A white powdery layer can be seen on some galvanized coatings when the protective layers of zinc carbonate can not form on the coating, due to lack of carbondioxide and presence of humidity. This is considered as a galvanizing defect and called white rust, or white storage stain.
In the normal cycle after galvanizing, first a ZnO and Zn(OH)2 layer forms on the coating, these layers react with CO2 and they turn to ZnCO3, called the zinc patina, which is dull grey, and has a slower corrosion rate compared to zinc or iron.
Susceptible environments for White rust / White storage stain are:
- Humidity
- Stagnant water
- Waterfront
- Marine
- Industrial areas
- Outdoor storage
Following products are susceptible for white rust:
- Newly galvanized articles
- Articles packed too tight
- Articles in poorly ventilated areas or packages
- Articles in contact with each other
Precautions
- Galvanized products should be clean
- Packaging should allow a good ventilation
- Nylon strings between the articles during packing should be used to allow air flow if contact between articles can not be avoided
- Articles should be raised from floor level
- Coating should be free of flux and ash inclusions
- Items should be stored in dry areas
- The most effective protection from white rust is using passivation chemicals
ANI METAL is one of the leading plant suppliers in hot dip galvanizing industry, provides supply of turnkey galvanizing plants and engineering supports as well.
Consultancy and engineering services include plant layout, training of employees, cost control etc. especially to the investors who have no galvanizing experience and who aim to enter the market.
As for the galvanizing factory equipments, with its business partners who are leaders in their own field of the Galvanizing Equipment, ANI Metal installs galvanizing factories with a wide range of products according to the budgets and demands of customers from manual plants operated by conventional systems to semi and full-automatic high technology factories.
