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Smacky (Mechanical) (OP)
16 Jun 09 11:26
Has anybody had experience with this? My client wants some HDPE pipe embedded into concrete. WHen finished, the total length will be 450 ft. There will be 6 pipes, varying in size from 1.5" to 8". There will be riser stations exposed every 100', but the pipe will transition to 316 stainless steel there.

I'm OK with embedding the pipe, but the thermal expansion has me concerned. Will restraining the HDPE damage either the pipe or the concrete?
Michael17 (Civil/Environmental)
16 Jun 09 15:23
why embed the pipe to begin with. will the HDPE not carry the load? Why not just trench it? might be cheaper to just buy or use RCP.
Smacky (Mechanical) (OP)
16 Jun 09 17:10
The customer requested it. And its on a pier over a river so my choices are to either embed it or suspend it.
cvg (Civil/Environmental)
16 Jun 09 17:37
put it in a steel casing
StephenA (Civil/Environmental)
17 Jun 09 3:08
HDPE creeps much more than other pipes so if you suspend it you will get a series of loops unless the suspension points are very close together.

It also has a very high coefficient of thermal expansion.

I can see why your client might want to surround the pipe with concrete especially if it is exposed to a lot of directly sunlight. The pipe would "snake" between supports but a continuous restraint would keep it in one place.

The only position that might give a problem is where the risers exit the concrete. The smaller risers might be ripped off the main pipe but leaving a slightly larger hole (protected so it does not clog up) should prevent this.

You will have to do some expansion calculations to determine the size of hole / slot to leave.

Unless the concrete surround is very thin I doubt that the concrete will be damaged.

Try this web site for guidance http://www2.pipelife.com/com/products/products_overview.php

They have several downloads



 

Stephen Argles
Land & Marine
www.landandmarine.com

rconner (Civil/Environmental)
22 Jun 09 17:50
While I suspect such pipes have been encased in areas and for some applications, I have also noticed some authorities reportedly prohibit or have special requirements concerning plastic pipes encased or embedded in, and/or transitioning to some concrete (e.g. see under heading "System Application and Material Usage" at  http://opus.mcerf.org/pair.aspx?appID=-7496903663424289591&;materialID=154908626734025302 , that includes in the opening paragraph, "Polyethylene (PE) is not approved for indoor use or for encasement in concrete slabs.".  See also e.g. points made at http://books.google.com/books?id=SG1uO8NV5AcC&;pg=PA122&lpg=PA122&dq=failure+concrete+encased+plastic+pipe&source=bl&ots=ChSDbnpyym&sig=UDpe_pHLpZOsM_MyRVw3KysjEm8&hl=en&ei=GIw_Su2tDZTKtgfRqpwL&sa=X&oi=book_result&ct=result&resnum=3  and http://www.vinidex.com.au/files//technical_notes/technical_notes/feb02concreteencasementgroutingofplasticspressurepipes.pdf etc.
Furthermore, if it is critical that there be an axial leak-proof transition between the outside of the plastic pipe and encasement, e.g. passing through a concrete structure wall etc. (this would not appear to be the case in your application), this sort of application apparently needs to be very carefully considered (as the plastic apparently does not bond with the concrete in the same fashion as a metal wall pipe, and or the transition is more susceptible to thermal and other movements, sliding, seal disturbance etc.?)  See e.g. the mention/explanation in "...Related Art" (prior art etc.) at http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&;Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&;l=50&s1=5340164.PN.&OS=PN/5340164&RS=PN/5340164 .
I guess you could contact these authorities as to their experience(s) that result(s) in such concerns/prohibitions.

On the other hand, I know at least one manufacturer of at least plastic composite pipes actually advertised in their roll-out of an allegedly "wear" etc. -resistant piping system a few years ago at http://www.allbusiness.com/construction/building-fixtures-mechanical-systems-plumbing/6504700-1.html a few years ago, "The chemical and corrosion-resistant plastic outer wall makes composite pipe ideally suited for concrete encasement and direct burial below grade." (however,  I'm not sure that  the applications of such piping system were really without any problems thereafter).   
 
raugeo (Geotechnical)
25 Jun 09 8:57
Hello Smacky,

The piping material that you are probably looking is PEX or more specifically PEXa. PEX is polyethylene crosslinked and it is HPDE extruded with high pressure peroxide which makes the crosslinking of the carbon molecules possible. The result makes the PEXa pipes tougher, more flexible, resistant to "creep", thermal expansion and slow crack growth inherent in HDPE pipes. Also PEXa is commonly used in concrete for Radiant Floor Heating and Geothermal Energy Piles configurations. The sizes range from 3/8" up to 2" in stock but larger diameter pipe can be custom made. I am attaching some documents that provide examples of the differences between PEXa and HDPE. If you want to know more just let me know

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