API 650 Allowables

I have coded API 650 nozzle with
24" sch 20 nozzle, nozzle height 1000 mm,
Tank dia 60000 mm, fluid height 18000 mm.
Just to check the effect of fluid height on allowables, i reduce the height to 9000 mm,
keeping all other data same.
The allowables are reduced as shown in caesar error check.
I was expecting to get the allowables more as reduction of tank height would be advantage.

The reason for the change is because Fp (the pressure load due to liquid head) changes.

Be very careful with these allowables, as they are actually the limits for the nomographs. They can not be taken out of context. Each value is the maximum (in the appropriate figure), assuming the other two are zero. To properly qualify an API-650 nozzle, you must draw the figures.

Thanks Richard for ur reply, Can i get more further detail reason for the output as we are expecting the limitation for allowables once the liquid height is reduced, the allowable should be higher but the outputis reverse. The higher the liquid level, limitation is increase which we are puzzled on the result. Can you please explain the output result on why the allowables is higher once the liquid level is high.

I don't think you can draw the conclusions you are. The values you are looking at are not allowables, they are limits used to construct the nomographs. You can't take them out of context.

If your analysis is considering everything, then lowering the fluid level changes the deflection and rotation of the nozzle, which affects the loads the piping puts on the nozzle, in addition to changing the limits on the nomographs. So one can't really say whether lowering the fluid height is beneficial or not, at least not without plotting the piping loads on the nomographs.