4 replies to this topic

[Ariel]

Hello!

I need to share a personal opinion about SDV fail position.

Many times, I read or hear something like that:

 

“A shutdown valve actuator shall pneumatic/hydraulic fail-safe spring-return type. Generally a shutdown valve failed to close (FC).”

 

I guess this comes from the possibility that you could have a problem with your instrument gas supply.

But….in cases where I have a completely reliable system to generate instrument gas (in this case air), provided by:

 

·         Two twin compressors (one is back up).

·         10m3 recipient for 24 hours consume.

·         Pressure transmitter to indicate and alarm of low-pressure air.

·         Independent pressure transmitter to generate emergency shut down in case of low low-pressure air (usually 4 bar).

 

Can I choose to install doble- action actuator? Especially for big ASME #600 valves (> 12in)?.

Thera are:

·         Less expensive

·         Much more smaller

·         Less maintenance need

·         Easy re-open or operate in start up/shut down operation. An operator can open/close de valve from a control panel beside the valve.

 

In advance, thanks for your expert opinions!

Ariel

[Bobby Strain]

If it is a shutdown valve, it should fail closed. Unless, maybe, you commit to a program to ensure that it is as reliable as it needs to be. But that would be a hard sell. Especially to your insurance provider.

 

Bobby

[fallah]

Ariel,

 

As far as i know in SDV's, type of actuators don't relate to their fail safe position; they should be fail closed with every type of actuator...

[Ariel]

Ariel,

 

As far as i know in SDV's, type of actuators don't relate to their fail safe position; they should be fail closed with every type of actuator...

fallah, thanks for your answer.

 

 

Yes of course I agree with you and SDV must be fail closed. What I wanted to ask, maybe I did it in a wrong way, if it´s safe enough to use a double acting actuator to close a SDV valve. 

 

 

Always consider the reliable air instrument system that I just have described.

 

 

Thanks in advance.

 

Ariel

Edited by Ariel, 24 July 2015 - 05:51 AM.

[Ariel]

Bobby thanks for you answer.

In this case, we performed a HAZOP study to analyze de safety of the system.  I think this could be a kind of backrest for a double effect actuator selection based on air system reliability.

Definitively I did my question badly because you are the second person that misunderstanding the main topic.  I want to emphasize that the SDV valve has been mounted with a double effect actuator and not with a simple spring return actuator like is common. Do you think it´s an unsafe situation?

 

Thanks again.

Ariel