UG99b Hydrostatic Pressure

[wailunwu]

Hi

I am getting mixed answers with the following as I read past threads and would like clarification:


When using UG99b to calculate hydrostatic pressure (P = 1.3 * M.A.W.P. * Sa/S), whether testing the vessel horizontally or vertically, I will need to ADD the water static head to get the actual hydrotest pressure.

Please correct me if I am wrong.

Thanks.

 

[SnTMan]

wailunwu, test pressure at the top of the vessel is calculated per UG-99(b), as you stated. Additional pressure due to static head is of course present at the bottom of the vessel and must be considered at design.

Test pressure would be potentially adjusted in the case of a vertical vessel tested horizontally. The pressure at a horizontal test must be the same, at the bottom of the vessel, as would be applied if the vessel were to be tested vertically, which is possible and likely after installation.

In this case the difference in static head between vertical position and horizontal would be added to the MAWP (or design pressure) before calculating the UG-99(b) test pressure.

Regards,

Mike





The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[wailunwu]

Hi mike

I think my confusion lies in whether to add static head water pressure to mawp before ug99b calculation or add static head pressure to calculated hydro test pressure after ug99b calculation.

Why do you suggest that static Head needs to be added to mawp before ug99b test pressure calculation?

To me, it seems to make more sense to use lowest mawp found among all the vessel components to calculate ug99b test pressure and then add the water static head (this will then give the hydrotest pressure reading at the bottom of the vessel since ug99b is the test pressure at top of vessel).

Thanks for your expertise.

 

[wailunwu]

I am referring to a vertical pressure vessel tested vertically.

 

[SnTMan]

wailunwu, for a vertical vessel tested vertically, and with the test gauge at the top of the vessel, no static head need be added to MAWP (or design pressure, if used) before calculating the UG-99(b) test pressure. Why? Because no static head is present at the top of the vessel.

If the gauge is located elsewhere (lower) then static head in the quantity rho*g*h (h being distance from top of vessel to gauge) is added to the MAWP, or design pressure before calculating UG-99(b) test pressure. Why? Because even with zero (gauge) pressure in the vessel static head of rho*g*h is present at the gauge location.

The basis for test pressure (MAWP or DP plus static head at the gauge location) is multiplied by the UG-99(b) factors to yield test pressure.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand