Pressure Vessel Piping Stress Analysis

As the temperature of the fluid inside the vessel fluctuates, thermal expansion and contraction can exert significant stress on the connected piping. Different behaviors of piping and the vessel have a crucial role in stress analysis. This is why piping engineers should carefully analyze the piping design by considering the vertical pressure vessel’s behavior under operation temperature.

Process requirements should be learned from process engineers and process-related load cases should be prepared together with the process engineer.

The external loads are also important for the piping stress analysis in addition to the thermal expansion. The equipment displacement must be considered before the analysis starts. These external forces are seismic and wind loads.

Piping stress analysis on vertical pressure vessels is a critical aspect of the design process, ensuring that the entire system operates safely and efficiently throughout its lifespan. Engineers must consider various factors, including thermal expansion, pressure loads, and external forces, to prevent failures that could lead to disastrous consequences. By employing advanced analysis methods and adhering to industry codes, designers can confidently create piping systems that meet the stringent safety requirements of vertical pressure vessels in diverse industrial applications.

Piping Design for Vertical Pressure Vessel

In general, pipe routing either starts from or ends at a pressure vessel.

Vessel and Piping System Routing

The effect of piping loads on a vessel nozzle and the effect of the vessel loads on piping design needs to be considered during the stress analyses.

Additionally, the effect of vessel shell flexibility also needs to be considered.

The effects of the piping loads are the weight of the pipe itself and thermal expansion.

The effect of the vessel loads on piping is due to external forces and thermal expansion of the vessel.

Stress analyses should be considered in combination with piping design, nozzle connection, and shell together.

Piping and Pressure Vessel Effects Each Other

If we analyze the piping only, you will have to accept the shell connection as a rigid connection, but it is flexible. And the output shell connection forces and moments from this analysis will become very high.

Due to high output values, you will have to add expansion loops on your design to reduce the loads which will be expensive and not safe because of the occasional loads, vibration, and earthquake.

So, we should consider in combination of piping, nozzle, and shell of the vessel together.

Pressure Vessel Nozzle Loads

Let’s look at some piping stress design examples on pressure vessels.

This is an ideal piping design that comes down from the vessel shell nozzle. Supporting the piping from the ground elevation will result in overstress at the top of the nozzle and piping because of the different expansion behaviors of the vessel and piping.   

Different expansion behavior is because of the height from the ground pipe supporting and pressure vessel. In this example, we can assume that the vessel expands in 3 units while the piping expands in 5 units due to the height differences. The difference, results in overstress on the nozzle and on various locations of piping. 

In some cases, the temperature of the vessel may be higher than the temperature of the piping. In this case, especially at high temperatures, the vessel expands upward, and the nozzle has to support the entire piping. You can understand this from the gap formed under the ground support. This situation leads to excessive stress on the nozzle.

You can consider moving the pipe support further and adding an elbow to your piping design. But again, the nozzle may carry the piping, or the nozzle and support may interact with each other while they are at the same temperatures.  

2D Change of Piping Design Doesn’t Help of the Nozzle Load Reduction

To make the piping connection more flexible you should change the design in 3 dimensions instead of 2.

As you can see from this 3-dimensional design change, the pipe is more flexible now. However, additional support is required for the pipe.

3D Change of Piping Help of The Nozzle Load Reduction

For this purpose, a welded support can be designed on the vessel. This support will move in the same way up as the thermal expansion of the vessel, so it will be always in contact with the trunnion. This means the trunnion support on each case will sit on the vessel’s attached support. As a result of this, nozzle loads will be shared and so, reduced.

Trunnion Support of Pressure Vessel Piping

The ground support should be replaced for even loading with trunnion support. This will also help the trunnion support sit on each loading case.

Ground Support Move to Share the Piping Load with Trunnion

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Pressure Vessel Piping Stress Analysis and Design

Pressure Vessel Piping Stress Analysis and Design