Why the Shutdown Period Is High-Risk for Instrumentation
The Christmas and New Year holiday period creates conditions that are genuinely harder on process instrumentation than normal operation. Staffing is reduced, management attention is elsewhere, and many facilities run with skeleton crews who are monitoring multiple systems simultaneously. Some processes shut down completely; others continue at reduced throughput. In cold climates, temperatures drop while heating systems are turned down or off in unoccupied buildings, putting exposed instrument connections and impulse lines at risk of freezing.
The result is a predictable pattern: instrumentation problems that were developing slowly during the year, a calibration drift, a relay beginning to stick, a small impulse line leak, reach the point of failure during the holiday period, when the consequences are harder to manage. Emergency callouts over Christmas and New Year carry premium rates and slow response times from suppliers. Parts that could have been ordered during normal business hours require emergency delivery at significantly higher cost.
A focused pre-shutdown check on critical instrumentation takes a few hours and protects against a problem that could consume days of holiday management time and significant unplanned expenditure.
Pre-Shutdown Level Transmitter Checks
Level transmitters controlling pump start/stop, fill valves, or high-level alarms on critical tanks are worth walking before the plant quietens down. The check does not require a full calibration — it requires a comparison of the instrument reading against an independent reference:
Compare against sight glass. Where a sight glass is fitted, compare the transmitter reading against the sight glass level. A discrepancy larger than the instrument’s stated accuracy (typically 0.1–0.5% of span for a quality pressure-based level transmitter) warrants investigation before shutdown. Small discrepancies that have grown since the last check suggest calibration drift.
Review SCADA trend history. Pull up the 30-day trend for each critical level measurement. An instrument drifting slowly will show a gradually changing zero or span in the trend data, often visible as a slow, consistent deviation from historical patterns. A sudden step change suggests a partial impulse line blockage. Either of these patterns visible in the trend data is a reason to investigate before the holidays, not after.
Check for unusual noise in the signal. Excessive noise or spikes in a level signal that is normally steady can indicate a failing connection, a partial impulse line blockage, or the beginning of an electronics fault. These are early-warning signs that are easy to dismiss during normal operations but are worth addressing before the shutdown.
Pre-Shutdown Pressure Transmitter Checks
For pressure transmitters on critical services, boiler drum pressure, pipeline pressure, compressor discharge, the pre-shutdown checks follow the same principles:
Verify readings against independent gauges. Every well-instrumented plant has pressure gauges at key points alongside the transmitters. Comparing the transmitter reading against the local gauge (which is independently calibrated) takes seconds and immediately reveals any significant discrepancy.
Inspect impulse lines for condensation, ice risk, or small leaks. Walk the impulse lines from the process tap to the transmitter housing. Look for signs of moisture, corrosion around fittings, white mineral deposits that indicate a slow weep. In facilities where temperatures will drop significantly during the shutdown, consider whether any exposed impulse line runs could freeze. Heat trace that is turned off or failed is a common cause of frozen pressure sensing lines in cold weather.
Check manifold valves for correct position. The instrument manifold (the valve assembly between the process tap and the transmitter) should be in its correct operating position, equalising valve closed for a differential pressure transmitter, isolation valves open. Valves left in incorrect positions during process interruptions are a cause of post-restart measurement failures that are easily overlooked.
Winterisation, Protecting Instruments in Cold Weather
Frozen impulse lines are one of the most common causes of pressure transmitter failures in cold climates during the winter shutdown period. Condensate or process fluid trapped in a nearly horizontal impulse line section freezes, expanding and blocking the line. The transmitter reads the pressure that was present when the line froze, which may have been the normal operating pressure hours or days earlier, not the current process pressure.
Practical winterisation steps before the holiday shutdown:
Verify heat trace continuity. Thermostatically controlled heat trace on impulse lines is only effective if the heat trace circuit is intact and the thermostat is set correctly. Walking heat-traced instrument runs before shutdown; checking for mechanical damage to the trace cable, verifying thermostat settings, and confirming that the trace is energised when ambient temperature demands it; takes very little time and prevents a common failure mode.
