Contact Form

Welcome to Credo, We are an Industrial Water Pump Manufacturer.

Split Case Centrifugal Pump Impeller Wear and Corrosion Analysis: Diagnosis, Repair Methods, and Replacement Criteria

During long-term operation of split case centrifugal pumps, the impeller is exposed to sand erosion, medium corrosion, and pump cavitation, which may cause thinning, grooves, pitting, perforation, cracks, and other forms of damage. These issues can directly result in reduced pump flow, insufficient pressure, increased power consumption, excessive vibration, leakage, and even unexpected shutdown failures.

This article simplifies complex industry standards and focuses on practical field applications. Based on the principles of easy inspection, practical maintenance, and clear evaluation criteria, it summarizes impeller damage diagnosis, repair classification, rejection standards, and prevention methods. It is suitable as a direct reference for operation and maintenance personnel.

Split Case Centrifugal Pump

1. Three Common Types of Split Case Centrifugal Pump Impeller Damage (Quick Identification)

Impeller failures can generally be classified into three types, which can be quickly identified through visual inspection and operating conditions.

Damage TypeVisual CharacteristicsCommon Operating Conditions
Erosion WearImpeller outlet edges become thinner with smooth wear grooves; flow gradually decreases and motor current increasesRiver water, papermaking white water, and water containing sand particles
Medium CorrosionPitting, honeycomb-like corrosion pits, and surface peeling; increased internal leakage and reduced efficiencySeawater, papermaking wastewater, acidic or alkaline fluids
Cavitation“Crackling” noise from the pump, high vibration, unstable pressure; honeycomb pits appear at the impeller inletLow liquid level, blocked suction line, or excessive pipeline resistance

2. Simple Diagnostic Methods (Without Shutdown or Disassembly)

2.1 Daily Operation Inspection (Simple and Practical)

If any two of the following conditions occur, impeller damage can generally be suspected, and maintenance should be scheduled:

Abnormal operating parameters:

Under the same valve opening conditions, clean water pumps show more than an 8% reduction in flow/head, while seawater or papermaking pumps show more than a 10% reduction, accompanied by increased motor current.

Increased vibration and abnormal noise:

Pump vibration increases or fine crackling sounds appear (after excluding bearing damage and shaft misalignment).

Abnormal temperature and leakage:

The mechanical seal area temperature increases, and leakage contains fine metal particles.

2.2 Accurate Judgment After Disassembly (Basis for Maintenance Classification)

After opening the pump casing and removing the rotor assembly, evaluate the impeller through three inspection methods:

Visual inspection:

Identify wear grooves, corrosion pits, and honeycomb cavities caused by cavitation.

Measurement:

Measure the remaining impeller blade thickness, wear depth, and wear ring clearance.

Non-destructive testing:

Check whether cracks exist. Root cracks and through cracks require immediate rejection.

Key Rejection Criteria:

Impeller blade remaining thickness < 2/3 of the original thickness

Wear ring clearance exceeds 1.5 times the original factory value (for general pumps) or 2 times (for chemical pumps)

The impeller must be repaired or replaced.

3. Impeller Damage Classification, Repair, and Rejection Standards (Direct Application)

Damage LevelEvaluation Criteria (Simplified)Recommended Repair MethodKey Requirements
Minor DamageWear/corrosion depth <1 mm, no holes or cracks, and sufficient wall thicknessCeramic wear-resistant and anti-corrosion coating repairSuitable for slight wear, minor corrosion, and shallow cavitation damage; not suitable for severe honeycomb cavitation
Moderate DamageDamage depth 1–5 mm, no perforation or root cracks, and wall thickness meets requirementsLaser cladding or stainless steel overlay welding + grinding and reshaping + dynamic balancingCast iron requires preheating to prevent cracking; seawater applications require duplex stainless steel welding materials; dynamic balancing is mandatory after repair
Severe Damage (Scrap)Damage depth >5 mm, wall thickness below 2/3 of the original thickness, perforation, blade cracks, or root cracksDirect replacement with a new impellerWelding repair for leakage sealing is strictly prohibited; high-speed operation may cause impeller fracture and serious safety hazards

4. Repair Restrictions for Different Types of Damage (Key Points to Avoid Mistakes)

Erosion Wear:

Do not use ordinary welding rods for simple overlay repair.

