When to use more than two saddles? 1

[victorpbr]

Hi,

I've been looking at some old drawings of refrigerated CO2 storage vessels, with capacities ranging from 500- 600 tons (DIA 3000-3800, length (30-50m), and all of them had 3 saddle supports.

In the searches I made, I've seen that it is not a good practice to use more than 2 saddles, and saw some people saying that have designed longer vessels with only 2 saddles.

I'm studying a case for a 3800mm diameter vessel , 44000mm long, with hemispherical caps and design pressure of 2.4 MPa, using ASME VIII-2.

My thinking is that a first try with two saddles should be made, and if the stresses fail the stress analysis (Per Part 4 of ASME-2), I should add an extra saddle to lower the vertical loads and see the results. Of course there will be the problem of differential settlement of the saddles, which will cause different loadings, but I guess that these loads can be factored towards safety (any thoughts on the factors to use?)

I also wonder if there are any practical rules of thumb to quickly evaluate the need of more than two saddles?

 

[r6155]

See ASME PCC-2 Article 5.1, Mandatory Appendix III
Safe Distance Calculations for Pneumatic Pressure Test

Regards
r6155

 

[MJCronin]

Like I said...... Maybe multiple vessels are a better choice !

MJCronin
Sr. Process Engineer

 

[Trestala]

Maybe consider using a soil bearing foundation for long bullet vessels, similar to a mounded LPG bullet (EEMUA 190), rather than resorting to 3 or more saddles (?).

 

[r6155]

I found in my library 2 horizontal large pressure vessel with 2 saddles

1)
ID= 6000 mm TL-TL= 56000 mm Ellip. heads
Empty= 355000 kg
Operating= 2716000 kg
Field hydrotest= 3634000 kg
Specific gravity of fluid= 0,534
Shell thk= 30, 32 and 34 mm

2)
ID= 7500 mm TL-TL= 56000 mm hemispherical heads
Empty= 875000 kg
Operating= 4098000 kg
Field hydrotest= 5771900 kg
Specific gravity of fluid= 0,460
Shell thk= 62 mm

Regard
r6155