7 replies to this topic

[ezie]

Dear All,

As I found all topics about ESD are dead so I'll create a new one if you allow. 
I have an PFD (see attachment) on which two ESD valves installed both at begin and end of unit. 20'' at inlet and 28'' at outlet.
Between them there are PCV 20'' and SSV 28'' (valves controlled by HIPPS).
When ESD valves are closed pressure increases to level of HIPPS activation.
This caused by fact that time of ESD valve close is 12 secs, and HIPPS valve close is 2 secs I believe.
From this there are questions. 
1. Is there general rules for choosing closing time of ESDV (I've heard about industrial practice allowing to take closing time of ESDV in seconds equal to DN of valve in inches)?
2. Does safety reason allow HIPPS activation during ESD activation and be called by consequences of ESD activation? I think it's not good idea. Single way to avoid this is fast close of PCV.
3. If I'm right in aforesaid point what method of PCV closing may be recommended: on direct signal from ESD system or as response on pressure increase (quick-action actuator)?
Thank you.

Attached Files

•  PFD Scheme_12.02.pdf   4.01KB   52 downloads

[fallah]

ezie,

 

1- Maximum closing time should be selected based on process requirement. Rapid closing may damage the valve internals and affects valve reliability also may create surge on associated pipeline. Anyway as a preliminary estimation one second for each inch of valve size could be considered as a base for valve closing time. 

 

2- HIPPS should protect the downstram system from high pressure in upstream. Then, in your system because you cannot rely on PCV fast closing, ESD activation should be followed by HIPPS activation. Of course, HIPPS might also be activated by high pressure sensing in its upstream due to, let say, malfunction of PCV to cause to be in full open condition.

 

3- IMO, being HIPPS downstream of the PCV there is no need to PCV closing on direct signal from ESD system.

 

Hope above helps you out...

Edited by fallah, 16 February 2013 - 02:45 AM.

[ezie]

Thank you, Fallah

 

Is it permissible do not put additional ESD valve on the 300/100 bar pressure border taking into account that HIPPS valves are closing during ESD activation?

[fallah]

_ezie,

 

_{HIPPS system (with SIL2 or SIL3) would protect downstream piping system from overpressure such that no need to design downstream piping system as per rating corresponding to 300 barg and also no need to put a PSV with 300 barg set pressure for downstream protection. Then appears there is no need to put additional ESD on the 300/100 border.}

Edited by fallah, 17 February 2013 - 02:52 AM.

[ezie]

Dear Fallah, thank you for your answers.

 

As per my calculations when increasing the closing time of ESD valves even to base value (1 inch of DN = 1 second) HIPPS valves do not close.

 

In this case, is there necessity to install ESD valve to separate pipelines with DP=300 and DP=100 bar when ESD activated?

 

It's understood that pressure in 100 bar pipelines does not exceed set pressure of HIPPS and of course their design pressure so I'm asking is there industrial practices which require to install such valve in spite of calculations.

 

Sorry for my importunity this issue is new to me.

[fallah]

ezie,

 

As long as the HIPPS valves would be opened the 100 barg pipelines isn't subject to the pressure higher than its design pressure, provided that the set pressure of the HIPPS to be a little bit lower than 100 barg. Then no need the HIPPS will be closed at the same time the ESDV's getting started to be closed.

[ezie]

Then no need the HIPPS will be closed at the same time the ESDV's getting started to be closed.

 

Yes, HIPPS valves are open and equipment both on 300 and 100 bar are within single area.

 

In this case, is there need in additional ESD valve as shown red on PFD (see attachment) to be closed by ESD signal?

 

I understand that HIPPS valve will be closed in case of the pressure increase but maybe there is need in mechanical segregation during emergency situation, not expecting HIPPS closing.

Attached Files

•  PFD Scheme_rev1_18.02.pdf   4.1KB   23 downloads

[fallah]

ezie,

 

If there would be any need to mechanical segregation during a special emergency situation not to be met/accompanied by HIPPS closing, then you might put those ESDV there...