8 replies to this topic

[satendra.deshmukh]

Hi all,

I am doing analysis of existing external floating roof tank, this is API 650 tank with PV vent and emergency vent, i did its sizing for all scenarios which are applicable for such kind of tanks with PV vent and found it adequate to handle loads.

 

My question is why manufacturer have provided emergency vent for such type of tanks, emergency vent is considered for fire relief cases but for ex floating roof tanks this scenario is unlikely considering fire vapors generated by moderate exposure will be able to escape tank readily and fires of greater magnitude will tip the roof giving the vapor free escape path.

 

I am less at knowledge of designing of ex floating roof tanks, but i think such tanks roofs are may be of week construction so ex fire scenario is not credible, but what if we are not sure about construction of roof is week or strong???

 

or if roof construction is strong enough to tolerate pressure resulting from fire, then shall we need emergency vent protection for tanks?

 

Please have some light over this……

 

Regards,
Satendra Deshmukh

Edited by satendra, 18 September 2013 - 03:27 AM.

[ankur2061]

Satendra,

 

Appendix C (External Floating Roof Tanks), Clause 3.9 - "Vents" of API STD 650 does not mention anything about emergency vents for external floating roof tanks. It only talks of bleeder vents to displace air (during filling) and sucking air (during emptying) at the external roof deck.

 

Providing an emergency vent is an overkill for an external floating roof tank. You should ask the manufacturer for justification. If you are paying extra money for something which cannot be really justified as per any codes and standards you have full right to question its necessity and seek an engineering explanation for its provision.

 

Hope this helps.

 

Regards,

Ankur.

[fallah]

satendra,

 

Below thread of this site, especially fourth post, might help you out on your query:

 

http://www.cheresour...l-storage-tank/

[satendra.deshmukh]

Thanks both of you,

 

In general ex floating tanks have rubbery seals between floating roof and tank wall also its roof is made up of weak material...

But in my case tank may be having metallic seals and also with strong seam construction, so manufacturer may have provided emergency vent for external floating roof tank....

 

 

 

Regards,

Satendra

[fallah]

 

But in my case tank may be having metallic seals and also with strong seam construction, so manufacturer may have provided emergency vent for external floating roof tank....

 

 

satendra,

 

Of course, if the metallic seal material on such floating roof prohibits sufficient venting in the fire case; the emergency vent should be provided...

[satendra.deshmukh]

Hi,

I have one more query related to external floating roof tank. Do we need to identify overfilling scenario on EFR tanks?

 

I have not seen any overflow line to EFR tanks. I read in our project guidelines that EFR tanks must have suitably sized overflow slots to avoid damage to tank in case of overfilling and that is the responsibility of tank designer.

 

If I don’t have any details of that overflow slot then how should i guarantee that tank will be okay in case of overfilling.  Shall we rely on tank manufacturer assuming he has taken care of that? 

 

Regards,

Satendra

Edited by satendra, 11 November 2013 - 08:18 AM.

[fallah]

Satendra,

 

Protection of external floating roof tanks would be done by tank gauging systems; in brief an alarm would be activated by a level sensor...

[satendra.deshmukh]

Dear fallah,

You are saying EFR tanks must be protected from overfilling by instrumentation logic.  Is this means there can't be mechanical system to protect EFR tanks from overfilling..

 

Thanks,

Satendra

[fallah]

Satendra,

 

A mechanical system can't be installed to protect EFR tanks against overfilling and a combination of tank gauging system and proper operating procedure should do the job; because considering any nozzle on the tank shell would interefere with the roof seal when the liquid level reaches to the nozzle elevation will result in vapor leakage...

 

API 2350 will help you to know more about the matter...