PREN Calculator
Calculate the Pitting Resistance Equivalent Number (PREN) to evaluate the corrosion resistance of stainless steels and high-alloy materials, especially in chloride-containing environments such as marine and chemical applications.
PREN
Calculator
PREN = %Cr + 3.3×(%Mo + 0.5×%W) + 16×%N
Cr%
Mo%
W%
N%
PREN: 0
Enter alloy composition values
Quick Answer
- Higher PREN = Better pitting corrosion resistance
- Widely used for stainless steel selection
- Critical for marine, offshore, and chemical environments
Core Formula
PREN = %Cr + 3.3(%Mo + 0.5%W) + 16%N
How to Use
- Enter alloy composition values:
- Chromium (Cr %)
- Molybdenum (Mo %)
- Tungsten (W %) (optional)
- Nitrogen (N %)
- The calculator will instantly output:
- PREN value
👉 Use the result to compare corrosion resistance between materials
What PREN Means
Chromium (Cr)
- Base element for corrosion resistance
- Forms protective oxide layer
Molybdenum (Mo)
- Improves resistance to pitting and crevice corrosion
- Critical in chloride environments
Tungsten (W)
- Enhances pitting resistance (similar to Mo)
Nitrogen (N)
- Strongly increases corrosion resistance
- Improves strength
PREN Interpretation Guide
| PREN Value | Corrosion Resistance | Typical Use |
|---|---|---|
| < 25 | Low | Mild environments |
| 25 – 32 | Moderate | General industrial |
| 32 – 40 | High | Marine environments |
| > 40 | Very High | Offshore / aggressive chemicals |
Example Calculation
Material Composition:
- Cr = 18%
- Mo = 2.5%
- W = 0%
- N = 0.1%
Step Calculation
PREN = 18 + 3.3(2.5 + 0.5times0) + 16times0.1
👉 Result:
- PREN ≈ 26.75
- Suitable for moderate corrosion environments
Common Material PREN Values
| Material | PREN |
|---|---|
| 304 Stainless Steel | ~18–20 |
| 316 Stainless Steel | ~24–26 |
| Duplex 2205 | ~35 |
| Super Duplex 2507 | >40 |
Engineering Applications
- Marine components
- Offshore oil & gas
- Chemical processing
- Heat exchangers
- Pumps and valves
Design Tips
When to Use High PREN Materials
- Seawater exposure
- Chloride-rich environments
- High temperature + corrosion
Material Selection Strategy
- PREN < 25 → indoor or low corrosion
- PREN 25–35 → general industrial
- PREN > 35 → harsh environments
Important Notes
- PREN is a guideline, not absolute
- Real performance depends on:
- Temperature
- Surface finish
- Stress conditions
FAQ
What is PREN?
A numerical index estimating resistance to pitting corrosion.
Is higher PREN always better?
Yes for corrosion resistance, but cost increases.
Does PREN apply to all metals?
No, mainly for stainless steels and alloys.
Why is nitrogen so important?
It significantly boosts corrosion resistance and strength.
Can PREN replace material testing?
No, always validate with real testing and standards.
