N08904 (904L) vs 316L vs 2205: Choosing the Right Corrosion-Resistant Alloy
N/A - Selection Guide · Published: 2026-06-01 · Updated: 2026-06-02
This is a selection guide, not a single material specification. When choosing between stainless steels for severe corrosive environments, the primary decision metric is PREN (Pitting Resistance Equivalent Number = %Cr + 3.3×%Mo + 16×%N). 304:...
This is a selection guide, not a single material specification. When choosing between stainless steels for severe corrosive environments, the primary decision metric is PREN (Pitting Resistance Equivalent Number = %Cr + 3.3×%Mo + 16×%N). 304: PREN 18-20 (atmospheric, freshwater). 316L: PREN 24-28 (coastal, mild chemical). 904L: PREN 34-38 (sulfuric acid, severe chemical). 2205 Duplex: PREN 34-38 (seawater, high strength needed). 254 SMO (6% Mo): PREN 42-44 (seawater heat exchangers, bleach plants). AL-6XN: PREN 45-48 (offshore, FGD scrubbers). Inconel 625: PREN >50 (ultimate seawater/chemical). Always verify with corrosion testing under actual service conditions rather than relying solely on calculated PREN values.
Quick Facts
| Category | Stainless Steel |
| Standard | N/A - Selection Guide |
| Density | 8.00 g/cm³ |
| Yield Strength | N/A - selection guide |
| Tensile Strength | N/A - selection guide |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| 904L | Compare |
| 316L | Compare |
| 2205 | Compare |
| 6% Mo Super Austenitic | Compare |
Related Materials
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Frequently Asked Questions
What PREN is sufficient for seawater service?
For ambient-temperature seawater with cathodic protection: PREN ≥32 (2205 duplex minimum). For warm seawater (>30°C) without cathodic protection: PREN ≥40 (super duplex 2507 or 6% Mo super austenitic). For seawater-chlorinated systems (hypochlorite generation): PREN ≥40 plus sufficient nickel for resistance to active corrosion. The European standard NORSOK M-001 provides detailed material selection guidance for offshore seawater systems.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu