"30% Sulfuric Acid and 316L"

Question:

"My experience suggests that although there may be better alternatives such as a duplex grade, 316L should be a good alternative for use in a 30% sulfuric acid environment at room temperature. We recently took a sample of 316L, and placed in in 30% sulfuric acid solution at room temp. for 24 hrs., and the sample developed a black discoloration. Is this actually a corrosion product, and if so, do you know what it is? Am I incorrect in my belief that 316L should be suitable for this environment? Will 316L tend to experience some corrosion rate over time in this solution?"

Answer:

The black corrosion product is probably a chromium oxide. I would not specify 316SS for long term use in room temperature, 30% sulfuric acid, expecially where velocities are present. The passive film can be unstable.

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