Insufficient hardness will result in rapid re-wear.

Seawater / Papermaking Corrosion:

Do not rely solely on ordinary coatings.

Coatings may easily peel off during long-term operation.

Severe Cavitation:

Do not cover severe cavitation damage with coatings.

Overlay welding or laser cladding is required; otherwise, failure may occur again within a short period.

5. Impeller Material Selection for Different Applications (Simple Reference)

Application ConditionRecommended MaterialDescription
Power plant clean water circulationDuctile iron, HT250 cast ironProvides the best cost-performance ratio and is sufficient for normal operation
Papermaking white water316L stainless steel / Duplex stainless steel304 stainless steel is not recommended for long-term operation due to a higher risk of pitting corrosion
Seawater transfer2205 / 2507 duplex stainless steelOrdinary stainless steel and cast iron are highly susceptible to corrosion failure
High-sand river waterHigh-chrome wear-resistant cast ironImproves wear resistance and reduces frequent maintenance requirements

6. Long-Term Prevention Measures (Lower Cost and Reduced Maintenance)

Ranked from highest cost-effectiveness to lower:

Install filtration equipment:

Use front-end filters and hydrocyclone sand separators to remove sand particles and fibers, reducing erosion wear by more than 70%.

Eliminate cavitation risks:

Maintain sufficient suction water level, increase suction pipe diameter, reduce unnecessary elbows, and prevent long-term cavitation damage.

Upgrade materials according to operating conditions:

For severe corrosion or wear applications, directly upgrade to wear-resistant and corrosion-resistant impellers to reduce repeated repairs.

Conduct regular inspection and maintenance:

During annual overhauls, measure wall thickness and inspect for defects. Predict replacement timing in advance to avoid unexpected failures.

7. Key Safety Reminders (Must Read)

All repaired impellers must undergo dynamic balancing:

General water pumps: G6.3 grade

Chemical pumps: G2.5 grade

Without proper balancing, excessive vibration may damage bearings, mechanical seals, and shafts.

Impellers with perforation or root cracks must be scrapped immediately.

Temporary welding repairs are strictly prohibited due to the risk of impeller fracture and high-speed failure.

Establish maintenance records and track impeller wear rates to optimize spare parts planning and overhaul intervals.

Summary

Impeller failures in split case centrifugal pumps mainly include three types: wear, corrosion, and cavitation. Operating parameters, vibration, and abnormal noise can be used for preliminary diagnosis, while disassembly inspection and measurement provide accurate damage evaluation.

Minor damage can be repaired with protective coatings; moderate damage requires overlay welding, reshaping, and dynamic balancing; severe damage requires direct replacement.

By combining front-end filtration, cavitation prevention, and material upgrades, the service life of impellers can be significantly extended, reducing pump station maintenance costs and minimizing unexpected downtime failures.

FAQ – for Split Case Pump

Learn about the key spare parts commonly used in split case pumps.

Split Case Pump Spare Parts & Qty (2 Years)
For Packing Seal Pump
Spare Parts/QtyPump Qty (Including Spare Pump)
1234568≥10
Shaft Sleeve11122345
Bearing Collar11122345
Impeller Collar00011123
Packing Seal123456810
O Ring123456810
Shaft00011123
Impeller 00011123
Wear Ring11122345
Packing Ring00011123
Packing Gland00011123
Bearing11122345
For Mechanical Seal Pump
Spare Parts/QtyPump Qty (Including Spare Pump)
1234568≥10
Shaft Sleeve11122345
Bearing Collar11122345
Impeller Collar00011123
Mechanical Seal11122345
O Ring123456810
Shaft00011123
Impeller 00011123
Wear Ring11122345
Mechanical Gland00011123
Bearing11122345

Discover how to select the right split case pump materials based on fluid properties and operating conditions.

