955 Aluminum Bronze for Fire Water Pumps
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CDA 955 Aluminum Bronze Wear Rings for Fire Water Pumps
Fire water pumps are kept in standby and must perform on demand, so the internal parts that govern long-term reliability deserve careful material selection. The wearing ring (also called wear ring) is one of those parts. This article explains why CDA 955, also known as UNS C95500 nickel aluminum bronze, is a practical material for fire water pump wearing rings, where the ring is located, and how it compares with alternatives. Content is provided by VIIPLUS SOLUTIONS ®, a supplier of bronze wear rings and self-lubricating bearings.
What Is CDA 955 Aluminum Bronze
/ UNS C95500?
CDA 955 is the Copper Development Association grade for UNS C95500 nickel aluminum bronze, a cast copper alloy in the Cu–Al–Fe–Ni system. The nickel addition is what separates it from C95400 aluminum bronze and supports seawater corrosion resistance and galling resistance.
Chemical Composition (ASTM B148, as-cast)
| Element | Content (wt%) | Role |
|---|---|---|
| Copper (Cu) | ≥ 78% (balance) | Matrix; corrosion resistance and thermal conductivity |
| Aluminum (Al) | 10.0 – 11.5% | Forms hard κ phase and protective oxide film; raises strength and corrosion resistance |
| Iron (Fe) | 3.0 – 5.0% | Grain refinement; improves strength and wear |
| Nickel (Ni) | 3.0 – 5.5% | Stabilizes structure; improves seawater corrosion and galling behavior (the key difference from C95400) |
| Manganese (Mn) | ≤ 3.5% | Deoxidation and solid-solution strengthening |
| Others total | ≤ 0.50% | Impurity control |
Standards and Equivalent Grades
| System | Grade |
|---|---|
| UNS (USA) | C95500 |
| ASTM casting | B148 (sand), B505 (centrifugal), B271 (continuous) |
| EN 1982 (EU) | CC333G |
| ISO / DIN | CuAl10Fe5Ni5 |
| BS 1400 (UK) | AB2C |
| SAE | J461 / J462 |
| AMS | 4880 |
Mechanical Properties of C95500
/CAD 955 Aluminum Bronze
(Typical As-Cast, ASTM B148)
| Property | Typical range | Note |
|---|---|---|
| Tensile strength | 620 – 760 MPa (90 – 110 ksi) | Higher than many bearing bronzes |
| Yield strength (Rp0.2 / 0.5) | 275 – 415 MPa (40 – 60 ksi) | Good resistance to permanent set |
| Elongation at break | 5 – 15% | Some toughness and shock resistance |
| Brinell hardness | 170 – 200 HB | Supports resistance to abrasive flushing |
| Density | 7.53 g/cm³ | About 86% of steel |
| Elastic modulus | 96 – 120 GPa | — |
| Magnetic permeability | ≈ 1.2 – 1.3 | Nearly non-magnetic |
Values vary with casting method (sand / centrifugal / continuous), heat-treatment condition, and wall thickness. Centrifugal casting (B505) gives sound blanks that suit wear-ring production.
Where the Wearing Ring Sits in a Fire Water Pump
The wearing ring is installed at the clearance interface between the rotating impeller (or impeller eye/neck) and the stationary pump casing on the suction side. Two rings form the seal: a stationary casing wear ring fixed in the casing, and a rotating impeller wear ring fixed on the impeller. A controlled running clearance is kept between them.
Functions of the Wearing Ring
- Limit internal recirculation: restricts short-circuit flow from the high-pressure discharge side back to the low-pressure suction side, maintaining hydraulic efficiency.
- Sacrificial protection: absorbs friction and erosion as a replaceable part, protecting the more costly casing and impeller.
- Rotor stability: the casing-side ring generates a hydraulic restraining force that helps damp vibration.
- Axial-thrust balance: in NFPA 20 fire-pump designs, the impeller is often balanced with balance holes and wear rings to manage axial load.
NFPA 20 / UL 448 / FM Material Position
| Component | NFPA 20 / UL 448 / FM requirement |
|---|---|
| Pump casing | GG25 grey iron / GGG40 ductile iron (by pressure class) |
| Impeller | Bronze or stainless steel casting (grey iron impeller not used) |
| Shaft | AISI 316 stainless steel |
| Wear ring | Bronze |
| Gland / lantern ring | Bronze |
Listed centrifugal types under NFPA 20 — end-suction, horizontal split-case, vertical turbine, and in-line — commonly use wear rings at the impeller–casing clearance. Fire-pump media are typically clean water and seawater (no solid particles); coastal, offshore, and port installations often draw seawater or brackish water, which raises the corrosion requirement on the ring.
