⚠️ Disclaimer: These tasks are guidelines only. They do not include lockout/tagout (LOTO), energy isolation, or other safety requirements. Review and verify suitability for your specific equipment and application. Add all required safety procedures per your company's policies and regulatory requirements before use. You are responsible for the safe and appropriate execution of all maintenance activities.
A Coriolis flow meter has no moving parts. No bearings to grease, no impeller to inspect, no mechanical wear to track. That makes it easy to ignore — and easy to assume it's fine when it isn't.
What it does have is a flowtube vibrating at its natural frequency, two pickoff sensors measuring phase shift, and a transmitter converting that phase shift into a flow reading your process depends on. Buildup changes the tube mass. Erosion changes the tube wall. A bad zero shifts every reading downstream. None of those failures announce themselves. They just drift — quietly, consistently — until someone notices the batch weights are off or the custody transfer figures don't reconcile.
This checklist covers PM tasks for Coriolis flow meters used in industrial process measurement applications.
For a complete framework on building and sustaining a sensor PM program, see industrial sensor and instrumentation preventive maintenance.
How to Use This Checklist
Record findings with specifics, not checkmarks. "Transmitter housing clean and dry" tells you nothing in six months. "Condensation present on terminal block, corrosion on T1 and T2 terminals, cleaned and treated with dielectric grease" gives you a trend.
The zero offset is the single most important data point in Coriolis PM. A meter reading 0.02 kg/min at confirmed no-flow isn't alarming the first time. It's alarming when it was 0.005 six months ago and 0.012 three months ago. You can't see that trend without the prior numbers.
Record as-found conditions before you change anything. A drive gain reading of 18% isn't useful without knowing it was 9% last year.
Field Checklist — Critical Tasks
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect the flow meter body, process connections, and transmitter housing for leaks, corrosion, physical damage, or coating deterioration. | Every PM | MEC |
| Inspect all process connection flanges, fittings, and gaskets for signs of leakage, seepage, or staining. Tighten or report as needed. | Monthly | MEC |
| Inspect conduit entries, cable glands, and junction box cover seals on the transmitter for integrity. Verify covers are fully secured. | Monthly | ELE |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Check transmitter display (if present) for active fault codes, alarms, or diagnostic messages. Record any codes and clear only after root cause is identified. | Every PM | ELE |
| Verify the measured flow rate and totalizer readings are consistent with expected process conditions. Flag unexplained deviations for investigation. | Every PM | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect meter mounting hardware — supports, clamps, or flanged bolting — for looseness, corrosion, or vibration-induced wear. Retorque as needed. | Semi-Annually | MEC |
Electrical Inspection
| Task | Freq | Type |
|---|---|---|
| Check and clean the transmitter housing vents or drain plugs if present. Verify the housing is free of moisture ingress. | Quarterly | ELE |
| Verify 4–20 mA output signal or digital output (HART/Modbus) matches the control system reading. Investigate any discrepancy greater than 1% of span. | Semi-Annually | ELE |
| Inspect all wiring inside the transmitter junction box for loose terminals, corrosion, or damaged insulation. Retorque terminal screws to spec. | Annually | ELE |
| Perform a zero-point verification with the meter in a no-flow condition (valves closed and pipe full). Record the zero offset value and compare to prior readings. Adjust if outside manufacturer tolerance. | Annually | ELE |
Reference Checklist — Full Task Library
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect the flow meter body, process connections, and transmitter housing for leaks, corrosion, coating deterioration, or physical damage. Compare findings to prior PM records. | Every PM | MEC |
| Inspect all process connection flanges, fittings, and gaskets for signs of leakage, seepage, or staining. Note process fluid type and verify gasket material compatibility. | Monthly | MEC |
| Inspect conduit entries, cable glands, and junction box cover seals for integrity and proper torque. Verify transmitter enclosure IP/NEMA rating is maintained — no cracked seals, missing plugs, or improper entries. | Monthly | ELE |
| Inspect flow tube and flowtube case externally for signs of erosion, corrosion, coating failure, or mechanical damage, particularly at the inlet/outlet bends. Flag any deformation or thinning for engineering review. | Semi-Annually | MEC |
| Inspect process isolation valves (if installed) for leakage, proper operation, and packing integrity. Confirm bypass line (if present) is closed and locked during normal operation. | Annually | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Review transmitter display and/or control system for active fault codes, alarms, or diagnostic messages. Document all codes and investigate root cause before clearing. | Every PM | ELE |
