This guide compares Alloy 20 and the Hastelloy C-276 family for ANSI chemical process pumps. It is intended for maintenance engineers, pump distributors and procurement teams evaluating casings, impellers, covers, sleeves and complete wet-end assemblies.
Alloy 20 vs Hastelloy C-276: The Short Answer
Alloy 20 is commonly considered for sulfuric-acid and other acidic services where its nickel, chromium, molybdenum and copper chemistry is suitable. The Hastelloy C-276 family is often considered when chloride-bearing, mixed-acid, reducing or contaminated process streams create a higher risk of pitting, crevice corrosion or stress-corrosion cracking.
Neither alloy is a universal answer. A material that performs well in one concentration and temperature range may fail in another. The selection must be based on the complete process envelope, not on the fluid name alone.
| Selection factor | Alloy 20 family | Hastelloy C-276 family |
|---|---|---|
| Typical strength | Strong option for selected sulfuric-acid and acidic services | Broad resistance in many oxidizing and reducing environments |
| Chloride risk | Requires careful concentration and temperature review | Often preferred for severe chloride, pitting and crevice-corrosion exposure |
| Material form | May be supplied as wrought Alloy 20 or a pump-casting equivalent such as CN7M | May be supplied as wrought C-276 or a cast-pump equivalent such as CW2M |
| Cost position | Often lower than C-type nickel alloys, subject to size and market conditions | Usually a higher-alloy and higher-cost option |
| Best next step | Check concentration, temperature, impurities and flow conditions | Check chloride level, oxidizing species, temperature and casting availability |
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Material-selection boundary: Fluid name alone is not enough. Confirm concentration, temperature, chlorides or fluorides, oxidizing or reducing conditions, velocity, solids and contaminants against qualified corrosion and application data before approving the pump material and product form.
Do Not Treat Alloy Names and Casting Grades as Exact Equivalents
One of the most important points for pump buyers is the difference between a general alloy family and a casting designation.
Alloy 20 is commonly associated with UNS N08020 in wrought product forms. Pump components may instead be specified using a casting grade such as CN7M. These materials may be selected for related chemical services, but their specifications, manufacturing route and qualification documents are not identical.
Likewise, Hastelloy C-276 commonly refers to UNS N10276 in wrought forms. A pump casing or impeller may use a C-type cast alloy such as CW2M. The purchase specification should identify the exact material standard and product form rather than relying only on a commercial alloy name.
For reference, the nominal composition published by Alleima for Alloy 20 includes approximately 32.5% nickel, 19.5% chromium, 2.2% molybdenum and 3.3% copper. Haynes lists nominal C-276 chemistry at approximately 57% nickel, 16% chromium, 16% molybdenum and 4% tungsten. Actual pump-casting requirements must be confirmed against the applicable material standard and mill or foundry documentation. See the Alleima Alloy 20 data and Haynes C-276 technical data.
When Is Alloy 20 a Reasonable Candidate?
Alloy 20 can be a practical candidate for selected sulfuric-acid, phosphoric-acid and related chemical services when the concentration, temperature and contaminants are within the material’s qualified range.
It may be considered when:
- Sulfuric acid is the primary process chemical and chloride contamination is controlled.
- The operating temperature and velocity are supported by corrosion data for the actual service.
- The project needs a higher-alloy wet end than 316 stainless steel but does not require a nickel-molybdenum superalloy.
- The supplier can provide the correct casting grade, heat traceability and inspection records.
Do not select Alloy 20 from acid concentration alone. Ferric ions, chlorides, fluorides, dissolved oxygen, erosion, velocity and stagnant zones can change the corrosion mechanism significantly.
When Is the Hastelloy C-276 Family a Better Candidate?
C-276 is a nickel-chromium-molybdenum alloy with tungsten. It is known for strong resistance to pitting, crevice corrosion and stress-corrosion cracking in many chloride-bearing environments, as well as useful performance in a broad range of corrosive chemical services.
It may be considered when:
- The process contains significant chlorides or mixed contaminants.
- The service combines oxidizing and reducing conditions.
- Localized corrosion is a greater concern than general uniform corrosion.
- A single pump must handle several aggressive process streams.
- Failure of a casing, impeller or seal chamber would create a high downtime or safety risk.
C-276 is not automatically the best option for every acid. Hot nitric-acid service, concentrated oxidizers and special process mixtures still require application-specific data and engineering review.
