Hydrotest Pressure : UG-99(b) OR UG-99(c)

[takiyasamsama]

Hi,

I got a question regarding test pressure. When I design a vessel in PV Elite, whenever I select hydrotest method to UG-99(b) my internal pressure calculation always failing and says that my stress are more than my allowable. Doesn't matter whether I tweak around with the thickness of the head or shell (mostly, the heads are the area that exceed the allowable pressure).

In the result says that test pressure to be used is UG-99(c) test pressure. After changing to UG-99(c) and re-run the study, the internal pressure calculation passed.

It would be much appreciated if someone can explain to me the difference between this two test pressure? I read through ASME and still not quite understand.

Design Pressure : ATM
Design Temperature : 60 degC
Material : SA-240-316L
Head : 2:1 Semi-Ellipsoidal

 

[fegenbush]

b) is the standard procedure for testing which includes the element of hydrostatic pressure from the testing fluid. That is, filled with water and pressurized, the bottom of the vessel will see more pressure than the top. Many vessels operate in-service in this configuration and it is a more rigorous examination.

c) is an alternate procedure for testing which does not include the element of hydrostatic pressure from the testing fluid. This configuation is used commonly with the following types of vessels:

-Vessels whose product is gaseous, thus hydrostatic head is not a major concern.
-Distillation columns with trays or packing not designed for the flooded condition, thus the hydrostatic pressure would overstress the lower regions.

I am sure there are other instances where c) is applicable as well.

 

[takiyasamsama]

thanks Fegenbush, my bad for not including the fluid in the vessel during the analysis. Well that solve the problems. Thank you very much!