That seems to be an internal factor applied to determine "standard nozzle loads" w/o doing FEA/calculations. Not sure I've seen that derived elsewhere.
It is not uncommon for owners to specify minimum allowable nozzle loads for vessels, usually just given as a table of numbers.
There is probably some rationale behind them, but what it is, is anybody's guess.
The idea is, you design the vessel for those loads, the piping designers design their piping not to exceed those loads.
They could have been derived based on some fraction of pipe strength, or typical nozzle strength based on some assumed nominal thicknesses, or based on bolt or gasket strengths, or just pulled out of the air.
I don't know exactly! But, I would like to say this one as below!
Nozzle Loads are closely related to Shell Thickness!
If a very Large Nozzle Load addes to a vessel, the shell thickness of the Vessel should be increased.
It means some vessel that has very low design press. can withstand very low nozzle load.
Clients will confirm everything such as cost, reasonable design carefully, and then they will decide the factors.
Not a "pressure vessel" but I had to re-design the steam piping into a modest (55 Meg) turbine (built and designed by a competing company) that had been destroyed when the steam piping loading grossly exceeded the turbine nozzle loads. Turbine casing got "pushed sideways" into the turbine blades, blades broke, turbine was destroyed.
The OEM manual was very clear about maximum nozzle loads - which (in my humble opinion) were much too low to be reasonable, but it didn't matter. "Book said these were maximum loads (on the order of +/-150 to 200 lb force total in all directions) on each nozzle under hot and cold conditions." Therefore, my pipe stress team met the conditions, then we verified them by sitting on the turbine and moving each pipe by hand until it kissed the flange with zero force cold. took a few minor adjustments to the pipe hangers, but cold and hot force limits were met.
What were the original design pipe actual loads? We may never know.
In tis table? Only corporate memory and lessons learned can be invoked. Most likely, NO real stress/strain/3D modeling was ever done to verify these arbitrary guidelines are realistic. They may be too high, and so the allowed nozzle loads are only marginally safe. They may be way too low, and so the needed pipe designs are much "too conservative" and could be relaxed in the real world. A FEA model of the actual PV under design for you "might" work if any single calculated pipe load is too high.
