FIRE ZONE FOR VESSELS 1

[orlenteam]

Dear Sirs,
Could you give us any information how we may determine the dimentions of fire zones for petrochemical and rafinery plants, on which standard we may based our calculation for fire resistance for vessels. Our question is not concern to explosive zones but to fire zones.
On our plant we will have pressure vessel with instrument air which is placed 6,2m from possible source of fire. Do we have to designe this one for external fire condition, design temperature 538°C (1000F)?
Best regards
M. Ambroziak
S.Portalski

 

[TD2K]

A common fire zone 'limit' is a 2500 ft2 circle to decide if another vessel will be engulfed in a fire around a particular vessel or leak point of fuel for the fire.

That said, you need to look at your system and satisfy yourself this is applicable. What are the fluids, what is drainage like, what is available for firefighting, etc?

I'm not sure what you mean by designing the vessel for 1000F, do you mean as a design temperature? I have not seen vessels designed for a 'fire' temperature as opposed to a process temperature. You will find your vessel is unrealistically expensive. Flanges etc would become much higher classes.

If the vessel is in the fire zone you decide on, you would 'design' its relief load for this case. That said, you need to remember a PSV won't prevent a vessel from failing due to overheating in a fire. The PSV simply maintains the vessel at or near the set pressure. Once the metal gets hot enough it can no longer hold that pressure, the vessel fails. To avoid that, you need to depressure the vessel through a depressuring system.

 

[orlenteam]

Thank you for your replay. We know that PSV have to be calculated for external fire condition relief, but our question is do we have to also calculate vessel for external fire condition. We mean external fire temperature 1000F; on this basis average metal temperature can be estimated, based on a max. fire duration of 1 hour.
Could you also give us a standard (rules) which you use to calculate 2500ft2.
Regards
Orlen Team

 

[johnnymist2003]

Hi,

I recall that NFPA Standards can be used for guidance on fire prevention and requirements for refineries. Unfortunately I used the specs only for a short period about 3 yrs ago when I was involved in the design of a tank farm and I cannot remember any spec numbers.
Sorry I could not be of more help.
John