Seamless pipe is the most used pipe fitting in oil and gas engineering pipelines and construction engineering pipelines. The pressure rating design of seamless pipe is introduced below. The pressure rating of seamless pipe includes two parts: the nominal pressure rating of standard pipe fittings expressed in nominal pressure. ;Wall thickness class of standard fittings expressed in wall thickness class.In specific applications, factors such as fluctuations in process operations, the influence of connected equipment, and the influence of the environment should be considered, and a certain safety margin should be given as a design condition on the basis of process operation parameters.
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: refers to the conditions that lead to the maximum wall thickness or the highest nominal pressure rating of pipes and pipe 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.
1. In general, the design pressure of piping components is determined
Under normal circumstances, for the convenience of operation, it is advisable to adopt the practice of pressure vessel, that is, to add a margin coefficient on the basis of the corresponding working pressure.
2. When there is a safety pressure relief device in the pipeline
The presence of a safety pressure relief device in a pipeline 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 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 pressure relief device.
3. There is a pump with high lift in the pipeline
For high-lift pumps, especially reciprocating pumps, a high closed pressure is often generated in the pipeline and pump before the first shut-off valve within a short time of starting.Sometimes this closing pressure can reach a very large value. At this time, the design pressure of the outlet pipeline of the pump should take the maximum closed pressure value of the pump.
4. Vacuum system
The pressure of the vacuum system pipeline is the external atmospheric pressure, so the design pressure should be 0.1MPa external pressure.
5. Pipes connected to container equipment
The design pressure of pipes connected to equipment such as towers or vessels should not be lower than the design pressure of the connected equipment. When there is a high 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, because in addition to the medium load, it also often suffers from the pipe system 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.
Pressure calculation formula of seamless pipe
1. Know the outer diameter and wall thickness of the seamless pipe to find the pressure
Pressure = (wall thickness * 2 * tensile strength of steel pipe material) / (outer diameter * coefficient)
2. Know the outer diameter of the seamless pipe and the pressure to find the wall thickness:
Wall thickness=(pressure*outer diameter*coefficient)/(2*tensile strength of steel pipe material)
3. Representation method of steel pipe pressure coefficient:
Pressure P<7Mpa Coefficient S=8
7<Pipe pressure P<17.5 Coefficient S=6
Pressure P>17.5 Coefficient S=4
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: refers to the conditions that lead to the maximum wall thickness or the highest nominal pressure rating of pipes and pipe 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.
1. In general, the design pressure of piping components is determined
Under normal circumstances, for the convenience of operation, it is advisable to adopt the practice of pressure vessel, that is, to add a margin coefficient on the basis of the corresponding working pressure.
| Working pressure Pw(MPa) | Design pressure P(MPa) |
| Pw≤1.8 | P= Pw+0.18 |
| 1.8<Pw≤4.0 | P= 1.1Pw |
| 4.0<Pw≤8.0 | P= Pw+0.4 |
| Pw>8.0 | P=1.05 Pw |
2. When there is a safety pressure relief device in the pipeline
The presence of a safety pressure relief device in a pipeline 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 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 pressure relief device.
3. There is a pump with high lift in the pipeline
For high-lift pumps, especially reciprocating pumps, a high closed pressure is often generated in the pipeline and pump before the first shut-off valve within a short time of starting.Sometimes this closing pressure can reach a very large value. At this time, the design pressure of the outlet pipeline of the pump should take the maximum closed pressure value of the pump.
4. Vacuum system
The pressure of the vacuum system pipeline is the external atmospheric pressure, so the design pressure should be 0.1MPa external pressure.
5. Pipes connected to container equipment
The design pressure of pipes connected to equipment such as towers or vessels should not be lower than the design pressure of the connected equipment. When there is a high 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, because in addition to the medium load, it also often suffers from the pipe system 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.
Pressure calculation formula of seamless pipe
1. Know the outer diameter and wall thickness of the seamless pipe to find the pressure
Pressure = (wall thickness * 2 * tensile strength of steel pipe material) / (outer diameter * coefficient)
2. Know the outer diameter of the seamless pipe and the pressure to find the wall thickness:
Wall thickness=(pressure*outer diameter*coefficient)/(2*tensile strength of steel pipe material)
3. Representation method of steel pipe pressure coefficient:
Pressure P<7Mpa Coefficient S=8
7<Pipe pressure P<17.5 Coefficient S=6
Pressure P>17.5 Coefficient S=4
