robsalv
Mechanical
- Aug 8, 2002
- 311
Dear Eng-tips members, could you please broadly describe your company's relief valve maintenance philosophy.
My work place was using an empirical approach that took performance and reported condition into account when setting overhaul intervals... but we're now moving to a SIL based PRV management process that doesn't take into account any condition data gleaned from the overhaul. This concerns me and the SIL process allows large interval increases (up to the predetermined maximum) which appear excessive. No consideration is given to condition information if the PRV passes the as received bench test.
In a nutshell, we're using the equation PFD=0.5xLambdaxT.
The allocated lambda (failure rate) is either based on actual failure data (if determinable) or taken from industry tables that relate to an assessment of service condition - i.e., clean, dirty, fouling etc., in conjunction with the type of valve e.g. pilot, PV vent, conventional PRV etc.
So clean service conventionals have a low lambda, i.e., low failure rate, where as clean service pilot ops have a high lamda, i.e., a known higer failure rate.
In addition, at our plant every PRV is treated as a safety critical device, i.e., it is seen as a last line of defence before an imminent uncontrolled Loss of containment. This means that every PRV has the same high maintenance priority when they're due for overhaul and work is being planned in amongst all the other priorities that struggle for resources. This leaves maintenance with a incentive to increase the time between overhauls for PRV's...
That pretty much covers our plant's philosophy on managing maintenance for PRV's.
How does your work place manage PRV's?
- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."
My work place was using an empirical approach that took performance and reported condition into account when setting overhaul intervals... but we're now moving to a SIL based PRV management process that doesn't take into account any condition data gleaned from the overhaul. This concerns me and the SIL process allows large interval increases (up to the predetermined maximum) which appear excessive. No consideration is given to condition information if the PRV passes the as received bench test.
In a nutshell, we're using the equation PFD=0.5xLambdaxT.
The allocated lambda (failure rate) is either based on actual failure data (if determinable) or taken from industry tables that relate to an assessment of service condition - i.e., clean, dirty, fouling etc., in conjunction with the type of valve e.g. pilot, PV vent, conventional PRV etc.
So clean service conventionals have a low lambda, i.e., low failure rate, where as clean service pilot ops have a high lamda, i.e., a known higer failure rate.
In addition, at our plant every PRV is treated as a safety critical device, i.e., it is seen as a last line of defence before an imminent uncontrolled Loss of containment. This means that every PRV has the same high maintenance priority when they're due for overhaul and work is being planned in amongst all the other priorities that struggle for resources. This leaves maintenance with a incentive to increase the time between overhauls for PRV's...
That pretty much covers our plant's philosophy on managing maintenance for PRV's.
How does your work place manage PRV's?
- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."