Why a Corrosion-Rate Table Cannot Replace an Engineering Review
Published corrosion data is useful for screening, but a universal table of corrosion rates can be misleading. Laboratory results may use static, reagent-grade solutions that do not represent a real pump containing velocity, solids, entrained gas, welds, crevices, impurities and temperature gradients.
Before approving a material, document:
- Chemical name, concentration and expected contaminants
- Normal, minimum and maximum temperature
- Flow velocity and suspended solids
- Oxidizing or reducing conditions
- pH, chloride and fluoride levels where relevant
- Start-up, shutdown and cleaning conditions
- Required corrosion allowance and expected service life
How Material Choice Changes the ANSI Pump Wet End
Material selection should be applied to the complete wetted assembly, not only the casing. Review each of these parts:
| Component | What to verify |
|---|---|
| Casing and cover | Correct casting grade, wall thickness, pressure rating, porosity control and hydrostatic test requirements |
| Impeller | Alloy, hydraulic trim, balance grade, wear pattern and compatibility with the casing clearance |
| Shaft sleeve | Alloy, hardness, surface finish, seal interface and galvanic compatibility |
| Wear rings | Material pairing, clearance, galling risk and replacement procedure |
| Mechanical seal | Face materials, elastomers, spring materials, flush plan and temperature limits |
| Gaskets and O-rings | Chemical compatibility, temperature rating and compression requirements |
Material Verification: MTR, PMI and Inspection Records
For corrosion-critical pump parts, request a documentation package that can be reviewed by quality and engineering teams:
- Material test report with heat number and applicable standard
- Positive material identification for critical alloy surfaces
- Foundry and heat-treatment records where required
- Dimensional inspection of casing, impeller and interfaces
- Hydrostatic test record for pressure-containing components
- Dynamic balance record for rotating components
- Approved drawing showing material and inspection requirements
PMI is a useful verification tool, but it does not replace the material certificate or prove corrosion performance by itself. The final package should identify what was tested, how it was tested and which specification was used for acceptance.
Alloy 20 or Hastelloy C-276: A Practical Decision Process
- Define the service. Record concentration, temperature, contaminants, velocity and cleaning conditions.
- Identify the corrosion mechanism. Consider general corrosion, pitting, crevice corrosion, stress-corrosion cracking, erosion and galvanic effects.
- Shortlist materials. Compare Alloy 20, C-type nickel alloys, duplex grades, titanium or other candidates using qualified data.
- Check the pump design. Confirm casing, impeller, shaft sleeve, seal, wear-ring and gasket compatibility.
- Verify the delivered component. Require the agreed MTR, PMI, dimensional, balance and pressure-test documents.
- Review lifecycle cost. Include replacement lead time, downtime exposure, inspection cost and expected service interval.
Goulds 3196 and Durco Mark III Alloy Wet Ends
For Goulds 3196 or Durco Mark III replacement projects, the alloy decision is only one part of the fitment review. The supplier should also confirm the pump size, frame, seal chamber, impeller design, adjustment mechanism, wear-ring arrangement and power-end interface.
Read our related resources on ANSI B73.1 interchangeability versus component compatibility and Goulds 3196 versus Durco Mark III replacement considerations. You can also use the OEM part-number cross-reference before requesting a quotation.
Need a Chemical Pump Material Review?
Send the pump nameplate, process fluid, concentration, temperature, OEM part number and photos of the existing wet end. Our engineering team can review material form, fitment and documentation requirements before production.
Frequently Asked Questions
Is Alloy 20 the same as CN7M?
They are related material choices used in similar chemical-service discussions, but they should not be treated as identical without checking the exact standard and product form. Alloy 20 commonly refers to a wrought alloy family, while CN7M is a casting designation used for pump and valve components.
Is Hastelloy C-276 the same as CW2M?
Not automatically. C-276 commonly identifies UNS N10276 wrought material, while CW2M is a cast-pump material designation. Confirm the exact specification, chemistry, heat treatment and inspection requirements.
Which alloy is better for sulfuric acid pumps?
Alloy 20 may be a suitable candidate for selected sulfuric-acid services, but concentration, temperature, impurities and velocity must be reviewed. There is no universal sulfuric-acid limit that applies to every pump.
Which alloy is better for chloride service?
The Hastelloy C-276 family is often considered for more severe chloride, pitting and crevice-corrosion exposure. The final selection still depends on temperature, chloride concentration, oxidizing species and the actual pump design.
What documents should I request for an Alloy 20 or Hastelloy pump part?
Request the applicable material certificate, heat-number traceability, PMI where required, dimensional inspection, hydrostatic testing for pressure-containing parts, balance records for rotating parts and an approved drawing.
