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White rust on galvanized and galvanized pre-painted steel - 8 Pages

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Catalogue excerpts

White rust on galvanized and galvanized pre-painted steel Technical Information

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White rust on galvanized and galvanized pre-painted steel White rust on galvanised steel Prevention It is easier to prevent white rust than to cure it! Reasonable precautions to protect steel during both transport and storage can considerably reduce the risk of white rust. Storage should be indoors if possible, preferably in a clean, dry area away from any source of chemical pollution. Since rapid changes in temperature may cause condensation leading to white rust, storage should, as far as possible, be at an even temperature above the dew point. In particular, storage of coil or sheet on site...

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White rust on galvanized and galvanized pre-painted steel Is white rust harmful? What action is required? Because of the large volume of white rust often apparent, it frequently gives the misleading impression of extensive corrosion. However, in the vast majority of cases, white rust does not indicate serious degradation of the zinc coating nor does it necessarily imply any likely reduction in the expected life of the product. Unless the sheets or components are to be over-painted later, superficial white rusting can be safely ignored. In most cases, when exposed to natural, acceptable environmental...

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White rust on galvanized and galvanized pre-painted steel Removal Where it is essential to remove white rust deposits, this can be achieved by using special proprietary cleaners or simple chemical solutions which can be made up on site. A suitable solution could be: 1 % solution of trisodium phosphate (NA3PO4) or 1 % solution of potassium or sodium dichromate slightly acidified with sulphuric acid (PH not less than 6). This solution may leave a stained surface. N.B. In all cases, affected sheets should be thoroughly washed and allowed to dry after treatment. Heavy white rust Visible effect: thick,...

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White rust on galvanized and galvanized pre-painted steel Notes 1. Simple hand-held magnetic thickness gauges suitable for the on-site or factoryfloor measurement of residual zinc coating thickness are available from a number of companies. 2. Coating weight should correspond to the relevant specification according EN 10346, Continuously hot-dip zinc coated structural steel strip and sheet. 3. Small areas of white rust can be removed by abrading with a stiff-bristled brush. Large areas can be treated with a proprietary product or with simple chemical solutions which can be prepared on site. 4....

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White rust on galvanized and galvanized pre-painted steel White rust on pre-painted steel Prevention For pre-painted material the same precautions counts as for galvanized steel, stated on page one. Storage should be indoors if possible, preferably in a clean, dry area away from any source of chemical pollution. Pre-painted material is also sensitive for rapid changes in temperature which may cause condensation leading to white rust. Storage should, as far as possible, be at an even temperature above the dew point. In particular, storage of coil or sheet on site can be improved by a few simple...

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White rust on galvanized and galvanized pre-painted steel Light white rust Visible effect: thin, white deposit (fig. D1 and D2) Remedial action Maybe not required for walls. The protective properties of zinc are not impaired by the presence of superficial white rust. Existing white rust deposits will slowly convert to protective basic zinc carbonate. However, for aesthetic reasons, light stains are in general easy to remove by cleaning with warm water and soap by means of a low pressure spray or brush, max 60ºC, max 60 Bar. Heavier stains may be cleaned with a basic solution which as well can...

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White rust on galvanized and galvanized pre-painted steel Heavy white rust Visible effect: thick, crusty deposit (fig. E) Remedial action In general, sheets or components showing this defect should not be used. In circumstances where there is no alternative but to use the defective material, a repair procedure may be undertaken if the purchaser agrees. Expert advice should be sought first.

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