PD5500 Branch vs Nozzle

[MechEngD]

Hi from the Newbie - I'm working through PD5500 to design a basic pressure vessel. I'm confused by the terminology branch vs nozzle. What is the clear distinction between branch & nozzle, in PD5500?

 

[DriveMeNuts]

That's an interesting question. I've used PD 5500 for decades and never noticed that.
I would say that 'opening' is the universal name of all holes in the shell.
Different types of opening include Studded pads, Nozzles and Branches. These terms encompass all the components such as the local shell and the Pad, or pipe welded into the shell, as well as the pipe end flange.
My best estimate is that a Branch is a nozzle which extends indefinitely (without a flange), whereas a nozzle has a Flange welded to the end of it, a diameter or so from the shell surface.
However, in PD 5500 Branch and nozzle seem to be used interchangeably. Some sections exclusively use one term or the other (when they should use both). Some mix the terms randomly. In many sentences, "Nozzle or Branch" is used. In one section 'nozzle' is exclusively used, and then that section is referred to in other sections with 'Branch'. It is a bit messy. But I don't think it matters. They are essentially the same thing.

 

[BJI]

I think the terminology goes back to PD6550-2 from which the methods in PD5500 were based. I would agree that they are all nozzles but only a nozzle in a cylinder could be called a branch. It is surprising this terminology hasn't been harmonised over the years.