Hot-Dip Galvanized Steel in Chemical Solutions
A primary factor governing galvanized coating corrosion behavior in liquid chemical environments is the solutions pH. Galvanizing performs well in solutions of pH above 4.0 and below 12.5. This should not be considered a hard and fast rule because factors such as agitation, aeration, temperature, polarization, and the presence of inhibitors also may change the corrosion rate. Within the pH range of 4.0 to 12.5 a protective film forms on the zinc surface and the galvanized coating protects the steel by slowing corrosion to a very low rate. The protective films exact chemical composition is somewhat dependent upon the specific chemical environment. Since many liquids fall within the pH range of 4.0 to 12.5, galvanized steel containers are widely used in storing and transporting many chemical solutions. Corrosion occurs in countless solutions and chemical environments, but the actual corrosion rates will vary dramatically depending on the specifics of each setting. While zinc typically offers excellent protection from corrosion in most situations, there are occasionally certain conditions where chemicals can react with zinc to produce acidic products that will increase the corrosion rate.
Frank C. Porter, one of the foremost authorities on zinc, has provided a number of charts in his book Corrosion Resistance of Zinc and Zinc Alloys, which provide detailed information on how zinc reacts with a large variety of chemicals and solutions. Mr. Porter has been kind enough to allow us to share these charts with you. The charts are not for reproduction or distribution and provided for general information only. Caution should be used when reviewing the information because a slight difference in the specifics of your environment can lead to inaccurate conclusions (for example looking at the figures for a dry chemical powder versus a concentrated solution).
The chemicals are listed in a variety of fashions (i.e. solutions, vapors, dry, moist, immersed, with varying degrees of strengths, and so forth), so it is necessary to have a complete understanding of the setting in question before attempting to make any specific assumptions. If you would like assistance in determining the reactivity of zinc when exposed to a particular chemical, or if you are interested in a chemical that is not listed in these charts, please email us.
© 2021 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.