Technical data

13
Compressed Air Applications Manual | Selection of material and pipe system Compressed Air Applications Manual | Selection of material and pipe system
For calculating the safety factor (SF)
and the operating pressure (p), it is
first necessary to know the endurance
strength of the material.
The endurance diagram for polybutene is
set out on page 15.
This diagram shows the relevant endur-
ance strength value (comparative stress)
as a function of the desired service life
and the maximum operating temperature.
The calculation must also take the pipe
dimensions into account.
The required safety factor SF for pipes
made of polybutene is
SF = 1.5
The effective safety factor should be cal-
culated using the following formula:
δB x 20 x s
SFe =
p x (d-s)
Example:
Service life 50 years
Temperature 70 °C
Operating pressure 6 bar
Material PB
Pipe d x s 32 x 3.0
δB from the
endurance diagram 7.5 N/mm
2
7.5 x 20 x 3
SFe = = 2.6
6 x (32–3)
This example results in a safety factor of
2.6.
Calculation of effective safety factor and permissible operating pressure
The maximum permissible operating
pressure is calculated analogously by
adapting the safety factor formula.
20 x s x δB
p =
(d–s) x SF
Example:
Service life 50 years
Temperature 70 °C
Operating pressure 10 bar
Material PB
Pipe d x s 32 x 3.0
δB from the
endurance diagram 7.5 N/mm
2
20 x 3 x 7.5
p = = 10 bar
(32–3) x 1.5
SF = required safety
factor
δB = comparative
stress
p = operating pres-
sure in bar
d = outside pipe
diameter
s = pipe wall thick-
ness