Material selection is critical for centrifugal pump reliability in chemical service, affecting corrosion resistance, mechanical strength, and cost. This guide compares stainless steel, Hastelloy, and duplex stainless steel for chemical pump applications.
Material Selection Factors
Corrosion Resistance
- General corrosion: uniform metal loss (acid, caustic)
- Pitting: localized (chloride, stainless steel)
- Stress corrosion cracking (SCC): tensile stress + corrosive
- Galvanic: dissimilar metals in electrolyte
- Erosion-corrosion: flow + corrosion (synergistic)
Mechanical Properties
| Material | Yield (MPa) | Tensile (MPa) | Hardness (HB) |
|---|---|---|---|
| 316L SS | 170 | 485 | 150 |
| Duplex 2205 | 450 | 620 | 220 |
| Super duplex 2507 | 550 | 800 | 270 |
| Hastelloy C-276 | 285 | 690 | 200 |
| Hastelloy B-2 | 350 | 750 | 230 |
Stainless Steel (316/316L)
Properties
- Austenitic stainless: 16-18% Cr, 10-14% Ni, 2-3% Mo
- 316L: low carbon (<0.03%), better weldability
- Advantages: good general corrosion, cost-effective, widely available
- Limitations: pitting in chloride, SCC in hot chloride, not for strong acid
- Use: water, caustic, mild chemical, food, pharmaceutical
Corrosion Resistance
- Good: caustic (NaOH), water, mild acid, organic solvents
- Poor: HCl, H2SO4 (dilute), HF, strong oxidizing acid
- Pitting: chloride >500 ppm, especially hot
- SCC: hot chloride + tensile stress (e.g., 80°C, >1000 ppm Cl)
- Temp: up to 400°C (oxidation), but corrosion limits
Cost and Availability
- Cost: low (baseline, 1×)
- Availability: excellent (standard material)
- Weldability: good (316L preferred)
- Machinability: fair (work hardens)
- Cast vs wrought: cast CF8M (316 cast equivalent)
Duplex Stainless Steel (2205/2507)
Properties
- Dual phase: austenite + ferrite (50/50)
- 2205: 22% Cr, 5% Ni, 3% Mo, 0.15% N
- 2507 (super duplex): 25% Cr, 7% Ni, 4% Mo, 0.27% N
- Advantages: high strength (2× 316), excellent pitting resistance
- Limitations: higher cost, limited high temp (>300°C), welding critical
Corrosion Resistance
- Excellent: chloride, seawater, brine, caustic
- Pitting resistance equivalent (PREN): 2205 = 35, 2507 = 42 (316 = 24)
- Good: H2SO4 (moderate), organic acid, phosphoric acid
- Poor: HCl (concentrated, hot), HF, strong reducing acid
- SCC: much better than 316 (resistant to chloride SCC)
Applications
- Seawater: desalination, marine, cooling water
- Chloride process: chlor-alkali, PVC, bleach
- Oil & gas: produced water, injection, desalination
- Pulp & paper: bleach plant, digester
- Chemical: mixed acid, high chloride, high strength needed
Hastelloy Alloys
Hastelloy C-276
- Nickel-molybdenum-chromium: 57% Ni, 16% Mo, 16% Cr, 5% Fe
- Advantages: excellent universal corrosion (oxidizing + reducing)
- Limitations: very high cost (5-10× 316), limited availability
- Use: severe corrosive, mixed acid, chemical process, flue gas desulfurization
- Temp: up to 1000°C (oxidation), but typically <500°C for corrosion
Hastelloy B-2/B-3
- Nickel-molybdenum: 68% Ni, 28% Mo, <1% Cr
- Advantages: excellent reducing acid (HCl, H2SO4 dilute)
- Limitations: not for oxidizing conditions, very high cost
- Use: HCl production, acetic acid, reducing chemical process
- Caution: oxidizing contaminants cause rapid corrosion
Hastelloy C-22
- Nickel-chromium-molybdenum: 56% Ni, 22% Cr, 13% Mo, 3% W
