It's #150.
PN 20 is equal to ANSI 150 & ANSI 300 equals PN 50.
The PN16 flange is equivalent to either the ASME 150 or 300. The PN is related to Nominal Pressure and the ASME is the standard for the American Society of Mechanical Engineers.
PN 16 static test pressure
Give me Call at +971 4 3212335, Confirm the Fig. NO. is it FL100-21, i,ll provide the Detailed Flowchart. Regards, Avanish
Answer I'm no expert here with this but through minimal experience with HDPE pipe, PE stands for polyethylene and is used for water supply because polyethylene is neutral in water - meaning nothing in polyethylene reacts with water which would seep into the water. There are different pressure grades "PN" which must be considered for your specific use. PN 2.5 through PN16 indicate how much pressure the pipe can withstand.