Adding Vessel Skirt Openings

[refined sweat]

Hello all - We have a vertical vessel which currently has a view access and vent openings in the skirt. We need to add a few more for access. My question is regarding buckling. Most likely when this vessel was designed a buckling check was performed and the skirt was found to be adequate, as a result when we add openings to the skirt should we mostly focus on a simple reinforcement calculation? In other words, assuming the vessel skirt is designed for the buckling case and as long as we provide adequate reinforcement for the new opening; that will be sufficient.

Thank you for any insight

Integrity above all else

 

[CuMo]

You can recheck the skirt using EN 13445-3

16.12.4 Design of skirts without and with openings

PV Elite & Visual Vessel Design can do this.

 

[MJCronin]

Refined .....

Can you provide us with more specific details ?

Perhaps some photos, or design drawings or a sketch of your proposed modification.

What is the material of the skirt ?

How old is the vessel and what is the reason for the additional openings ? .... was something else changed inside of the skirt ?

Best Regards

MJCronin
Sr. Process Engineer

 

[jtseng123]

The key point is what "adequate reinforcement" is.
If you use COMPRESS, it will apply full area replacement and ends up thicker sleeve or a ridiculous large re-pad for the sleeve. That is incorrect by COMPRESS treating skirt opening as vessel nozzle. Using PV Elite is much better which adopts European standard for stress analysis. We had a project vendor using COMPRESS and shocking us that even a 4" skirt vent needed a re-pad. We told them to switch to PV Elite.

In the old time, we use hand calculations, which is complicate due to odd cross sectional area and complicate moment of inertia.
The basic concept is to find out the remaining area, moment of inertia, and the new location of neutral axis for the cross-sectional area that has openings with sleeves. Then calculate the maximum compressive stress and compare with the allowable compressive stress from code. Also check tensional side and compare with allowable. Repeat this if you have openings at different elevations. Using FEA may be much simple. Any cross section not meeting allowables, increase sleeve thickness and/or add a re-pad, and repeat the calculation.