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Emergency Depressurization Valve Stuck Close


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#1 Sara Owens

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Posted 28 November 2018 - 12:53 PM

Team,

I have a hazop item that i find very hard to resolve.

I have an emergency depressurization valve being stuck close. the recommendation is to  determine if the emergency depressurization rate can be covered by the existing relief valve. the existing relief valves are sized for fire. given the EDP rate, the relief valves will not be able to take care of the high rate. Is there any way to resolved this? has anyone ever seen a HAZOP done on a EDP valve being stuck close? the EDP valve is already my safeguard, i don't  see how a HAZOP can fail a safeguard. anyhow i need some ideas on how to close this hazop. i don't want to buy any more relief valves. 



#2 Zauberberg

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Posted 28 November 2018 - 02:41 PM

Emergency depressurization is a different topic from pressure relief. Depressurization removes the inventory from process systems whilst pressure relief just prevents from system overpressure yet maintaining inventory, so you cannot compare the two or interchange their basic functions.

 

If you need a certain reliability of the depressurization loop (including the EDV), you can achieve that with appropriate SIL rating of the entire loop.



#3 fallah

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Posted 28 November 2018 - 03:27 PM


 

Hi Sara,

 

Agreed with Dejan's viewpoint on your query.

 

Besides, an EDP system comprising depressurization valve is an additional layer of protection. It's not mandated by code, hence cannot be a substitute for the pressure relief device mandated by code.The matter should be evaluated in a, at least semi quantitative, risk assessment method such as LOPA study to check the adequacy of existing layers of protection and it's obvious during such assessment, the depressurization valve stuck close would come into play as a negative feedback for relevant protection layer.



#4 12345656

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Posted 30 November 2018 - 12:40 AM

In case of Fire the voting system activate the BDV. However if the HAZOP study considering the contingency of fire than the another contingency should n't be consider.

 

As per my understanding at a time only one occurrence should be consider.



#5 fallah

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Posted 30 November 2018 - 03:12 AM

In case of Fire the voting system activate the BDV. However if the HAZOP study considering the contingency of fire than the another contingency should n't be consider.

 

As per my understanding at a time only one occurrence should be consider.

 

You mean it's a double jeopardy...

 

If so, i don't think to be; because it's a case in which an instrument wouldn't respond to a request when needed to be activated, besides it might the valve already being stuck close and the malfunction recognized when needed to be opened...



#6 Zauberberg

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Posted 30 November 2018 - 11:37 AM

BDV stuck closed is a hidden failure (because you won't see it is stuck until there is a demand for it to go to open position). This means it could have failed anytime before the initiating event for BDV opening, and hence it is not a double jeopardy case.



#7 12345656

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Posted 03 December 2018 - 01:57 AM

 

In case of Fire the voting system activate the BDV. However if the HAZOP study considering the contingency of fire than the another contingency should n't be consider.

 

As per my understanding at a time only one occurrence should be consider.

 

You mean it's a double jeopardy...

 

If so, i don't think to be; because it's a case in which an instrument wouldn't respond to a request when needed to be activated, besides it might the valve already being stuck close and the malfunction recognized when needed to be opened...

 

 

Thanks for your response. its a learning point for me. But as you mention that Instrument response failure when needed to be activate.

 

This is a double Jeopardy like fire and BDV failure.

 

Mostly the scenarios which consider is the instrument air failure (ESD system failure), in that case BDV should be Fail open position but we can't take double Jeopardy that instrument air failure and BDV stuck close. If we will consider like this than in this way we have to consider the failure of other emergency valve failure cost will increase. 

 

If we consider ESD system failure is a cause in which power failure, instrument air failures are consider but if we consider BDV failure in the ESD system failure than we have to consider other ESD system failure which will increase the cost and complex control system.

 

Thanks



#8 Zauberberg

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Posted 03 December 2018 - 03:43 AM

Double jeopardy refers to any scenario where two unrelated events occur simultaneously. BDV stuck-open could have occurred in any point in time, therefore it goes out of the equation for considering double jeopardy. It is like determining if a hole on the road and sudden failure of your brakes are double jeopardy - they are not because the hole could have been there sitting on the road since long time ago. You are comparing apples and oranges in your example.



#9 Sharma Varun

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Posted 04 December 2018 - 12:31 AM

As rightly put by both Dejon & Naser, the depressurization valve shall be selected based on risk assessment & SIL Study. 

To comment on HAZOP recommendation, please share the details of HAZOP sheet,

Have you ignored any of the operating relief scenarios based on this EDV? Remember ESD valves (Instrumenattion say EDP valve) are pen-ultimate safeguards & relief valves are ultimate safeguards.

Please confirm if the deviation in HAZOP is external fire, because in that case PSV sized for fire shall suffice as safeguards.


Edited by Sharma Varun, 04 December 2018 - 12:34 AM.


#10 shan

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Posted 06 December 2018 - 08:13 AM

Double Jeopardy is defined as considering two unrelated causes of overpressure simultaneous occurrence. 

BDV malfunction is a latent failure as defined in API 521 (2014) 4.2.4, which is an existing condition and not a cause of overpressure. 






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