Is it possible that the API 650 nozzle calculations are yielding wrong computed values of stiffness in caesar version 5.10? There is considerable difference between those values and the provided by tank vendor.

Caesar II values:

API-650 NOZZLE NODE = 7001
INPUT PARAMETERS:
Tank Diameter ............................. (in.)= 1729.129
Nozzle Height above bottom plate .......... (mm.)= 675.000
Nozzle Outer Diameter ..................... (in.)= 16.000
Shell Course Thickness .................... (mm.)= 25.400
Max Fluid Height above bottom plate........ (mm.)= 16000.000
delta Temperature ......................... (C)= 0.000
Modulus of Elasticity ................(KPa )= 0.200000E+09
Expansion Coefficient ...............(mm./mm./deg)= 0.000000E+00
Fluid Specific Gravity .................... = 0.860
Reinforcement on (S)hell or (N)ozzle ...... = S
COMPUTED VALUES:
AXIAL TRANSLATIONAL STIFFNESS (N./cm. )= 192010.
LONGITUDINAL BENDING STIFFNESS (N.m./deg )= 109525.
CIRCUMFERENTIAL BENDING STIFFNESS (N.m./deg )= 93811.
RADIAL DEFLECTION DUE TO FLUID & TEMP (in.)= 0.42
LONGITUDINAL ROTATION DUE TO FLUID & TEMP (deg)= -0.47
MAX ALLOWED RADIAL FORCE (N. )= 24437.
MAX ALLOWED LONGITUDINAL MOMENT (N.m. )= 10148.
MAX ALLOWED CIRCUMFERENTIAL MOMENT (N.m. )= 59339.


VENDOR VALUES:

AXIAL TRANSLATIONAL STIFFNESS (N./cm. )= 162560.
LONGITUDINAL BENDING STIFFNESS (N.m./deg )= 84347.
CIRCUMFERENTIAL BENDING STIFFNESS (N.m./deg )= 28116.

Doubtfull these are incorrect, this is a rather mature, stable routine, it has been in use for 15+ years.

Issues with manuallyt trying to verify these stiffness values are:

1) Log interpolation of the charts is necessary. The charts are rather course, so any two people likely come back with differing values.

2) If your L/2a ratio is between 1.0 and 1.5, then the software interpolates (linearly) between the two sets of charts.