Polyethylene Pipe Supports

[Bariutt]

The company that I work for uses HDPE pipe on trestles to trasport slurries. The trestles were originally designed for steel pipes. Because of the large coefficients of expansion with HDPE we at times have problems with pipe support details. Is anyone on the forum familiar with pipe support details that work or other companies supporting polyethylene pipes in this fashion. The pipes we are using are 14", 16" and 20" diameters. The manufacturer of the pipes says most people do not support their pipes on trestles. Where we are located it can get to -40 deg F in the winter and 90 deg f in the summer.

 

[MikeHalloran]

Can you be more specific about the nature of the pipe support details problems?



Mike Halloran
Pembroke Pines, FL, USA

 

[Bariutt]

We are looking for pipe support details used by others - anchors, guided supports and sliders - spacings, etc. Trying to benchmark others experience with this pipe on trestles. Because the pipe expands so much (probably 10 times more than steel) if the system that is installed cannot accomodate this expansion then at times it will tear the trestle apart (especially at bends). We have used this pipe on trestles now for 20 years however we would like to know if others are using it and what type of details they have success with. Our experience is that you have to install some type of anchors at strategic locations. Our trestles are thousands of feet long. We have up hill grades and down hill grades. The trestles have bends in them. We find that if we don't anchor at locations the pipe tends to "creep" downhill and not return. Most of our expansion is taken up by the pipe snaking in a serpentine fashion. Would like to find others with experience supporting this pipe on trestles and visit their facilities to benchmark successes and challenges.

 

[BigInch]

Do you do any expansion, contraction and perhaps stress analysis on these pipelines? I can't see where the mechanics is that much different than steel, except you might need 10 times as many expansion loops and anchors. Those should be much easier to design and cheaper to install than what steel lines require, as the modulus of elasticity is so much less there would be only 20% of the forces of a steel line to deal with. Do you cross brace your tressels together every 50 meters or anything?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[civilperson]

Try a 360 degree expansion loop, (four 90 degree bends), before and after the trestle with an anchor point in the mid-span region. The loops can be made bigger for the longer trestles.

 

[rjstephens]

If you use a vendor catalogue i.e. Main Industries. they give snaking calculations, expansion loop and anchor block load calculations based on field operation and strain gauge testing.
The HDPE pipework will snake, one just has to calculated the amount of snaking, and position guides and anchor block to accomodate the amount of load and movement that one requies. I have designed Copper refinery HDPE like this (1.2M Dia) and have verified the calculation with CAESAR II in doing a "shrinkage" calculation, i.e. control the snaking effect and contract the pipework to get inverse sign loads and stresses, they are about 25% conservative in comparison to the strain gauge method.

HDPE also experiences visco-elastic creep and does not return to it's original state if the pressures/loads etc are to high for the required design life of the pipe/fitting. A PE 80B material for instance may be rated to 10bar at 21 deg C, but at 55 deg C will only be able to handle 5 bar for a life span around 12-15 years, sorry, do not have the info handy and am just approximating the life span.

Hope this helps.

Cheers

Rob

 

[HEC]

we use cable tray and just lay the PE pipe in it.

Mark Hutton