A. Exposed Installations:

Longitudinal expansion depends on the temperature variation the pipes are exposed to. If the working temperature of the system undergoes variations up to 10 -15°C the pipe elongation should be evaluated and considered. Cold water pipes have low linear expansion and hence can be neglected. But in case of hot water and heating installations, the longitudinal expansion must be considered and the installations must be planned and performed accordingly.

Thermal expansion of Polypropylene pipes can be evaluated using the following formula:

   ∆L = α x L x ∆t

Where:

∆L = Linear expansion in mm.

α = Coefficient of linear expansion = 0.18mm/mK

L = Initial pipe length in m.

∆t = The difference between the temperature at which the system is installed and the operating temperature.

Compensation of Longitudinal Expansion:

For exposed installations, the length variation due to longitudinal expansion should be compensated by a calculated and planned change of direction.

The free pipe length “Ls” is the length of pipe that should be kept free without clamping so as to compensate for the expansion. It is calculated with the following formula:

Ls = K x √d x ∆t

Where:

Ls = Free pipe length in mm

∆L = Linear expansion in mm

d = External diameter of pipe in mm.

K = 20 Constant for the PP-R material.

Example:

If a pipe of 25mm diameter with 4m length, undergoes a potential temperature variation of 50° C. The thermal expansion calculations result the following:

The variation in length:

∆L = α x L x ∆t = 0.18 x 4 x 50 = 36mm

The free pipe length:

Ls = K x √d x ∆L = 20 x √25 x 36 = 600mm

B. Concealed Installation

Concealed installations generally do not require any special consideration  for  linear  expansion as there  is  enough  room  to  accommodate  the  expansion  of  the  pipe  as  per  the  guidelines of installation according to DIN 1988. Where  there  is  no room to accommodate such expansion, the material absorbs all the stress arising from residual expansion.