Centrifugal pump repair procedure: rebuilding the casing and impeller with epoxy

A centrifugal pump repair procedure with epoxy follows a fixed sequence: identify the damage mechanism at teardown, record dimensions, decontaminate and blast the wetted surfaces, rebuild lost metal with a metal- or ceramic-filled compound, restore geometry and clearances, apply a topcoat matched to the mechanism, cure fully, rebalance, reassemble and test.

Skipping any of these steps is a known cause of early failure. This guide explains what to check at each stage for casings (volutes), impellers, suction covers and wear-ring areas.

Why centrifugal pump casings and impellers fail

A pump usually loses metal to one dominant mechanism, sometimes two together. The repair material depends on it, and some mechanisms have a root cause no coating can fix.

• Particle erosion (abrasion). Solids cut the metal where velocity and direction change: the cutwater (volute tongue), suction cover or liner, vane tips and shrouds.
• Cavitation. Where local pressure drops below the liquid's vapour pressure, vapour bubbles form and then collapse as pressure recovers, removing metal. Classic damage sits in the low-pressure zone: the impeller eye and the suction side of the vanes, just behind the leading edge.
• Corrosion. Electrochemical attack by the fluid: uniform thinning, pitting or crevice attack at gasket areas.
• Erosion-corrosion. Flow strips the protective oxide film faster than it can reform, so the metal corrodes much faster than in still fluid.
• Wear-ring and internal clearance wear. The running clearance between impeller and casing rings opens up; leakage from discharge back to suction increases and performance drops even if the casing looks intact.

How to tell the mechanisms apart at inspection

Inspect before cleaning: deposits, colour and damage shape are evidence that disappears once the part is blasted. Photograph every area and mark it on a sketch.

Cavitation damage on the pressure side of the vanes, or at the vane outlet tips and cutwater, can point to recirculation at flows well below the best efficiency point rather than to classic inlet cavitation. In both cases, rebuilding the impeller without correcting the NPSH margin or the operating point only resets the clock.

Step-by-step centrifugal pump repair procedure

1. Teardown and as-found records

Isolate, drain and lock out the pump, then disassemble. Before cleaning, record:

• photographs and a damage map of casing, impeller, suction cover and back plate;
• wear-ring diameters and clearances, compared with the manufacturer's data;
• remaining casing wall thickness in the worst areas, by ultrasonic gauge;
• suspected cracks, checked by dye penetrant or magnetic particle testing;
• impeller runout and shaft condition — a bent shaft will destroy a repaired impeller just as fast.

Without drawings, capture geometry now: templates of the vane profiles, the volute tongue and the ring fits. Where a part is too far gone, reverse engineering the replacement part from the worn original is an option.

2. Cleaning, decontamination and degreasing

Remove deposits and scale, then degrease. Cast iron and other porous castings absorb oil and process fluid, which bleeds back to the surface and prevents adhesion; repeated cleaning and, where the data sheet calls for it, a controlled heat bake-out draw it out. Where the fluid carries chlorides, test for soluble salts after blasting (ISO 8502-6 sampling, ISO 8502-9 conductivity) and wash until the specified limit is met.

3. Abrasive blasting and anchor profile

Mask machined fits, gasket faces and threads. Blast to the required cleanliness, typically near-white metal: SSPC-SP 10 / NACE No. 2, equivalent to ISO 8501-1 Sa 2½. Use angular abrasive to reach the profile on the data sheet and measure it (ISO 8503 comparator or replica tape per ASTM D4417). Remove dust (ISO 8502-3), keep the surface at least 3 °C above the dew point, and apply before flash rust appears. The NACE No. 2 surface preparation guide details these checks.

4. Rebuilding lost metal

Mix at the data sheet ratio. Work a thin first layer firmly into the profile, then build up in layers no thicker than the product allows, with reinforcement for deep losses where the instructions call for it. In high-velocity zones, terminate into a keyed edge or shallow undercut rather than a feathered edge, so flow cannot get under the repair. Use templates or a reference part to restore vane profiles, the volute tongue and suction cover faces.

5. Dimensional control

Dress or machine the rebuild back to the original geometry: volute tongue, vane inlet and outlet shape, impeller outside diameter, suction cover face. Wear-ring clearances follow the manufacturer's values; for API 610 pumps, the standard's minimum running clearances also apply. Epoxy does not replace a wear ring: worn rings are replaced or remachined, and the compound stays off running-clearance surfaces unless the product is designed and machined for that duty.

