Thermal Contraction Control in HDPE HDD 2

[rocklin]

I am designing a 100' HDD under a creek that will connect to Ductile Iron on both sides of the HDD. I am concerened about the thermal contraction of the pipe as it would not be tolerated in this design due to flanged connections. I am uncertain of how to design the concrete collars. My initial thought is that I need to fuse branch saddles to the side of the pipe and then pour the concrete collar, but your advice would me much appreciated..........thanks for any input. By the way this is a 4" main

 

[vzeos]

I have attached a link to PE Pressure Water Piping Systems Mechanical Restraint and Poisson Effects. I think this deals directly with your concerns.

http://www.cpchem.com/docs/PP813TNPoissonEffectsMarch03.pdf

 

[rconner]

Perhaps the whole line, including the pipe in the crossing, could be installed reasonably homogeneously with ductile iron e.g. as noted at

http://www.acipco.com/ADIP/trenchless/index.cfm

(and for optimum damage resistance etc.)in this critical area. This would appear to also minimize uncertain thermal-related or other transition issues, or questions of who to call in the event of a problem etc. at same?, as the coefficient of linear expansion of ductile iron pipe is only 0.0000062 per degree Fahrenheit(0.0000112 per degree Celsius). The pulled length of ductile iron pipe is incidentally also not subject to pipe material, creep-related contraction or "recoil" in the pulled length due to tensile pulling forces like the plastic, that may further complicate transition/connection issues/concerns.

 

[vzeos]

Nice site. My piping experience is mainly in the natural gas industry where we don’t use DI pipe. I can see some advantages in using HDPE under a creek, mainly in pressure testing the HDPE pipe string prior to pulling it through the HDD liner and not having to worry about leaks. I do agree that the Poisson effects and thermal contraction could be a problem. What I have done in similar cases, in addition to installing joint reinforcements, is to offset the lane of the HDPE from the lane of the main run of pipe, creating something like an expansion loop so that the tensile pulling forces of the PE don’t act directly on the mechanical pipe joint. Any thoughts on this?

 

[rocklin]

The reason we had to use HDPE was because after we pass the bottom of the creek, we had a very limited distance before the location of the tie-in. I ended up using a wall anchor and anchor blocks on both sides of the HDPE. Thanks for the valuable information.

From my understanding......if you use the wall anchor and anchor block system....the tensile forces will be distributed into the concrete and then into the soil.

 

[rconner]

Of course "pre-testing" of an HDD pipeline segment to make sure there are no leaks up front is primarily a design/installation philosophy (if folks want to spend a little time and money to do same), and it is certainly not a reason to choose one piping material over another for horizontal directional drilling (of course the link to the site document I provided earlier indicates pre-testing can be done in at least a couple different fashions with ductile iron pipe, if desired by the designer or installer). Of course also, standard or trimmed short pipes and/or often rather readily available fittings can be provided with ductile iron pipe systems, or perhaps even cut/modified in the field where necessary, that allow directional changes with flexible ductile iron pipe systems to a far tighter radius (if required for some special "tie-ins" etc.) than the allowable bending radii for hdpe pipe!