Pressure pipe PVC-U 50 mm x 2,4 mm
For non-standardised pipes wall-thickness is an indication only.
Pressure pipes that are non-standardised have greater tolerances in wall thickness and guarantee the mentioned working pressure.
This can be explained easily by the safety rate between bursting pressure and working pressure, which is a multiple of the working pressure.
The safety rate will be lower, but the working pressure is surely applicable.
For standardised pipes, the wall thickness is specified by DIN and NEN-ISO standards as well as Kiwa/DVGW institutes.