Standardized Protection Measures for Split Case Centrifugal Pumps During Extended Shutdowns

When a split case centrifugal pump remains out of service for an extended period due to equipment idling, suspended operating conditions, or seasonal shutdowns, failure to implement proper shutdown protection measures can easily lead to internal corrosion, bearing seizure, seal deterioration, frozen or cracked piping, impeller scaling, and other problems. These issues can significantly shorten the service life of the equipment and may also cause excessive vibration, leakage, pump seizure, and other operational risks when the pump is restarted, substantially increasing maintenance costs and the risk of unplanned downtime.

Based on the structural characteristics of split case centrifugal pumps and standard industry maintenance practices, this article systematically explains standardized protection measures for extended shutdown periods. The objective is to maintain the equipment in good condition while it is out of service and ensure smooth and reliable recommissioning whenever required.

1. Pre-Shutdown Cleaning and Draining

Proper preparation before shutdown is the foundation of effective protection. It helps prevent corrosion, scaling, and freeze damage caused by residual process fluid.

1.1 Standard Shutdown Procedure

The correct shutdown sequence is:

Gradually close the discharge valve → disconnect the motor power supply and wait until the pump comes to a complete stop → close the pressure gauge and vacuum gauge isolating valves → close the suction valve → open the drain plug at the bottom of the pump casing to completely drain the pump.

Do not shut down the pump while it remains pressurized, as this may cause pressure surges or water hammer that can damage critical internal components.

1.2 Complete Draining and Flushing

After shutdown, all residual liquid must be completely drained from the pump and associated piping. Open the drain plug at the bottom of the pump casing and remove all accumulated water, contaminants, and process-fluid residues from the pump chamber, flow passages, and seal chamber.

If the pump has handled wastewater or acidic or alkaline corrosive liquids, thoroughly flush the internal surfaces of the pump casing, impeller, shaft, and other critical components with clean water. All residual contaminants must be removed to prevent corrosive substances from remaining on metal surfaces and causing long-term oxidation and corrosion.

1.3 Drying

After draining and cleaning, allow all components to dry thoroughly and ensure that no standing water or residual moisture remains inside the pump.

Where necessary, use compressed air to blow dry low points and other areas where moisture may collect. Accessible internal surfaces may also be wiped with a clean, dry cloth and then allowed to air-dry in a well-ventilated environment.

2. Rust and Corrosion Protection for Critical Components

During extended shutdown periods, metal components of a split case centrifugal pump can corrode much more rapidly in humid environments than during normal operation.

During operation, the movement of the pumped fluid and the heat generated by bearing operation help keep component surfaces relatively dry, while lubricating oil films continuously protect metal surfaces. After shutdown, these protective mechanisms are no longer present. Moisture in the air can condense on metal surfaces, significantly accelerating corrosion.

Therefore, critical precision components such as bearings, shafts, impellers, and mechanical seals require particular attention.

The following table summarizes the standardized rust and corrosion protection requirements for major components. Unless otherwise specified, these measures should be carried out once on the day the pump is taken out of service.

Protection Precautions

Rust preventive oil should uniformly cover the metal surface without excessive runoff or accumulation. Do not apply excessively thick layers, as hardened deposits may affect rotational accuracy.

Do not apply excessive grease, as it can attract contaminants and affect sealing surface performance and sealing accuracy.

After protection measures have been completed in humid environments, maintain adequate ventilation and drying conditions to prevent moisture condensation on the pump.

3. Freeze Protection and Insulation in Low-Temperature Environments

Low-temperature seasons are high-risk periods for freeze-related damage during shutdown. Freeze protection should be implemented using the following three-level strategy.

3.1 Complete Draining — Preferred Method

As described in Section 1, ensure that no water remains inside the pump casing, at low points in the piping, inside valve cavities, at drain connections, or in any other areas where liquid may collect.

Particular attention should be given to low points and dead legs, such as U-shaped piping sections and instrument pressure-sensing lines.

3.2 Filling Non-Drainable Areas with Antifreeze — Supplemental Measure

For areas that cannot be completely drained, such as seal chambers and instrument tubing, fill the remaining spaces with an industrial antifreeze compatible with the pump materials.

An ethylene glycol-based antifreeze may be used, with the concentration selected according to the lowest expected local ambient temperature. Formulations containing chloride ions must not be used.

The antifreeze volume should be sufficient to protect all internal metal surfaces within areas that cannot be completely drained.

