# Pitting Resistance Equivalent Number (PREN)

Written by Jerry Ratzlaff on . Posted in Metal

PERN, a dimensionless number, is a way to measure the pitting corrosion resistance of various types of stainless steel in a chlorine based environment.  The composition of the stainless steel will affect the corrosion resistance.  The higher the number, the more pitting corrosion resistance the material has.

## Pitting Resistance Equivalent Number (PREN) Formula

$$\large{ PERN = C \;+\; \left( 3.3 * M \right) \;+\; \left( 16 * N \right) }$$
Symbol English Metric
$$\large{ PERN }$$   (Greek symbol alpha) = pitting resistance equivalent number $$\large{ dimensionless }$$
$$\large{ C }$$ = chromium in percentage $$\large{ dimensionless }$$
$$\large{ M }$$ = moybdenum in percentage $$\large{ dimensionless }$$
$$\large{ N }$$ = nitrogen in percentage $$\large{ dimensionless }$$

Tags: Corrosion Equations