UG piping within Frost depth 3

[pangi]

Hi,

Regarding underground piping, one gentleman came up with a new idea. The frost depth at site is 3.9 m and he tries to put u/g piping at 2.0 m below surface with 100 mm Styrofoam layer 150mm above the pipes. The Styrofoam should be working as an insulator.

But, I have two concerns.
1)Does it work as insulator to prevent piping from freezing within the frost depth area? In my opinion, the Styrofoam just delays heat transfer between cold surface and piping and at equilibrium state, the service in pipe might be reaching to freezing temperature.

2)Is it durable for life time 20 years? The Styrofoam seems not strong enough to sustain the weight of soil and is going to be squeezed and to lose its insulation effects as time goes.

Could you advise me about this approach, please?

Many thanks,

 

[BigInch]

Insulation works to reduce heat loss by increasing the total resistance to heat flow. That reduces the slope of the temperature loss with distance between hot and cold areas, thus tending to maintain warmer temperatures on the warm side of the insulating material and cooler temperatures on the cold side.

With an insulating layer above a pipe, you must somehow prevent water from entering the soil from around the edges of the insulation sheeting, which is very difficult to guarantee will never happen.

http://www.schundler.com/pipe.htm

These guys say to wrap the entire installation with PVC. I don't think that will reliably maintain dryness and other measures will probably also be needed. By the time you do that, it may be better just to bury below the frost depth, no matter how deep that may be.

In any case don't use styrofoam. As you already know, strength is not sufficient. Normally a casing pipe with a pressure filled polyurathane is used if product and pipe temperatures are not too high.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[drywall]

It is always interesting to see someone try out a new idea but I have serious doubts about this one. A properly buried pipe almost never freezes and one with other "stuff" on the top almost always does.

 

[BigInch]

Because dirt is really not a bad insulation material at all and whatever else they put on top is. Even digging up a trench and installing pipe, then backfilling is good, unless the dirt is compacted too much and the air voids are eliminated. Unfortunately that's what you usually try to do. Concrete is not good at all for insulation purposes. It would be better to bury cmu units above. At least you might get some added insulation from the air space, as long as you can keep it full of air, but then there's that old water problem again.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[Sid7]

Hello all,

How about wood? the powdered wood may be split moulded to form a casing around pipe and this may be made rot proof over 20 years or so??

Just a idea.
regards
Siddharth

Siddharth
These are my personal views/opinions and not of my employer's.

 

[CarlB]

The idea of insulation over a pipe to protect it/contents from freezing is nothing new. Often referred to as a "frost shield". The true "styrofoam" insulation, extruded polystyrene (such as DOW blueboard) , is designed for subgrade use, and should maintain suitable properties for the life of most projects. It also has minmial absorbtion of water. Having it get wet is not a concern. It is also used as a flotation device for various watercraft.

The particulars of the thickness & width of the insulation required depends on design surface temperature (or annular variation), soil characteristics, pipe size, temperature & flowrate of product, etc.


See this link for one study:

http://www.tpub.com/content/ArmyCRREL/SR97_01/SR97_010007.htm

 

[BigInch]

CarlB, you reminded me with your excellent references to USCOE tech publications. I absolutely hate "re-packers" of US GOV publications that are already bought and paid for by hard-earned tax dollars, so I will furnish the original links. Odering the CD from one of the repackers takes more effort than downloading them and burning a copy yourself.

ALL USCOE materials are available for
FREE DOWNLOADING here,

http://www.crrel.usace.army.mil/library/technicalpublications.html

SR97-1 here,

http://www.crrel.usace.army.mil/library/specialreports/SR97_01.pdf

maybe you'll want to add this one too.
SR97-29,

http://www.crrel.usace.army.mil/library/specialreports/SR97_29.pdf

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[rconner]

CarlB, I was previously aware of and had read the ~10 year old report by CRREL on frost protection of pipelines. I was also aware that for probably for an even longer time some folks had been providing some frost protection to even underground pipelines with various foams etc., I thought with either at least the local knowledge or assumption that this would do what they wanted with regard to protection from freezing. However, I had not responded to this thread as I am not an expert in the insulations nor the thermodynamics involved. I am nevertheless specifically interested in what you said, i.e. “It also has minimal absorbtion of water. Having it get wet is not a concern.”.
I believe unless underground (or for that matter any) insulation is shielded with an impermeable vapor barrier, it will in addition to undergoing some level of mechanical stressing also be exposed to moisture/vapor in a great many underground environments. I have also seen more in depth discussions that even closed cell foams can be subject to some forms of aging and there will be over time some degree of diffusion of the blowing agent out of the foams, and diffusion/permeation of substances (e.g. water vapor?) into even the cells of the foam. I have also heard that water in insulations can/will? decrease the initial “R-value” (an maybe even bring up other questions if it freezes etc.?) While all of this may of course be immaterial if the foam is sufficiently durable and also appropriately conservative (considering all effects) long-term insulation values are chosen for design, I didn’t happen to see these specific issues discussed specifically in the CRREL report. Do you know of any good studies or references that address the long-term issues specifically with regard to buried insulations? Since the idea of buried insulation is being sort of legitimized in this thread and by these references, we should probably also mention the caveat in the CRREL report that under some conditions insulation can actually cause a narrow sheet of ice to exclusively form on roadways (I guess immediately over the protected pipe?).

 

[BigInch]

Please note I only confirmed the insulation theory as valid for the question asked. I myself do not personally believe that foams work long term in anything other than labratory conditions, which is why I suggested CMU with its inherent air space might be considered, assuming there is some other way to keep out any water. As you say, insulation would tend to allow freezing more readily in layers above it and could present other dangers.

I certainly wouldn't put uncased insulation material of any kind under a road or other high load areas, especially in a pipeline environment and I'd be pretty damned careful wherever I tried using it, to the point of being suspicious of compression by soil loads above or by pipe movement. So far, for uncased buried pipelines, earth and appropriate burial depth is all I have ever needed to keep product temperatures sufficiently high for my purposes.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[CarlB]

The use of subgrade insulation is very common once you venture north of about the 50th parallel (& probably 50 south as well). It's installed on virtually every foundation wall in Alaska, & probably most of Canada. It's a proven material, and it's not difficult to find information on. Yes Big Inch, it even works outside of the lab

In a few minute search, this document seems to address the longevity question pretty well-

http://www.xpsa.com/enviro/PDFs/Fabian_Hoffee_Herrenbruck_Earthtech_2004.pdf

 

[BigInch]

Thanks CarlB. I wouldn't want to contradict anyone's good experience with UG insulation, including the USACOE. You mention foundation walls, which don't tend to move too much and probably have relatively light loads applied to the insulation boards. Are you aware of any projects (specifically crude, or refined products) where these materials have been applied to large diameter pipelines?

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[CarlB]

No, havent heard of it used for large diameter pipes. I don't believe extruded insulation can be provided in other than fairly simple shapes.

Here's a data sheet for styrofoamm pipe insulation.

http://building.dow.com/na/dowpipe/prod/styrofoam.htm

It was used on smaller diameter pipes at this brewery, sounds like it was cut to shape and strapped on.

http://findarticles.com/p/articles/mi_m3469/is_n20_v49/ai_n27537042

 

[BigInch]

Thanks Carl.
Its summertime now. I'll have a look in Jan.


"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[civilperson]

Foam boards come in different compressive strengths. 100 psi is the strongest foam sold with 50 psi and 20 psi as common strengths under foundations.

 

[mark416]

Are there any thoughts of using what is suggested by the Army TM 5-852-5 report "ARCTIC AND SUBARCTIC CONSTRUCTION: UTILITIES, Chapter 12: Thermal Considerations"

 

[CarlB]

Can you make your question a little more specific? Yes many of those techniques have been and continue to be used in arctic & subarctic construction.

-what kind of pipe and product
-temperature & flow variations
-where located/climate
-soils conditions
-depth of bury
..etc..