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

The AGA has published multiple resources (see the publications Specifiers Guide or Performance of Hot-Dip Galvanized Steel Products) listing chemicals, substances, and environments hot-dip galvanized steel can successfully be used in or with. However, there are fewer resources available that discuss chemicals and substances hot-dip galvanized steel should not be used with, or where caution should be used if galvanized steel will be specified for an application. Although it is impossible to list all the chemicals extremely corrosive to galvanized steel, there are some chemicals and substances specifiers often ask about concerning the corrosion rate of galvanized steel.

The following is a list of these chemicals and substances: 

• Bleach, even when mixed with water, is very corrosive to galvanized steel. An alternative cleaning solution is a mixture of one part ammonia with 10 parts water and then rinsing the galvanized coating with fresh water and allowing it to thoroughly dry. 
• Chlorine, the base for many commonly used bleaches, is also very corrosive to galvanized steel. This means galvanized steel should not be used in chlorine water; however, hot-dip galvanized structural steel has performed acceptably when used indoors above chlorine pools. Painting or powder coating galvanized structural steel in indoor pool environments is recommended to greatly increase the service life of both the paint or powder coating and galvanized steel. 
• Acids with a pH below 5.0 are corrosive to galvanized steel. The lower the pH and/or the stronger the acid solution, the more corrosive the acid will be to galvanized steel.
• Acidic foods including tomatoes and fruit juices can aggressively attack the galvanized coating, 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 pH and/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 5 and 12, but other factors such as aeration, agitation, ion levels, and temperature also affect the corrosion rate of the galvanized coating. For example, soft water (low level of magnesium and/or calcium ions) that has a high oxygen or carbon dioxide level can be extremely corrosive to galvanized steel. Hard water (high level of magnesium and/or calcium ions) develops protective scales on the galvanized coating that acts as a barrier to corrosive substances and can greatly extend the service life of galvanized steel in water. 
• Aluminum cleaners are extremely aggressive to galvanized steel and many product data sheets 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. When dry, they do not tend to excessively corrode the galvanized coating, but because road salts are used for preventing/reducing icing, water is usually present, so care should be taken 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 is not excessively corrosive to galvanized steel, but when it combines with water it creates calcium hydroxide, which is extremely corrosive to galvanized steel. In addition, the reaction 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 a very high corrosion rate, but damp granular fertilizers are especially corrosive as well. In terms of dampness, as little as 3% moisture by weight is enough water when combined with granular fertilizers to attack the galvanized coating. 
• In larger gasoline fuel tanks, corrosion of the galvanized coating does not usually present an excessive corrosion concern; however, in small gas tanks, such as those used on lawnmowers, the zinc corrosion products that form can clog filters. 

This list of chemicals and compounds that can cause excessive consumption (or even complete destruction) of the galvanized coating is by no means exhaustive. There are many obscure chemicals and compounds specifiers would like to store/use galvanized steel in/with. The book Corrosion Resistance of Zinc and Zinc Alloys by Frank Porter has corrosion rate listings for many chemicals on galvanized steel and is a fantastic resource for researching whether galvanized steel is appropriate for a particular application. One last thing to consider is even though some of these chemicals can be very corrosive to galvanized steel when combined with high-performance paint, epoxy, or powder coating, the duplex system of galvanized steel and top coating can still offer significant cost savings over competing for protective coatings or stainless steel. Please contact the AGA Technical Department at 720-361-4485 with questions concerning the corrosion rate of a particular chemical on galvanized steel.