Conceptual design of submerged pipeline in reservoir
Conceptual design of submerged pipeline in reservoir
(OP)
I've also posted this in the offshore pipelines forum.
I'm undertaking a concept design/preliminary costing for a submerged pipeline approx 5mi long in a reservoir. Location is California. The pipeline will be conveying freshwater (non-drinking), peak flows of up to 2400cfs and under pressure (not sure how much pressure yet).
My questions are:
Is PVC or HDPE pipe suitable? Do these pipe types come in rolls, or lengths?
Does the pipe need to be anchored, or just weighed down? If anchored, what method? I assume bottom is mostly mud/silt.
Are there any standards/guidelines for this type of construction?
Any guidance appreciated.
I'm undertaking a concept design/preliminary costing for a submerged pipeline approx 5mi long in a reservoir. Location is California. The pipeline will be conveying freshwater (non-drinking), peak flows of up to 2400cfs and under pressure (not sure how much pressure yet).
My questions are:
Is PVC or HDPE pipe suitable? Do these pipe types come in rolls, or lengths?
Does the pipe need to be anchored, or just weighed down? If anchored, what method? I assume bottom is mostly mud/silt.
Are there any standards/guidelines for this type of construction?
Any guidance appreciated.





RE: Conceptual design of submerged pipeline in reservoir
RE: Conceptual design of submerged pipeline in reservoir
If the reservoir contains the same undrinkable water as the pipe, why do you need a pipe at all?
Mike Halloran
Pembroke Pines, FL, USA
RE: Conceptual design of submerged pipeline in reservoir
Weighting using discrete concrete collars is a very common method of weighting down HDPE pipe.
Pipelife (www.pipelife.com) have an almost complete design manual under their downloads section.
The main problems with pressure pipes in HDPE are temperature if exposed to the sun (the PE is weakened, and the joints. PE creeps and flange joints may leak. We have used Aquagrip couplings to get round this problem. I am sure that there will be other solutions on your side of the Atlantic
Stephen Argles
Land & Marine
www.landandmarine.com
RE: Conceptual design of submerged pipeline in reservoir
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Conceptual design of submerged pipeline in reservoir
I am not sure that I understand your question as the pipe would presumably always be full of water, except during installation by probably the S lay method, so there would never be a nett external pressure.
It would also depend on the SDR of the pipe.
Have I missed something?
Stephen Argles
Land & Marine
www.landandmarine.com
RE: Conceptual design of submerged pipeline in reservoir
RE: Conceptual design of submerged pipeline in reservoir
Then, there will probably be some time in the future where maintenance might require displacing all the water for a fill with air or other gas. Never discount that possibility lightly.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Conceptual design of submerged pipeline in reservoir
I'm not sure about the boat traffic on the reservoir but will take prop and anchor damage into consideration. Perhaps the pipe/s will be buried in shallower sections of the reservoir.
Could you explain what S lay method is?
RE: Conceptual design of submerged pipeline in reservoir
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Conceptual design of submerged pipeline in reservoir
http:
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Conceptual design of submerged pipeline in reservoir
This method is usually used where the pipe will never be emptied again, such as an outfall. Alternatively auxilliary buoyancy can be used during the laying so that the pipe is always heavier than water even when empty.
For propeller snagging burial may be easier that stone covering, it all depends on what plant and materials are available.
Stephen Argles
Land & Marine
www.landandmarine.com
RE: Conceptual design of submerged pipeline in reservoir
Would you be able to sail a barge in? If not you would have mobilise and fabricate one at the site with full lay spread. Granted it wont be as complicated as with a steel pipe but it will still need a firing line of one form or another.
Could you do it in a less controlled manner using floating reels (precursor to modern reel lay systems)? Similar to the way the allies laid fuel lines across the English Channel during WWII. It would of course be restricted in diameter.
http://en.wikipedia.org/wiki/Operation_Pluto
http://w
Alternatively, fabricate on the bank and tow the pipeline across the reservoir?
RE: Conceptual design of submerged pipeline in reservoir
Can anyone recommend sources (URL or other) of data for pipeline design, eg pipe sizes/lengths/unit weights, max design flow pressures/velocities, pipe couplings? Perhaps names/links to manufacturers and vendors?
StephenA: Thanks for that link to the Pipelife site, I haven't had the chance to browse the site yet, but hopefully it will give me some answers to my queries.
I've just found out that the pipeline outlet may need a diffuser. Are these typically prefabricated/proprietary products, or constructed insitu?
RE: Conceptual design of submerged pipeline in reservoir
I think you might need to find a pipeline engineer. (?)
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Conceptual design of submerged pipeline in reservoir
RE: Conceptual design of submerged pipeline in reservoir
The Pipelife site gives information on diffusers as well. They have made diffusers for us in the past.
Stephen Argles
Land & Marine
www.landandmarine.com
RE: Conceptual design of submerged pipeline in reservoir
This esteemed group is responding only to the sketchy picture you've painted. The best solution might be affected by factors not in evidence here, and perhaps not known to you for lack of the right questions.
