"We are a valve manufacturer, there is a inquiry for valve in Napthalitic Acid with a TAN rating between 4.4 and 8.0, the operating temperature is 950 degrees F. I never heard of this Acid before, I hope someone can tell me what is the characteristic of Napthalitic acid, the meaning of TAN and help me with the selection of trim material. The resistance material must contained greater than 2.5% Molybdenum content and the presence of Chromium and Nickel. I believe Inconel 718 will do the job however, I'm looking for alternate material for cost reduction."
I believe that you are referring to naphthenic acid, an organic acid occurring in some crude oils, as produced. TAN refers to Total Acid Number, and is an analytical procedure for quantifying the amount of naphthenic acid. Our experience with naphthenic acid is in the refining industry, where either 316SS or 317SS is used to resist corrosion from high temperature naphthenic acid. Certainly alloy 718 should be resistant. Specifying an optimium trim material for your valve service, based on your description, is difficult as other variables may also influence selection, including the need for wear resistance, and other combustion products that can cause corrosion, including vanadium and sodium salts.
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