1、 Nominal pressure

The nominal pressure is a reference value related to the pressure resistance of pipeline system components, and refers to the design given pressure related to the mechanical strength of pipeline components.

The nominal pressure refers to the compressive strength of a product at a reference temperature.

Different materials have different reference temperatures and compressive strengths.

The compressive strength of a product at a reference temperature is called nominal pressure, represented by the symbol PN (MPa). PN is a combination of letters and numbers used for reference, which is related to the mechanical properties and dimensional characteristics of pipeline system components.

If the nominal pressure is 1.0MPa, it is denoted as PN10.

For cast iron and copper, the reference temperature is 120 ℃; The reference temperature for steel is 200 ℃, and the reference temperature for alloy steel is 250 ℃.

The reference temperature for plastic products is 20 ℃, and the nominal pressure is also close to the compressive strength of the material at room temperature; Therefore, for plastic pipelines, their nominal pressure is the maximum working pressure of the pipeline, pipeline accessories, and pipeline fittings at 20 ℃.

2、 Work pressure

Work pressure refers to the maximum pressure specified for the safe operation of pipeline systems based on the maximum working temperature of the medium transported by the pipeline at each level.

Simply put, work pressure is the maximum pressure that a system can withstand during normal operation.

3、 Design pressure

For pipeline systems, design pressure refers to the maximum instantaneous pressure exerted by the pressure pipeline system on the inner wall of the pipe.

The design pressure, together with the corresponding design temperature, shall be used as the design load condition, and its value shall not be lower than the working pressure.

In general, the maximum pressure that the selected system can withstand during design calculations is taken as the design pressure.

4、 Test pressure

For the installed pipeline system, the test pressure refers to the pressure that the pipeline, container, or equipment must reach for the pressure resistance and airtightness tests specified.

5、 The relationship between nominal pressure, working pressure, design pressure, and test pressure

From a safety perspective, the test pressure must be greater than the nominal pressure.

The nominal pressure refers to the compressive strength at the reference temperature, but in many cases, it does not operate at the reference temperature.

As the temperature changes, the compressive strength of pipelines, components, and equipment also changes accordingly.

The working pressure that a product with a certain nominal pressure can withstand is determined by the working temperature of the medium.

The nominal pressure and allowable working pressure of the same product may vary at different operating temperatures.

In engineering, test pressure>nominal pressure>design pressure>working pressure.

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