When selecting materials for split case pumps in aggressive environments—seawater cooling, chemical processing, or desalination—duplex stainless steels are the gold standard. But which one is right for your application: Duplex 2205 or Super Duplex 2507?
Choosing incorrectly can lead to premature pitting, stress corrosion cracking (SCC), or unnecessary capital expense. At Hunan Durafort Pumps, our XSP series horizontal split case pumps are available in both Duplex SS2205 and Super Duplex SS2507, along with other high-performance alloys. This guide will help you make the right material decision for your split case pump investment.
Why Duplex Stainless Steel for Split Case Pumps?
Duplex stainless steels offer a unique combination of:
- High strength (twice that of 304/316L) – Allows thinner casings and lighter weight
- Excellent chloride corrosion resistance – Ideal for seawater, brackish water, and chemical duty
- Good fatigue resistance – Critical for pumps with variable flow or frequent starts
- Cost-effective alternative to titanium or nickel-based alloys
For horizontal split case pumps like Durafort’s XSP series (flows 135–38,000 m³/h, heads 12–205 m), duplex materials ensure decades of reliable service in marine, power plant, and desalination cooling water systems.
Quick Comparison: Duplex 2205 vs Super Duplex 2507
| Property | Duplex 2205 (UNS S31803/S32205) | Super Duplex 2507 (UNS S32750) |
|---|---|---|
| Pitting Resistance Equivalent (PREN) | 34–38 | >40 (typically 41–45) |
| Yield strength (MPa) | ≥450 | ≥550 |
| Tensile strength (MPa) | ≥620 | ≥795 |
| Critical pitting temperature (CPT) | ~50°C in 3.5% NaCl | ~80°C in 3.5% NaCl |
| Chloride limit (ppm) | ~1,000–2,000 ppm | ~5,000–10,000 ppm |
| Stress corrosion cracking resistance | Good up to ~100°C | Excellent up to ~150°C |
| Relative cost | Baseline (1.0x) | ~1.5–1.8x |
| Typic pump applications | Seawater cooling, brackish water, low-to-medium chlorides | High-chloride seawater, produced water, sour service |
PREN = %Cr + 3.3×%Mo + 16×%N – Higher PREN means better pitting resistance.
How to Choose: A Decision Framework for Split Case Pumps
Choose Duplex 2205 When:
- Chloride concentration is below 2,000 ppm – Typical for brackish water, river estuaries, or treated seawater.
- Fluid temperature is below 50–60°C – Cooling tower circulation, river water intake, municipal wastewater.
- Budget is a primary concern – 2205 offers excellent value with much better corrosion resistance than 316L.
- No hydrogen sulfide (H₂S) or sour service – For oilfield water injection, upgrade to 2507.
Ideal XSP split case pump applications for 2205:
- Power plant cooling water (brackish or low-chloride seawater)
- Desalination pretreatment pumps
- Marine ballast pumps (moderate salinity)
- Chemical plant cooling loops with mild chlorides
Choose Super Duplex 2507 When:
- Chloride concentration exceeds 2,000 ppm – Full-strength seawater (19,000–26,000 ppm Cl⁻).
- Fluid temperature exceeds 60°C – Hot seawater return lines, condenser outlet service.
- Presence of H₂S or low pH – Oilfield produced water, sour gas plant cooling, FGD scrubber slurry.
- High erosion-corrosion risk – Sand-containing seawater or abrasive slurries.
- Maximum uptime required – Offshore platforms, nuclear power plant safety-related pumps.
Ideal XSP split case pump applications for 2507:
- Direct seawater intake pumps (once-through cooling)
- Offshore platform firewater and cooling pumps
- High-temperature condenser circulation (>70°C)
- Desalination high-pressure feed (with appropriate rating)
Material Compatibility Table for XSP Split Case Pumps
Hunan Durafort manufactures the XSP horizontal split case pump in both 2205 and 2507, plus other alloys:
| Material | PREN | Best For | Relative Cost |
|---|---|---|---|
| Carbon steel | N/A | Clean, non-corrosive water | Lowest |
| Ductile iron | N/A | Municipal water, low chlorides | Low |
| SS304 | 18–20 | Clean, low-chloride (<200 ppm) | Low-moderate |
| SS316L | 24–26 | Chlorides <500 ppm | Moderate |
| Duplex 2205 | 34–38 | Chlorides 500–2,000 ppm, to 60°C | High |
| Super Duplex 2507 | 41–45 | Chlorides >2,000 ppm, to 150°C | Very high |
| 904L | 34–36 | Acidic, low-chloride (better for sulfuric acid) | Very high |
| CD4MCu | 35–40 | Abrasive + corrosive (ash sluicing, mine water) | Very high |
| Titanium | >50 | Extreme chlorides (>50,000 ppm), hot seawater | Highest |
Real-World Example: Power Plant Seawater Cooling
Scenario: A 1,000 MW coastal power plant needs circulating water pumps (CW pumps) for once-through seawater cooling.
- Chloride: 19,000 ppm
- Temperature: 15°C (winter) to 35°C (summer)
- Flow per pump: 25,000 m³/h
| Material | Expected Life | Issue |
|---|---|---|
| SS316L | <2 years | Severe pitting and crevice corrosion |
| Duplex 2205 | 5–8 years | Acceptable but some pitting in crevices |
| Super Duplex 2507 | 20+ years | No pitting, excellent performance |
Conclusion: Super Duplex 2507 is the correct choice despite higher upfront cost—lower total cost of ownership over 20 years.
Maintenance Considerations for Duplex Split Case Pumps
Whether you choose 2205 or 2507 for your Durafort XSP pump:
- Avoid galvanic coupling with less noble metals (carbon steel, copper alloys)
- Welding requires qualified procedures – Duplex alloys need proper heat input and post-weld cleaning
- Inspect for chloride pitting annually in seawater service
- Replace gaskets with PTFE or EPDM – Avoid graphite which can promote galvanic corrosion
The split case design of the XSP makes all inspections and wear ring replacements straightforward without pulling piping or motor.
Get Expert Help Choosing the Right Duplex Material
Hunan Durafort Pumps provides material selection engineering for every XSP split case pump. Send us your water chemistry, temperature, and expected runtime—we’ll recommend 2205, 2507, or alternative alloys like CD4MCu or titanium.
📧 Email: sales@deyangforge.com
🌐 Website: https://deyangforge.com
