What is the pipeline pressure rating

Pipeline pressure grade
Pressure piping components are generally standard parts, so the design of pressure piping components is mainly the selection of its standard parts, and the determination of pipeline pressure grade is also the determination of its standard part grade.
The pressure rating of the pipeline consists of two parts:
the nominal pressure rating
of the standard pipe fittings expressed in nominal pressure; the wall thickness grade of the standard pipe fittings expressed in the wall thickness grade.
Pipeline pressure rating: Usually, the parameter that reflects the pressure characteristics of the pipeline, which is determined by the nominal pressure rating and wall thickness rating of the standard pipe fittings in the pipeline, is called the pipeline pressure rating. In order to simplify the description, it is customary to refer to the nominal pressure rating of the pipe fittings as the pressure rating of the pipeline.
The determination of the pressure level is the foundation and the core of the design of pressure piping. It is the design prerequisite for pressure pipeline layout and pressure pipeline stress check, and it is also an important factor that affects pressure pipeline infrastructure investment and pipeline reliability.
5.1 Design conditions In
engineering, process operating parameters should not be directly used as design conditions for pressure pipelines. Factors such as fluctuations in process operations, the impact of connected equipment, and environmental impacts should be considered, and a certain safety margin should be given on the basis of process operating parameters. Quantity as a design condition. The design conditions mentioned here mainly refer to the design pressure and design temperature.
The design pressure of the pipeline: should not be lower than the pressure under the most severe conditions composed of internal pressure (or external pressure) and temperature during normal operation.
The most severe conditions: refer to the conditions that lead to the maximum wall thickness or the highest nominal pressure level of pipes and piping components.
Design pressure determination: Considering the influence of factors such as the hydrostatic column pressure of the medium, the design pressure should generally be slightly higher than the maximum working pressure under the most severe conditions composed of (or) external pressure and temperature.
a. Under normal circumstances, the design pressure of piping components is determined
. Under normal circumstances, in order to facilitate the operation, it is advisable to adopt the method of pressure vessel, that is, to increase a margin factor on the basis of the corresponding working pressure.

    ※ When the design pressure determined according to this principle will cause changes in the pipeline pressure level, it should be judged whether the working pressure is the highest working pressure under the most severe conditions composed of internal pressure (or external pressure) and temperature. If so, please report With the approval of the relevant technical person in charge, the design pressure can be the highest working pressure at this time without adding a coefficient. b. When there is a safety relief device in the
pipeline, and when there is a safety relief device in the pipeline, it indicates that the pipeline may exceed its normal operating pressure during operation. The purpose of setting up safety pressure relief devices (such as safety valves, bursting discs, etc.) is to automatically release the pressure when the system exceeds its normal operating pressure so that the hardware of the equipment, pipelines and other systems can be protected. At this time, the design pressure of the pipeline should not be lower than the set pressure of the safety relief device.
c. High-lift pumps in the pipeline.
For high-lift pumps, especially reciprocating pumps, a relatively high sealing pressure is often generated in the pipeline and pump before the first shut-off valve within a short time of starting. Sometimes this sealing pressure will reach a very large value. At this time, the design pressure of the outlet pipe of the pump should be the maximum closed pressure of the pump.
D. The pressure of the
vacuum system piping of the vacuum system is its external atmospheric pressure, so its design pressure should be 0.1MPa external pressure;
e. The piping connected to towers or vessels and other equipment

The design pressure of the piping connected to towers or vessels and other equipment should not be lower than the design pressure of the connected equipment. When there is a higher liquid column in the pipeline, the influence of the hydrostatic head should also be considered. In fact, for the pipeline, its force is more complicated than that of the equipment. This is because in addition to the medium load, it also often suffers from the piping forces caused by the thermal expansion and contraction of the pipeline. Therefore, the design pressure of the pipeline should generally not be lower than the design pressure of the equipment.

5.1.2 Design temperature

The design temperature of the pipeline: It should not be lower than the temperature under the most severe conditions composed of internal pressure (or external pressure) and temperature during normal operation.

The most severe conditions: Refers to the conditions that lead to the maximum wall thickness, the highest nominal pressure level, or the highest material level of pipes and piping components.

Determination of design temperature: Considering the influence of factors such as environment, heat insulation, operation stability, etc., the design temperature should be slightly higher than the maximum operating temperature under the harshest conditions composed of internal pressure (or external pressure) and temperature.

a. Under normal circumstances, the design temperature of piping components is determined

In general, in order to facilitate the operation, we might as well adopt the method of pressure vessel, and increase a margin factor (except flanges and bolts) on the basis of the corresponding working temperature.

※When the design temperature determined in accordance with this principle will cause changes in the pipeline pressure level or material, it should be judged whether the operating temperature is 
  the highest operating temperature under the most severe conditions composed of internal pressure (or external pressure) and temperature. If it is, In the case of requesting the approval of the relevant technical person in charge, the design temperature can be the highest working temperature at this time without adding a factor.
The design temperature of flanges and gaskets
should not be lower than 90% of the maximum working temperature; the design temperature of bolts and nuts should not be lower than 80% of the maximum working temperature.
b. Jacketed or external heat tracing pipeline.
For jacketed or externally heated pipelines, when the temperature of the process medium is higher than the temperature of the heat tracing medium, the design temperature is selected according to the above table; when the temperature of the process medium is lower than the temperature of the heat tracing medium, a jacket for heating the heat medium temperature is taken with the design temperature, and then take the external heating medium heating temperature minus 10 deg.] C with a larger value of both the design temperature process temperature;
. C pipeline safety relief
safety relief The highest or lowest temperature that may occur when the pipeline is discharged is the design temperature;
d. The steam-purged pipeline
adopts steam-purged pipelines. When the temperature of the medium is higher than the temperature of the purged steam, the design should be determined according to the medium temperature according to the above table temperature. When the temperature of the medium is lower than the temperature of the purge steam, it should be determined according to the specific situation. For example, when the pipes and components selected according to the temperature of the medium cannot withstand the conditions of the purging medium, the grade should be appropriately increased to adapt to the conditions of the purging medium.

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