Best pipe material for sewage pipeline over sea channel 1

[macki]

I intend to install a 4" sewage pipeline 120' long (approx).
pipe exits from a commode on a dockhouse with a very good slope for gravity drain along a distance of 120' to shore.
there are issues with UV light on PVC, however cast iron, carbon steel etc will be overkill, will require a lot of supports, and too expensive for such a low presure system.
I am very worried about environmental hazards with a potential spill into the channel, trying to select a pipe material smooth enough to allow the solids/suspension to gravity glide to a tank at shore, strong enough to withstand 110 degrees F and a lot of UV. any advice would be appreciated.
thank you

 

[SJones]

PTFE

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[TomDOT]

Paint the PVC after installation. Done.

 

[SJones]

But that means maintenance painting later on.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[cvg]

why wouldnt you bury this pipeline, then no UV protection needed

 

[TomDOT]

SJones: Shouldn't be much need for maintenance painting on a PVC line running under a dock until it peels wholesale. Should be decades.

cvg: It sounds like a suspended line under a dock. Burial seems an impractical and expensive alternative. It also may make gravity drain to the local sewage/septic connection impossible (as subsea burying may well end up lower than the local sewage/septic connection)

 

[cvg]

I get it now
HDPE with carbon black is resistant to UV and the entire thing could be fused, no fittings and C factor of 150. would weight the same or less than PVC and would be tougher. biggest problem with plastic pipe is thermal expansion

http://www.ajdesigner.com/phppipeexpansion/unrestrained_length_change_equation_alpha.php

 

[TomDOT]

Even better.

 

[Latexman]

Relocate the toilet to shore?

Good luck,
Latexman

 

[vpl]

Not sure where you're located, but if this is a DIY project, make sure that you're complying with all the right codes, especially if there is any chance that the suction for a municiple water suplly is anywhere close. It's better to be a bit cautious and do it right then to be explaining why raw sewage is being dumped into some cities water supply. That old saw about an ounce of prevention ...

Patricia Lougheed

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[SJones]

HDPE with carbon black is resistant to UV

For how long?

Shouldn't be much need for maintenance painting on a PVC line running under a dock until it peels wholesale. Should be decades.

Should be, but what if it isn't? The OP has indicated that he feels a high risk associated with a leak. Having to use paint as a barrier to degradation and ensuing leak is not the best option for an 'inherently safer design.'

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[cvg]

60 mil HDPE film, about 20 years lifetime exposed to full sun. for thicker wall pipes - longer. If you mount the pipe below the dock, then you will not have direct exposure to sunlight.

http://www.layfieldenvironmental.com/pages/EGI/Specifications.aspx?id=5030

 

[stanier]

PE is the answer to your dilemma.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[bimr]

Why do you say that there are more supports for a metallic piping systems?

All of the plastic systems will require more pipe supports than metallic pipe. Probably a pipe support every 7-8 feet at your operating temperature. Netallic systems only need pipe supports every 20 feet. You also will have problems with thermal expansion with the plastics.

It probably makes more sense to install a pump and use a 2-Inch force main. It will simplify your piping and you will not have to worry about installing the pipe with a slope.

 

[ProcessHVAC]

The idea of using a forcemain is a good one. But check your local codes, around here you can't use smaller than 4" for sewage.

 

[stanier]

ProcessHVAC,

Have you not heard of pressure sewer systems? Many households are fitted with an individual sump, pump and controls. The pump operates when the system pressure allows. The majority of the piping is DN50 PE. This would be ideal for this application. It overcomes any blockage potential.

http://www.monopumps.com.au/en-au/pressure-sewer-system-pss

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[cvg]

either ductile or pvc would work, see the attached examples. this pier is much longer than yours. sewer on this pier appears to be 2 inch force main, fire water is ductile iron and electrical in pvc.

 

[macki]

thank you so much for all the suggestions, here is what TCEQ recommends "The pipe shall be constructed of cast iron, ductile iron, polyvinyl chloride (PVC) Schedule 40, standard dimension ratio (SDR) 26 or other material approved by the executive director", but of course they are not concerned about maintenance, corrosion or reliability issues with specific entities, thats why I am seeking more reliable options. I am leaning towards HDPE with carbon black.
1) Stanier: the PSS system using PE you suggested is very good but would involve a lot of maintenenace, I intend to avoid using any pumps because i have a very good slope so there are no issues with blockage, flow etc. My proposal will be simple and cheaper as well. I want to make sure that whatever material is used for the pipe will be reliable so I don't get leaks into the sea channel.

2)cvg:that looks very similar to my application but I intended to install the pipe on the outside of the gangway (not as depicted on your attachment).Now you have got me thinking.

 

[77JQX]

I'm a big fan of HDPE. It's durable, abrasion reisitant, and won't burst if water freezes in it. But it will sag between supports, and it will expand and contract with temperature changes. If you go with HDPE, you'll need to design for this - maybe snake the pipe in a tray, rather than use intermittant supports. If this was my design, I'd probably go DI for rigidity, UV resistance, and protection from third-party damage.

 

[macki]

thanks 77JQX, please take a look at the attachment from "cvg", I can put as many supports as possible, allow for expansion. I will also look into a tray for a 4" pipe and enough piping to "snake".