As per the standards followed by some of the consultants, the piping loads on the equipment nozzles should be limited to certain allowable values. These allowable loads are specified in terms of nominal pipe size like, 200D, 250D etc. For radial loads and bending moments, seperate expression are given in terms of 'D'. Some people consider only radial force and B.M. But some other people take shear force and torsion also into account while checking the equipment nozzle qualification.

Can anyone tell me how these expressions are derived? What is the significance of D multiplied by some numerical values? Is it related to any WRC test result?

Please add, whether shear force and torsion are having any considerable effect on the nozzle loads?

200D?
An indianism for DN200= 8"NB or a generic 8" pipe/nozzle.

Allowables are given in FxFyFz & MxMyMz
Ie forces and moments.

the magnitudes are given by the vendors.
Their generation sometimes do not follow logic.
But, ignore them at you peril.

If you have overloads, the vendors can approve values you send them, in in the case of OCC events, they can be well over their published figures

(note) usually at the face centre of the nozzle flange

I see these "specifications" as merely an agreement between the buyer and seller of the equipment. If I make equipment, I guarantee that it can hand "X" load. If I buy equipment, I guarantee it won't put more than "X" load on it.

No analysis of the equipment is necessary. Just follow the rule and no one gets hurt.

I've seen a good table like this from Australia. It sets all six nozzle loads (F&M)based on the connecting flange size and class.

Where they apply depends on the equipment. API air coolers take the allowables around the flage face as you said, but talk to any vessel guy about allowable nozzle loads and you'll find they take the allowables at the nozzle / shell interface as that is the critical point [PD5500 App G / WRC] to them. If the allowables loads are on the flange, they need to allow for the moment arm of the nozzle neck with lateral shears.
You really need to be clear with the vendor/client where these loads are to apply.
For instance the outlet of a column typically consists of a bend directly on the bottom dome, and then a long length of pipe to take the nozzle flange outside the skirt. You cannot apply the same level of loads to the flange of this nozzle as you can to the flange of a shorter nozzle [of the same size] fixed directly onto the shell.
Most local load calculations I've done [PD5500 App G & EN13345] only calculate shell stresses for axial force, and circumferential and longitudinal moments. These three components tend to give rise to bending stresses within the shell and these are the critical points for a pressure vessel.
Both codes largely neglect the three shears [circ force, long force and torsion] as these are usually of negligble magnitude [PD5500 does give equations if you feel they are high].

When the consultants make the rule they need to bring the buyer ( mostly piping designer ) and seller ( mostly equipment designer ) to a point on that all the parties can agree and do their design to agreed limits.

Getting some numbers multiplied by diameters and their combination on the agreed limits does not mean the nozzles can take the load without any calculation. The nozzle is to be designed to take the load by the equipment designer. On the other hand the piping designer is to make the piping flexible enough not to exceed the agreed load.

The agreed loads and moments are statisticly driven by the consulting companies and they made it the function of the diameters to show them exotic. That is all. Nothing fancy about it.

Hope this helps.

I Demir