Pump PartsFor Clear WaterFor SewageFor Seawater
 CasingCast IronDuctile IronS.S / Super Dulex
ImpellerCast IronCast Steel S.S / Super Dulex / Tin Bronze
Shaft  Steel  SteelS.S / Super Dulex
 Shaft Sleeve Steel    SteelS.S / Super Dulex
Wear RingCast IronCast Steel  S.S / Super Dulex / Tin Bronze
RemarkFinal material depends on the liquid condition or the client’s request.

Follow the essential installation steps to ensure safe and reliable operation of the split case pump.

Standardized Installation Procedure for Split Case Pump
Work StageNo.Main StepsKey Operations & Notes
I. Pre-Installation Preparation1Site & Foundation Inspection• Clean the installation site and ensure sufficient space for operation and lifting.
• Check the concrete foundation strength, dimensions, elevation, and anchor bolt positions according to drawings. The foundation surface should be flat and free of oil.
2Equipment Unpacking & Inspection• Verify that the pump, motor, and accessories match the contract specifications.
• Inspect the equipment for any transportation damage and ensure all parts are complete.
• Check that all accompanying documents (drawings, manuals, certificates) are complete.
3Tools & Material Preparation• Prepare lifting equipment (hoist, sling), shims, level, dial indicator, wrenches, feeler gauge, lubricants, sealant, etc.
• Prepare cleaning agents and cloths for cleaning mating surfaces.
II. Pump Body Installation4Lifting & Positioning• Lift the pump using the lifting holes or lugs; never lift by the pump shaft or inlet/outlet pipes.
• Place the pump on the foundation, insert anchor bolts into base holes, do not tighten yet.
5Initial Leveling & Alignment• Place a level on the pump’s inlet/outlet flange or machined surface, adjust shims to roughly level the pump (tolerance ≤0.1 mm/m).
• Use the pump shaft centerline as a reference to preliminarily align the pump.
6Primary Grouting• Pour high-strength non-shrink grout into the anchor bolt holes; the grout layer should be dense and slightly below the foundation surface.
• Curing: wait until the grout is fully cured (usually 3–7 days) before fine adjustment and tightening.
7Final Leveling & Alignment• After grout curing, tighten anchor bolts.
• Recheck pump level with a precision level.
• Motor installation & alignment: lift the motor in place, use a dial indicator or laser alignment device, align the motor to ensure pump and motor shafts are coaxial (radial & axial deviation ≤0.05 mm). Tighten motor anchor bolts after alignment.
III. Piping & Accessories Installation8Piping Connection• Principle: never force pipe connections using the pump flanges to avoid stress on the pump body.
• Piping should be independently supported, ensure natural alignment without stress.
• It is recommended to install expansion joints near the pump inlet/outlet to absorb thermal expansion/contraction and installation errors.
9Seals & Cooling System• For mechanical seals, connect flushing/cooling piping, ensure smooth flow, flushing pressure 0.05–0.15 MPa higher than seal chamber.
• For packing seals, install packing and adjust gland tightness (do not overtighten initially).
10Lubrication & Instruments• Add specified grade and quantity of lubricant to bearing housing to oil mark midline.
• Install pressure gauge, thermometer, etc.; pressure gauge should be between pump outlet and first valve.
IV. Post-Installation Checks & Test Run11Final Checks• Manual rotation: rotate coupling, ensure rotor turns smoothly, no friction or binding.
• Check all bolts are tightened and guards are in place.
• Jog motor: confirm rotation direction matches pump casing arrow.
12Priming & Test Run• Open inlet valve, fill pump with conveyed medium, completely expel air.
• Close outlet valve, start motor.
• Slowly open outlet valve to desired condition, check pressure, flow, vibration, noise, bearing temperature (≤80 ℃), and seal leakage. Test run ≥2 hours.

