Do negative pressure vessels consider liquid column static pressure?
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Dear seniors, I would like to ask, do we need to consider the static pressure of the liquid column in a negative pressure container? If we consider it, wouldn’t the actual calculation pressure be less? As shown in the picture:
Generally, the liquid column static pressure is not considered because the liquid column static pressure is insignificant. For a negative pressure container, the liquid column static pressure it receives when it is working will be due to the pressure exerted by the container itself on the liquid.* * exceed this static pressure. However, if the maximum working pressure is calculated, the liquid column static pressure should be added. -
It is recommended not to consider it because some shells do not have liquid column pressure and should be considered under harsh working conditions.
If you consider the static pressure of the liquid column, there will be a problem: SW6-2011 software needs to enter a larger value when inputting the calculated length. Taking the container as shown in the figure, the lower part of the cylinder just accommodates the liquid medium, and the calculated pressure under the calculated length of the lower part should be relatively small. At this time, is it appropriate to enter the larger calculated length value below?
The so-called negative pressure is for atmospheric pressure, for reference only.
Be sure to remove the hydrostatic column. SW6 is calculated based on the pressure difference. Keeping the hydrostatic column will offset the internal pressure and external pressure.
Regardless of the static pressure of the liquid column, the strength calculation of the negative pressure container is input as -0.1MPa. Based on the calculation results, the cylinder wall thickness is first determined, and then the stability is checked.
Calculated according to the most severe working conditions, and the liquid column static pressure is only for part of the shell
Considering the harsh pressure, for storage tanks, the impact of hydrostatic column pressure on the shell is far less than the impact of internal negative pressure. It is recommended not to consider the hydrostatic column and calculate it entirely based on the internal negative pressure. To put it bluntly, when this container was tested for pressure when it left the factory, was it still equipped with a hydrostatic column for pressure testing?
. The design pressure in the figure has been determined, and all calculations are performed according to the requirements of the design pressure without considering other； The pressure of the liquid column must be considered (including ignored after consideration), but this is the work when determining the design pressure. For example: In the figure, the upper and lower pressure of the tank is determined to be 0.1MPa based on (taking into account) the tank pressure when the tank is empty. .