PREN calculator
Calculate the Pitting Resistance Equivalent Number for stainless steels, duplex and nickel alloys, and compare grades on a single corrosion-resistance scale.
What is PREN?
PREN (Pitting Resistance Equivalent Number) ranks the pitting-corrosion resistance of stainless steels and nickel alloys on one scale, calculated from chromium, molybdenum, tungsten and nitrogen content. A higher PREN means greater resistance to pitting in chloride environments such as seawater. As a benchmark, 316L stainless steel has a PREN of about 25.
PREN = %Cr + 3.3 x (%Mo + 0.5 x %W) + 16 x %N. It compares grades against each other on a single scale; it does not predict absolute performance in a specific service condition. For more on how the figure is used, see Understanding PREN.
Calculate PREN
Enter a composition in weight %. Leave tungsten at 0 for grades that don't contain it.
Always confirm against the grade's own datasheet before specifying.
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PREN explained
PREN in under a minute
Prefer to watch? This short explainer covers what PREN is, the formula, and where it helps and where it does not.
- The formula and the role of chromium, molybdenum and nitrogen
- The thresholds that matter: PREN ≥ 40 for seawater, ≥ 48 for the toughest service
- The limits: pitting only, not crevice, temperature or fabrication effects
Frequently asked questions
What is the PREN formula?
PREN = %Cr + 3.3 x (%Mo + 0.5 x %W) + 16 x %N, using chromium, molybdenum, tungsten and nitrogen content. Grades without tungsten simply use a %W value of 0.
What PREN counts as super duplex?
A PREN above 40 is generally considered the super duplex range. A PREN of 32 to 40 falls in the duplex range, and lower values are typical of standard austenitic stainless steels such as 316L.
Does a higher PREN always mean better performance?
Not on its own. PREN compares grades against each other on a single scale; it does not predict absolute performance in a specific service condition - temperature, surface finish and other environmental factors all matter too.
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