⚠️ 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.
Thermal fluid systems run hot. Not warm. Not elevated. Hot — 300°F to 600°F in most industrial applications. When a thermal fluid circulation pump fails, it doesn't just stop moving heat. It stops your process. And if it fails at the seal or at a flange, it doesn't fail quietly.
This checklist covers the PM tasks that keep thermal fluid circulation pumps running — and keep the fluid inside the pipe where it belongs.
Full program context for pumps in thermal fluid service: Centrifugal Pump Preventive Maintenance: The Checks Most Programs Get Wrong
How to Use This Checklist
Record every finding with specificity. "Seal OK" tells you nothing six months from now. "Seal dry, no staining, no discoloration at 450°F operating temp" tells you everything. The difference between a checkbox and a data point is the difference between a PM and a history.
Trend your readings. Suction and discharge pressures, motor current, bearing temperatures, expansion tank level — these numbers only matter when you have something to compare them to. The first time you record a reading, you're establishing a baseline. Every PM after that, you're watching for drift.
A bad finding sounds like this: "Bearing housing at 210°F. Prior reading: 160°F. Same operating conditions. Increase of 50°F in one PM interval. Flagged for follow-up."
A checkbox answer sounds like this: "Bearings OK."
Field Checklist — Critical Tasks
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect pump and piping for thermal fluid leaks at seals, flanges, fittings, and connections. Mark any leak points for follow-up. | Every PM | MEC |
| Inspect mechanical seal area for leakage, weeping, or discoloration indicating thermal fluid contact. Note condition. | Every PM | MEC |
| Inspect expansion tank fluid level and condition. Low level may indicate a system leak or fluid degradation. | Monthly | MEC |
| Inspect all thermal fluid piping, supports, and insulation near the pump for damage, deterioration, or missing sections. | Quarterly | MEC |
| Verify all safety relief valves and high-temperature shutdowns are in place and have not been bypassed or tampered with. | Quarterly | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Check pump suction and discharge pressure gauges. Record readings and compare to baseline operating range. Flag deviations. | Every PM | MEC |
| Verify pump flow rate or system differential pressure is within normal operating parameters. Investigate unexplained drops. | Every PM | MEC |
| Check pump motor operating current with a clamp meter. Compare to nameplate FLA and prior readings. | Every PM | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Listen and feel for abnormal bearing noise, vibration, or roughness while pump is running. Flag any change from baseline. | Every PM | MEC |
| Inspect pump coupling and guard — check for wear, cracking, or looseness. Verify guard is secure and undamaged. | Monthly | MEC |
Lubrication
| Task | Freq | Type |
|---|---|---|
| Lubricate pump and motor bearings per manufacturer type, quantity, and interval. Do not over-grease. | Semi-Annually | MEC |
Reference Checklist — Full Task Library
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect pump and all associated piping, flanges, and fittings for thermal fluid leaks. Document any leak location, severity, and trend from prior PM. Even minor weeping indicates seal degradation. | Every PM | MEC |
| Inspect mechanical seal for leakage, thermal fluid staining, or carbonized deposits around the seal faces. Evaluate seal condition trend and plan replacement proactively rather than reactively. | Every PM | MEC |
| Inspect expansion tank fluid level and fluid condition. Low level may indicate a system leak. Dark, sludgy, or acidic-smelling fluid suggests thermal degradation — collect a sample for analysis if suspected. | Monthly | MEC |
| Inspect all pump-area piping, supports, expansion joints, and insulation for damage, deterioration, or missing sections. Note any insulation gaps that could cause hot spots or personnel burn hazards. | Monthly | MEC |
| Inspect pump baseplate and motor mounting for looseness, cracking, corrosion, or grouting deterioration. Re-torque mounting bolts to spec. | Annually | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Record suction and discharge pressure gauge readings. Calculate differential pressure and compare to baseline curve. An increasing differential may indicate impeller wear or fouling; a decreasing differential may indicate internal recirculation or bypass. | Every PM | MEC |
| Verify system flow rate is within design range. If a flow meter is installed, record reading. Compare to prior values and flag any unexplained reduction greater than 5–10% of baseline. | Every PM | MEC |
