Nickel Insitute - Nickel Alloys in Organic Acids & Related Compounds

extensive testing of the candidate alloys must be conducted beforehand to assure an adequate economic life of the equipment. When appraising stream compositions for corrosion testing or the designation of materials of construction, it is important to understand the unstable nature of the one- carbon compounds. Formaldehyde reacts readily with oxygen to produce the acid, and it is difficult to handle and store the aldehyde without generating sufficient formic acid to make a corrosive agent out of what would otherwise be a rather innocuous compound. It is for this reason that Type 304 stainless steel is often selected as the material of construction for formaldehyde storage tanks. Not only does the use of the stainless steel provide a trouble-free material of construction, but the lack of contamination of the aldehyde maintains good color in the solution and reduces the rate of oxidation of the product to additional acid. A brief summary of proper formaldehyde storage is provided by Teeple in reference 26. Formate esters are also most unstable. The methyl ester is often encountered in process streams, and, when any water is present, must be considered as contributing to a significant acidity in the medium.

FIG 7–Isocorrosion Chart for Type 304 Stainless Steel in Formic Acid

FIG 8–Isocorrosion Chart for Wrought “20 Type” Alloy in Formic Acid

FIG 5–Comparison of Types 304 and 316 Stainless Steels in Various Concentrations of Boiling Formic Acid

FIG 9–Isocorrosion Chart for HASTELLOY alloy B in Formic Acid

FIG 10–Isocorrosion Chart for HASTELLOY alloy C (C-276) in Formic Acid

FIG 6–Isocorrosion Chart for Type 316 Stainless Steel in Formic Acid

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