time delay between SDV and BDV 1

[processengineer1998]

Dear Friends;
As you know in case of fire occurrence on platform; it is necessary to consider an appropriate time delay to ensure that Emergency shutdown valves(ESDVs) are closed before Blowdown valves are opened to prevent any problem like flare overloading.
I want to know how much the required time and what relevant criteria or standard for this matter is.
Is the time to be considered from time the ESDVs are being closed or it is considered after full closure of ESDVs.
Tnx

 

[JLSeagull]

The logic could consider the typical rate of one second per inch NPS; or consider the shutdown valve closed position status. I left my offshore platform assignment nearly seven years ago. I don't recall the logic associated between the SDV and BDV logic if it existed. Each shutdown valve was associated with a process shutdown. As a platform fire was the key (perhaps only) blowdown initiator thus we may not have delayed the blowdown waiting for the SDV to close.

 

[JLSeagull]

I checked my 2001 copy of API RP 14C and saw no mention of a time delay. The content of the 2001 edition appears to still be valid.

 

[processengineer1998]

I am sure about delay between ESDV and BDV in our projcet.I am just looking for the reference.

 

[dcasto]

who cares about time, just use interlocks on the ESD valves limit switch. When the ESD valve is closed and the close limit switch has been satisfied, then allow the BDV to open.

 

[pmover]

i agree with dcasto . . . not aware of any time limitations; however, the BDVs should not open until the ESD valves (isolation valves) are closed. at least this is the logic i see used at many facilities.

 

[processengineer1998]

reference is made to TOTAL specification- GS EP SAF 261 "Emergency Shut-Down and Emergency De-Pressurisation (ESD & EDP)":
Section 5.2.7- BDV timers:
In order to prevent flare overload, local BDV timers (pneumatic or hydraulic) shall be installed to ensure that ESDVs are closed before BDVs are opened.

 

[processengineer1998]

Also in the same standard in section 4.2.4.2 which explains Actions for ESD-1 (fire zone emergency shutdown) it is mentioned that:
"Upon confirmed fire and/or gas detection, automatic emergency de-pressurisation (EDP) offshore, and optional onshore. Open all the BDVs (Blow-Down Valves) in the fire zone with a pre-set time delay (30 s to 1 min.). If de-pressurisation is not automatically initiated upon ESD-1/F and/or ESD-1/G, a push button located in the CCR initiates ESD-1/F and/or ESD-1/G and opens all BDVs with a pre-set time delay."

 

[processengineer1998]

Two post upper I wrote a portion of standard.To prevent misunderstanding I should write whole
Section 5.2.7- BDV timers(this section is subsection of 5.2 EDP requirements):
In order to prevent flare overload, local BDV timers (pneumatic or hydraulic) shall be installed to ensure that ESDVs are closed before BDVs are opened (short delays in the order of a few seconds and in the limits of rules set forth in section 7.1.2).
Such local timers shall be forbidden to achieve phased depressurisation (say, one minute or more). If such phasing is necessary, a proposal shall be submitted for COMPANY’s approval indicating its justification and technical provisions selected to ensure that common mode
failures will not impair the flare/vent system integrity.

 

[JLSeagull]

It sounds like TOTAL defines your path forward. Client standards are important for their projects. The TOTAL standards may provide a good discussion point on projects for other clients. Goverment and industry standards are more applicable for the other clients.

 

[dcasto]

I'm lost. the TOTAL, that is the company TOTAL from France? If so, how the heck do you expect everyone to know what in the world GS EP SAF 261 is??? We give opinions and not engineering consultations on company rules.

I'll still standby my opinion including implications on flare system overloads, If the risk of further problems in a locatione wher humans are versus overloading a flare system which is out of the way, I'd overload the flare. If TOTALS policy favors underloading a flare and allowing a backup that could cause failure in a populated area, thats their risk.

 

[atayto]

I can share the experience which is used in caspian sea,Azerbaijan. We have Production shut down which closes all Process ESDVs. Blowdown valves are opened only in case of fire and gas detectionwhich is called Yellow or Emergency shut down. It depends on what triggers this shut down. In case of fire detection all vessels are depressurized to the flare without any delays. In case of gas detection it is slightly complicated. On gas detection production shut down will occur and CRT have 150seconds to press delay blowdown button. If it is done blow down will be delayed for 4 hours, if not then blow down occurs straight away. Blow down rates from all points designed so that pressure in vessels will be reduced during blowdown from initial pressure to pressure of 6.3 barg (determined as a safer limit) within 15 minutes. I will try to find more information tomorow aruond design basis.