- Advantages: better than C-276 in oxidizing, mixed acid
- Limitations: high cost, less common than C-276
- Use: pharmaceutical, chemical, waste treatment, flue gas
- Temp: similar to C-276
Material Comparison
| Fluid | 316SS | Duplex 2205 | Hastelloy C-276 |
|---|---|---|---|
| Water (fresh) | ✓ | ✓ | ✓ |
| Seawater | △ (pitting) | ✓ | ✓ |
| NaOH (caustic) | ✓ | ✓ | ✓ |
| HCl (dilute) | ✗ | △ | ✓ |
| HCl (conc) | ✗ | ✗ | △ (B-2 ✓) |
| H2SO4 (dilute) | ✗ | △ | ✓ |
| H2SO4 (conc) | △ | △ | ✓ |
| HF | ✗ | ✗ | △ (Monel ✓) |
| Organic solvent | ✓ | ✓ | ✓ |
| Chloride (hot) | ✗ (SCC) | ✓ | ✓ |
Cost Comparison
- 316SS: baseline (1×)
- Duplex 2205: 1.5-2×
- Super duplex 2507: 2-3×
- Hastelloy C-276: 5-10×
- Hastelloy B-2: 6-12×
- Consider: lifecycle cost (corrosion, downtime) vs material cost
Selection Guide
When to Use 316SS
- Mild to moderate corrosive (caustic, water, organic)
- Low chloride (<500 ppm, cold)
- Cost-sensitive application
- Food, pharmaceutical, general chemical
- Not for: strong acid, hot chloride, seawater
When to Use Duplex
- High chloride (seawater, brine, chlor-alkali)
- High strength needed (high pressure, large pump)
- Moderate acid (H2SO4, phosphoric)
- Need SCC resistance (hot chloride)
- Not for: HCl concentrated, HF, >300°C
When to Use Hastelloy
- Severe corrosive (mixed acid, strong oxidizing/reducing)
- HCl (all concentrations, B-2 for reducing)
- High temp corrosive (>200°C)
- Critical service (safety, environmental)
- Consider: cost vs downtime, material availability
Common Issues
- 316SS in chloride: Pitting, SCC. Use duplex or Hastelloy.
- 316SS in strong acid: Rapid corrosion. Use PTFE, Hastelloy, or duplex (per acid).
- Duplex welding: Phase imbalance, corrosion. Use proper filler, heat control.
- Hastelloy cost: Over-specification. Evaluate if 316/duplex sufficient.
- Galvanic corrosion: Dissimilar metals. Use compatible, isolate, or cathodic protection.
- Stress corrosion: 316 + chloride + stress. Use duplex, stress relief.
- Erosion-corrosion: High velocity + corrosive. Lower speed, use resistant material.
- Wrong alloy grade: B-2 in oxidizing, C-276 in HCl. Verify per fluid.
Procurement Recommendations
- Provide: fluid composition, concentration, temp, pressure, chloride, impurities
- For chloride/seawater: specify duplex 2205 or 2507
- For severe corrosive: specify Hastelloy C-276 or B-2 (per fluid)
- Require material certificate (MTR EN 10204 3.1)
- For duplex: require ferrite content check (30-70%)
- For welded: require weld procedure (WPS) and inspection
- Specify all wetted parts (impeller, casing, shaft, seal faces)
- Consider: galvanic compatibility (all wetted parts same or compatible)
- For critical: require corrosion test or reference list
- Evaluate lifecycle cost (not just material cost)
- Verify supplier has material selection experience for chemical pumps
Related Industries
Centrifugal pump material selection applies to chemical processing (acid/caustic/solvent), oil & gas (produced water, injection), pharmaceutical (API, solvents), semiconductor (high purity), desalination (seawater), pulp & paper (bleach, digester), mining (leaching, acid), and general industrial (process pumps). The core principle — proper material selection based on fluid chemistry, temperature, and mechanical requirements for reliable pump operation — is consistent across all chemical pump applications.