3.3 Insulation and Heat Tracing — Auxiliary Measures

Wrap pump suction and discharge piping, valves, drain connections, and other freeze-prone areas with thermal insulation having a thickness of at least 50 mm, or use suitable removable insulation jackets.

For outdoor equipment or pumps installed in unheated pump rooms, provide an enclosed temporary thermal shelter.

For equipment operating under critical conditions, install self-regulating electric heat tracing to maintain the equipment surface temperature at approximately 5–10°C. A temperature controller and residual-current protection must be provided. Adequate clearance must also be maintained to ensure proper motor cooling and prevent overheating.

3.4 Environmental Monitoring

During the shutdown period, regularly monitor the temperature in the pump room.

When the ambient temperature is expected to remain within 5°C of the freezing point of the pumped liquid for an extended period—typically when the ambient temperature is 5°C or below—the above freeze protection measures should be fully implemented.

Even when the pump itself has been completely drained, piping insulation should still be maintained when the ambient temperature falls to 0°C or below.

Never leave equipment containing water idle throughout the winter. In cold and humid environments, if complete draining is not possible, the remaining liquid must be replaced or protected with suitable antifreeze, together with adequate insulation, to prevent the pump casing and piping from freezing and cracking.

4. Periodic Inspection and Maintenance During Shutdown

Equipment preservation does not mean simply leaving the pump unattended. Periodic maintenance is essential for preventing seizure, lubricant hardening, and localized corrosion.

The following inspection requirements are recommended:

Additional Requirements for Manual Shaft Rotation

Manually rotate the shaft by at least two complete revolutions (720°) every month.

The shaft position should be offset from the previous inspection position. A rotation offset of approximately 120°–180° is recommended for each inspection. This helps ensure that bearing raceways and sealing surfaces are evenly exposed to the protective lubricant and prevents the same position from remaining under load for extended periods, which could cause localized deformation.

Regularly inspect the pump room environment and maintain dry, well-ventilated, and clean conditions free from standing water and excessive dust. Prevent moisture-related deterioration, mold growth, and electrochemical corrosion.

At the same time, check the condition of protective covers, insulation, and rust preventive coatings. Any coating damage, loose covers, or damaged insulation should be repaired promptly as part of routine preventive maintenance.

5. Equipment Preservation and Identification Management

After all protection measures have been completed, provide overall dust protection for the equipment.

Use a waterproof and dustproof protective cover to completely enclose the pump and motor, protecting them from dust and moisture. Attach an out-of-service preservation tag indicating:

Shutdown date

List of protection measures completed

Date of the next scheduled inspection

Name of the responsible person

A corresponding equipment preservation record should also be maintained to ensure standardized management and full traceability of all inspections, repairs, and corrective actions.

6. Pre-Startup Inspection Before Returning the Pump to Service

Before the equipment is returned to service, complete the following checks and confirm that all requirements have been met before performing a trial run:

Step 1: Remove Preservation Measures

Remove all protective materials and preservation devices, including dust covers, suction and discharge opening covers, preservation tags, and other temporary shutdown protection items.

Step 2: Remove Protective Oils and Grease

Thoroughly remove rust preventive oil and grease applied to the pump shaft, bearings, seal areas, and other relevant components to prevent contamination of the pumped medium or adverse effects on sealing performance after startup.

Step 3: Inspect Component Condition

Check the mechanical seals, bearings, coupling, bolted connections, and other components for corrosion, deformation, looseness, or other damage.

Step 4: Verify Free Rotation by Manual Turning

With the pump unloaded, manually rotate the shaft through 2–3 complete revolutions and confirm that it rotates freely without binding or abnormal friction noise.

Step 5: Restore the Piping System

Confirm that the suction and discharge valves are in their correct operating positions, instrument isolating valves are open as required, and all drain plugs are securely tightened.

Step 6: Perform a Bump Test

For the initial startup, perform a bump test by briefly energizing and immediately de-energizing the motor. Confirm the correct motor rotation direction and verify that no abnormal vibration occurs before proceeding with continuous operation.

Conclusion

The key principles for protecting a split case centrifugal pump during an extended shutdown can be summarized as:

Drain and control moisture → prevent corrosion and freezing → perform periodic maintenance → preserve and manage the equipment systematically.

The corresponding measures are summarized below:

Strict implementation of these protection measures can effectively prevent common equipment failures during extended shutdown periods, maintain mechanical condition and operating accuracy, extend equipment service life, and ensure efficient, safe, and reliable operation after recommissioning. Proper shutdown protection also helps reduce maintenance costs and unnecessary equipment replacement.

Appendix: Quick Reference Table for Key Parameters