| Verify measured flow rate, density, temperature, and totalizer readings are consistent with expected process conditions. Investigate unexplained deviations exceeding ±1% of span. | Every PM | ELE |
Electrical Inspection
| Task | Freq | Type |
|---|---|---|
| Check transmitter housing vents and drain plugs (if present) for blockage or moisture. Inspect interior of transmitter junction box for condensation, corrosion, or insect intrusion. | Monthly | ELE |
| Verify 4–20 mA output signal calibration by comparing transmitter loop output to actual flow conditions at a known stable point. Check against control system and any flow totalization records. Investigate discrepancies greater than 0.5% of span. | Quarterly | ELE |
| Check HART or digital communication link (if applicable) — confirm device is online, tags match, and configuration parameters are unchanged. Document firmware version and any unexpected parameter changes. | Quarterly | ELE |
| Inspect and retorque all wiring terminations inside the transmitter junction box. Check for loose terminals, heat discoloration, corroded or brittle insulation, and proper wire management. Apply dielectric grease to susceptible connections in corrosive environments. | Semi-Annually | ELE |
| Perform a zero-point verification with the meter in a confirmed no-flow condition (block valves closed, line full of process fluid). Record the displayed zero offset. If offset exceeds manufacturer's threshold, perform a zero adjustment and document pre- and post-values. | Semi-Annually | ELE |
| Review transmitter configuration parameters — flow units, density setpoint, damping, low-flow cutoff, and alarm setpoints — against the current site configuration document. Correct any drift or unauthorized changes. | Semi-Annually | ELE |
| Verify meter grounding continuity. Measure resistance between transmitter ground terminal and plant earth ground — should be less than 1 Ω. Poor grounding can cause signal noise and measurement error. | Annually | ELE |
| Perform a loop calibration check — compare transmitter output at 0%, 50%, and 100% of span against a known reference or portable standard. Document calibration as-found and as-left values. | Annually | ELE |
| Review transmitter diagnostic data — drive gain, pickoff signal amplitude, tube frequency, and density offset — against baseline values. Significant shifts in drive gain may indicate buildup, erosion, or tube damage. | Annually | ELE |
| Perform a full configuration backup of transmitter parameters using HART communicator or manufacturer software. Store backup on file with the equipment record. | Annually | ELE |
| Review and trend all recorded data from this PM period — zero offsets, diagnostic values, calibration results, and defect history. Identify deteriorating trends and adjust PM scope or frequency if warranted. | Annually | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect meter mounting structure — supports, clamps, or flange bolting — for looseness, corrosion, or vibration damage. Verify pipe stress or external vibration is not being transmitted to the meter body. Retorque flange bolts to spec in cross pattern. | Quarterly | MEC |
Failure Modes This Checklist Targets
Flowtube Buildup Deposits on the inside of the flowtube add mass, shift the tube's resonant frequency, and inflate drive gain — the meter works harder to maintain oscillation while the reading drifts. Drive gain trending catches this before it becomes a calibration problem.
Zero Offset Drift A Coriolis meter that can't read true zero at no-flow can't read true flow at any rate. Zero drift accumulates from thermal effects, mechanical stress on the flowtube, and process pressure changes. Periodic zero verification catches it; documented records show the trend.
Process Connection Leakage Flanged joints, threaded fittings, and compression connections all degrade over time — especially under thermal cycling or vibration. Leakage starts as staining. It ends as a process incident.
Transmitter Electrical Degradation Moisture ingress, loose terminals, and corroded connections degrade the low-level pickoff signals that carry the phase shift data. A bad connection doesn't just introduce noise — it can cause the transmitter to drop into fault or report a stable reading that no longer reflects reality.
Signal Output Error A 4–20 mA loop that reads 12.3 mA at the transmitter and 12.1 mA at the DCS has a problem somewhere in the wiring or I/O card. At 0.5% of span, that's an error most process applications can't afford — and most PM programs don't check for.
External Vibration and Mechanical Stress Pipe strain from thermal expansion, improper support, or nearby rotating equipment transmits force into the flowtube. A Coriolis meter measures the tube's vibration relative to itself. Introduce external vibration and the measurement degrades. Mounting inspection isn't busywork — it's protecting the physics the meter depends on.