Pressure Vessel Saddle

[AlexanderChacin]

Hello everyone
I am using the attached equation to calculate the K8 factor used by the Pressure Vessel Handbook, in calculating the flexural stress at the bottom, which comes out using the attached procedure
The problem is that I have a difference between my calculation and the tabulated value

 

[JStephen]

For theta = 120 degrees, I get K8 = 0.604 versus 0.603
For theta = 150 degrees, I get K8 = 0.877 versus 0.876
For theta = 180 degrees, I get K8 = 1.193 versus 1.183
I don't see any obvious reason for the difference.
If you're far off, make sure delta is in radians in the equation.
Fiddling with different factors in the equation tends to throw results far off.
Using 3.14 instead of 8-12 digits of pi affects results slightly, but doesn't match up to the table, either.
Similarly, adjusting the decimals used in 1/6 varies results but doesn't match the table.
I find the same tabulated numbers in an online version of Moss's book (it's K7 there). It seems odd that either would just copy something from the other, though.

 

[AlexanderChacin]

yes, I got the same, plus the book "Pressure Vessel Design
Concepts and principles "gives the same equation for K8

 

[r6155]

See the original paper from ZICK.

Regards

 

[SnTMan]

It is possible the original calculations were made with a slide rule....

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[AlexanderChacin]

r6155
Zick's original paper makes no mention of bending stress at bottom, nor does it determine any way to calculate an associated factor (K8 or K7, depending on the reference), which makes me think that it does not contribute significantly to the stress state in the pressure vessel, but despite this I would like to know how it is calculated and why there is a difference between authors

Mike
The lack of precision in the calculations is a possibility, but I only have significant differences in the mentioned factor K8

Regards

 

[r6155]

I have no more time, also you can see:

PD 5500
EN 13445-3
ASME VIII Div 2
AD-2000 Merkblatt
Process Equipment Design – Brownell Young
PV Design Handbook - Bednar

Regards