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topic 21047

Treating galvanized steel sheets to avoid white rust

A discussion started in 2003 but continuing through 2020


Q. Hello,

Can anybody help in finding solution for treatment of galvanized steel sheets against white corrosion. The sheets are exposed to very humid conditions. I am looking for a treatment which can give prolonged protection without paints. Any suggestion is highly appreciated.

Thanking you,

Ramchander Gegula
- Hyderabad, Andhrapradesh, India


? Hi, Ramchander. Are you already chromate quenching these galvanized sheets?

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


A. Hi,

Hope you have chromate treatment facilities there in your process. Keep chromate solution temperature above 80 °C to dry up the sheet after chromate treatment, next you can use hot air to dry up the sheet after treatment. Corrugate the sheets as soon as possible in the humid condition.Arrange cross ventilation during storage--if necessary use pedestal fan at the storage area.Last of all if the condition does not improve your last resort would be to use oil in the corrugation machine (through special arrangement), which may help you to beat white rust formation.


Mahbub Hossain
- Dhaka, Bangladesh


Q. Chromating unit is surely a good solution to prevent Galvanised sheet from white rust formation. But chromic acid is another factor which can arise problem of pollution.
Please suggest whether this problem can be minimised by using chemical coaters? If yes, can coating by chemical coater avoid the use of cleaning section in Color coating line?
Please explain the merits and demerits of this alternative.


Sunil Chauhan
- Indore, M.P, India


A. Hello Sunil. During a panel discussion at Sur/Fin 2006 in Milwaukee, one of the participants claimed that the TCP hexavalent-free chromate conversion coatings developed for aluminum work well on galvanized materials as well. I would suggest that you contact one of the four licensees for further discussions. They are Henkel, Luster-On, Metalast and Surtec. Good luck!

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

October 20, 2018

Q. Dear sir I am starting new galvanizing plant. But starting material looking good, but some few days in, my material comes to white rust peach^patch so how I can control?

sachin PATEL
- Vadodara gujarat india

October 2018

A. Hi Sachin. Please re-check your posting and confirm what word you have misspelled as 'peach' ... sorry but I can't figure it out from the context :-(

Even with a chromate quench, galvanized materials must be stored dry and with good air exposure because carbonates which form from exposure to the atmosphere are one of the factors which discourage white rusting.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

October 21, 2018

A. I think he means "patch".

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs

June 25, 2020

Q. I'm a Galvanizer in South Africa. We make use of a continuous Hot dip Galvanizing line and supply skinpassed chromated steel coils to a drum manufacturer in Cape Town South Africa. The drum manufacturer sends the drum to a juice supplier. The drums are kept under subzero temps (-18 °C) But from time to time they need to defrost to take out the juice to be replaced. During that process of increasing the temps the Galvanized drums started to form condensation and subsequently white rust forming. We did an in-depth investigation through labs but could not establish pin point root cause of it all.
We used OKEMCOAT F2( hexavalent chrome) to passivate.
Could it be micro cracking of the CHROMATE LAYER?

Albe Hoffman
- Vredenburg, West Coast,South Africa

July 16, 2020

A. The chromate layer is thin, soft, and not very resistant to acids. It's probably gone, or at least compromised by acidic orange juice.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

July 2020

A. I assume that Albe is talking about the outside of the drums (which may indeed have juice dripped or spilled on them), and assume the inside is lined with something. I don't think chromated galvanized steel would be an appropriate surface for any drink or wet food.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

July 18, 2020

You're correct Ted.The juice is inserted into double layered bags and not in contact with the drum surface. The atmosphere within the warehouse where they cool down the frozen juice maybe too acidic and can contribute to the white rust formation.

Albe Hoffman [returning]
- Vredenburg,South Africa

July 2020

A. Hi. Although there are things that can be done in the galvanizing process and chromate quench process that may improve resistance to white rust, it seems that galvanizing may not be the ideal finish for these conditions.

Ideally, per my understanding, galvanizing in open air very slowly reacts with the carbon dioxide and forms glassy zinc carbonate reaction products which tend to seal the underlying zinc away from the atmosphere, and which are relatively inert. When the environment is too wet, possibly too cold, too still, too acidic, and too enclosed, galvanizing cannot perform at its best. Painting or powder coating the drums may be called for in this application.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

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