What's a critical valve

[anymous]

Hi all,

I'm a newcomer here. I work in a bio-ethanol plant. The valves in following services will be considered critical (in the opinion of our Contractor):
1) Safety and relief valves.
2) Control valves in the severe corrosive/erosive service if specified by Licensor / Owner.
3) Valves for which Licensor has required specific performance testing like helium testing etc.
4) ESD valves in inventory isolation service
5) Valves with gearbox or actuator on extended bonnet
6) Main isolation valves for HHP Boilers in HHP steam service. The valves in vent, drain, instrument isolation and other small diameter valves in HHP steam service are excluded from the critical valves list.
7) Two slide valves in Regenerator Flue gas service.

I don't know it's enough or not. Could you give me some comments on this list if any ?

 

[anymous]

More details:
"Criteria’s for the identification of the critical valves have to take into account the following general considerations -
4.1.1 Valves of “Large” quarter turn type (For plug valve>10”, for ball valve>24”and for butterfly valve>60’)
4.1.2 Valves that are in service requiring specific performance testing like Helium testing etc.
4.1.3 Valves which have critical functions (eg. frequent operational isolation duties, or emergency shutdown isolation, or venting duties).
4.1.4 Valves which have gear box or motor actuator mounted on extended bonnet. (Refer Instrument summary for Instrument valves)
4.1.5 Valves which are otherwise novel or in extreme or unusual applications.
4.1.6 All relief valves and safety valves (Refer Instrument summary for Instrument valves).
4.1.7 All high pressure valves (1500# and above)."

 

[gerhardl]

A question for anonymus: could you please inform about the source for your information?

Any other sources or cross references anyone?

 

[JLSeagull]

What is the significance of "critical" valve. Do these require QA testing?

I sometimes see a client specification that mentions critical instruments, critical valves etc. I rarely see a definition. Those valves listed with the 4.1.-series appear to be someones definition. I doubt that these are from an industry standard. If this is your contractor you could make them comply with the implication. Perhaps this list is made by the QA department to justify boondoggle trips. If this is from your client make sure that you comply.

 

[saplanti]

I guess the CRITICAL is indicating that those are going to take a long time to obtain, because you can not find them as a shelf material bacause of the material and additional test requirements.

Regards,

Ibrahim Demir

 

[itascot]

In my experience the following types are definitely CRITICAL, their very definition explains why.
ESDV = Emergency Shut Down Valve.
EBDV = Emergency Blow Down Valves.
SRV = Safety Relief Valves.
The use of the word CRITICAL in specifications used to be easily understood/interpreted, as it was directly linked to conditions of: product ,service, performance, hazard.
Below is my interpretation on described CRITICAL issue.
4.1.1 This due to long delivery/high cost to replace.
4.1.2 Helium leak testing may have been special some years ago, but is now quite common due to fugitive emmissions being an important issue, seat testing with Helium at ambient temperature just means they want a tight seal.
4.1.3 Speaks for itself.
4.1.4 Gearboxes (manually operated) I dont get the CRITICAL issue, unless they have a dedicated guy at every manually operated valve "as a precaution", manually operated valves are specidfied when few & far between oparations are required.
4.1.5 Down to long lead times in delivery.
4.1.6 Speaks for itself.
4.1.7 High pressure = high possible risk.

The differences are;
One department is only conterned about functionality, safety of personnel & Plant, the other is concerned about the time-loss in production should they have to shut down operations due to unavailability of a particular valve.