We are doing a Stress Analysis for a high pressure CO2 line (Urea Plant) with the following parameters,

Design Pressure 228 kg/cm2, Maximum Line Temperature of 70 deg Celsius, 6” pipe Sch.160, flange rating 2500#, Piping material SS.

The scope of work involves slight modification in the pipe routing with the addition of Check valve (6”-2500#) as marked in the attached drawing. The Co2 line is supported by two spring supports near to the Stripper Vessel (attached in this forum). We required to check whether the existing spring support shall be suitable as per new pipe routing.

Since the Stripper Vessel is provided with an expansion joint (Total axial displacement 15mm), also it is the first time for me to deal with such a vessel, I request the forum members to give me a suggestion for modeling a vessel. Also the Vessel nozzle (N3) shall be checked with WRC 297, I modeled the vessel nozzle (without considering expansion joint – since I am not sure to model it) as per “Coade Pipe Stress Analysis Seminar Notes, Sec. 3.4.3.2 – Modeling Nozzles for flexibility calculation, figure 3-90 – More complex model.

The Caesar Input sheet is also attached with the forum.

I request the members to provide me a method of modeling vessel with expansion joint, also comments (if any) on the modeling of vessel nozzle.

Also, when the vessel nozzle is modeled in a simple method, for the [b]sustained and hydrostatic case the vessel nozzle load seems to be much higher, while locating the spring support at the same location. Can someone find me a solution to solve this.[/b]

The tube connections on tubesheets on both ends are not shown. The expansion joint on the shell indicates that the heat exchanger is fixed tube sheet heat exchanger. And I guess that the connection of N3 on the shell is welded, not sliding through the shell.

Under these assumptions, I would guess the upper tube sheet will rise by the thermal expansion of the shell temperature and the lower tubesheet will expand downwards from the upper tubesheet with the temperature of tubes. You may have different temperature in the cavity from the lower tubesheet to the N3 nozzle location. You need to consult your process engineer to understand the temperature distribution in and on the vessel. You may have more than one load thermal case to simulate the process on the vessel, be ready.

So, I would model the shell expansion to the upper tubesheet from the support location, thermal expansion to the lower tubesheet from the upper tubesheet, and the thermal expansion to the nozzle location from the lower tubesheet.

I do not want to go into the details how to make these here. You must know what you are doing.

As far as I can see from the thickness of the shell the nozzle does not have any flexibility, you may accept it as rigid. So model of the vessel can be finished on the face of the flange of N3 nozzle. It simplifies your model.

The others will require the piping arrangement to comment on. If the assumptions I made above are not correct you need to come with more description of the vessel, such as internals and their connections.

Hope it helps.

Ibrahim Demir