Gas Outlet Piping

As an engineer, your role in the design of gas outlet piping for a pressure vessel is pivotal. You are the one who ensures the system operates safely and efficiently under various conditions. This is a complex task that demands a profound understanding of piping stress analysis principles. This blog will walk you through the crucial aspects of designing gas outlet piping, with a special focus on stress analysis, equipment behavior, and the necessary supporting details.

 Our discussion on this topic is not just theoretical. We will enrich it with photos from real oil and gas plants or petroleum refineries. These photos are not just for show, they showcase actual gas outlet piping designs and their function in different scenarios, providing tangible examples of how these principles are applied in real-world engineering.

Now, let's shift our focus to the gas outlet nozzle of a pressure vessel located at the top head of the vessel. If you're unfamiliar with pressure vessels, we have a previously published video that covers their fundamental details. You can find it from the link. This video will provide a solid foundation for understanding the concepts we'll discuss.

The pressure vessel is part of an oil and gas industry plant. The gas outlet piping is connected to the top nozzle. Let's look at the gas outlet piping in this example. As you can see, the first support is rigid support. This means that the line is supported from the top and hangs downward. Also, the vertical pipe is guided at two points. This design approach is commonly used for gas lines.

Gas Outlet Piping Design Approach

Another gas piping design uses the same approach: a rigid support at the top and the pipe hanging downward, including guided supports. 

And more examples of gas outlet piping. The same principle is applied to piping design.

The reason for supporting the piping from the highest elevation is the different expansion behaviors of piping and pressure vessels. If we support the piping from the lowest elevation, the expansion will differ at the top of the vessel, and the nozzle connection with the vessel head will most probably be overstressed.

Wrong Supporting Example of Gas Outlet Piping

 While we use an overhanging approach for piping in pressure vessels, the horizontal continuation line should not be supported close to the vertical pipe. We should let the pipe expand downward; we can put a rigid support after a certain distance. This will prevent contradiction between the rigid supports at the top elevation. Otherwise, the trunnions will not sit on the rigid support at the top due to expansion starting from the horizontal support. So, the expansion will cause moment and so over stress on top of the nozzle, as we explained.

KEEP THE HORIZONTAL LINE SUPPORT AWAY FROM THE VERTICAL LINE

 We have a previously published blog about the piping stress analysis of pressure vessels. You can find it from the link.

The elevated pressure vessel requires a long run from the top nozzle, so the trunnion needs to carry all the piping system. Piping Stress Engineers should consider the trunnion design and add all the piping and component weights, such as insulation, flange, bolts, etc., to the calculation.

For a trunnion check, we should have the load at thermal and sustained cases, pipe diameter, pipe thickness, corrosion allowance, pipe material, design pressure, and temperature. We should also select a trunnion, which can be either a pipe or a steel profile. We should add the size and thickness of the trunnion to the calculation.

Pipe Trunnion Support

If the trunnion assessment fails and you do not want to increase the trunnion size, you can perform the calculation by adding a reinforcing pad.

Kellogg Companies calculation method can be used for the trunnion assessment.

Designing the gas outlet piping for a pressure vessel involves a comprehensive application of piping stress analysis principles to ensure the creation of a safe, reliable, and efficient system. This process requires a thorough understanding of stress analysis, which involves assessing the impact of pressure, temperature, and other factors on the piping system.

Incorporating supports and anchors is crucial to ensure the stability and structural integrity of the piping system. These elements help to minimize vibration and movement, thereby reducing the risk of fatigue failure and ensuring long-term reliability. Managing thermal expansion is another key consideration, as temperature variations can cause the piping system to expand, leading to stress and potential damage. By implementing strategies to accommodate thermal expansion, engineers can mitigate these risks and enhance the overall performance of the system.

 Adhering to safety standards is paramount in the design of gas outlet piping, as it ensures compliance with industry regulations and best practices. This includes considerations such as material selection, corrosion protection, and pressure ratings to guarantee the safe operation of the system. Furthermore, utilizing advanced software can provide valuable insights into the behavior of the piping system under different operating conditions, enabling engineers to optimize the design and identify potential issues before implementation.

You can watch the video from the link below.