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PREN (pitting resistance equivalent)

The pitting-resistance equivalent number used to estimate the pitting resistance of stainless steels: %Cr + 3.3·%Mo + 16·%N.

PREN (Pitting Resistance Equivalent Number) is a rule-of-thumb formula to estimate a stainless steel's resistance to pitting. It adds the three most important elements, weighted: chromium, molybdenum (factor 3.3) and nitrogen (factor 16). The higher the value, the more resistant to chlorides. Benchmarks: below 24 = little chloride, 24–32 = coastal, above 32 = seawater and aggressive media.

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