Skirt vs. Legs for vertical pressure vessel 2

[StaticPressure]

Hello every one,

I know skirts have better load distribution on the shell/bottom head, act better in cyclic services and less local stresses, and legs give better ventilation and better access to bottom nozzle. I would appreciate if anybody let me know other limitation and advantages of these two kinds of supports.

Thanks in advance
SP

 

[doct9960]

StaticPressure,

Large or tall vertical vessels are usually supported on skirts while small to medium sized vertical vessels are usually supported on legs. Now to distinguish what is small or medium sized vessels, I use Bednar's guidelines for leg supports...

Maximum D = 6'-0"
Maximum H/D = 5
Maximum L/D = 2
where:
D = diameter
H = tan-tan length
L = leg height

 

[StaticPressure]

Thanks doct9960

 

[PipingEquipment]

Generally, skirts are used if the vessel is very tall, or if there are external forces, due to being a stronger base.

In terms of cost, legs will be the better choice most of the time. We usually use angle iron for the legs with repads on the leg to shell attachment for better stress distribution.

 

[r6155]

Do not use skirt support for small vessel diameter because visual inspection / ultrasonic test of bottom head is impossible during in-service inspection

My opinion only

Regards

 

[roca]

On small vessels some clients use a half skirt arrangement.
I have found this to be an adequate solution on many projects.
As per the use of legs, half skirts should not be subjected to vibration / fatigue