Sandbag as Permanent Pipe Support 2

[McDermott1711]

A 42" line-break valve has a 2" sensing line which shall be branched min. 5D downstream in an underground gas pipeline. 2" branch shall be done at 12 o'clock. Is it acceptable (from engineering point of view)to use sandbags under 2" pipe (as it is shown in the below picture) permanently and backfill the line?

Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has. Rene Descartes

 

[zdas04]

I don't know if any standards address this or not, but too often when I've had underground problems, when we dig it up we find "permanent" sandbags that had torn, rotted, or just leaked all the sand out. Buried sandbags are a huge problem for the next guy (they seem to generally last 3-5 years if not torn on installation).

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[IRstuff]

sandbag ≠ permanent in my view

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[cvg]

whether you place sand in a bag or just place sand bedding without a bag, when you dig up anything bedded in sand, the sand will move. If you dont dig it up then all will be fine. But since this whole thing is buried, how else are you going to bed it and support that pipe? Would it perhaps be better to place this whole thing inside a vault or manhole?

 

[racookpe1978]

Could they pack in cement-filled/grout-mortar "sandbags" so the cement would harden in place after being pushed into position?

 

[rconner]

Decades ago it was common practice to lay underground pipes first on hard (flat) blocks or mounds for various reasons. It was later found that this contributed to non-uniform, particularly axial load support conditions(i.e. creating a sort of underground pipe-on-supports installation with high local/beam reactions), and such laying was removed e.g. from most standards an dspecs. Anything localized "hard" supports, or that creates a whole lot different load support conditions than surrounding soil might thus be suspect, unless the piping is specially designed for same.

 

[zdas04]

I have seen unopened bags of quickcrete used under valve risers with really good effect. Come back in 10 years and the bags have all absorbed enough water to set the quickcrete and they are really stable.

The problem with sandbags are the sand is not contained. If I bed a pipe with sand, the sand is contained by the ditch walls and the rest of the fill. With sandbags the sand migrates laterally toward the minimal stress in the backfill. When we dig it up the sand is never far from the pipe, just not under it.

rconnor,
I've seen that too, we never seem to get the bedding right and the pipe is cantilevered between the supporting blocks. When you try to use sandbags to keep the pipe off the ditch (and I see that too often in fiberglass) then when the bags fail, the unsupported lengths increase while axial movement is constrained, not a good combination in any pipe and results in way too many leaks in fiberglass.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Gator]

Are they using 3D modelling software like SolidWorks to layout the buried, large bore piping?

 

[IRstuff]

What's the issue with using actual brackets?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[MikeHalloran]

First thought:
Brackets need to attach to a structure. Dirt is not a structure.

But you know that.

If you're thinking, 'attach the little pipe to the big one via brackets', then the brackets become stress raisers on the big pipe, and the dirt becomes an irresistible force, using the brackets to damage the big pipe.




Mike Halloran
Pembroke Pines, FL, USA

 

[bimr]

Don't believe that sandbags are a recognized support material.

There are a few firms selling structured pipeline support pillows. BASF has a product:

http://www.polyurethanes.basf.us/applications/segment/selected/pipelinefoam

PipeSak Inc. also has a product:

http://www.pipesak.com/support/default.aspx

Unopened bags of quickcrete are a Contractors ppor substitute for an engineered thrust block.

 

[cvg]

backfill the entire trench with CLSM and forget about the sand bags and bedding

 

[McDermott1711]

To Gator:
You can do many things with 3D modeling software (such as SW), but it not normal in piping.

I got very helpful discussion here and I highly appreciated your advice, my friend.

Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has. Rene Descartes

 

[LittleInch]

This type of connection (small bore to large bore) historically has a large failure rate.

Some of this is due to movement, corrosion ( wall thickness is usually much less than the main pipe) and stress concentration at weldolets, elbows etc. They are also virtually impossible to inspect once installed. Remember to electrically isolate it so it doesn't ground the CP system...

If this was me I would make the small pipe vertical, encase it in a PE or similar pipe about 3 pipe sizes bigger and fill the annulus with pea gravel. I would also consider making the connection 100mm then reducing t0 50mm to give the connection some strength. Those two 90 degree elbows could easily become overstressed with even a small amount of compaction or "leakage" of the sand bags

In answer to the original question, No, it's not acceptable for all the reasons given above. If you have to do it this way then piggyback it using proper blocks like they do subsea, probably at about 500mm centres.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[McDermott1711]

Remember to electrically isolate it so it doesn't ground the CP system...

What does that mean, when this sensing line is going to attach to the LBV somewhere above ground?

BTW, What about using a pickup strap clamp?

Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has. Rene Descartes

 

[LittleInch]

The sensing line goes somewhere. If this is an instrument it is normal for the instrument to be earthed or the pipework or supports to be earthed. As it is welded to the pipe, it is (hopefully) being subject to CP and if you effectively attach an earth to the pipe, then you flatten the CP system and it stops working. It doesn't take much to lower a CP potential.

Same thing applies to the valve, but often the stem is electrically isolated from the valve to prevent this.

your clamp as shown is even worse than a sandbag as it provides a concentrated point load. The piggyback clamps shown in the post above would need to be nearly continuous in this instance to provide sufficient support to that rather weedy little line.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[McDermott1711]

Same thing applies to the valve, but often the stem is electrically isolated from the valve

This surprised me, because that 42" LBV is a trunnion-mounted ball valve with anti-static system which let electric charges being discharged from ball to the body via stem.

Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has. Rene Descartes

 

[LittleInch]

I didn't explain it very well. Within the valve everything is connected, but for buried valves you normally have an extended stem. At some point the extension electrically isolates the buried section from the above ground bit which can then be earthed, especially if there is an actuator.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[McDermott1711]

Sorry LittleInc to bother you with my questions, but I'm still confused. If the anti-static system is to prevent accumulation of electric charges on ball, so these charges should dischages to the ground (am i right? Or there is other way). In this case the valve is connected, no matter the stem is somewhere isolated from extended portion. Otherwise, anti-static does not work.

Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has. Rene Descartes

 

[LittleInch]

No, the anti-static is to prevent a voltage difference between the ball and the rest of the valve to prevent any potential for a spark. So long as all the bits are electrically connected to each other then it doesn't matter whether the valve body is earthed or not. Above ground pipework is normally earthed, below ground it sits at a few volts potential due to the CP system.

Buried pipeline valves become part of the pipeline CP system and need to be coated / painted to prevent corrosion and current loss, but it is important that anything (like your 2" line) electrically connected to the pipeline is isolated and not earthed.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.