It was a blustery night shift, and a wind gust blew the lid off an instrument enclosure atop the largest reactor. Fortunately, no one was in the vicinity when this dual-instrument enclosure lid comprising more than two-thirds of the pre-insulated enclosure’s total mass smashed into the ground. It was also fortunate the instruments inside were not especially sensitive to the elements.
When Stosh investigated, he found another issue. Birds were nesting in the instrument box. These were not a particularly rare species or songbirds prized for their charming melodies. Some derisively referred to them as “rats with wings.” The young birds or unhatched eggs Stosh found might have been given a quick shortcut to the pavement. In other such cases, creatures inhabiting what might be an inviting enclosure perished thanks to the nitrogen or other inert gases that leaked inside. In any event, Stosh procured a new enclosure, hopefully one that didn’t attract more avian invaders.
Instrument enclosures are commonly used at higher latitudes. Some sites employ enclosures or even a “sunshade” simply to distinguish instruments from other infrastructure, with the aim of discouraging their use as a foothold or other abuse. Enclosures can become a source of injury, such as when the site forgets to shut off seasonal steam tracing or an electric heater is stuck in the “on” position. Fuses buried in some enclosure heaters can trip unexpectedly, freezing the instruments. In Stosh’s case, random creatures make a home in them.
This seemingly simple repair faced other challenges, as Stosh took stock of the other devices on the same fieldbus segment with the two transmitters he sought to replace. An earlier project used what had been a spur to one of the bird-nested devices, and repurposed it as an extension of the trunk, relocating the terminator. It enabled the project to interconnect a half-dozen or more instruments in the remote location (10 stories up and on top of a reactor). It meant Stosh had to worry what his “live” maintenance would have on these other devices. Since the segment also provided power for the devices, fumbling with the wiring or a momentary short circuit could send some valves to their “fail” positions.
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When the job was explained to the board operator, Stosh said, “I’m 99% sure you won’t see anything.” I compare these conversations with operations to the captain of a commercial flight announcing a pause in the in-flight entertainment, “Folks, please stand by while we reboot the plane’s computers.” A passenger couldn’t be blamed for asking, “Can’t this wait until we’re on the ground?” With process plants and refineries, for which startups and shutdowns are complex and hopefully infrequent, possibly running for years between them, onstream maintenance should aim to be totally mistake-free.
Today’s visionaries and early adopters can’t be blamed for following the creed of “design for the future,” challenging cultures so conservative that no one was ever fired for doing what we always did. Novel network solutions for instrumentation and control are compelling to control professionals, but we’re not the stars of the show. Whatever deliverables achieved by a novel bus or network could be wiped out by the actions of “future Stosh.” Investments pay off by smoothing production of useful chemicals and fuels at promised rates, unhindered by instrumentation distractions.
When future Stosh finds invaders in an instrument enclosure, removal and replacement of field devices should be easier, as proposed topologies are largely point-to-point. His network management counterparts should be more mindful of their impact. Early adopters should ensure all the personnel who remain at the plant are trained in activities that pose a threat to operations.
