HDPE/PVC for Water Main Replacement within Bridge

[oahu93]

I have a steel main that crosses 400' span bridge. The water main resides within a below-grade cell and supported at 10' intervals. The water main has experienced significant corrosion at the existing bell & spigot joints and will need to be replaced.

One potential option is to replace the pipe with either HDPE or PVC. Since it will reside in a below-grade cell, there will be minimal UV exposure. What are your opinions with this material selection?

 

[MikeHalloran]

You may need to add intermediate supports.

I found conflicting information about whether PVC is suitable for water service.
The gray DWV stuff i have worked with has a distinct odor, and I'd expect a taste.



Mike Halloran
Pembroke Pines, FL, USA

 

[ashtree]

oahu93

Either could work but HDPE would be better. PVC is suitable for water service but is probably better buried.
HDPE has the advantage that you can weld it all into one long length and install it whereas PVC would probably have to be installed length by length.If you pull all 400 foot of HDPE in at once that would allow you to join it out on the bank somewhere, pressure test it then pull it in.

Depending upon the size and wall thickness etc you may have to support at closer than 10 foot intervals but this will apply equally to PVC or HDPE. For reference see the comments below and the attached file from the Poly pipe Engineering Guide

SAG
The amount of sag in mid-span depends upon the weight of the pipe per foot, including effluent. Figure J-1 gives
the recommended spacing for a mid-span deflection of one-quarter of an inch when full of water. However, in
situations where a dry gas is being carried, the indicated span can be doubled. When condensation occurs in the
pipeline, the liquid accumulates in the sag, unless the pipe is sloped; therefore, accelerating the sag due to the
increased weight. If less deflection is desired, new support spacing can be determined by multiplying the spacing
by the following correction factors:
1. 0.67 for 0.05 inch (1.3 mm) deflection
2. 0.80 for 0.10 inch (2.5 mm) deflection
3. 0.88 for 0.15 inch (3.8 mm) deflection
4. 0.95 for 0.20 inch (5.1 mm) deflection



Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[cvg]

hdpe and pvc will expand and contract with temperature change. not the best application for plastic pipe. maybe FRP would be better. if you use steel, than provide cathodic protectioin and bond all the joints

 

[dicksewerrat]

Ductile iron?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

I found conflicting information about whether PVC is suitable for water service.
The gray DWV stuff i have worked with has a distinct odor, and I'd expect a taste.

PVC is commonly used for water, see AWWA C900 and C905
gray DWV is intend for Drainage, Waste and Vents, and is not intended for potable water.

 

[ashtree]

Expansion and contraction with temperature change is a problem with any pipe system and must be catered for. However HDPE would be able to be used in this application okay with a few requirements. I have attached one of the relevant sections of the Poly Pipe Engineering Guide.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[jgailla]

I would use cement lined ductile iron for this application based on the little information provided, restrain all the joints, and provide expansion couplings at either end.

Mike,
PVC has been used for decades for potable water and in the several areas I've practiced is the default material for potable water, sewage force mains, and gravity sewage lines.
Can you post a link or links to articles which have found PVC unsuitable for potable water?

 

[ashtree]

jgailla

I don't have a link but in the past some of the concern has been around lead levels in some of the pipes but i think it was discovered that this primarily related to sewer and drainage grades.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Agree with cvg, this is not a good application for HDPE or PVC. The expansion of FRP with temperature will be much less and equivalent to steel. Steel or ductile iron are also good alternatives.

Consider the use of a higher quality coating system.