How is PREN calculated?
The Pitting Resistance Equivalent Number (PREN) is the standard measurement for corrosion resistance. While basic calculators often ignore Tungsten (W), Sverdrup Steel uses the extended formula required for high-performance alloys.
The Extended Formula
PREN = %Cr + 3.3 × (%Mo + 0.5 × %W) + 16 × %N
Why Tungsten (W)?
In Super Duplex grades like UNS S32760, Tungsten is added to stabilize the material and increase resistance to pitting.
| Grade | Typical PREN | Application |
|---|---|---|
| 316L | ~ 24 | Basic corrosive environments |
| Duplex (2205) | ~ 35 | Stress corrosion resistant |
| Super Duplex | > 40 | Severe marine conditions |
| 6Mo / 254 SMO | > 50 | Chemical processing (H2SO4) |
Frequently Asked Questions
+ What PREN is required for seawater?
For seawater service and severe marine environments, the industry standard (such as Norsok) typically requires a PREN > 40. This is why Super Duplex is the preferred choice for subsea applications.
+ Which elements increase PREN?
Chromium (Cr), Molybdenum (Mo), and Nitrogen (N) are the key elements. Nitrogen is particularly effective, having a factor of 16 in the formula.
+ Is PREN the only factor for corrosion?
No. PREN only predicts pitting resistance. Factors like temperature (CPT), pH level, and crevice design also play a massive role in material selection.
Note: PREN is a theoretical indicator. For specific applications involving acids like H2SO4, please consult our technical team.
