Wet tap on HDPE pipe

[PEorl]

I have a contractor on one of my jobs that is asking if we would allow wet taps on HDPE pipe. He said that it has been done before, it requires a different saddle type than for wet taps on pvc. THANKS FOR ANY INFO!

 

[dicksewerrat]

It shouldn't be a problem if the saddle will seal well.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[PEorl]

Do you have a detail or specs for this?

 

[Ussuri]

Ferrule Strap.

http://www.tycowaterworks.com/talbot/product_list.php?ID=57

 

[rconner]

All aspects of all lateral connections to particularly very low long-term strength and moduli (and with large thermal expansion coefficient) piping materials (and maybe particularly “wet taps” to same) should be very carefully considered. A hole cut in a pipe is of course a stress concentration, meaning along with other factors a potentially weak spot in the piping system. Plastic pipe materials like hdpe are also subject to substantial (axial etc.) movement as the temperature changes, as well as considerably greater (than e.g. long used iron and steel) additional Bourdon and Poisson and (axial etc.) movement effects once the piping is put under any degree of inexorable, long-term pressure. The movement couild even be some "rebating" in nature, with thermal or pressure cycling. While the amount of movement/potential movement etc. or stress to be encountered should be calc/evaluated by engineers competent in such terms and analyses, as well as that of any normally low coefficient resisting friction interactions e.g. of the outside of the bell-less piping system with any earth surround etc., movement could conceivably be a quite surprising amount in some circumstances (e.g. several inches or even feet!) Adding (or subtracting as the case may be!) to all this is the fact that also in sections of hdpe pipelines installed e.g. by potentially high load pulling installation methods like HDD there is yet another source of axial movement, i.e. “recoil” (a sort of memory behavior) in such pipes particularly in the end connection areas! Affected transverse connections must of course somehow handle all this.
Early on as when some contractors/utilities attempted to use such pipe (with which they were not as familiar) and with conventional mechanical/seal saddles for service and lateral connections, I understand one of the first things that happened was some more or less conventional mechanically sealing saddles eventually ended up some distance axially either upstream or downstream of the hole cut in the hdpe pipe, which of course didn’t do much for the continuity of the service or main! This and other problems e.g. inward creep of pipe walls under high bolted compressive loading (at least without internal steel ring “stiffener” support understandably gave way in some quarters to arguably more vigorous promotion of variously fused insertions or lateral connections (leading also to promotion of e.g. “electrofusion” saddles etc.) However, there have also been some problems even at fused connections. While defective locations of heating wires, faulty installation/heating/surface prep etc., and even hydrocarbon contamination absorbed into the pipe wall have been blamed for some unsuccessful connections/fusions, one has to wonder looking at the manifestation and specific location of some damage if unexpected movement or stress as same was attempted wasn’t a factor in some of these problems as well (as discussed

http://www.ntsb.gov/Publictn/1998/SIR9801.pdf

, and per illustration that once appeared at

http://www.battelle.org/energy/cases/field.stm

etc.)
If connections are to be made with proprietary mechanical-type devices, sleeves or saddles and seals etc., all of the various “cautionary” and “limitation” statements should of course be reads and understood (e.g. see

http://www.romac.com/Installation-Instructions/FTS-423-H-install.pdf

and

http://www.smith-blair.com/uploaded/products/installation/39_39_ti-024_371_372.pdf

etc.)
I know incidentally that DIPRA also tested the resulting relative strength of a sidewall fusion method to connect to/tap hdpe they reported recommended by PPI in 2001 vs simple direct wall/thread tapping of ductile iron piping, and they published the protocol/ results that are accessible at

http://www.dipra.org/pdf/directServiceDIPvsPoly.pdf

.

One other thing that is perhaps worth mentioning (as you have not mentioned the sizes of piping involved and this inquiry is posted on the Waste...Forum) is that while "wet" or hot-tapping is of course sometimes done to sewer mains etc. and even maybe in some cases to even sewer forcemains under pressure, most wet-tapping equipment is most commonly used for potable water pipe tapping. What would obviously make some folks and maybe even the public or regulators some queasy might be the use of potable water tapping machines for making a sewer tap, and then "vice versa". It would proably make most sense for separate equipment to be maintained, and/or at the very least some effective disinfection procedure be followed to avoid any hint of unintentional contamination or cross-connection etc.

 

[dicksewerrat]

No spec here. Call the people that supplied the pipe the first time. Cleaning tapping euqipment is not that difficult . We used bleach.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com