How to protect your galvanized steel pipe from white rust in applications
Whether you are facing such a problem that your galvanized steel pipes are affected by white rust over time in projects? Don’t worry! We would like to help you out there.
In many cases, once galvanized surface has been attacked and the zinc hydroxide compounds have formed, it is desirable to remove the oxide products from the surface. And the effect on the galvanized coating can range from very minor to extremely severe and various levels of remedial treatment are available to deal with white rust problems at the various levels at which they are likely to occur. The following treatments are recommended to deal with white rust on your galvanised products:
1.Light White Rusting
This is characterized by the formation of a light film of white powdery residue and frequently occurs on structural steel pipes used in building frames during periods of heavy rain. It is particularly evident on areas that have been buffed or filed during quality assurance operations. These treatments remove the passivated surface from the galvanizing and expose unoxidised zinc to attack from rainwater. Provided the items are well ventilated and well drained, white rust rarely progresses past this superficial stage. It can be brushed off if required but will generally wash off in service with normal weather. No remedial treatment is generally required for this level.
2.Moderate White Rusting
This is characterized by a noticeable darkening and apparent etching of galvanised coating under the affected area, with the white rust formation appearing bulky for your hot dipped galvanized steel pipe in projects. The galvanised coating thickness should be checked to determine the extent of attack on the coating. In the majority of cases, less than 5% of the galvanised coating will have been removed and thus no remedial work should be required as long as the appearance of the affected area is not detrimental to the use of the product and the zinc hydroxide residues are removed by wire brushing.
3.Severe White Rusting
This is characterized by very heavy oxide deposits. Items may be stuck together. Areas under the oxidized area may be almost black and show signs of red rust on your cold rolled steel pipes in applications. A coating thickness check will determine the extent to which the galvanised coating has been damaged. Remedial treatment to reinstate the coating should be undertaken as follows:
Wire brush or buff the affected area to remove all oxidation products and rust if any;
Apply one or two coats of approved epoxy zinc-rich paint to achieve required dry film thickness of 100 microns minimum.
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