete08_en.pdf

Suggest you talk to a Contractor that does this type of work.