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Chemical and Process Engineering Resources

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Category: Corrosion
Question: Is it possible to compare the resistance to chloride attack of several materials of construction?
Keywords: v1i11,pitting,resistance,index,pre,chloride,attack,comparison,materials
Answer: The Pitting Resistance Equivalent Index (PRE) can be used for such a comparison if the chemical make-up of each material is known. The formula for the PRE is:PRE = % Cr + (3.3 x % Mo) + (30 x % N)As an example, let's say that one wanted to compare the resistance to pitting of 316 SS, Incoloy 825, and 254 SMO. The major components of each material is:316 SS : 17% Chromium, 2.5% Molybdenum, and 0.10% NitrogenIncoloy 825:21.5% Chromium, 3.0% Molybdenum, and no N2254 SMO:19.5% Chromium, 6.0% Molybdenum, and 0.18% NitrogenPRE (316SS) = 28PRE (Incoloy 825) = 31PRE (254 SMO) = 45So, we can confirm from this index that under most circumstances, 254 SMO will be more resistant to cloride pitting attack that both 316 SS and Incoloy 825.