Nozzle loads and AS1210

[Pete17]

I am trying to check the loads on a nozzle which is coming out of the cone-shaped bottom of a vertical vessel. Due to this geometry, WRC107 does not seem applicable.

AS1210 Section 3.7 deals with 'cylindrical or spherical shells or cylindrical or spherical parts of vessels subject to internal pressure and combined loading'. Can I use 3.7.5 (vertical cylindrical or conical vessels) to check the nozzle? (calculates minimum wall thickness for combined loading)

I'm quite hesitant to use the above as it does not seem to include a local stress check or stress concentrations (the cone is angled at 45degrees). It seems to only be a check of the vessel shell.

Please forgive me if any of these questions seem stupid or don't make sense. I'm still green, so please be gentle.

Cheers

 

[JStephen]

First off, check WRC 297 in addition to 107.

You can approximate the loading in a cone by treating it as a cylinder, taking the radius as the radius normal to the plate.

If there is generalized software that can handle the situation, that would obviously be much better.

 

[TomBarsh]

I agree, Pete, WRC-107 is not applicable in the case of a "nozzle" attached to the end of a cone. Per most pressure vessel codes (and engineering mechanics) this nozzle acts no differently than a cylinder attached to the end of the cone; in fact that's what it is, it just functions as a nozzle.

The difference for external loads and moments between this case and that for a nozzle attached to the *surface* of a shell (head, cylinder, or cone) is that in the former case the loads and moments are resisted by the entire (circular) cross-section of the nozzle or cone, whereas in the latter case the loads from the nozzle are applied at only a "point" on the surface of the shell.

Thus in the latter case WRC-107 and related analyses apply. But in the case of the nozzle attached to *end* of a cone these analyses are not applicable. Instead, treat the analysis as for a beam-column...apply the axial and shear forces over the cross-sectional area and the bending moments to the section modulus.

 

[JStephen]

Pete, does it come out of the tip of the cone? If so, I didn't catch that, and the WRC 107/297 approach wouldn't accomplish anything. If it's higher up on the cone, then take a look at that.

If you have an axial nozzle ON the tip of a cone, you can treat that to a certain extent with shell-analysis methods in Timoshenko or Formulas for Stress or Strain. I seem to recall that the cone solutions tended to be messier than the cylinder cases. I believe ASME references some other work for cone analysis, but I'm not familiar with it.

If it comes out of the tip at a 45 degree angle, my first thought would be to make it axial, and then add a 45 degree ell in the piping, just for the sake of an easier analysis. Otherwise, consider finite element approaches.

 

[Pete17]

Thanks Tom and JStephen for the help.
Yes, the nozzle is coming out the end of the cone (at the 'tip')

It seems then that I treat the nozzle like it was just a smaller cylindrical section of the vessel and check the allowable loads accordingly.

 

[TomBarsh]

Eggsactly, stress due to bending moment M = M/S (S=section modulus); stress due to axial load Fx = Fx/A (A=circular cross-sectional area of the nozzle cylinder).

Shear stress due to lateral loads V = VQ / It. (normally I might not bother to check the shear stress for wind and seismic loads, but the specified nozzle loads might be unusual and might cause high stress).

Good luck.