PREN Calculator
PREN Calculator (Pitting Resistance Equivalent Number)
Compare pitting corrosion resistance for stainless steels and nickel alloys using Cr / Mo / W / N chemistry. For contract-critical decisions, use values from your mill test certificate (MTC).
Why PREN Matters in Real Procurement
PREN (Pitting Resistance Equivalent Number) is a fast way to compare how different alloys handle chloride-driven pitting corrosion. It is widely used in specification reviews for seawater piping, offshore structures, desalination, chemical service, and any system where “304 vs 316L vs duplex” decisions directly affect lifecycle cost.
For stainless projects, buyers often upgrade from 304 to 316L, duplex 2205, or super duplex grades to improve chloride pitting resistance. For contract-critical work, always use the exact chemistry from your MTC/EN 10204 3.1 certificate. See: Stainless Steel Sheet & Plate and Stainless Steel Strip & Coil.
How to Read PREN Bands (Practical Guidance)
| PREN Range | Practical Level | How buyers typically use it |
|---|---|---|
| < 24 | Basic austenitic range | General indoor or mild exposure; not recommended for chloride splash or warm stagnant brine. |
| 24 – 32 | Improved pitting resistance | Common “upgrade” zone (often 316/316L) for light marine washdowns with controlled chlorides. |
| 32 – 40 | Duplex-level resistance | Selected for chloride service where higher strength and better pitting resistance are required. |
| 40 – 50 | Super duplex / 6Mo range | High-risk chloride environments; used when 316L is insufficient and downtime is costly. |
| > 50 | Seawater / Ni-alloy range | Extreme resistance zone; nickel alloys are considered when temperature + chlorides + crevice risks stack up. |
Worked Examples (What the Calculator Shows)
- 304 often lands around PREN ≈ 19 (basic range) when Mo is near zero.
- 316L often lands around PREN ≈ 25 (improved range) due to Mo addition.
- Duplex 2205 commonly lands around PREN ≈ 35 (duplex-level) with higher Cr, Mo, and N.
- Super Duplex 2507 / 254SMO can move into the 40+ range (very high resistance).
- Nickel Alloy 625 / C-276 may exceed 50 depending on Mo/W (extreme zone).
When You Should Use PREN
- Seawater or brackish water piping and fittings
- Desalination and offshore equipment
- Chemical tanks where chlorides are present
- Heat exchangers with seawater cooling circuits
- Process lines where pitting failures create downtime risk
FAQ
What if my alloy is not listed?
Select Custom composition and enter Cr / Mo / W / N from your mill test certificate (MTC).
Is PREN a “pass/fail” standard?
No. PREN is a comparative index based on a limited set of elements. Final selection should consider temperature, crevice conditions, fabrication, finishing, cleanliness, and real service media.
Where can I learn more about corrosion vs grade choice?
See our related guides: Can Stainless Steel Rust? and 304 vs 316 Stainless Steel.
Related Resources on LYH Steel
About LYH Steel
LYH Steel supports global buyers with stainless steel, carbon steel, and coated steel supply, plus processing and export logistics. If you need help confirming grade choice for chloride environments, share your target standard and MTC requirements via our inquiry form.
