Cleaning Galvanized Steel
How do I clean grease or wet storage stain from galvanized steel without damaging the appearance of the coating?
Regardless of how clean any galvanizing operation is, at some point, organic contaminants like grease or oil will find their way onto your newly galvanized steel. Similarly, when it is especially damp or humid outside, moisture can accumulate on stored galvanized steel waiting to be shipped and cause wet storage stain. In the interest of providing your customer with the highest quality service, you like to clean those contaminants or impurities from the surface prior to delivery of the product. However, to keep customer satisfaction intact, you want to use cleaning products that affect the finish of the coating as little as possible. The following will provide you details of a cleaning study conducted by the AGA.
Cleaning Organic Contaminants from Galvanized Surfaces
The AGA recently conducted a study to test which commercially available products are best at removing organic contaminants from galvanized steel. Many products were tested, and most of them worked very well at removing the contaminants without affecting the finish of the coating. Cleaning with these products consisted of applying and removing the product to the galvanized surface in accordance with the manufacturers instructions, rinsing with water and then drying. The following products did not damage the coating:
- Comet®
- Bleach
- Goof Off®
- Simple Green®
- The Must for Rust®
- Stainless Steel Cleaner
Even though these products did not damage the appearance or cause other damage to the coating in the study, you should still test a small area at first to be cautious. There were other products that effectively removed grease and oil, but also affected the appearance of the galvanized coating in some way. These products include:
- Vinegar
- Muriatic acid
- Ammonia
Cleaning Wet Storage Stain from Galvanized Steel
The best way to treat wet storage stain is to prevent it. Preventing wet storage stain is accomplished in two ways:
- Providing adequate air flow to newly galvanized surfaces
- Removing standing water from newly galvanized surfaces.
Properly storing newly galvanized steel does both. However, there are times when the formation of wet storage stain cannot be prevented and must be removed. Wet storage stain can range in severity from light to heavy. Light and medium wet storage stain do not affect the service life of the coating, while heavy wet storage stain can. The first step in treating wet storage stain is to dry the galvanized surface. Light wet storage stain can usually be left untreated as long as the surface will remain dry and will be exposed to adequate air flow. Over time the coating will regain its normal appearance as the zinc patina forms. Medium and heavy wet storage stain must be removed from the surface to prevent continued consumption of the galvanized coating. In cases of very heavy wet storage stain, the part may need to be stripped and re-galvanized. The AGA conducted a study to test various products for removing wet storage stain without damaging the galvanized coating or the appearance. Five products were found that meet these criteria:
- CLR®
- Lime juice
- Naval Jelly® Rust Dissolver
- Picklex 10G
- White vinegar
These products can be applied to the affected areas and then scrubbed with a nylon-bristled brush. After cleaning the wet storage stain, you will need to rinse the surface and dry it.
Additional Resources
The studies to test these various products for removing organic contaminants and wet storage stain from galvanized steel have been summarized into Galvanizing Notes, and are available for download in the members area of the AGA website. Alternatively, you can contact the AGA Technical Department to obtain copies of these publications.
© 2023 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.
Comments
Hi Top LLC
Please explain the best way to remove the painted lettering on galvanized steel pipe without damaging the coating. Thank you.
(AGA)
Hello Hi Top, In our studies, the most effective products at removing paint are: Kean-Strip, Graffiti Remove, and Motsenbockers Lift Off 4.
Lisa
How do you remove the print off galvanized steel? Also, is it possible to seal the galvanized steel to protect it from water damage? Thanks
(AGA)
Hi Lisa, Can you clarify what you mean by "print"? To protect from water staining, it is possible to apply a passivation treatment but typical treatments only last a few weeks to a few months. Instead, if you experience some slight water staining, it is possible to let the galvanizing weather in an exterior environment (approx 6 months to 2 years) where a uniform appearance will develop over time.
Athol
How is a person able to remove the buildup inside of water supply cold water galvinized pipe
(AGA)
Hello Athol, You can use one of the above cleaning chemicals if using a pipe/tube brush sized for the pipe to assist in removal of the corrosion products.
Dpo
I seem to have a mixture of white rust and regular rust? On my galvanized tubs I use in the garden. How can I remove this and paint over them so they do not become further damaged?
Norm
I have a heating duct galvanized which had water leaking on it and it molded and someone clean the mold with some kind of mold remover causing the galvanized to corrode and oxidize , leaving a bumpy powdery substance on the area where it was cleaned I can see a little rust in a couple of places where the galvanized was put together How can I clean this and then reseal it or paint it, The duck work is hidden from sight ?
(AGA)
Hello Norm, You can clean any white oxides or staining using the instructions on this page. Then, to repair the coating in areas which have rusted, follow the instructions on our website under "repairing HDG steel": https://galvanizeit.org/specification-and-inspection/repairing-hdg-steel
John
What would be best for removing concrete splatter from galvanized beams?
Tim smith
I seem to have a mixture of white rust and regular rust? On my galvanized Gas tank , How can I remove this and paint over them so they do not become further damaged?
(AGA)
Hi Tim, You may be experiencing heavy wet storage stain. Clean the wet storage stain per instructions in this article, then you can perform a galvanizing repair of any bare areas per the following instructions at galvanizeit.org/repair.
(AGA)
Hi Tim, You may be experiencing heavy wet storage stain. Clean the wet storage stain per instructions in this article, then you can perform a galvanizing repair of any bare areas per the following instructions at galvanizeit.org/repair.
Absolutely Clean Window Washing
There was a fire inside of a curved galvanized building where a farm machine started on fire. The tires burned and all that was left was the metal on the machine. What is the best way to clean this soot? Would steam be of any use? What about a specific cleaning chemical application? Thank you for your answer to follow.
(AGA)
During bushfires, a layer of soot may become deposited on the surface which can be cleaned using a dry sponge, with remaining residue removed using a degreaser solution and sponge if required. If residue remains it can be cleaned using a weak acid or base cleaning solution and scrubbing with a nonmetal bristle brush. It is important to thoroughly rinse the surface with water, preferably twice, after cleaning.
Highway Trading Company
Really useful and valuable content, Thank you.
Ryan Hayward/Glenmor Equipment
Is there a product that would clean road salt/oxidization off of galvanized metal? We sell grain dryers and during transport they get road salt/dust on them and need a product that can clean them. These are large machines averaging 16ft long and 12ft tall, so something that can be used with a pressure washer would be great.
(AGA)
Hi Ryan, To remove road salts, the hot-dip galvanized parts can be pressure washed or rinsed twice with clean water. If a power wash is used, ensure the blast pressure is less than 1,450 psi to prevent damage to the coating. A water bath should not be used, as salts will simply collect in the bath. Once road salts have been removed, separate the parts in an area with good airflow to fully dry before installation or storage. See our article on trucking HDG in winter here: https://galvanizeit.org/knowledgebase/article/trucking-transport-of-hdg-steel-in-winter