What Pump Corrosion Looks Like
Corrosion may appear as broad surface loss, localized pitting, attack around crevices or deposits, or damage concentrated in particular wetted areas. Visual inspection is useful for documenting the pattern, but a photograph alone should not be treated as a definitive failure diagnosis.
Record the damaged component, process-contacting area, deposits, direction of flow, nearby joints and the service history. Keep photographs with scale references and note whether the part was cleaned before inspection.
Corrosion vs Erosion vs Cavitation
| Damage type | Typical visual clue | Operating clue | What to verify |
|---|---|---|---|
| Corrosion | Chemical surface attack, pitting or general loss | Material/process incompatibility | Fluid chemistry, temperature and material |
| Erosion | Directional wear or high-velocity surface loss | Solids or high local velocity | Solids, flow path and velocity |
| Cavitation | Pitted or hammered appearance in characteristic hydraulic areas | Low NPSH margin or off-design operation | NPSHA, NPSHR, suction conditions and operating point |
Real failures can involve more than one mechanism. Use the pattern as a starting point and confirm it against process and operating data.
Why the Impeller and Casing May Fail Differently
- Local velocity and recirculation expose different surfaces to the fluid.
- Deposits and crevices can create locally aggressive chemistry.
- Solids can combine erosion with corrosion.
- Different alloys may create galvanic combinations at interfaces.
- Hydraulic regions such as the cutwater, vane passage and seal area experience different flow conditions.
Compare the failure location with the pump curve, suction condition, process changes, cleaning procedure and material records. Avoid treating the most visibly damaged part as the only source of the failure.
Data Required Before Selecting a Different Material
- Exact chemical and concentration
- Temperature and pH when relevant
- Chloride and other contaminants when relevant
- Solids type and loading
- Existing component material
- Operating point and suction conditions
- Failure location and damage photographs
- Service life history
- Cleaning chemicals and process changes
Corrosion-Resistant Material Selection Is Application-Specific
There is no single corrosion-resistant pump material that is best for every chemical service. Material selection should be based on the actual fluid composition, concentration, temperature, contaminants, solids and the observed failure mechanism.
Alloy 20/CN7M, CD4MCuN, Hastelloy C-276/its applicable casting grade and other alloys can be relevant in different service envelopes. Distinguish wrought designations from casting grades, confirm the applicable specification and obtain an application-specific engineering review before changing a wetted component.
Material selection is only one part of the fix. Check the operating point, NPSH margin, solids management, seal arrangement, cleaning procedure and any galvanic interfaces at the same time.
What to Send for an Engineering Review
- Pump model and size
- Existing wetted-part material
- Liquid, concentration and temperature
- Operating flow, head and suction data
- Damaged-part photographs with scale
- Failure location and service life history
- Required replacement scope
The ANSI pump selection resource can help organize duty and material inputs. For replacement sourcing and inspection scope, see aftermarket solutions.
Request a Corrosion Failure Review
Send the process data, material record, pump details and photographs. A configuration-specific review can help separate corrosion, erosion and cavitation indicators before a replacement alloy is selected.
Request a pump corrosion review
Frequently Asked Questions
Can a photograph prove that pump damage is corrosion?
No. A photograph documents the pattern, but the diagnosis should be checked against fluid chemistry, temperature, operating data, materials and other possible mechanisms.
Why can an impeller corrode differently from a casing?
Local velocity, recirculation, deposits, crevices, solids, galvanic interfaces and hydraulic location can expose the two components to different conditions.
Is there one corrosion-resistant alloy for all chemical pumps?
No. The correct material depends on the complete process envelope and observed failure mechanism. An alloy name alone is not a universal selection rule.
What should be sent before changing pump material?
Send the exact chemical, concentration, temperature, contaminants, solids, existing material, operating data, failure location, photographs and required replacement scope.
