Corrosive Chemicals and Galvanizing (2024)

What are some chemicals/substances hot-dip galvanized steel should not be used with?

The AGA has published multiple resources (see the publicationsSpecifiers GuideorPerformance of Hot-DipGalvanized Steel Products) listing chemicals, substances,and environments hot-dip galvanized steel cansuccessfully be used in or with. However, there are fewerresources available that discuss chemicals and substanceshot-dip galvanized steel should not be used with, or wherecaution should be used if galvanized steel will be specifiedfor an application.Although it is impossible to list all the chemicals extremelycorrosive to galvanized steel, there are some chemicalsand substances specifiers often ask about concerning thecorrosion rate of galvanized steel.

The following is a list ofthese chemicals and substances:

• Bleach, even when mixed with water, is very corrosive to galvanized steel. An alternativecleaning solution is a mixture of one part ammonia with 10 parts water and then rinsingthe galvanized coating with fresh water and allowing it to thoroughly dry.
• Chlorine, the base for many commonly used bleaches, is also very corrosive to galvanizedsteel. This means galvanized steel should not be used in chlorine water; however, hot-dipgalvanized structural steel has performed acceptably when used indoors above chlorinepools. Painting or powder coating galvanized structural steel in indoor pool environmentsis recommended to greatly increase the service life of both the paint or powder coatingand galvanized steel.
• Acids with a pH below 5.0 are corrosive to galvanized steel. The lower the pH and/or thestronger the acid solution, the more corrosive the acid will be to galvanized steel.
• Acidic foods including tomatoes and fruit juices can aggressively attack the galvanizedcoating, so storing of these types of foods is not recommended in galvanized containers.
• Bases with a pH greater than 12.0 are corrosive to galvanized steel. The higher the pHand/or stronger the solution, the more corrosive the base will be to galvanized steel.
• Generally, hot-dip galvanized steel performs well in solutions with a pH between 5and 12, but other factors such as aeration, agitation, ion levels, and temperature alsoaffect the corrosion rate of the galvanized coating. For example, soft water (low level ofmagnesium and/or calcium ions) that has a high oxygen or carbon dioxide level can beextremely corrosive to galvanized steel. Hard water (high level of magnesium and/orcalcium ions) develops protective scales on the galvanized coating that acts as a barrier tocorrosive substances and can greatly extend the service life of galvanized steel in water.
• Aluminum cleaners are extremely aggressive to galvanized steel and many product datasheets for these types of cleaners state they should not be used on zinc-coated steel.
• Road salts can be extremely aggressive to galvanized steel when they are wetted. Whendry, they do not tend to excessively corrode the galvanized coating, but because roadsalts are used for preventing/reducing icing, water is usually present, so care should betaken when storing road salts in galvanized containers or trailers.
• Quicklime (calcium oxide) is a widely used chemical compound used for mixing mortar,acting as a flux in smelting processes, and treating wastewater. When dry, quicklime isnot excessively corrosive to galvanized steel, but when it combines with water it createscalcium hydroxide, which is extremely corrosive to galvanized steel. In addition, thereaction of quicklime with water is an exothermic reaction (meaning it releases heat),which will further add to the corrosion of the galvanized coating.
• Fertilizers can be very corrosive to galvanized steel. As expected, liquid fertilizers have avery high corrosion rate, but damp granular fertilizers are especially corrosive as well. Interms of dampness, as little as 3% moisture by weight is enough water when combinedwith granular fertilizers to attack the galvanized coating.
• In larger gasoline fuel tanks, corrosion of the galvanized coating does not usually presentan excessive corrosion concern; however, in small gas tanks, such as those used onlawnmowers, the zinc corrosion products that form can clog filters.

This list of chemicals and compounds that can cause excessive consumption (or evencomplete destruction) of the galvanized coating is by no means exhaustive. There are manyobscure chemicals and compounds specifiers would like to store/use galvanized steel in/with.The bookCorrosion Resistance of Zinc and Zinc Alloysby Frank Porter has corrosion ratelistings for many chemicals on galvanized steel and is a fantastic resource for researchingwhether galvanized steel is appropriate for a particular application.One last thing to consider is even though some of these chemicals can be very corrosive togalvanized steel when combined with high-performance paint, epoxy, or powder coating, theduplex system of galvanized steel and top coating can still offer significant cost savings overcompeting forprotective coatingsorstainless steel.Please contact theAGA Technical Departmentat 720-361-4485 with questionsconcerning the corrosion rate of a particular chemical on galvanized steel.