Expansion joint on polyproplene pipe

55degC down to what exactly? A Basildon Winter <cough, splutter>?

Why not just snake the pipe into a few loosely-constrained gentle curves along the way?

Do the calculations. Find the co-efficent of linear expansion for polypropolene.

Figure the expansion length due to the maximum temperature differential. See if the expansion joints will handle that length.

Remember that the pipe will not be installed at either the maximum or minimum temperature. If close to the max temperature the pipe will decrease in length.

good luck

Also remember that it will be full of water! if the water is always flowing then this will help keep the system cooler! Is it on the surface or sub-terrain?

Assuming the thickness of the pipe walls to be negligible in comparison with the length of the pipe, we shall take into account the Co-efficient of Linear Thermal Expansion.
The Co-efficient of Linear Thermal Expansion of Polypropylene is (8.6/ celsius)*10 raised to -5. (Please verify the exact value of your Pipe material). Now since the you have said that the temperature may reach upto 55 Degrees C, I am assuming an ambient temperature of 25 degree C (You may take a suitable value, in accordance with the actual ambient temp of the region). Therefore the maximum temperature difference that the pipe will be subjected to will be 25 Degrees C

Now the formula of Co-efficient of Linear Thermal Expansion is



where
ΔL= Change in length due to temperature difference
ΔT= Change in Temperature
α= Coe-fficient of Linear Thermal Expansion
L= Original Length


Now since the only unknown value here is ΔT, by substituing the other values in the equation, we will get the total change in length of the pipe due to increase in temperature. In this case, it would be 322.5 cm or 3.225 m. In order to keep a certain margin of safety, let us assume that the totalt elonagtion of the pipe through the 1500 m length would be 4m.

Now, you have mentioned that you will be using 5 expansion joints. Thus you must know how much expansion in length each joint will allow.

Knowing this, 5*(expansion lenght allowed by each expansion joint)≥4m
If this condition is satisfied, then i guess your pipeline should be safe. I sugges that you take the exact values of each quantity to calcualte the total elonagtion of the pipe, since the values I have assumed are somewhat approximate and simplified
As for weather, your pipe can sustain the pressure of 80psi, I suggest that you refer to the Tensile properties of Polypropylene pipe/material

Hope it helps :-)

Well it appears that while I was typing out my answer, someone already gave the correct solution :-)

Verify with your pipe supplier any manufacturer recommendation. Without looking it up, I seem to recall PP needs support on 2 or 3 meter centers, and possibly special saddles to distribute the load if run overhead. Provide an adiquate anchor at each branch connection. If space allows, I would recommend an expansion loop instead of an expansion joint to deal with expansion. pipe should have guides on 15-30 meter spacing to direct the expansion/contraction straight into the loop. Again, a good manufacturer will be willing to give recommendations to a customer that is buying 1500 meters.