Emergency shutdown time delay
Emergency shutdown time delay
(OP)
Hello everybody,
One of my coworkers brought this question to me. Based on what should we set the time delay for rotating equipment emergency shutdown is there specific standards on the API, ISO or whatever ?
For example, some compressors are set to shutdown if the vibration exceeds the specified shutdown limit if it stays for 3 seconds. Other machines are set to trip if vibration continues for 5 seconds and so on.
Thank you,
One of my coworkers brought this question to me. Based on what should we set the time delay for rotating equipment emergency shutdown is there specific standards on the API, ISO or whatever ?
For example, some compressors are set to shutdown if the vibration exceeds the specified shutdown limit if it stays for 3 seconds. Other machines are set to trip if vibration continues for 5 seconds and so on.
Thank you,





RE: Emergency shutdown time delay
So I think using any time delay to try to avoid spurious trips is not a generally accepted approach. Some alternate strategies to the same end may include:
1 - voting logic which trips only if the signal is seen by 2/2 or 2/3 or 3/4 etc.
2 - Standard FMEA circuit review
3 - suitable selection of setpoints, including alert to operators to allow investigation prior to shutdown in many cases, as well as trip setpoint not so low that it trips during normal expected system transients.
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(2B)+(2B)' ?
RE: Emergency shutdown time delay
As already noted, use voting schemes where practical to reduce the spurious trip risk. But, for a real event such as a trip of the main lube oil pump, you may need to consider adding a delay to allow time for the auxiliary pump to come up to speed and avoid a unit shut down. This is especially true if the unit shut down involves some inherent great risk to personnel.
A delay can be used to allow a system to make it through a transient event that would not necessarily create a hazard greater than the hazard associated with the trip. It can give the control system time to regain control. Every situation must be analyzed individually.
Johnny Pellin
RE: Emergency shutdown time delay
Is there any logic where we can rely on such as machine speed or HP ? I think the time delay should be less for higher speed machines. But I don't have any clue for that.