Nozzle close to tan line 2

[ANK72]

Hello all,
I need to evaluate shell stresses at a nozzle attachment on a pressure vessel. PD5500 requires that the distance between the end of the cylinder and the edge of the attachment should be not less than r/2. Where 'r' is the radius of the shell.

In my case the nozzle is less than r/2 away from the tan line.
Can someone please recommend what to do? Is there an alternative calculation procedure that takes into account the stiffening effect of a 2:1 SE head.
FEA is not an option at this stage.
Regards

 

[codeeng]

Outside of FEA there's not much you can do to take into account the stiffness of the head. Years ago, for ASME vessels, we applied stress correction factors to the WRC107 analysis. These ranged from 0.4 for r/4 to 1.0 for r/0.25. However I'm not sure if you could apply these to PD5500. Certainly WRC and PD5500 are pretty much obsolete as far as local load analysis.

 

[jte]

ANK72-

As codeeng pointed out, FEA is really the best tool. However, since you stated that that is not an option, the use of stress reduction (correction) factors is just about the only way to go. The values I've seen have also varied from 1 to a max (min?) of 0.4. In other words, if the nozzle is very close to a stiffening element then you'd calc the stresses as if the nozzle is distant from any discontinuities using whatever method you have available. Then you'd reduce that stress by a factor of as much as 0.4 depending on the actual proximity to the discontinuity.

One published source of stress reduction factors is API-650 in Appendix P3 figure P11. This figure was developed for tanks, but unless you find other sources it may be the only thing for you to go with.

On the positive side, the stiffening element will carry some of the load, so you can conservatively calculate the stresses as though the nozzle is in the middle of nowhere. If they are acceptable, you're done.

The negative side is that if you are using nozzle spring rates to calculate the piping loads, the presence of a stiffener will obviously reduce the flexibility of the nozzle thereby driving up the pipe loads.

jt

 

[LSThill]

ANK72 (Mechanical)and Team Members

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