Nozzle Differential Pressure

[Karloss12]

I have a vessel at pressure 4 bar.

A nozzle passes through the wall of this vessel. The pressure inside the nozzle pipe is 7 bar.

What pressure do I use to design this nozzle?

I would like to calculate the minimum thickness of the pipe on both the inside and outside at 7 bar and use the remaining pipe material as reinforcement. Where the rest of the nozzle reinforcment is calculated for the vessel pressure of 4 Bar.

Where UG-40(d)(2) says 'differential pressure causing opposing stresses is not allowed' does it mean I now have to use 7 bar for the entire reinforcement calc including the shell minimum thickness. Or is it just saying that I can't use 7 - 4 = 3 bar for the internal projecting part of the nozzle?

 

[fegenbush]

I use the worst case. Ask yourself "is it possible for the pipe to be pressurized when the vessel is not?" If so, use 7 bar. Do the same thing for the other differential, then design for 4 bar for the vacuum calculation of the nozzle.

That is my method. I have had AIs say that I was too conservative on the design, but I would rather be on that side of the argument than the other.

 

[Karloss12]

Thanks,

I would expect if the pipe was at 7 bar and vessel had no pressure there would be no need to do a reinforcment calc.

And if the chamber was at 4 bar and pipe at zero, I would do a regular nozzle calc as though both pipe and shell were at 4 bar. (UG-40(d)(2) says 'differential pressure causing opposing stresses is not allowed')

The worst case is if the shell was at 4 bar and nozzle is at 7 bar. How do you deal with that? Designing the entire opening for 7 bar seems very conservative.