Definition, cycle and procedure of centrifugal pump overhaul

Centrifugal pump overhaul refers to a systematic maintenance process involving the complete disassembly of the pump and the comprehensive inspection, repair, replacement, and calibration of major components and auxiliary parts after long-term operation (usually reaching a specified cycle or experiencing a major malfunction). Its main objective is to thoroughly eliminate hidden dangers accumulated during long-term operation, restore the equipment's original performance parameters, extend its service life, and ensure long-term stable operation. It falls under the category of "comprehensive overhaul and in-depth repair," and is characterized by a long construction period, high cost, and high technical requirements. It must be performed by professional maintenance personnel and requires a considerable downtime (usually several days).

 

 

• Overhaul cycle

The overhaul cycle for centrifugal pumps is determined comprehensively based on operating conditions, media, and equipment type. The typical cycles are as follows, and should be dynamically adjusted based on minor repair records and equipment operating status:

 

1. Normal operating conditions (clean water, ambient temperature, low pressure, continuous operation): Overhaul cycle is 12-18 months, or 10,000-20,000 cumulative operating hours, whichever comes first. If the equipment operates stably and no major hidden dangers are found during minor repairs, it can be extended to 24 months, but the maximum period should not exceed 1/3 of the equipment's design service life.
2. Harsh operating conditions (corrosive, containing impurities, high temperature and high pressure, frequent start-stop): Overhaul cycle is shortened to 6-12 months, or 5,000-10,000 hours of cumulative operation, with a focus on checking the wear and corrosion of major components.
3. Special Scenarios (pumps used in critical production processes, high-value equipment, pumps without backup): The overhaul cycle can be adjusted earlier or later based on condition monitoring results (such as vibration spectrum analysis and non-destructive testing), but it must be ensured that major components are free from serious damage and significant safety hazards; if the cumulative operating time is less than 2,000 hours, the overhaul cycle can be appropriately extended depending on the specific circumstances.

 

Furthermore, when a centrifugal pump experiences a major malfunction (e.g., impeller breakage, pump shaft bending, pump casing cracks, severe and irreparable seal leakage), there is no need to wait for the prescribed cycle; the pump must be shut down immediately for overhaul.

 

• Specific steps for centrifugal pump overhaul

The overhaul work focuses on "comprehensive disassembly, comprehensive inspection, in-depth repair, and precise calibration," encompassing all aspects of the minor overhaul and adding the disassembly, inspection, repair, and replacement of major components. Specific work is carried out in stages to ensure overhaul quality:

 

Preparatory Work Before Overhaul

1. Shutdown and Safety Isolation: Stop the centrifugal pump, disconnect the motor power, close the inlet and outlet valves, effectively isolate the pump from the pipeline system, drain the medium inside the pump (especially corrosive, flammable, and explosive media), and implement safety protection measures (such as warning signs and on-site monitoring);
2. Tool and Spare Parts Preparation: Prepare disassembly tools (wrenches, pullers, jacks, non-destructive testing equipment, etc.), measuring tools (dial indicators, micrometers, coordinate measuring machines, etc.), and spare parts (impellers, pump shafts, bearings, mechanical seals, gaskets, etc.), ensuring that spare parts specifications match the equipment;
3. Technical briefing and solution development: Clearly define the maintenance objectives, procedures, and quality standards. Provide technical briefings to maintenance personnel. Based on equipment operation logs and minor repair records, develop a detailed maintenance plan, specifying the key inspection points and repair standards for major components.

 

Complete pump disassembly

Disassemble the centrifugal pump step-by-step, following the order of "from outside to inside, from accessories to core": First, remove the motor, coupling, bearing end cover, and bearing housing; then remove the mechanical seal and pump cover; finally, remove the impeller and pump shaft. During disassembly, clearly label and categorize the components to avoid confusion. Handle components gently during disassembly to avoid damaging major components (such as the impeller and pump shaft). Record any abnormalities encountered during disassembly (such as component adhesion, wear marks, etc.).

 

Inspection and Repair/Replacement of Key Components

Key components are crucial for the operation of the centrifugal pump and require comprehensive inspection and thorough repair, as follows:

