Use of HDPE flange connections in buried force main 1

[plastcc]

Does anyone have experience with buried HDPE force-main flange connections or a suitable design, such as encasement, to protect these joints? The situation is for a 48" and 54" FM project, on steep grades, where it will be difficult to use a fusing machine in the trench. The flange joints are planned to be spaced at 150' - 200' intervals. I want to find an economical way to ensure that the buried flange joints are protected from the starting and stopping of flow.

 

[bimr]

"Where pipe is connected to rigid devices such as fabricated directional fittings or where flanges or other rigid connections are employed, the pipe must be protected from shear, flexing and bending. Flanges laid on the surface can become anchored in the soil, and should be supported on sleepers. Figures 34 and 42 illustrate a method for protecting connections to directional fittings and flanged connections to other appurtenances. Wrap elastomeric or rubber sheet material around the pipe under the clamps."

See page 44

http://www.performancepipe.com/bl/p.../Field Handbook revision 8-09 web version.pdf

 

[plastcc]

Good info, bimr. Thanks!

 

[stanier]

I have search for many years for a manufacturer of PE flanges who has actually designed the stub end for externall loads. it would appear that the industry has just drawn them and then made and tested a few. I have been unable to find anyone who has analysed such a flange as has occurred for steel flanges.

I was about to invest in one of the Paulin research FEa packages and analyse the behaviour myself when the project changed and i was left with no one to pay the bill. one problem with using FEa to analyse the flange behaviour is the non linear charactristics of the PE and the soil

 

[rconner]

Flanged joints were originally applied, even hundreds of years ago and since, predominantly in quite stiff and strong metallic piping systems. While not always advertised, and particularly with some modern special sealing gaskets, such metal pipe connections are capable of handling substantial tensile and even bending moment loads, even though there are typically some relatively high and localized stresses in flanged connections due to the radial off-set or eccentricity between the bolt circle consisting of normally steel bolts tensile loaded in assembly and the inner gasket area and pipe barrel (that is subsequently stretched and bent etc. by all manner of service loadings).

Flanged joints in plastic piping systems are obviously inherently weaker connections, more subject to viscoelastic deformations, and additionally plastic piping systems are subsequently subjected after original installation to much more pronounced thermal, Bourdon, and Poisson etc. effects (that can also in various fashions also load, and/or repetitively load flanged joints). As you are apparently in this case dealing with underground systems, I guess we could throw in imperfect axial support and/or differential settlement as well as any present corrosive or environmental stress cracking agents also into the mix.

I guess these technical realities, along with some third-party accounts I’ve heard over the years of unexpected or preferential problems in the field with at least some flavors of polyethylene flanged joint connections (I suspect you could readily find more, even published, with a key word web search e.g.

http://www.onepetro.org/mslib/servlet/onepetropreview?id=NACE-03609&soc=NACE

), leads me to believe flanged joints in general could well be further points of vulnerability in plastic pipe systems. It thus may be advisable to work very closely with a trustworthy supplier and installer, with proven experience for such large connections.