# Calculating Vessel Depressurization: What Factors Affect the Time Required?

• mdvalhe
In summary, pressure inside the vessel will equalize in about half a second after a crack forms in the container. You would need to do some heavy duty modelling to get realistic results.
mdvalhe
Hi,

I want to know how I calculate the mass flow rate, volumetric flow rate and time required to depressurize a vessel, knowing the pressure inside the vessel, the output pressure, the orifice and the gas characteristics.

For example, imagine a vessel full of compressed air (let’s say 10 bar, 10 m3), for any reason the vessel fail, a known orifice is formed (model for a crack, 10 mm diameter), how long will take for the pressure inside to equalize the atmospheric pressure.

Thank you

This problem is more dificult than you might think, due to several coupled properties. The gas is cooling, the pressure is changing, and it's likely the flow will transition from choked flow to free flow. If you describe the differential equations of the fluid flow accurately, you can probably solve it with a robust solver package. Otherwise, you'll have to go with some reasonable estimate based on empirically derived equations.

Here is a thread here on this exact subject which gives a few suggestions: https://www.physicsforums.com/showthread.php?t=341015

mdvalhe said:
Hi,

I want to know how I calculate the mass flow rate, volumetric flow rate and time required to depressurize a vessel, knowing the pressure inside the vessel, the output pressure, the orifice and the gas characteristics.

For example, imagine a vessel full of compressed air (let’s say 10 bar, 10 m3), for any reason the vessel fail, a known orifice is formed (model for a crack, 10 mm diameter), how long will take for the pressure inside to equalize the atmospheric pressure.

Thank you

After the crack propogates and the vessel explosively decompresses...

...about half a second.

Seriously, "a crack" involves many orders of magnitude of variance, with answers ranging from between a few seconds to a few days. You're going to have to be more specific, and I'd recommend focussing on known geometries, such as a simple hole, or a tube of length L and diameter D protruding through the vessel wall.

As stated above, getting results for a crack isn't easy to do. You would have to calculate the crack opening displacements, then calculate the conductance based on the geometry and fluid dynamics.

I looked at the abstract of the paper titled "Circulation in Blowdown Flows," and they point out some interesting facts. Heat transfer between the gas and container walls creates a radial temperature gradient in the vessel, and buoyancy driven flow recirculates the gas. You're talking about stress analysis, fracture mechanics, thermodynamics, and CFD in one problem. I think you would need to do some heavy duty modelling with ANSYS or NASTRAN to get realistic results.

Last edited:

## What is vessel depressurization?

Vessel depressurization is the process of reducing the pressure inside a closed container, such as a tank or pipeline, to a lower level. This can be done to safely release gases or liquids from the vessel or to lower the pressure for maintenance purposes.

## Why is vessel depressurization important in scientific research?

Vessel depressurization is important in scientific research because it allows for the safe handling and transfer of hazardous materials. It also allows for the manipulation and control of reaction conditions, which is crucial in many experiments.

## How is vessel depressurization achieved?

Vessel depressurization can be achieved through various methods, including opening a valve to release the pressure, using a vacuum pump to extract the gas or liquid, or using a pressure relief device to vent the vessel.

## What are the potential hazards of vessel depressurization?

The potential hazards of vessel depressurization include the release of hazardous materials, exposure to high-pressure gases or liquids, and the risk of implosion if the vessel is not properly vented or depressurized.

## How can vessel depressurization be safely conducted?

To safely conduct vessel depressurization, it is important to follow proper protocols and procedures, such as wearing appropriate protective gear, ensuring proper ventilation, and using equipment designed for depressurization. It is also important to regularly inspect and maintain vessels to prevent malfunctions or accidents during depressurization.

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