1.Pipeline pressure rating
The components of the pressure pipeline are generally standard components, so the design of the pressure pipeline components is mainly the selection of its standard components, and the determination of the pressure level of the pipeline is also the determination of the standard component level.
The pressure rating of the pipeline includes two parts:
a. The nominal pressure level of standard fittings expressed in nominal pressure
b. The wall thickness grade of standard pipe fittings expressed in wall thickness grade
The pressure rating of the pipeline: The parameter that can be determined by the nominal pressure rating and wall thickness rating of the standard fittings in the pipeline and can reflect the pressure-bearing characteristics of the pipeline is called the pressure rating of the pipeline. In order to simplify the description, the nominal pressure level of the pipe fittings in the pipeline is often called the pressure level of the pipeline.
The determination of the pressure level is the foundation of the pressure pipeline design and the core of the design. It is a design prerequisite for the layout of pressure pipelines and stress checking of pressure pipelines, and it is also an important factor affecting the investment in pressure pipeline infrastructure and the reliability of pipelines.
2.Design conditions
In engineering, the process operation parameters should not be directly used as the design conditions of the pressure pipeline. Factors such as fluctuations in the process operation, the influence of the connected equipment, and the environment must be considered. A certain safety margin is given as the design based on the process operation parameters condition. The design conditions mentioned here mainly refer to 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 demanding conditions: refers to the conditions that lead to the maximum wall thickness or the highest nominal pressure level of the pipe and pipe components.
Design pressure determination: Considering the influence of media's hydrostatic column pressure and other factors, the design pressure should generally be slightly higher than the maximum working pressure under the most demanding conditions composed of (or) external pressure and temperature.
a. Under normal circumstances, the design pressure of piping components is determined
In general, for the convenience of operation, it may be possible to adopt the method of pressure vessel, that is, add a margin factor on the basis of the corresponding working pressure.
※ When the design pressure determined according to this principle will cause the pipeline pressure level to change, it should be judged whether the working pressure is the highest working pressure under the most demanding conditions composed of internal pressure (or external pressure) and temperature. With the approval of the relevant technical person in charge, the design pressure may be the highest working pressure at this time without adding a factor. b. When there is a safety pressure relief device in the pipeline,
The presence of a safety pressure relief device in the pipeline indicates that the pipeline may exceed its normal operating pressure during operation. The purpose of installing safety pressure relief devices (such as safety valves, rupture discs, etc.) is to automatically release the pressure when the system exceeds its normal operating pressure to protect the hardware of equipment, pipelines and other systems. At this time, the design pressure of the pipeline should not be lower than the set pressure of the safety relief device.
b. There is a high-lift pump in the pipeline
For high-lift pumps, especially reciprocating pumps, within a short period of time after starting, a high closing pressure is often generated in the pipeline and pump before the first shut-off valve, and sometimes this closing pressure will reach a large Value. At this time, the design pressure of the outlet pipe of the pump should be the maximum closed pressure of the pump.
c. Vacuum system
The pressure of the vacuum system pipeline is the external atmospheric pressure, so the design pressure should be 0.1MPa external pressure.
d. Pipes connected to equipment such as towers or vessels
The design pressure of pipes connected to equipment such as towers or vessels shall 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 liquid static head should also be considered. In fact, for the pipeline, the stress is more complicated than the equipment, because in addition to the medium load, it often suffers from the piping force 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.
The components of the pressure pipeline are generally standard components, so the design of the pressure pipeline components is mainly the selection of its standard components, and the determination of the pressure level of the pipeline is also the determination of the standard component level.
The pressure rating of the pipeline includes two parts:
a. The nominal pressure level of standard fittings expressed in nominal pressure
b. The wall thickness grade of standard pipe fittings expressed in wall thickness grade
The pressure rating of the pipeline: The parameter that can be determined by the nominal pressure rating and wall thickness rating of the standard fittings in the pipeline and can reflect the pressure-bearing characteristics of the pipeline is called the pressure rating of the pipeline. In order to simplify the description, the nominal pressure level of the pipe fittings in the pipeline is often called the pressure level of the pipeline.
The determination of the pressure level is the foundation of the pressure pipeline design and the core of the design. It is a design prerequisite for the layout of pressure pipelines and stress checking of pressure pipelines, and it is also an important factor affecting the investment in pressure pipeline infrastructure and the reliability of pipelines.
2.Design conditions
In engineering, the process operation parameters should not be directly used as the design conditions of the pressure pipeline. Factors such as fluctuations in the process operation, the influence of the connected equipment, and the environment must be considered. A certain safety margin is given as the design based on the process operation parameters condition. The design conditions mentioned here mainly refer to 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 demanding conditions: refers to the conditions that lead to the maximum wall thickness or the highest nominal pressure level of the pipe and pipe components.
Design pressure determination: Considering the influence of media's hydrostatic column pressure and other factors, the design pressure should generally be slightly higher than the maximum working pressure under the most demanding conditions composed of (or) external pressure and temperature.
a. Under normal circumstances, the design pressure of piping components is determined
In general, for the convenience of operation, it may be possible to adopt the method of pressure vessel, that is, add a margin factor on the basis of the corresponding working pressure.
※ When the design pressure determined according to this principle will cause the pipeline pressure level to change, it should be judged whether the working pressure is the highest working pressure under the most demanding conditions composed of internal pressure (or external pressure) and temperature. With the approval of the relevant technical person in charge, the design pressure may be the highest working pressure at this time without adding a factor. b. When there is a safety pressure relief device in the pipeline,
The presence of a safety pressure relief device in the pipeline indicates that the pipeline may exceed its normal operating pressure during operation. The purpose of installing safety pressure relief devices (such as safety valves, rupture discs, etc.) is to automatically release the pressure when the system exceeds its normal operating pressure to protect the hardware of equipment, pipelines and other systems. At this time, the design pressure of the pipeline should not be lower than the set pressure of the safety relief device.
b. There is a high-lift pump in the pipeline
For high-lift pumps, especially reciprocating pumps, within a short period of time after starting, a high closing pressure is often generated in the pipeline and pump before the first shut-off valve, and sometimes this closing pressure will reach a large Value. At this time, the design pressure of the outlet pipe of the pump should be the maximum closed pressure of the pump.
c. Vacuum system
The pressure of the vacuum system pipeline is the external atmospheric pressure, so the design pressure should be 0.1MPa external pressure.
d. Pipes connected to equipment such as towers or vessels
The design pressure of pipes connected to equipment such as towers or vessels shall 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 liquid static head should also be considered. In fact, for the pipeline, the stress is more complicated than the equipment, because in addition to the medium load, it often suffers from the piping force 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.
