Is trench alignment critical when laying PE pipe?
No. The flexibility of PE allows it to be placed with some variations in alignment to suit local terrain if necessary.
The alignment of the trench in the vertical plane is dependant on the application for which the pipe is being used. For example, gas and water PE distribution mains can be laid to follow the contours of the ground beneath which the pipe is being laid. PE gravity sewers, however, should be laid to the specified gradient to ensure their correct hydraulic function.
In the horizontal plane the pipe can be laid to follow, for example, the alignment of a road or footpath. However there is a limit to the bending of PE pipes. The minimum advisable bend radius at which PE can be laid is dependent on the SDR of the pipe. To avoid any risk of kinking, buckling and overstressing the following minimum bend radii are recommended. These are for pipes without ovality at 20°C
|Pipe SDR||Minimum Bend Radius|
|9||DN x 12|
|11||DN x 15|
|13.6||DN x 21|
|17 / 17.6||DN x 25|
|21||DN x 35|
|26||DN x 45|
|33||DN x 65|
Example ; the minimum radius of bend for placing a 500mm, SDR 11 pipe is;
(500 x 15) mm = 7.5m
It should be noted that joints should not be included in bends of the minimum radius in order to avoid high local stresses at fittings or butt fusion joints. Also it is advisable to increase the quoted minimum radius at temperatures below 5°C
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