Pitting Resistance Equivalent Number
Pitting Resistance Equivalent Number (PREN) is a value used to evaluate the pitting corrosion resistance of stainless steels. It takes into account chromium, molybdenum, and nitrogen. Higher PREN values mean more resistance to chloride attack.
Physical-Chemical Mechanism of Action
The Pitting Resistance Equivalent Number (PREN) is a formula that quantifies the influence of chromium (Cr), molybdenum (Mo), and nitrogen (N) on the pitting corrosion resistance of stainless steels. These elements protect the metal against local chloride attacks by forming a stable protective layer on the surface.
Metallurgical Relevance & Welding Risks
A high PREN value means the steel is more resistant to local chloride attacks. At lower values, pitting can occur, especially in environments with chloride-rich air or water. This can impair the service life and safety of the components.
Workshop Practice & Instructions
To ensure a high PREN value, the following measures should be taken:
• Use steels with a high content of chromium and molybdenum.
• Keep the weld at the correct temperatures and times to obtain a homogeneous structure.
• Avoid overheating and overmelting of the steel, as this can reduce the PREN value.