Pipeline For Small hydropower plant - culvert concrete pipes 1

[hansforum]

Hello,

I am analyzing one potential location for micro hydro power plant. Gross head will be between 4,1m and 4,5m. To achieve this head I need 73m long pipeline. It will be placed 1m below ground level in the soil near the river. I analyzed steel and GRP pipes and their prices, but I wonder is it possible to make it cheaper. I know that culvert concrete pipes are 3 times cheaper than GRP pipes, so I wonder is it possible to make pipeline with this type of concrete pipes. Maybe there is a way how to seal joints and then place them in ferroconcrete or plain concrete bedding. What problems could I encounter with culvert concrete pipes? If I plan GRP pipes in 0.8m diameter then I wound use 1,0m diameter concrete pipes because of roughness.
I just wonder if this could work out and if not, why?
Link so you can see what kind of pipes I mean:

http://www.humes.com.au/fileadmin/templates/HUMES/doc/Brochures/Humes_ConcretePipeManual.pdf

If I posted this in wrong subforum, please could you suggest me where I can get this kind of info?

Thans in advance!

 

[SlideRuleEra]

hansforum - There are concrete pipes that manufactured for exactly the use you have described. Here is a link to general information on that type pipe:

http://acppa.org/what-is-cpp/

The pipe reference manual shown in your post would not be the best choice. That type is not intended for pressurized use.

As for the sizing of the pipe, don't guess at the diameter that would be correct. A civil or mechanical engineer with the proper training and experience in hydraulics and fluid flow can accurately calculate which size to use.

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[hansforum]

Thanks for reply!
I am not familiar with the prices of CPP so I don't know if this could be better option then GRP. I am interested in culvert concrete pipes only because their low price. You sad that those pipes are not designed for pressure use, but what pressure can they withstand if buried?

 

[SlideRuleEra]

hansforum - Your reference manual does show concrete pressure pipe that should be suitable (see Section 6, starting on Page 27 of the manual). For the drainage culverts that you are considering the problem is not the strength of the buried pipe, it is leaking joints. I assure you, I am familiar with hydroelectric installations. Using a pipe that will most likely leak (at the joints) will be a big problem for the Owner. Also, the cost of 73 meters of a suitable pipe 1 meter, or so, in diameter will be only a small portion of the project.

Since you are not familiar with CPP and it is listed in your reference manual, perhaps you can make the contacts to find out how the cost compares with the alternate materials.

Good luck on your project.

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[hansforum]

Actualy potential Owners are suggesting those pipes because of low price. I need arguments against those pipes. The fact that they will leak under pressure is good reason. You sad that You have expirience with hydropower, can you please mention if those pipes need concrete bedding and how strong. What else would make expenses compared to GRP?

 

[SlideRuleEra]

You have a very good reference manual, for recommendations on bedding, see the section beginning on page 3. Of course the comments there are general. This is because the soil conditions at the project site will determine exactly how the pipe installation should be performed. It would be best to consult a geotechnical engineer concerning soil properties at the site.

As for reasons to use a pipe intentionally designed for pressurized use, there are other things to consider besides the static 4.5 meter head. One could be transient pressure from quick closing of valves, waterhammer. See page 31 of your reference manual. Having a pipe with joints not intended for that condition can result in sudden, dramatic failure.

Here is another reason to be concerned about underground leaks (from cheap pipe joints).
Hydroelectric stations are, or should be, closely monitored for leakage, especially for leaks that appear to be coming through soil. The concern is that soil erosion can cause a sudden catastrophic failure of the dam or water retaining structure that provides the hydraulic head.

Note: Interesting that we are discussing this subject right now. Thirty years ago this week, July 6, 1983, I was involved in a suspected underground leakage event at a fair sized electric utility's hydroelectric station's dam. The leak itself potentially threatened to flood a historic city downstream. Fortunately, we were able to stop the leak and, over time, make permanent corrections. The entire event, from the discovery of the leak to permanent solution of the problem (several weeks later) received national press coverage in the USA.

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[cvg]

CPP concrete steel cylinder pressure pipe is used for much higher pressures than what you need. it is not generally used for low head applications such as culverts. this would probably not be 3 times cheaper than steel or GRP. given that you have a very low pressure pipeline (less than 6 psi) and since it is gravity flow, only the downstream end sees maximum pressure, you could use ordinary gasketed reinforced concrete pipe (RGRCP) which is commonly used in the US for storm drains (up to about 10 psi). You can also specify ASTM C361 – 12 reinforced concrete pipe which can be designed for pressures up to about 50 psi.

RGRCP is quite smooth, not nearly as rough as what you seem to think. I doubt that oversizing to the degree you indicate should be necessary assuming that you have relatively low velocities, your headloss should be minimal with such a short pipeline.