| Measure and record motor operating current on all applicable leads. Compare to nameplate FLA and prior readings. Investigate any upward trend or readings exceeding 105% FLA. | Every PM | ELE |
| Check pump and motor bearing housings for elevated temperature using a contact thermometer or IR gun. Record readings. Bearing housing temp should not exceed ambient + 40°C or manufacturer limit. | Every PM | MEC |
| Verify all isolation valves are in the correct position and operate freely. Check valve packing or seals for leakage. Operate any infrequently used valves through their full range to prevent seizing. | Quarterly | MEC |
| Perform a pump performance test: record suction pressure, discharge pressure, flow rate (if metered), and motor current at normal operating conditions. Compare to pump curve and prior data. Flag degradation. | Semi-Annually | MEC |
| Verify all safety interlocks, high-temperature switches, flow switches, and low-level shutdowns are functional. Test by simulation or manual actuation where safe to do so. Document test results. | Semi-Annually | ELE |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Listen for abnormal bearing noise (rumble, squeal, or grinding) during operation. Assess vibration level by hand or with a vibration pen. Document and compare to prior PMs. | Every PM | MEC |
| Inspect pump coupling — check flexible element for cracks, chunking, or deformation. Verify hub set screws and keyways are tight. Assess coupling alignment if any vibration or wear is noted. | Monthly | MEC |
| Inspect and re-torque all pump casing bolts, flange fasteners, and pipe connection hardware. Check for corrosion or heat-damaged hardware — replace as needed. | Semi-Annually | MEC |
Lubrication
| Task | Freq | Type |
|---|---|---|
| Lubricate pump and motor bearings per manufacturer specifications — grease type, quantity, method, and interval. Do not over-grease. For purge-type housings, run briefly after greasing. Record lubricant type and quantity. | Semi-Annually | MEC |
Electrical Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect pump motor electrical connections in the terminal box — check for looseness, corrosion, heat discoloration, or damaged insulation. Re-torque to spec and clean as needed. | Annually | ELE |
| Perform insulation resistance (megger) test on pump motor windings to ground. Record results in MΩ at 500V or 1000V DC per motor rating. Values below 1 MΩ require immediate follow-up. Trend data over time. | Annually | ELE |
Fluid Analysis
| Task | Freq | Type |
|---|---|---|
| Collect a thermal fluid sample for laboratory analysis (acid number, viscosity, moisture content, suspended solids). Fluid degradation accelerates wear and can cause deposits and seal failures. Compare to prior results. | Annually | MEC |
| Review all PM data recorded this period — pressures, temperatures, currents, fluid analysis, and defect history. Identify degrading trends. Adjust PM frequency or scope if warranted and document recommendations. | Annually | MEC |
Failure Modes This Checklist Targets
Mechanical Seal Failure High operating temperatures accelerate seal face wear and cause thermal fluid to carbonize on the seal faces — a slow degradation that starts as a minor weep and ends as a leak you can't ignore.
Bearing Failure from Heat and Contamination Thermal fluid systems create a hostile environment for bearings. Heat soak from the pump casing, thermal fluid contamination from seal weeping, and improper lubrication intervals are the three fastest paths to bearing failure on this equipment.
Thermal Fluid Degradation Fluid that has broken down chemically becomes acidic and corrosive. It deposits varnish and sludge on pump internals and system components. Most programs wait until there's a visible problem. By then, the damage is already distributed throughout the system.
Impeller Wear and Flow Degradation Gradual erosion from suspended solids or cavitation events reduces impeller efficiency over time. Flow and pressure readings drop slowly enough that nobody notices — until something downstream stops getting heat.
Coupling and Alignment Failure Thermal growth in high-temperature systems changes shaft alignment between cold and operating conditions. Couplings that look fine at ambient can be running misaligned at operating temperature. The coupling absorbs it — until it doesn't.
Safety Interlock Bypass or Failure High-temperature shutdowns, flow switches, and low-level protection exist specifically because thermal fluid failures can be severe. These devices get bypassed "temporarily" and then forgotten. Verifying them on a scheduled interval is the only reliable check.