1. Pump Shaft: Inspect the pump shaft for bending, roundness, and cylindricity. Use a dial indicator to measure straightness. If the bending exceeds 0.06mm, straightening treatment is required (pressure straightening, flame straightening, etc.). Inspect the pump shaft surface for wear, corrosion, and cracks. Use non-destructive testing methods such as penetrant testing (PT) to detect cracks. Minor wear can be repaired by spraying or electroplating. For severe wear or cracks, replace the pump shaft directly. Measure the journal dimensions to ensure they meet design requirements.
2. Impeller: Inspect the impeller for wear, corrosion, and cavitation. Check the blades for deformation, cracks, and erosion marks. Clean scale and debris from the impeller surface. Measure the impeller runout and blade thickness. If wear or cavitation is severe, repair can be done using laser cladding or welding techniques. Replace the impeller if repair is not possible. Perform a dynamic balancing test on the repaired or replaced impeller to ensure it meets the dynamic balance standards (imbalance meets equipment design requirements).
3. Pump Casing: Inspect the pump casing for cracks, corrosion, and wear. Use non-destructive testing to check for internal cracks. Minor cracks can be repaired by welding. Replace the pump casing if there are severe cracks or corrosion. Measure the inner diameter of the pump casing and the flatness of the sealing surface. Clean scale and debris from inside the pump casing. Repair scratches and wear on the sealing surface. Ensure the clearance between the pump casing and the pump cover/sealing ring meets design requirements. Check the clearances of the shaft sleeve, gland, wear ring, bushing, and other sealing components. Repair or replace components that exceed tolerances.
4. Bearings and Seals: Conduct a comprehensive inspection of the disassembled bearings. If issues such as ball wear, raceway pitting, or corrosion are found, replace the bearings directly. Replace the mechanical seal components (dynamic ring, stationary ring, spring, etc.), ensuring the sealing surface is smooth, free of scratches, and that the sealing performance meets standards. Replace aged or damaged gaskets, packings, and other vulnerable parts, selecting materials suitable for the medium characteristics and working pressure.

 

Auxiliary Component Inspection and Repair/Replacement

1. Couplings: Inspect the couplings for wear and deformation. Replace damaged elastic gaskets and bolts. Perform precise alignment and calibration of the couplings to ensure coaxiality meets standards. If the couplings are severely worn and cannot be repaired, replace them directly. Check for any looseness in the key and keyway fit and correct it promptly.
2. Piping and Valves: Conduct a comprehensive inspection of inlet and outlet pipelines for corrosion, wear, and cracks; repair leaks; replace aging or damaged pipelines. Inspect valves for opening and closing flexibility and sealing performance; disassemble valves for cleaning and repair; replace damaged valve discs and seals to ensure reliable valve operation. Clean cooling water and lubrication pipelines to ensure they are unobstructed and leak-free.
3. Electrical System: Inspect the insulation performance of motor windings and the connection of terminals; troubleshoot potential leaks and poor connections. Inspect motor bearing wear; replace grease. Calibrate electrical instruments (pressure gauges, flow meters, thermometers, etc.) to ensure accuracy; replace inaccurate instruments. Inspect the operating status of frequency converters and control cabinets; clean internal dust to ensure stable operation of the electrical system.

Pump Assembly and Precise Calibration

Assemble the centrifugal pump step-by-step in reverse order of disassembly, strictly adhering to assembly process requirements: First, install the pump shaft and impeller, adjusting the impeller-to-pump casing clearance; then install the mechanical seal and pump cover, tightening the cover bolts; install the bearings and bearing housing, adding grease and adjusting bearing clearance; install the coupling, recalibrating coaxiality; connect the motor, pipelines, and valves, ensuring all components are tightly connected and secure. During assembly, conduct an inspection after each step to ensure assembly accuracy meets standards, measuring and adjusting the rotor's axial movement, and checking the pump's levelness to prevent improper assembly from causing equipment malfunctions.

 

Trial Operation and Acceptance

1. Comprehensive Inspection Before Trial Operation: Confirm that all anchor bolts and connectors are tightened, and perform manual rotation to ensure smooth operation without jamming or friction, and without abnormal noise; check that the lubricating oil/grease is sufficient and of acceptable quality, and ensure the cooling water system is unobstructed and leak-free; have a professional electrician check the motor insulation, and only supply power after confirming it is qualified; confirm that the pump's inlet valve is fully open and the outlet valve is fully closed; confirm that pressure gauges, ammeters, and other instruments are installed and functioning properly.
2. Jogging to Confirm Rotation: Connect the power supply, momentarily start the motor, and immediately disconnect the power (i.e., "jogging"). Observe from the motor fan end; the rotation direction should be consistent with the arrow marking on the pump body. If the direction is incorrect, disconnect the power and swap any two power phase wires.
3. Formal Start-up and Monitoring: After confirming the correct rotation direction, formally start the motor and allow the unit to begin load operation. During operation, continuously monitor and record the following items to assess the equipment status: vibration and noise, bearing temperature, sealing performance, instrument counts, etc.
4. Inspection and Acceptance: After the load test run is successful, organize professional personnel to conduct an acceptance inspection. Check each inspection item (component replacement records, repair records, measurement data, etc.) against the inspection plan and quality standards to ensure the inspection quality meets the standards. Compile an inspection log, recording the inspection process, component replacement details, and test run data, and archive it for future maintenance. Only after successful acceptance can the equipment be officially put into use.

 

A well-executed centrifugal pump overhaul ensures its reliability, efficiency, and extended service life. Follow the original manufacturer's guidelines for your specific pump model and always prioritize safety.