PREN Value

The PREN value (Pitting Resistance Equivalent Number) is a theoretical index used to evaluate the resistance of stainless steel to pitting corrosion, particularly in chloride-containing environments such as seawater. A higher PREN value indicates better corrosion resistance. The PREN value is calculated based on the chemical composition of the steel, taking into account the chromium (Cr), molybdenum (Mo) and nitrogen (N) content. A common formula is:

PREN = %Cr + 3.3 × %Mo + 16 × %N

For some alloys, the tungsten (W) content is also included:

PREN = %Cr + 3.3 × (%Mo + 0.5 × %W) + 16 × %N

Typical PREN values for different types of steel:

Steel grades	PREN values
1.4162	17-21
1.4301	18-19
1.4404	25-26
1.4410	33-35
1.4435	28-30
1.4439	31-33
1.4462	32-34
1.4501	12-13
1.4529	38-40
1.4539	40-42
1.4541	18-19
1.4571	25-27
1.4828	25-27
1.4841	20-22

Stainless steels with a PREN value above 32 are considered seawater resistant.