How to repair a centrifugal pump with epoxy mastic

Why repair instead of replace

A centrifugal pump in mining, chemical or petrochemical service suffers three simultaneous wear mechanisms: cavitation (vapour-bubble implosion at the impeller eye), erosion-corrosion (particles + electrochemistry) and abrasion by the slurry. These mechanisms gouge the pump casing, enlarge the wear rings and destroy flange-face sealing.

Depending on damage extent, repair may reduce cost and lead time compared with full replacement. Feasibility still has to be confirmed from inspection, pump tolerances and product limits; repairing the casing does not remove required checks on rotating components.

Step 1 — Diagnose the wear mechanism

Before any application, identify the dominant mechanism. Cavitation leaves deep, shiny pits around the impeller eye. Erosion-corrosion forms dull, irregular craters. Abrasion creates parallel grooves in the flow direction. The diagnosis determines which epoxy system to use (high-toughness, ceramic-filled, or moisture-tolerant).

Step 2 — NACE 2 / SSPC-SP10 surface preparation

Surface preparation is critical to adhesion. When the system requires it, perform SSPC-SP10 “near-white metal” blast cleaning with the anchor profile defined by the technical data sheet and procedure. Cleaning must remove oil, glycol and other contaminants without redepositing them.

• Drain, isolate and lock out the pump (LOTO)

• Remove impeller and internal components if possible

• Grit blast with metallic shot (G16/G40) to SSPC-SP10

• Measure the anchor profile (Replica Tape comparator test)

• Degrease a second time with clean solvent

Step 3 — Apply the repair mastic

Mix the two components to the exact ratio stated on the technical data sheet (often 2:1 or 1:1 by volume). Apply a thin priming coat (wet-on-wet) with a spatula to wet the substrate thoroughly, then rebuild the geometry in successive 5 to 10 mm layers. For large material loss, use a light fibreglass reinforcement between layers.

Mould the final surface to the original geometry using a template or reference part. Let it cure for the stated time (typically 4 to 24 h at 20 °C, faster with gentle heating at 40-60 °C).

Step 4 — Finishing and inspection

Once cured, the mastic can be sanded, machined or grooved. Apply a ceramic-epoxy topcoat to protect the repair against future erosion and corrosion. Test adhesion by pull-off (ASTM D4541 — target > 10 MPa), measure the final thickness (DFT) and document everything in a QA/QC sheet.

How long does an epoxy repair last?

Service life depends on the wear mechanism, fluid, temperature, velocity, preparation and product. It should be estimated from operating history, system qualification and an inspection plan; no universal lifespan applies to every pump.

Conclusion

Epoxy mastic can extend casing service when the damage, product and procedure are compatible. API 510 addresses pressure vessels and is not a blanket authorization for pump repairs. The decision should rest on engineering assessment, surface preparation and the project's acceptance criteria.