Nozzle reinforcement query - area available in shell

[starrproe]

I am adding a new 16" nozzle to an existing process column:

1. Column dimensions - 8840mm ID x 47000mm T/L to T/L
2. Design pressure and temperature - 3.5 Kg/cm^2(g), 367C
3. Shell and Nozzle neck MoC - SA 516-70
4. Provided shell course thickness - 27mm

Required shell thickness due to int / ext pressure per UG-27 calcs is around 14mm.
I believe that the excess thickness provided in shell is partly to account for effect of wind / seismic loadings on the vessel. Other probable reason for increasing the shell thickness could be plate availability.

My query is - While calculating excess area available in shell, don't I need to account for shell thickness required for sustaining wind/seismic loadings?

Code formulae seem to suggest that all the excess thickness in shell (27-14 = 13mm, in my case above) can be used to get area available for reinforcement.

What am I missing here?
Can I really take all excess shell thickness for reinforcement?

Regards,
Starrproe

 

[vesselfab]

first excess to take away is corrosion allowance.

the excess is most likely wind if at bottom but also be lower joint efficency in original design and you using 1.0 for nozzle reinforcement

 

[EngAddict]

Excess would be opening reinforcing or for external loads. Can be often be easier and more effective to increase the thickness of the shell or head over using pads. Or they happened to have that thickness steel lying around.

I find it unlikely the thickness was increased for wind load. Perform a shell stress check for imposed loads from supports to make sure the thickness is suitable.

 

[prex]

To answer precisely your question:
- when you perform an opening reinforcement calculation per UG-37 you are normally considering only pressure as the loading, therefore the required thickness will be consistently calculated for pressure only (UG-27)
- then you have of course to check it also against other loads, but here the procedure may vary: for wind and EQ you'll generally have to check the reinforcement for longitudinal stress, and the associated pressure stress is near half the circumferential stress that governed the reinforcement for pressure only; the required thickness is here is the thickness calculated for a longitudinal stress equal to the allowable
- for your proportions (a relatively large diameter column) I wouldn't expect the longitudinal stress to govern, even for a nozzle close to column base

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes and launchers for fun rides

http://www.levitans.com

: Air bearing pads

 

[jte]

One way to get a handle on the effect on wind/seismic is to calculate the moment of inertia of the shell without an opening, then calculate the same for a cross section of the shell through the middle of an opening without reinforcement, then including the reinforcement.

jt