ASME B&PV SECTION VIII OVERPRESSURE PROTECTION

[749KDV]

If a Section VIII vessel normally operates with a gas bubble, but under extreme circumstances can be lined up to fill the tank solid, does one need to protect the tank from over pressure with a gas relief AND a water relief? Would Section VII code requirements for overpressure protection be met if one could provide a gas relief for normal operation and use administrative guidelines i.e., procedures, to ensure that the valve line-up that would fill the vessel solid never happens?

 

[dtn6770]

The details of your situation will greatly influence the answer to your question. Heat & material balances, in & out rates, overall configuration, procedures etc. etc. etc. all come into play. I get the impression that the water level would be the source of compressor to the gas. If so, once the gas gets to the relief pressure the water level will continure to increase to the point of complete gas displacement. No you're looking at a liquid relief rate that needs to match the liquid in flow rate.

I'd think a relief valve sized for vapor/gas relief would cover the liquid relief requirements, in general.

 

[749KDV]

In this case, the gas relief is sized sufficiently for overpressure protection due to the gas, but after solid, the gas relief capability for water is only 20 GPM. This is way too low to pass the incoming 150 gpm and prevent over pressure. The admin control in this case is to ensure the valves are shut to prevent this inflow of liquid. Do you think the code is violated if admin controls prevent the tank from becoming solid, and, therefore, overpressurized?

 

[dtn6770]

Your use of the term "solid" is confusing me. Do you mean full or are there three phases involed?

In any case, as a genereral statement it is probably acceptable to take credit for administrative controls. I would highly recommend the decision to do so be made by a process hazards ananlsys or risk assessment group, not any one individual. Everyone involved in the decision needs to be familiar with the process, systems, equipment, and operating practices.

 

[749KDV]

Solid in this case means full with water, no gas.

Thanks for your response!