How to prevent water mains from freezing in the snow zones in water supply projects?

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How to prevent water mains from freezing in the snow zones in water supply projects?

I have been ​looking into ​the design ​of a water ​supply system ​for approx. ​8500 households ​in the ​Himalayas of ​Nepal. The ​total ​transmission ​pipeline is 47 ​km, and ​distribution is ​178 km. The ​pipes we are ​using HDPE ​pipes of 15-​280mm diameter (​PE 100 and PN 6,​10,12,5 and 16 ​pressure rating)​, and at some ​sections ​Seamless Carbon ​Steel Pipes (​150-200 mm ​diameter) ​referring to ​ASTM-S40, are ​also used. ​The larger ​diameter HDPE ​pipes are used ​at transmission ​line at ​freezing zones. ​It is a ​rural setting ​with no ​electricity for ​the time being. ​It's a ​gravity supply ​project, with ​the water ​source at 4000m.​ above sea ​level and ​service area at ​2200m. above ​sea level. The ​transmission ​main of about ​15 km. lies in ​the section of ​4000-3700m. ​above sea level.​ I am concerned ​about the ​freezing of ​water inside ​pipelines ​during winter ​in the night ​time (when the ​water in the ​pipe is not ​moving due to ​no consumption),​ where certain ​sections along ​the pipe ​alignment are ​filled with ​snow for 2-3 ​months. I have ​allocated 1.25-​metre depth in ​the depth of ​the pipeline ​trench for the ​transmission ​and 90 cm depth ​in the ​distribution ​alignment. ​I have ​been looking ​for codes and ​references ​worldwide. ​Would be ​grateful if you ​can share your ​experiences or ​ideas, and any ​special codes ​to refer to. ​

I have shared ​some slides for ​easy understanding ​of my case. ​

 

Thanks,

Mahesh Neupane

B.E. Civil ​Engineering/ M.​E. Environmental ​Engineering ​

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7 Answers

  1. 1- I think water should flow constantly in the pipeline. 2- It solves this problem by using the pipeline anodizing method in several points.1- I think water should flow constantly in the pipeline. 2- It solves this problem by using the pipeline anodizing method in several points.

  2. I agree, bury below local frost depth.  If this cannot be achieved there is an option of adding insulation above the pipe.   In a recent project I specified Owns Corning closed cell extruded polysytrene insulation board, 2-inch thick, across the width of the trench just above the pipe.  It was difficult to find exact design guidance but I came to the conclusion that this works better in soil not rock and one 2-inch layer could reduce depth by 1 foot. 

  3. Hi Mahesh. I agree with the responses already published and would add a couple of thoughts for you to consider. Firstly, early tests on the performance of PE included laying in permafrost (I believe in Canada by the oil and gas industry) and pressurising with fluid and some gas. The PE failed and we learnt how notch sensitive PE can be at low temperature. Secondly, I see that your source is at elevation 4000m and distribution area is at 2200m, i.e. 1800m (approx 180 bar) pressure. I assume that you will have some very good pressure management on this scheme, especially given my first item. Good luck.

  5. finntreat@pp.inet.fi

    In Finland we install the piping under the deepest frost level. Br Paavo Vaittinen, Water and WW chemist.

  7. Mahesh

    this link might help you 

    https://www.gov.nl.ca/eccm/files/waterres-training-adww-2014-05-jason-phillips.pdf

    You'll note 2 meter depth

    Now I have no idea if this will help or not, but it may be handy to automate this process by registering all of the data properly - see www.wateroffice.com - than combining that with a machine learning tool that ingests connected asset data, your constraints, goals and the hydraulic model such as Optimatics - where Water Office has been integrated with. 

    Gr John