Explore proper disassembly and maintenance procedures to maximize the split case pump service life.

Standardized Disassembly & Maintenance Procedure for Split Case Pump
Work StageNo.Main StepsKey Operations & Notes
I. Pre-Disassembly Preparation1Shutdown & Isolation• Safety first: slowly close the outlet valve, cut off power, and apply lockout/tagout (LOTO).
• Close the inlet valve, open the pump vent and drain valves, completely drain the medium. For toxic or hazardous media, perform purging and verify safe conditions.
2Disconnect External Connections• Remove coupling guard and connecting bolts.
• Disconnect all pipes, instrumentation lines, and cooling/seal water lines if the pump will be lifted as a whole.
Seal open ends to prevent foreign object entry.
3Tools & Preparation• Prepare pullers, hydraulic wrenches, copper bars, lifting equipment, and various wrenches.
• Prepare parts boxes and labels to organize and mark removed bolts and small parts for easier reassembly.
II. Pump Body Disassembly4Remove Accessories• Remove pressure gauges, thermometers, and other instruments.
• Open bearing housing oil drain and collect used lubricant.
5Remove Coupling & Bearing End Covers• Use a puller to smoothly remove the half-coupling from the pump shaft; avoid hammering.
• Remove bearing end covers and gland bolts in sequence, then remove the covers.
6Lift Out Rotor Assembly• Remove bearing housing bolts on both sides of the pump and horizontally lift the entire rotor assembly (shaft, impeller, bearings, sleeves) smoothly. Avoid collisions.
7Disassemble Split Case Pump Body• Loosen and remove pump casing bolts in a diagonal sequence.
• Lift the pump casing carefully and place on a padded or wooden platform. Protect the split case mating surface—avoid dents or scratches.
8Remove Internal Components• Before disassembly, measure and record key clearances (e.g., impeller to wear ring, bearing clearance).
• Use special wrenches to remove impeller locknut, then remove impeller. Remove shaft sleeve, mechanical seal or packing housing sequentially.
III. Inspection, Maintenance & Reassembly9Parts Cleaning, Inspection & Measurement• Clean all parts thoroughly, inspect for wear, corrosion, cracks.
Focus on:
– Impeller: cavitation, wear, dynamic balance.
– Wear ring/seal ring: measure wear gap; replace if exceeding limits (typically >1.5× original gap).
– Pump shaft: check straightness (total runout ≤0.05 mm).
– Bearings: check clearance, rolling surface for pitting or spalling.
– Mechanical seals: check stationary/rotating faces and spring elasticity.
• Decide whether to repair or replace parts.
10Reassembly (Reverse Order of Disassembly)• Core principle: clean, align, and tighten evenly.
• Replace all seals (O-rings, gaskets). Apply a thin layer of sealant (e.g., anaerobic) on split case mating surfaces.
• Lift pump casing, tighten bolts diagonally in stages to manufacturer torque.
• Reinstall rotor assembly, adjust impeller axial clearance to manufacturer spec.
• Install bearings and adjust bearing clearance.
• Reinstall coupling and perform precise pump-to-motor alignment (same as installation standard).
11Final Verification• Manually rotate to ensure smooth, unrestricted motion.
• Connect piping, add new lubricant to specified level.
• Conduct final verification according to installation procedure “Priming & Test Run” to ensure normal operation parameters.

Find practical solutions to the most common split case pump operating issues.