Inspect insulation for gaps and moisture damage. Insulation around impulse lines and instrument housings that has been damaged by maintenance activity, rodent damage, or moisture ingress does not provide its rated thermal protection. Gaps in insulation at connection points and instrument heads are where freezing initiates. These are quick to identify and quick to rectify with insulation tape or replacement insulation jackets.
Consider drain-down for non-critical lines. Impulse lines on non-critical instruments that can be taken out of service during shutdown can be drained and left under nitrogen blanket to prevent freeze damage. This is a common approach for seasonal facilities or lines that will not be required until production restarts.
Scheduling January Calibrations
The post-Christmas period; January, when production often ramps up slowly; is an ideal time to schedule the annual calibration cycle for instruments that ran all year. Scheduling calibrations in advance, before the holiday break, ensures that calibration equipment is booked, technicians are available, and the work can proceed without competing with production pressure in the February–March ramp-up.
Instruments that showed any drift or unusual behaviour in the pre-shutdown check should be prioritised for early January calibration. Instruments that passed the pre-shutdown check and have a clean history can be scheduled later in the calibration cycle. This risk-based prioritisation is more efficient than a fixed rotation that treats all instruments identically regardless of their recent performance history.
Remote Monitoring During the Shutdown
For facilities that operate with reduced staffing during the holiday period, remote monitoring of critical measurement points significantly reduces the risk that an instrumentation problem develops undetected. Modern process transmitters with HART or fieldbus communication can feed data to cloud-connected monitoring platforms that send alerts by SMS or email when readings cross defined thresholds or when diagnostic faults are detected.
The configuration of remote monitoring alerts before the shutdown; checking that alarm thresholds are correctly set, that notification lists include the right people who are available during the break, and that the telemetry connection is working; is straightforward and takes an hour or two. The alternative is a skeleton crew checking an HMI screen intermittently and hoping that nothing critical develops between checks.
Frequently Asked Questions
What if I find a drifting instrument the day before the shutdown? If the drift is small, stable over recent trend history, and the instrument is on a non-critical service, document it, flag it for early January calibration, and leave it running. If the drifting instrument is on a critical safety service, a level high-high, or a measurement that directly controls a hazardous process, address it before the plant goes quiet. Running through a holiday period with a known fault on a safety-critical instrument is not an acceptable risk, regardless of how inconvenient the timing is.
We don’t have remote monitoring set up, what’s the minimum manual check frequency for skeleton crew? For critical continuous processes left running, regular manual rounds covering key instruments; frequency determined by the site’s risk assessment and the consequence of undetected failure; are the baseline. For processes that are safely shut down and fully isolated, once per shift is typically sufficient. The emphasis should be on instruments that control or protect systems left in a live state; utility systems, refrigeration plant, standby fire protection; rather than on process instruments that are completely isolated and carrying no process pressure or level.
Should instruments be recalibrated immediately after startup, or is a comparison check enough? A comparison check against an independent reference at startup; sight glass, local pressure gauge, or a known test input; is usually sufficient if the instrument passed the pre-shutdown check and nothing unusual occurred during the shutdown. Full recalibration is warranted if the instrument was exposed to abnormal conditions during the break: a confirmed freeze event, an overpressure incident, physical impact during maintenance, or a comparison check at startup that shows a discrepancy larger than the instrument’s stated accuracy specification.
The Bottom Line
The Christmas shutdown checklist for instrumentation is not complicated. It is a matter of taking a few hours before the break to walk critical instruments, compare readings against independent references, check winterisation, and confirm that any remote monitoring alerts are correctly configured. The instruments ran all year; the shutdown is the right time to acknowledge whether any of them need attention before they create a problem in the new year.
A quiet January restart is not an accident. It is the result of a thoughtful pre-shutdown check in December.