Here is some knowledge on the relationship between different pressures of pipes.

Terms: nominal pressure, working pressure, design pressure.

Relationship among design pressure, working pressure and nominal pressure of pipes

1. What is the nominal pressure PN (MPa)?

It is a reference value related to the compressive capacity of the pipes, and refers to the design given pressure related to the mechanical strength of the pipe fitting.

The nominal pressure is generally expressed in PN.

2. What is work pressure?

It refers to the maximum pressure specified by the maximum working temperature of the pipeline transport medium at all levels under the safe operation condition of the pipeline system.

Usually, the working pressure is represented by Pt.

3. What is design pressure?

The maximum instantaneous pressure of the water supply pipeline system acting on the inner surface of the pipeline is usually taken as the sum of the working pressure and the residual water hammer pressure.

The design pressure is usually represented by Pe.

4. What is test pressure?

It refers to the pressure required to achieve the compressive strength and airtightness test of pipelines, containers or equipment.

The test pressure is usually indicated by Ps.

5. The relationship between nominal pressure, working pressure and design pressure

For the convenience of design, manufacture and use, the name of nominal pressure is adopted. The unit of nominal pressure is “Pa”, not “N”. Nominal pressure is nominal in name or form, but it is not. The nominal pressure of the pressure vessel refers to the nominal pressure of the pressure vessel flange.

The nominal pressure of the pressure vessel flange is divided into 7 grades: 0.25, 0.60, 1.00, 1.60, 2.50, 4.00, and 6.40 MPa.

Relationship between nominal pressure, design pressure and working pressure:

  • Nominal Pressure ≥ Design Pressure
  • Design Pressure = 1.5 x Working Pressure

(Refer to GB/T50332-2002 “Pipeline Structure Design Standards for Water Supply and Drainage Engineering” to design the standard internal pressure value in the piezometric pipe.)

The maximum allowable working pressure, the nominal pressure varies according to the temperature-to-pressure reduction coefficient.


  • MOP – the maximum allowable working pressure (MPa);
  • PN – nominal pressure (MPa)
  • fT——The reduction coefficient of temperature to pressure according to the specified service life of 50 years.

Related News