Split Case Pump Common Faults and Solutions
ProblemCausesSolutions
1. Pump not priming / Cannot discharge liquid1. Suction pipe, suction valve, foot valve not primed; air ingress.
2. Pump casing or suction pipe contains trapped air.
3. Motor rotation reversed.
4. Suction inlet leakage or failure.
5. Suction lift exceeds allowable maximum.
1. Prime suction line and foot valve; eliminate air leaks.
2. Vent casing & suction line.
3. Correct motor wiring/rotation.
4. Repair suction inlet.
5. Reduce suction lift or add booster.
2. Flow insufficient / Small discharge1. Inlet valve closed or partially closed; suction screen blocked.
2. Impeller blockage, foreign objects.
3. Wear at suction port (seal ring), impeller or casing wear.
4. Suction line contains air.
5. Pump speed too low.
1. Fully open inlet valve; clean filter/screen.
2. Remove blockage/clean impeller.
3. Repair/replace worn components.
4. Purge air from suction.
5. Restore correct operating speed.
3. Low head / Insufficient pressure1. Impeller clearance too large or impeller damage.
2. Low rotation speed.
3. Cavitation.
4. Suction pipe diameter too small.
5. Discharge head exceeds pump capacity.
1. Adjust or replace impeller.
2. Increase speed within rating.
3. Improve suction conditions or reduce NPSH.
4. Increase suction pipe size.
5. Reduce discharge head.
4. Excessive vibration / Abnormal noise1. Shaft misalignment.
2. Bearing damage.
3. Loose motor mounting.
4. Coupling or impeller imbalance.
5. Motor vibration.
6. Base/frame loose.
7. Improper pipe support causing resonance.
1. Re‑align pump & motor.
2. Replace bearings.
3. Secure motor base.
4. Correct balance; inspect coupling.
5. Reduce motor vibration.
6. Tighten base.
7. Add pipe supports.
5. Bearing overheating1. Improper lubrication (insufficient, wrong type, contaminated).
2. Bearing damage.
3. Poor alignment.
4. Bearing housing misfit.
5. Insufficient cooling.
6. Excessive rotational speed.
1. Re‑lubricate with correct grease/oil.
2. Replace bearings.
3. Realign pump & motor.
4. Adjust housing fit.
5. Improve ventilation/cooling.
6. Operate within speed rating.
6. Mechanical seal leakage• Seal faces worn, uneven, O‑ring aging, spring failure.
• Packing not lubricated or tightened.
• Replace mechanical seal and O‑rings; inspect shaft finish.
• Adjust packing gland; ensure correct packing and tension.
7. Motor overload / Tripped protection1. Insufficient power supply.
2. Phase loss / Power imbalance / Poor wiring.
3. Excessive load (impeller blockage), pump stalled.
4. Excessive starting current.
5. Motor overheating.
6. Short‑circuit or earth fault.
1. Restore proper supply voltage.
2. Check wiring and phases; correct imbalance.
3. Remove blockage; clear shaft rotation.
4. Use soft start or reduced voltage starter.
5. Improve cooling.
6. Find & repair electrical fault.
8. Cannot start or slow start1. Power supply abnormal (voltage drop).
2. Starter contactor open.
3. Motor winding open circuit.
4. Control circuit faulty.
1. Check power and restart.
2. Check and replace contactor.
3. Repair/replacement of winding.
4. Correct control wiring.
9. Pump vibration increases at no load1. Rotor imbalance, bent shaft.
2. Loose rotating parts.
3. Coupling looseness.
4. Pump suction/delivery line back‑pressure issue.
1. Balance rotor or repair shaft.
2. Tighten rotating assembly.
3. Tighten coupling.
4. Eliminate back‑pressure and correct piping.
10. Efficiency drop / Performance deterioration1. Wear of impeller & casing.
2. Internal passage clogging, scale/slag.
3. Air entrainment in suction.
4. Operating point far from BEP.
1. Replace worn parts.
2. Clean flow passages; flush.
3. Eliminate suction air leaks.
4. Adjust operating conditions toward BEP.

Learn the maintenance practices that help improve split case pump reliability and reduce downtime.

