Hydrostatic drain in a burried pipe

[lhwingking]

I have a piping system that is above ground in which Hydrotest is going to be performed. At a particular location it goes underground and comes above ground after a certain span. In this location where it goes underground, it makes a low point that calls for a hydrostatic drain. But it is going to be fully burried. How will the the drain valve in this underground location be operated? If I do not provide a drain valve here, how will the water be drained after hydrotest?

 

[europipe]

extended spindle?

 

[StoneCold]

Why not pig the line after you hydrotest it so that it is dry? I don't think I would put a drain underground if your line contains hydrocarbon. Maybe you could elaborate on the size, length, diameter, pressure, material being transported and code that apply to your line. Others here then could make better suggestions.

Regards
StoneCold

 

[lhwingking]

It is just a 3 inch Stainless Steel line carrying acid. It is going to be operated at atmospheric pressure and the length of burried portion is around 3 meters. I am using ASME B31.3.

 

[BigInch]

Got 4 meters of rope? Tie a rag onto the rope and pull the rag through the pipe.

I hate Windowz 8!!!!

 

[LittleInch]

You have a few options if you can't do any of the options above
- install a plug in the low point and dig a small hole around it, hydrotest, remove plug and drain into ground / bucket then plug and backfill
- install a small tee or vent close to the elbow for the buried section big enough to insert a tube and then suck out the water
- blow air through at high velocity (10m/sec +) until it stops spraying water then de-water by blowing super dry air or vacuum dry if you need the pipe water free

Buried drain lines / plugs are not a great idea as they often corrode or leak after a few years.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Ripz]

For new construction piping you need to be able to inspect the underground section as well during hydrotest. If you now have to provide access, then you have the ability to operate the drain valve.

Chances are you won't need it again after construction.

 

[lhwingking]

Exactly Ripz. I initially thought that backfilling will be done after hydrotest. But I do not know how the construction people are going to do it. They may perform hydrotesting of the burried portion separately or they may just carry out holiday detection in coating. I just do the engineering of the line.

And I am also hearing that you never provide drain valve in an underground piping system if you do not have a culvert.

I am looking for knowledge about the general practice of hydrotesting of underground lines (line is above ground, goes underground for a few meters and then comes above ground).

 

[LittleInch]

Generally you want to hydrotest the pipe in its finished condition (in this case buried) so that it is representative of the stresses being taken by the pipe. I agree you don't want to put a valve underground only for the hydrotest drain.

I've often seen a spool piece or access tee incorporated above ground so that you can insert a suction tube and suck most of the water out (similar to what you would get if you just drained it)

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Ripz]

Thinking about it, all our underground piping has drains within culverts.

Hydrotesting underground piping after backfilling is ridiculous. Imagine having a leak, and now having to remove all the backfill now to find the source.

 

[LittleInch]

No it's not ridiculous - common practice on pipelines - Imagine testing the pipeline, backfilling it then discovering you have a leak caused by the backfill or the strain induced because of that. Yes, finding a leak is a real pain, but that's why you test the welds before you drop it in the ground... A test should be a test in the final installed condition. Of course you could hydro the buried spool separately before tieing it in and testing the whole thing, but not backfilling is not the way to do it IMHO.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way