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Storage Tank Overfill Protection


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#1 linda_pro

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Posted 23 October 2019 - 05:40 AM

Dear all, 

 

we have an issue with my current design of tank overfill protection.

we have chemical storage tanks with foam chambers installed at tank side. As per API 2350 recommended, the minimum distance between LSHH level to overfill is 3 inches (76mm). 

 

Current design the response time is calculated from tank LSHH level to the bottom of foam chamber nozzle and it meets API recommendation (it equals to 2 minutes).

 

However, Client has just provided us their design guideline that response time from LSHH level to overfill level should be minimum 2 minutes plus a margin of 2 minutes. it means total of 4 minutes from LSHH level to overfill. 

 

We already purchased  all level switches (LS and the their length can not be adjusted. So, initial we planned to trim the nozzle of LS or relocate the nozzle location to meet the 4 minutes of response time (avoid a new order).

 

However, someone in my team defends that the foam chamber is designed to go up to the top of tank, create an U turn before going down to ground. Hence, the overfill level can be considered higher than foam chamber nozzle as the current calculation. therefore, 4 minutes that Client standard can be met. So we don't have to make any change at site.

 

If anyone of you have  experience with this matter, could you please advise me if with this kind of foam chamber, could the overfill level be higher than bottom nozzle?

 

I attach here a snapshot for tank model for information.

I do appreciate all opinion.

Thank you   

 

Attached Files


Edited by linda_pro, 23 October 2019 - 09:32 AM.


#2 breizh

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Posted 23 October 2019 - 06:16 AM

Hi ,

No document uploaded !

Breizh



#3 linda_pro

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Posted 23 October 2019 - 09:34 AM

HI Breizh,

I have just added the attachment.

Sorry for that.

 

Hi ,

No document uploaded !

Breizh



#4 PhilippM

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Posted 23 October 2019 - 03:51 PM

So the client provided this design guideline after the design was already finished? Was your design approved by the client before you purchased the level switches?



#5 linda_pro

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Posted 24 October 2019 - 04:47 AM

Unfortunately yes, it was. They assigned operators to check the engineering documents hence I think they are not familiar with the checking procedure. 

They contracted to another company to do PMC for them and this company has done FEED. During FEED they calculate the gap upto the tangent line and they did not write down that basis in any document.

That's a long story .....:(

 

So the client provided this design guideline after the design was already finished? Was your design approved by the client before you purchased the level switches?



#6 Pilesar

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Posted 24 October 2019 - 01:42 PM

How is 'overfill' defined? One option: Until the contents reach the nozzle flange, they are still within the vessel. The nozzles are an integral part of the vessel according to pressure vessel practice. With the upturned overfill nozzle, does that give you enough extra time? A second option is to define overfill as 'when the contents spill out'. That would allow contents to reach the apex of the u-bend before overfill occurs. I think that is legitimate, but not as clear as the first option. Your best course of action would be to get client's approval. Send donuts to the operators when you send them the approval document.






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