Skip to content
Home » Knowledge » What Is PREN (Pitting Resistance Equivalent Number)

What Is PREN (Pitting Resistance Equivalent Number)


What is PREN – Pitting Resistance Equivalent Number, abbreviated as PREN, is a set of algorithms calculated on the basis of the mass fraction of certain elements in the metal. The value is often used in the evaluation method for comparison of pitting corrosion resistance.

what is PREN

There are several Pitting Resistance Equivalent Number formulas in different versions of the data, but generally speaking, this formula is the most widely used:

PREN = 1*Cr% + 3.3 * Mo% + 16 * N%.

There is a version of the pitting corrosion resistance equivalent value Pitting Resistance Equivalent Number formula is more accurate: There are a few stainless steels which add tungsten (W), for thosethe following formula is used PREN = 1 x Cr% + 3.3 ( Mo% + 0.5 x W% ) + 16 x N%

Metals with higher PREN values appear to be more resistant to localized corrosion than metals with lower Pitting Resistance Equivalent Number values.

In general, metals with a PREN value greater than 32 can be used to resist seawater pitting corrosion. For safety and stability, materials with a PREN value greater than 40 such as S31254 super stainless steel pipe and 2507 super duplex pipe are often used in the seawater environment and offshore service.

Anti-pitting measurement method:

ASTM G48 standard specifies the precise pitting corrosion test procedure.

The Pitting Resistance Equivalent Number values of common special metals are as follows:

Tungsten (W) is known to have an effect on the piting resistance and for some grades a modified formula is used: PREN = Cr+ 3.3(Mo +0.5W)+ 16N

Stainless Steel and Duplex Steel PREN
PREN values for Stainless Steel and Duplex Steel

Kaysuns provide super duplex pipe and fittings with Pitting Resistance Equivalent Number>=40 to match the requirements of shipping building and seawater equipments.