6. Erosion- or cavitation-resistant topcoat

Apply the topcoat selected for the mechanism (table below) within the data sheet thickness range and overcoat window. Check thickness, and holiday-test surfaces facing corrosive immersion.

7. Cure

Cure to the data sheet before service, including any heated or post-cure it specifies; low temperature slows the reaction. Returning a pump to service on a partly cured repair is one of the most common causes of early failure.

8. Balancing, reassembly and testing

If material was added to the impeller, rebalance it to the grade required by the manufacturer or purchase specification (balance quality per ISO 21940-11, formerly ISO 1940-1). Reassemble with new rings and seals as needed, verify clearances and runout, and align pump and driver. If the casing pressure boundary was affected, pressure-test per the owner's procedure. At start-up, record vibration, bearing temperatures and the flow–head point against the pump curve as a baseline.

Choosing the repair material by damage mechanism

The usual approach is a rebuild compound for lost metal, then a topcoat chosen for the dominant mechanism.

For heavy slurry duty beyond what epoxy handles, alumina ceramic versus AR steel compares harder liner options.

Limits of epoxy pump repair

• Temperature. Each product has a maximum service temperature, generally lower in immersion than dry. Check it against upsets and steam-out, not only normal operation.
• Incompatible fluids. Strong oxidizing acids and some solvents attack many epoxies; check the manufacturer's chemical resistance data at the actual concentration and temperature.
• Structural cracks. Epoxy does not restore the strength of a cracked casing or a cracked vane root. These need engineering assessment, a metallurgical repair or a new part.
• Pressure. A compound restores the flow surface, not the pressure-retaining capacity of a casing thinned below its required minimum wall.
• Uncorrected cause. Cavitation from insufficient NPSH margin, or erosion from running far from the best efficiency point, will attack the new surface too.

The cold bonding versus welding comparison covers when hot work is the better repair, and the castings where welding carries its own risks.

The same sequence applies to valve bodies, pump and valve flanges and compressor casings where metal loss is on static wetted surfaces. It does not apply to highly loaded contact surfaces such as gear-pump teeth, bearing journals or seal faces.

Repair or replace: decision criteria

Vibration, the foundation and alignment

A rebuilt impeller will not survive a pump that vibrates. Soft foot, cracked grout and a baseplate moving on its foundation loosen repairs, damage wear rings and shorten seal life. If the pump keeps losing alignment, look at the foundation before blaming the repair: the pump foundation and baseplate repair guide explains the diagnosis. API 686, the recommended practice for machinery installation, covers foundations, grouting and alignment; API 610 governs the design of centrifugal pumps for petroleum, petrochemical and natural gas service. Neither is an epoxy repair standard, but both define conditions a repaired pump must meet again.

FAQ

Can an impeller be repaired with epoxy? Yes, when the damage is erosion, corrosion or cavitation and the impeller is structurally sound. It must be dressed back to its original profile and rebalanced, since added material changes its mass distribution.

Does an epoxy coating stop cavitation? No. Resilient coatings resist cavitation damage better than rigid ones, but the cause is hydraulic. Check and correct the NPSH margin and operating point, or the new surface will be attacked too.

Can epoxy restore wear-ring clearances? Wear rings are normally replaced or remachined to the manufacturer's clearances. Epoxy is used on the static casing surfaces around them, not as a running surface, unless the product is designed and machined for that duty.

Which standard applies to an epoxy pump repair? None governs epoxy pump repair specifically. Surface preparation follows SSPC-SP 10 / NACE No. 2 or ISO 8501-1, the product follows its data sheet, and the pump must meet the manufacturer's requirements — for process pumps, API 610 for design and API 686 for installation.

How long does an epoxy pump repair last? It depends on mechanism, fluid, temperature, velocity, preparation and product. Estimate it from the operating history and inspect at the next outage; no universal lifespan applies.

In practice

Induscoat repairs centrifugal pump casings, impellers and suction covers without hot work — teardown records, surface preparation, rebuild, dimensional control and topcoat — through its maintenance and rehabilitation service for plants in Quebec and Ontario. The pump repair application page describes the scope. Photos of the damaged parts, the pumped fluid, its temperature and the operating history are enough to start an assessment: request a quote. Technical data sheets for the Induscoat range are published on the brand site, induscoat.com.