Pipe extruder manufacturers share with you knowledge about nominal pressure/working pressure/design pressure, as well as pipeline pressure classification

Usually, when customers purchase pipelines, they will give clear pressure requirements based on the drawings. We are also accustomed to giving the price of the corresponding specifications step by step, but we have neglected to study the concept of specific pressure. Little do we know that "pressure" also has the same Complex knowledge.Next, let the pipe extruder manufacturer share with you knowledge about nominal pressure/working pressure/design pressure, as well as pipe pressure classification.

 1. Nominal pressure

The nominal pressure refers to the working pressure of the pipe when delivering water at the secondary temperature (20°C). If the water temperature is between 25°C and 45°C, the working pressure should be corrected according to different temperature drop coefficients.

Nominal pressure is a nominal pressure artificially specified for the convenience of design, manufacturing and use. The unit of this nominal pressure is actually pressure. Pressure is the common name in Chinese, and the unit is "Pa" instead of "N". It is represented by "PN" on the pipeline. For example, PN20 means that the water pipe has been operated at a water temperature of 20°C for 50 years, and the working pressure it can withstand is 20bar (20bar=2Mpa).

2. Work pressure

Working pressure refers to the maximum continuous operating pressure acting on the inner wall of the water supply pipeline under normal working conditions, excluding the fluctuation pressure of water.

3. Design pressure

Design pressure refers to the maximum instantaneous pressure of the water supply pipeline system acting on the inner wall of the pipe. Generally, the sum of the working pressure and residual water hammer pressure is used.

The most important factor affecting the design pressure is the wall thickness of the water pipe. The thicker the pipe wall, the greater the maximum instantaneous pressure it can withstand. In addition, the mechanical properties of the raw materials themselves and the different production processes of different manufacturers will also affect the pressure-bearing capacity of the water pipes to a certain extent. If there is uneven mixing during production, the water pipes will have shortcomings in mechanical properties. .

Note: Water hammer pressure refers to the instantaneous fluctuation in pressure caused by sudden changes in the flow rate of water during the operation of the pipeline system.

4. Pipeline pressure classification?

Normally, our pipeline systems are divided into the following four levels: low pressure, medium pressure, high pressure, and ultra-high pressure.

——Low pressure pipeline:

The nominal pressure does not exceed 2.5MPa, such as water supply, gas supply and other industrial and civil low-pressure liquid and gas transportation;

——Medium pressure pipeline:

Nominal pressure 4-6.4MPa, such as oil and natural gas transportation, chemical plant process pipelines, refrigeration systems, etc.;

——High-pressure pipeline:

Nominal pressure 10-100MPa, such as high-pressure oil and natural gas transportation, high-temperature and high-pressure steam pipelines, chemical pipelines, etc.;

——Ultra-high pressure pipeline:

The nominal pressure exceeds 100MPa, such as nuclear power plant cooling cycle pipelines, high-pressure test equipment, spacecraft propulsion systems, etc.

It can be seen that the water pipelines we usually discuss are generally low-pressure pipeline systems, so the nominal pressure generally does not exceed 2.5MPa.

Tips: Commonly used units of pressure (pressure to be precise) are: bar (bar), MPa (megapascal), kgf/cm² (kilogram force/cm²).

bar (bar) is a commonly used unit in the engineering field; MPa (megapascal) is an international unit; kgf/cm2 (kilogram force/cm²) is a unit commonly used to express pressure in China. The conversion relationship between the three is: 1 bar = 0.1 Mpa = 1.01971621 kgf/cm²

6. How to choose the pressure grade of pipes?

After understanding the concept of pipe pressure, how to choose the pressure grade of pipes? In addition to referring to the concept of pressure, it should also be combined with the actual situation. For details, you can refer to the following formula:

Select the pressure grade of the pipe =

Pipeline working pressure + water hammer pressure of about 0.3MPa + safety margin of 0.1-0.2MPa.

For example: The working pressure of a certain tap water pipeline is 0.4MPa. What pressure grade pipe material should be selected?

a.Using pressure=0.4MPa

b. Water hammer pressure = 0.3MPa

c.Safety factor=0.1-0.2MPa

d.Pressure level=0.4+0.3+0.1=0.8MPa

Conclusion: Pipes with a nominal pressure above 0.8MPa should be selected.

Fangli, a professional pipe extruder supplier, we look forward to cooperation and win-win results with you!