Why C95500 Is Selected for Fire Water Pump Wearing Rings
1Standard compliance. NFPA 20 classifies the wear ring as bronze. C95500 is a bronze casting under ASTM B148, so it meets that clause. Fire pumps emphasize standby reliability, and the standard favors corrosion-resistant bronze over ordinary iron.
2Galling resistance with 316 stainless steel. Fire-pump shafts and impellers are often AISI 316. Bronze and stainless steel are dissimilar metals, so contact is less prone to same-hardness friction welding/seizure. C95500 paired with 316 stainless steel is a common arrangement for wear rings in large fresh- and saline-water pumps.
3Erosion-corrosion resistance in the high-turbulence zone. The ring sits in a high-velocity region near the impeller eye. In saline water, selecting a material with strong resistance to erosion-corrosion in this zone helps slow clearance growth and the resulting efficiency loss.
4Seawater and chloride corrosion resistance. The nickel addition strengthens the protective oxide film, giving favorable resistance to pitting and crevice corrosion for coastal, offshore, and brackish service. In systems using cathodic protection, the potential relationship between bronze and stainless steel is also manageable.
5Strength and hardness for wear. Tensile near 760 MPa and hardness near 200 HB support resistance to flushing by small suspended solids, shock loading, and dimensional stability, which helps extend inspection intervals.
6Nearly non-magnetic and non-sparking. Magnetic permeability around 1.2 – 1.3; aluminum bronze is generally non-sparking, which suits fire and potentially flammable environments.
7Casting and machinability. Sand, centrifugal, and continuous casting are available. Centrifugal casting gives sound blanks for rings, and the machinability rating (about 50, with free-cutting brass at 100) supports tight clearance fitting.
C95500 vs C95400 vs 316 Stainless Steel
| Property | C95500 Ni-Al Bronze | C95400 Al Bronze | 316 Stainless Steel |
|---|---|---|---|
| Nickel content | 3.0 – 5.5% | ≤ 1.5% | — |
| Tensile strength | 620 – 760 MPa | ≈ 655 MPa | ≈ 515 – 620 MPa |
| Hardness | 170 – 200 HB | ≈ 170 HB | ≈ 150 – 200 HB |
| Galling vs 316 SS | Favorable | Good | Moderate (same-hardness risk) |
| Seawater corrosion | Favorable | Good | Good (Mo-bearing) |
| Erosion-corrosion in high-turbulence zone | Favorable | Good | Moderate |
| Fire-pump wear-ring suitability | High (seawater / heavy duty) | Medium–High (clean fresh water) | Medium (needs galling control) |
“Favorable / Good / Moderate” are relative qualitative ratings for selection discussion, not a substitute for case-specific calculation and standard verification. Grey iron is not used for fire-pump wear rings under NFPA 20.
When to Specify C95500
Specify C95500 when:
- The water source is seawater, brackish water, or a coastal/offshore chloride environment;
- The pump is a high-speed, high-flow unit held in standby (typical fire duty);
- The ring runs against an AISI 316 stainless steel impeller/shaft and galling control matters;
- Long inspection intervals and lower maintenance cost are required.
Pairing guidance: use C95500 for the stationary casing ring (prefer centrifugal casting, ASTM B505), and AISI 316 for the rotating impeller/shaft, so the dissimilar metals reduce galling risk. C95500 vs C95400: for clean fresh water with low corrosivity, C95400 may be the lower-cost option; where seawater or high-turbulence erosion-corrosion is expected, the nickel addition in C95500 adds value.
C95500 Wear Rings from VIIPLUS SOLUTIONS ®
VIIPLUS SOLUTIONS ® supplies C95500 nickel aluminum bronze wearing rings and related bronze components for fire water pumps and other centrifugal pump services. Rings are produced to drawing, with casting method, heat treatment, and material test reporting reviewed against the specified standard.
For bronze wear rings, self-lubricating bearings, and pump components, visit bronzeoilless.com.
Frequently Asked Questions
Is C95500 accepted by NFPA 20 for fire pump wear rings?
NFPA 20 classes the wear ring as bronze. C95500 is a bronze casting under ASTM B148, so it meets the bronze requirement. Final acceptance depends on the specific pump listing and project specification.
Can C95500 run against a stainless steel impeller?
Yes. C95500 paired with AISI 316 stainless steel is a common arrangement because the dissimilar metals reduce galling risk compared with same-hardness contact.
Should I choose C95500 or C95400 for a seawater fire pump?
For seawater or brackish service, C95500 is generally preferred because the nickel addition improves corrosion and galling behavior. C95400 may suit clean fresh water with lower corrosivity.
