Material selection for centrifugal pumps is a critical decision beyond a procurement checklist that impacts performance, reliability, safety, and the project's CAPEX and OPEX. Centrifugal pumps transfer various fluids from clean water to acidic solutions, and choosing a pump with the right material combination isn't optional; it's a must.
The following are important factors to evaluate when choosing materials for centrifugal pump components.
Understand the Operating Environment First
Before proceeding with the material selection, the main questions to answer are: what will the pump handle, and where will it operate?
- Fluid composition: is it clean water, raw sewage, seawater, an acid, or a slurry? Each fluid has unique challenges, such as corrosive chemicals, solid particles, or scaling compounds.
- Operating conditions: we should consider operation parameters such as flow rate, pressure, temperature, pH, and the presence of dissolved gases.
- Installation environment: will the pump be outdoors, in a harsh marine environment, or near aggressive vapors?
Failing to assess the operating environment is one of the leading causes of premature pump failure.
Key Criteria for Material Selection
Some of the most important factors to consider:
- Corrosion resistance: pumps that handle corrosive fluids (e.g., acids, chlorides, or seawater) need materials like 316 stainless steel, duplex steel, or Hastelloy. A mismatch here can lead to pitting, crevice corrosion, or total material degradation.
- Erosion and abrasion resistance: slurries or fluids with suspended particles will erode impellers and casings over time. Hardened stainless steel, rubber linings, or ceramic coatings are common choices for such cases.
- Temperature resistance: carbon steel or high-grade alloys are needed for high-temperature applications such as hot oil or steam condensate.
- Mechanical strength: the material's mechanical strength and fatigue resistance become critical for high-pressure services. Specific applications may demand ductile iron, alloy steels, or even titanium.
- Compatibility with seals and bearings: material compatibility extends beyond the pump volute and impeller. All wetted components, including elastomers and seal faces, must be suitable for the pump's actual operating conditions.
- Cost-effectiveness: exotic alloys offer performance but can be costly. Achieving a balance between durability and budget is a practical approach in most scenarios where safety is not compromised.
- Standards and compliance: some industries (e.g., oil & gas, pharmaceuticals) require compliance with API, ISO, NFPA, or NACE standards. Be sure your material selection meets these guidelines.
Pitting Resistance Equivalent Number
PREN is a calculated value that estimates a material's resistance to localized corrosion, particularly pitting, in chloride-containing environments. It is commonly applied to stainless steel and duplex alloys. The PREN is determined based on the chemical composition, primarily the chromium, molybdenum, and nitrogen amounts. In material selection for pumps, especially those handling seawater, brine, or aggressive industrial effluents, a higher PREN indicates better corrosion resistance and helps engineers choose materials that offer long-term durability and safety in harsh conditions. For general guidance, a PREN of 25–30 is typically sufficient for freshwater or mildly corrosive environments, while PREN values above 40 are recommended for seawater, high-chloride media, and aggressive industrial effluents. Extremely harsh environments, such as those involving acidic chlorides or oxidizing acids, may require materials with PREN > 45 or specialized alloys designed for maximum corrosion resistance.
Common Materials in Centrifugal Pumps
Pump manufacturers offer a wide range of materials to meet the diverse requirements of various industries, fluids, and operating environments. Material selection plays a crucial role in ensuring pump performance, longevity, and cost-effectiveness. KSB, a global leader in pump and valve technology, provides a comprehensive range of materials for standard and severe service applications. The following list outlines the most commonly used cast materials in KSB centrifugal pumps.
1. Grey Cast Iron
- Designation: EN-GJL-250 (ASTM A48 Class 35B)
- Applications: clean or mildly contaminated wastewater, stormwater, etc.
- Features: cost-effective, excellent vibration damping.
2. Nodular Cast Iron
- Designation: EN-GJS-400-15 / EN-GJS-500-7 (ASTM A536 Grades 60-40-18 & 80-55-06)
- Applications: general wastewater with moderate mechanical loading.
- Features: high tensile strength, ductility, and shock resistance.
3. Norihard: High Chromium White Iron
- Designation: GX250CrMo15-3 (ASTM A532 Class III Type A)
- Applications: slurries, raw sewage, aluminum oxide suspensions.
- Features: exceptional abrasion resistance (750–1000 HV).
4. Noriloy: Wear & Slightly Corrosive Service
- Designation: GX170CrMo25-2
- Applications: slurries, aggressive pit water, acidic wastewater.
- Features: hardened ferritic matrix with high chromium and molybdenum; high wear resistance.
- Hardness: ≥ 500 HV
- PREN: ~33–35
5. Austenitic Stainless Steel
- Designation: 1.4408 (ASTM A743 CF8M)
- Applications: chlorinated water, light chemicals, food and beverage.
- Features: strong corrosion resistance, weldable.
- PREN: ~25
6. Norinox: Low-Carbon Austenitic Stainless Steel
- Designation: GX3CrNiMo19-11-2 (1.4409 approx.), ASTM A743 CF3M
- Applications: wastewater, offshore, marine, general industry.
- Features: excellent corrosion resistance, impact toughness, and weldable.
- PREN: ~25–28
7. Duplex Stainless Steel
- Designation: 1.4469 / GX2CrNiMoCuN25-6-3-3 (ASTM A890 Grade 5A)
- Applications: seawater, desalination, brines, chemical effluents.
- Features: high strength, excellent resistance to pitting, crevice corrosion, and SCC.
- PREN: ~40–41
8. Noridur: Duplex Stainless Steel
- Designation: GX3CrNiMoCuN24-6-2-3 / 1.4593 (ASTM A995 Grade 1B)
- Applications: marine, chemical, wastewater, FGD, offshore.
- Features: excellent strength, corrosion, and cavitation resistance; weldable.
- PREN: 35.7
9. Noricrom: Triplex Stainless Steel
- Designation: GX150CrNiMoCuN41-6-2 / 1.4475
- Applications: highly acidic, chloride-laden media with solids.
- Features: exceptional wear + corrosion resistance from carbide network; not weldable.
- PREN: ~36–39 (estimated based on composition)
10. Noriclor: Super Duplex Stainless Steel
- Designation: GX3CrNiMoCuN24-6-5 / 1.4573
- Applications: aggressive chloride-rich and acidic media, marine systems.
- Features: extremely high corrosion resistance and strength; weldable.
- PREN: 43.7
11. Noricid: High-Silicon Austenitic Stainless Steel
- Designation: GX3CrNiSiN20-13-5 / 9.4306
- Applications: nitric, chromic, and sulphuric acids (boiling concentrations).
- Features: superior resistance to oxidizing acids; weldable.
- PREN: low (~23–25), but corrosion resistance is driven by the SiO₂ passive layer, not the Cr-Mo-N balance.
Conclusion
Material selection in centrifugal pumps is both a science and a strategic decision. Choosing the right material means better performance, longer service life, and fewer failures. Since every application has own challenges, such as corrosion, abrasion, temperature, or chemical exposure, aligning the pump's construction with real-world conditions is essential. Pump manufacturers and designers have the technical knowledge and field experience to guide you in selecting the most suitable and cost-effective material for project needs. If you're planning a new installation or reevaluating existing equipment, consider talking with a pump manufacturer for further assistance and consultation.