Daily Maintenance and Care for Split Case Pumps
Maintenance CategoryMaintenance ItemDetails & Standards
I. Pre‑Operation Inspection1. Visual & Connection Check• Check the pump casing, motor, coupling, etc., for cracks, deformation or damage.
• Check all connection fasteners (especially pump‑to‑base and base bolts) for tightness to prevent leakage or vibration.
• Check piping and joint areas for looseness.
2. Lubrication Inspection• Oil lubrication: Check if the oil level in the oil chamber is at the center mark; whether the oil is clean.
Replace promptly if oil is turbid or contains impurities.
• Grease lubrication: Check if the grease is sufficient and clean.
Note: Water‑based bearings use grease X; motors use grease Y — the two must not be mixed.
3. Turn Shaft & Rotation Confirmation• Manually rotate the coupling to check if the pump shaft rotates freely with no friction noise.
• Start motor briefly to confirm the rotation direction is consistent with the direction indicated by the pump arrow.
4. Seal & Suction Check• Check the mechanical seal and packing seal condition.
• Open pump suction valve and drain water until the casing is full, then vent air (no dry running).
II. Monitoring During Operation1. Parameter Monitoring• Pressure & Flow: Monitor inlet and outlet pressures and flow to ensure operation within the rated range for optimum efficiency.
• Bearing Temperature: Bearing temperatures should remain between 40–60 °C, and the motor temperature should not exceed 80 °C. If overheated, check lubrication and cooling systems.
2. Vibration & Noise• Listen to running noise: should be smooth hum. If there are abnormal noises, impacts, etc., stop and inspect immediately.
• Observe vibration condition; abnormal vibration may indicate imbalance, bent shaft, uneven wear, or cavitation.
3. Seal & Leakage Monitoring• Mechanical seal: Normal leakage rate should not exceed 5 drops per minute.
• Packing seal: Through adjustment tighten, leakage rate should be controlled at about 10‑15 drops/min (approx. 30 ml/min) depending on packing size. Adjust to desired leakage.
4. Instruments & Motor• Check all instruments (pressure gauge, temperature gauge, etc.) for normal readings.
• Check motor current and electrical system; no abnormal heating.
III. Periodic (Planned) Maintenance1. Lubrication Management• Oil lubrication: Change first after 100 operating hours, then every 500 hours.
• Grease lubrication: Generally replenish or change every 3 months; follow manufacturer service schedule.
2. Seal System Maintenance• Packing seal: Replace packing rings as needed; ensure stuffing box is properly tightened and align packing ring gaps at 90°–120°.
• Mechanical seal: Check flushing liquid pressure; it should be 0.05–0.1 MPa. Replace seal if excessive wear or leakage.
3. Bearing & Coupling Check• Monthly manually check coupling and shaft for smooth rotation, no abnormal noise.
• Periodically check bearing housing for dirt, wear and proper lubrication.
4. Impeller & Flow Passage Cleaning• Every 3 months or based on water quality, check impeller for buildup, corrosion, wear; clean off sediment, debris.• Check impeller clearance; if gap is too large (e.g., >0.1 mm), replace as required.
5. Alignment & Tightening• Periodically check alignment between pump and motor; allowable deviation ≤0.05 mm.
• Retighten base bolts and major fasteners as needed.
IV. Shutdown & Long‑Term Stop1. Normal Shutdown• Procedure: close outlet valve first → power off → close inlet valve and pressure gauge valves.
2. Winter Anti‑Freeze• When ambient temperature is ≤ 0 °C, after shutdown drain water from pump body, and ensure piping is drained to prevent freezing.
3. Long‑Term Storage• Drain all internal water and clean thoroughly.
• Apply rust preventive oil (shaft, impeller, contact areas), reinstall and protect for storage.
V. Cleaning & Record Keeping1. Equipment Cleaning• Weekly wipe pump body, motor, and base surfaces; especially clean motor cooling fins.
• Regularly clean around instrument panels to prevent dust accumulation.
2. Operation Records• Establish and maintain operation & maintenance logs including operating hours, pressures, temperature, vibration, lubrication replacement time, fault handling, etc., to facilitate equipment condition tracking and planned maintenance.
Share It