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Thermal Movement

uPVC has coefficient of linear expansion of 7 x 10 C°. This means that 1 meter of uPVC pipe will expand approximately 0.7mm per 10C° with rise in temperature of the pipe material. However, due to the short duration of most effluent flows and the slow temperature response of the material, the greatest thermal take place due to variation in environment temperature rather than the effect of hot effluent discharge. Successful accommodation of thermal movement is dependant on the controlled direction and distribution of this movement.

The following information is intended as a general guide & reference should be made to the relevant code practice issued by the appropriate statutory authority.

Unless thermal movement can be accommodated by alternate means, expansion joints should be fitted. Maximum spacing intervals for locating expansion joints are 6 meters for cold pipelines and 4 meters for hot pipelines. The maximum length of pipeline between fixed points should be 2 meters for cold pipelines and 1 meter for hot pipelines.

Vertical SWV stacks and discharge pipes should have expansion joints located on each floor where fixtures or branch lines are connected, directly above the highest branch connection. They should also be located at the base of a stack or at the end of a drain connection for a discharge pipe if the length of pipe between fixed point exceeds the distances stated above.

On Graded Pipelines expansion joints should be placed immediately upstream of the entry to a vertical stack pr other graded line, & immediately upstream of each change of direction in graded lines.

Expansion joints may be omitted in the following locations:

  1. At the top floor of a stack where the stack is free to move through a weather proofed sleeve through the roof.
  2. At the base of an external stack connected to a drainage trap where the stack is free to move through a sleeve fitted in the drain connection.
  3. At a junction or bend in a graded pipeline where the thermal movement in the pipeline can be accommodated by deflection of the offset leg without affecting the grade of the pipeline, subject to the length of the pipeline & offset leg. Supporting of the pipe shall not impede expansion movement in such cases.

Table 1. Alternative Expansion Provision

Normal Size of Pipe (mm)Maximum Pipe Length(L) (Meters)Maximum Pipe Length (L) (Meters)
32/40/5020.50
30.60
40.80
61.00
65/80/10020.75
31.00
41.10
61.20
15021.00
31.10
41.20
61.20

Table 2. Maximum Spacing of Pipe Supports For Material Temperature up to 45°C

Normal Size of Pipe (mm)Maximum Pipe Length(L) (Meters)Maximum Pipe Length (L) (Meters)
32/40/500.91.8
40/501.02.0
65 to 1501.22.5