This guide helps maintenance and procurement teams distinguish corrosion morphology from erosion, cavitation and mechanical damage. It is an engineering-screening framework, not a corrosion-rate table or a guarantee of service life.
Corrosion Is a Failure Mechanism, Not a Material Name
Inspect the location, shape and distribution of damage before choosing a new alloy. Uniform thinning, localized pitting, crevice attack, galvanic attack, erosion-corrosion and stress-assisted cracking can have different causes and remedies. Deposits, stagnant zones, gasket interfaces, fasteners and seal chambers may create conditions that are more severe than the bulk liquid suggests.
| Observed damage | Investigate first | Do not assume |
|---|---|---|
| Uniform wall loss | Bulk chemistry, temperature and exposure time. | That a thicker casting alone will solve it. |
| Discrete pits | Chlorides, deposits, crevices, inclusions and local chemistry. | That the nominal alloy name proves compatibility. |
| Attack at joints or gaskets | Crevice, galvanic and stagnant-liquid conditions. | That the casing material is the only variable. |
| Directional grooves | Solids, velocity, flashing, cavitation and erosion-corrosion. | That the damage is pure chemical corrosion. |
| Cracks or brittle areas | Stress, temperature, fabrication and service environment. | That a visual polish is a repair. |
What Process Data Must Be Collected?
- Liquid identity and complete chemistry, including contaminants.
- Concentration, temperature, pressure, pH and expected excursions.
- Oxidizing or reducing conditions where relevant.
- Chloride, solids, crystals, gas content and abrasive loading.
- Flow, head, speed, velocity, startup and shutdown conditions.
- Cleaning fluids, flush or barrier fluids and washdown exposure.
- Current casing, impeller, shaft, sleeve, seal and fastener materials.
- Photos, thickness or dimensional records, failure timing and operating history.
A material that performs well in one concentration or temperature range may not perform the same way after dilution, contamination, heat-up, aeration or a process change. Treat each service envelope as a specific engineering case.
When Alloy 20 May Help
Alloy 20 and its relevant cast equivalents are often considered for selected acidic and sulfuric-acid services because of their corrosion-resistance characteristics. Whether Alloy 20 is appropriate depends on concentration, temperature, contaminants, velocity, oxidizing or reducing conditions and the construction of the complete wetted system.
Do not describe Alloy 20 as suitable for all concentrations or all acid duties. Confirm the exact material designation, casting standard, heat treatment, weld or repair history and traceability. Also review non-metallic components, seals, gaskets, fasteners and any dissimilar-metal interfaces.
For a direct C-276 versus Alloy 20 comparison, see the Hastelloy C-276 vs Alloy 20 chemical pump selection guide. This article stays focused on failure analysis and the information needed before a material decision.
Wrought Grade Is Not Automatically a Cast Pump Grade
Pump casings and impellers commonly use cast material designations, while shafts, sleeves or fabricated parts may use wrought grades. A wrought trade name is not an automatic one-to-one claim about a casting equivalent. Procurement should confirm the specified ASTM or project material, chemical composition, mechanical requirements, heat treatment and MTR or PMI evidence where applicable.
Why Velocity and Hydraulic Condition Matter
High local velocity, turbulence, flashing, entrained gas and suspended solids can accelerate erosion-corrosion or expose fresh metal after a protective surface film is disturbed. Cavitation can create pitting that resembles chemical attack. Check suction conditions, operating point, impeller condition, clearances and pipe geometry alongside the chemistry.
If cavitation is suspected, review the centrifugal pump cavitation guide. If the failure is repeated after a material change, review process conditions and assembly rather than assuming that another alloy alone will solve it.
A Practical Material-Selection Workflow
- Define the normal and upset chemistry, temperature and operating envelope.
- Identify the damage morphology and current material for each wetted component.
- Separate corrosion, erosion, cavitation, wear and mechanical failure modes.
- Shortlist material families using authoritative corrosion data and the project specification.
- Confirm the actual cast grade or wrought grade and required heat treatment.
- Review seals, elastomers, gaskets, fasteners, flushes and galvanic interfaces.
- Specify PMI, MTR, dimensional and inspection records appropriate to the risk.
- Confirm the exact pump model, size, interfaces, hydraulic duty and quotation scope.
What to Send for an Alloy Pump RFQ
Send the pump model and size, drawing or nameplate, liquid composition and concentration, temperature range, flow, head, speed, current material, photos of the failure, inspection measurements, seal arrangement, contaminants, solids and required documentation. State whether you need a casing, impeller, shaft, sleeve, seal chamber, complete wet end or another defined scope.
Compatibility is reviewed against the specific model, interfaces, materials, hydraulic duty and available records before quotation. ANSI Pumps Pro is an independent aftermarket manufacturer; brand names are used for identification and cross-reference only.
FAQ
Is Alloy 20 suitable for every sulfuric-acid pump?
No. Concentration, temperature, contaminants, velocity and oxidizing or reducing conditions can change the material decision. Confirm the exact service envelope and grade.
What is the difference between corrosion and erosion-corrosion?
Corrosion is chemical or electrochemical degradation; erosion-corrosion combines material attack with flow, turbulence or solids. A failure can involve both mechanisms.
Can a Hastelloy or titanium pump always replace Alloy 20?
No. Different alloy families have different limits, casting options, fabrication requirements and cost. Compare the complete process and construction requirements.
What evidence should a supplier provide for a replacement alloy part?
Depending on the project, request the specified grade, MTR or heat traceability, PMI, dimensional records, inspection results and any required testing. The required package should be agreed before quotation.
Sources and Related Reading
- Hastelloy C-276 vs Alloy 20 chemical pump selection.
- Exotic alloy pump-material selection framework.
- Chemical pump maintenance and reliability plan.
Request a Corrosion and Material Review
Send your pump identity, chemistry, temperature, duty, current material, failure photos and required replacement scope. We will identify the process and fitment evidence needed before quotation.
