Supports for HDPE pipes

[Zlmndra]

Hi all

I'm reposting - my first attempt to post this thread seems to have been swallowed up by dark spaces of the internet.

I have 3 m high T shaped cantilever pipe supports supporting 2 off DN450 HDPE pipe and support trays. The height of the structure is to avoid flood water during heavy rainfall. The pipework runs for several kilometres, and supports are spaced at 6 m.

For a 6 m length of HDPE I calculated the expansion to be 100 mm (delta L = L x alpha x delta T, with a 70 deg C change in temperature). The corresponding force for this expansion is some 480 kN (using delta L = PL/AE). As I deemed it uneconomical for my structure and footing to try resist this lateral load of 2 x 480kN = 960 kN at 3 m height, I advised the client that the loads would have to be taken out in the pipe design ie thrust blocks, loops to allow for expansion, etc. However my client is concerned that the pipes might expand and jump out of the trays unless they are tightly bolted down - which I do not wish to do, due to the aforementioned thermal expansion loads.

Has anyone had experience in dealing with this problem and can offer solutions or suggestions?

Thanks!

 

[Zlmndra]

I should add that previously the HDPE pipes were located at ground level, so expansion was previously not an issue.

 

[patprimmer]

I don't suppose bellows type sections are available for the pipe. It certainly is technically possible to make them, but the tooling cost would be very high.

Regards
Pat
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[JedClampett]

Most HDPE is buried for just this reason. If your HDPE is in trays (I don't understand from your questions), you can build in some give by weaving it through the trays. What is your pipe diameter?
There are places where HDPE is not appropriate. This might be one of those places. But don't try to fight the thermal forces of the HDPE. You're not likely to win.

 

[dhengr]

Zlmndra:
I’ve never done your exact design problem before, so just some imagineering here with some dimensions and sizes for you to finalize. You don’t mention the dia. or number of pipes, or the size of the tray. You don’t want thrust blocks either because your structure has to pick this reaction up too, sooner or later. They intentional build zig-zags into pipe lines, as opposed to long straight runs to allow some expansion and contraction in a way and at a point where they can manage it. Assume a 1m wide tray with a steel plate floor, side sills are 300mm high channels with toes pointing inward. This should span 6m, carry the piping and take wind loads, etc.? The piping, however many and what types, are just laid in the tray, so they can become serpentine to accommodate expansion; and they will flex a bit, or just straighten out, at a zig-zag to accommodate contraction. You might band (group), like types of pipe together into bundles so they act together, since they react alike; i.e. HDPE one bundle, copper or steel pipe in other bundles. These banding points and systems might actually have wear plates on the bottom which move on the tray floor pl. so the pipe doesn’t wear very much. They are spaced as a function of the pipe spanning ability btwn. these wear pls. On the top of the tray, every 1.5m there is a cross piece, a retainer, which keeps the pipe in the tray, prevents vert. expansion, forces lateral movement. It is bolted to hinge at one side channel, and at the other end a finger tight bolt or locking pin holds it in place, but allows it to be moved out of the way to work on the pipe.

 

[Hsang]

I am curious how 2 DN450 HDPE pipes in two cable trays will behave when supported at 6 m centres by T-shaped cantilever posts over long distance. Being relatively large pipes with large bending radii, can the serpentine that dhengr and JedClampett described be introduced in the system by providing 'stagger' at interval(say every 20 m)and closing the span at the 'stagger' to 4m to allow the pipes to be self supporting and move. Can someone familiar with HDPE pipe comment?