Operating temperature and allowable pressure.
PN marked on water supply pipe is defined at 20 °C. At higher temperatures, maximum operating pressure (MOP) must include a temperature factor fT: MOP = fT × PN.
If direct solar exposure raises pipe temperature to 40 °C, allowable pressure on PN10 pipe may be approximately 7.4 bar — operating at 10 bar risks damage.
The design engineer must account for line temperature, fT and service factors. For preliminary diameter and pump estimates, use the pipeline design calculator — not as a substitute for full hydraulic design.
