Preventative Maintenance and Self Diagnostics
Instrumentation operating within hazardous areas in petrochemical refineries are subject to challenging conditions.
When instrumentation falls out of calibration and fails to provide basic process control, unplanned shutdowns often occur. Similarly when the instrumented safety function fails to provide protection, injuries and deaths can unfortunately occur.
Preventive maintenance (PM) is essential to the safe and proper operation of refineries. Transmitters, switches and valves are placed on a periodic PM schedule. This is to inspect, calibrate, rebuild and if necessary replace faulty equipment. This PM cycle may occur during a planned outage or turnaround where the plant is shut down.
Turnarounds can be very costly when considering the time involved and the loss of production that occurs during a typical PM cycle. We should also consider failures that can occur immediately following a turnaround, leaving instrument faults undetected until the next PM cycle is performed.
So how do plants deal with the need to perform regular PM while keeping the plant running?
When there is a mandate that the plant continue to operate, PM cycles may be lengthened and occasionally missed, which creates a dangerous work environment for everyone.
Is there a better way?
Self-diagnostics provide the ability for smart instrumentation to monitor its own health in real time. This makes certain that the control, alarm and shutdown functions will be performed when needed. Self-diagnostics add an additional layer of protection against undetected failures that might occur.
UE manufactures a smart self-diagnostic switch called the One Series, which includes a feature called I Am Working (IAW®). IAW® will detect and report diagnostic faults on its integral digital display. Simultaneously, the programmable switch will trip to its fail-safe position (open or closed), and a separate diagnostic (IAW®) output will fail open. This is a remote indication that a fault has occurred.
Some limitations exist with self-diagnostics. For example, self-diagnostics have no way to determine if the sensor remains calibrated or if the diaphragm has suffered damage. Another limitation involves the sensitivity of the diagnostics. This makes it necessary to consider how to interpret detected faults and whether the plant should initiate a shutdown or regard the fault as a warning. When safety is the main concern, an automatic emergency shutdown is likely to prevent accidents.
With all this said, we can conclude that instrumentation must undergo regular PM cycles to check basic operation and calibration, but will benefit from the intelligence provided by smart self-diagnostics.
About the Author: Rick Frauton, Inside Sales Manager
Rick Frauton has been with UE for over 20 years. He is the Inside Sales Manager for United Electric Controls and provides support to UE’s channel partners. Previously, he was product manager for the One Series Smart Electronic Switch.