High density polyethylene - HDPE - is a very popular material for water pipes. It is

• resistant to chemicals
• easy and light weighted
• long living
• low friction
• relatively cheap
• flexible
• sun resistant

PE pipes can be used in range of temperatures -40 ^oC to 60 ^oC considering the change of operating pressure. Typically the standard specification identify class of a HDPE pipe is by the nominal pressure class - PN - up to PN 20 or 20 bar. HDPE pipe can also be classified by the material used - PE 100, PE 80, PE63, PE 40 or PE 32.

Pressure Nominal - PN

PE pipes are produced in different pressure grades (PN grades), which indicates the pressure in bars the pipe can support with water at 20 ^oC.

The pressure grades available according to European standards are

• PN 2.5 - max pressure 2.5 bar
• PN 4 - max pressure 4 bar
• PN 6  - max pressure 6 bar
• PN 10  - max pressure 10 bar
• PN 16  - max pressure 16 bar

• 1 bar = 10⁵ Pa (N/m²) = 0.1 N/mm² = 10,197 kp/m² = 10.20 m H₂O = 0.9869 atm = 14.50 psi (lb_f/in²) = 10⁶ dyn/cm² = 750 mmHg

Color Codes and Pressure Grades

Color codes used to indicate the pressure grades on the pipes are

Classed by Materials

Polyethylene pipes are also classified by the type of material used:

• PE 32 - low pressure piping systems
• PE 40 - low pressure piping systems
• PE 63 - medium pressure piping systems - irrigation system - drinking water connections
• PE 80 -  gas pipe for natural gas distribution network with pressure rate up to 4 bars - drinking water pipe with pressure rate up to 16 bar - sewers, outfall pipes, industrial pipes
• PE 100 - high demands piping applications

The Minimum Required Strength - MRS - according ISO 4427 for the different materials are:

Color Codes and Materials Classifications

Common colors used to classify the pipes

• completely black for industrial applications
• completely blue, or black with blue stripes, fro potable water
• completely yellow, or black with yellow stripes, for gas conduits

Note that the colors may depend on country.