You need a pipeline guy, there, now.
Mike Halloran
Pembroke Pines, FL, USA
RE: Conceptual design of submerged pipeline in reservoir
Plastic pipe is from manufacturing, experience and/or practical matters also some limited in size. I really can’t imagine how e.g. one could possibly do a demanding underwater job (at least successfully) for a two thousand four hundred cubic feet per second flow quantity with a “pvc” pipeline? Likewise, I’m rough guessing that it might take in parallel something like FIFTEEN OR TWENTY of even the very largest hdpe pipelines available (assuming they were acceptable in all other respects for such installation?) to come close to handling that magnitude of flow volume at reasonable flow velocity for plastic pipes!
That being said, in my opinion some underwater pipe installation and (perhaps more importantly) subsequent trouble-free performance of underwater pipelines is a very rigorous application perhaps/arguably worthy of the very strongest, toughest pipe available. To get a feel for some extreme demands on some large underwater pipelines in even rather shallow water, and in some cases not too long after original design/installation, you might want to read e.g. the ASCE paper, “Marine Outfall Performance II: Stabilization and Case Studies” etc. available at htt
Some closer to home, I am aware of a significant 36” hdpe line that was laid across a rather shallow bay in Florida a few hours from where I live just a very few years ago (reportedly also by an experienced marine contractor). I understand this line, that I think was shorter than your job being a little less than a mile long, was initially required to be trenched, and also was very frequently concrete-weighted. I have heard third-hand this line also somehow encountered some weight slippage, I guess resulting in a sort of bunching up of weights from their original assembled positions. For whatever reasons also (I believe there may have been much time$?-consuming debate as to who/what exactly was responsible), a significant extent of this line also ended up being too shallow. Apparently also there was additionally at some point a realization or fear that the inside diameter of this newly line might not be adequate for (future?) flows (this is also something that should be very carefully considered proably best upfront, as the plastic pipe inside diameter used for such purposes can be quite small for nominal pipe sizes), as I eventually even noticed a budget issue request apparently once contemplated to replace at least some of the new line at http://w
I do not write this to diminish the utility of the specified/suggested pipe nor those who have thus trusted it (no pipe material is invulnerable, and I suspect there are quite probably many more claimed successes than problems with even the plastics); however, I just wanted to make the point that this can be very rough business with some sobering though perhaps some non-obvious realities for even the very strongest/most gouge resistant pipes conventionally used for such purposes. Additionally, I think some of this sort of work is sometimes done with very heavy equipment and rip-rap etc. working/rubbing around the pipes, and in conditions with zero visibility of what is actually going on beneath the surface. Over the years when I have been associated with marine pipeline work, I have even heard from some contractors in many situations that instead of long welded strings of pipe, individual shorter or segmented pipe assemblies can be easier or maybe even critically needed in some areas to get them installed properly where they are intended to go (I suspect examples could include strong winds or currents and/or unstable trenches that fill more rapidly than most lay folks might realize).
Just a couple other comments – while I guess it could be argued that conditions in a “reservoir” might be kinder than say that on the Cape of Good Hope, I don’t know enough of your perhaps inland application to know that there might not be some significant storms, cyclonic or tornado, marine traffic, erosion, or seismic activity to challenge the location and integrity of even your line(s) over many years. According to Al gore and his ilk some of these sorts of events are even increasing and not necessarily "Acts of God"?!!
If you have gotten this far reading this or other references, you might realize also that an ability to dependably repair a broken or damaged marine pipeline in place might also be an admirable consideration for at least some Engineers/Owners in upfront material selection (in this regard, I wonder if it is difficult to get a proper fusion job on a pipeline underwater?) Finally, I’m not even exactly sure how one can safely make an assumption that even some underwater pumped pipelines will always be totally full of water, maybe particularly if when installed they really end up looking some like “Nessie”, instead of a profile view straight line on paper!
While I probably have not addressed all issues in even this very long post, in summary I think this can be a complicated business, that is thus perhaps/arguably not for the faint of heart, pocketbook, nor experience (perhaps this was also sort of the gist of the admittedly much shorter messages of others including Mr. Halloran). [I will also post this response on the "Off Shore" site thread, where I first saw this now dual inquiry.]
RE: Conceptual design of submerged pipeline in reservoir
Since then I have installed many HDPE pipelines in trenches in the sea without any problems. Diffusers on any Outfall need special consideration regardless of the material.
Most HDPE outfalls are installed by the Float and Flood method and this needs to catered for in the design as air in the pipe during operation could bring the pipe to the surface. This happened in Richards Bay on a paper mill Outfall where the pumps were too high and cavitating. The newspaper reports were that the locals thought that it was a Russian submarine.
HDPE pipe has a high thermal expansion but also creeps and loses strength at elevated temperatures (above about 40 degrees C) but as with all things it is "horses for courses" and HDPE is the most suitable materials for certain cases.
Sizewise HDPE / HPPE is now made in up to 2000mm diameter and has been towed to Brazil from Norway in around 500m lengths.
Our website has several examples
Stephen Argles
Land & Marine
www.landandmarine.com