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White metal blast cleaning is to be used to clean unpainted or painted steel surfaces prior to applying high-performance protective coating or lining systems. Therefore, it is often better than other blast cleaning as it requires higher standards of a clean surface. Please note random staining, light shadows, discoloration are not allowed to remain on the surface. White metal blast cleaning is also used when immersion service requires the highest level of cleaning.
In order to be able to apply white metal blast cleaning be sure that all visible oil, grease, and other contaminant residues are removed. The coating specification also might call for chloride testing to ensure deposited soluble salts are not higher the permissible limit. Substrate temperature should not be colder surrounding air temperature; otherwise, the moisture can condensate on the cleaned-blast surface and cause flash rust.
The sandblasting process should not be done if the surface temperature is less than 5-degree Fahrenheit or 3-degree Celsius above the dew point. The dew point is the temperature that condensation starts. Besides, all conditions mentioned in the coating specification documents must be met.
The procurement documents are part of the contract and have established requirements that must be met per project. Abrasives are used for grinding, polishing, or cleaning hard surfaces. The abrasives selected for this method depend on a variety of factors. In order to select an appropriate abrasive, the type, grade, and surface condition of the steel need to be considered.
The abrasive used for White metal blast cleaning should be dry and free of any contaminants, such as oil, grease, etc.
The air compressor also should be checked for oil and water contamination by Blotter Test. Once the methods above have been applied, be sure to remove all visible residues from the surface. This can be achieved with the use of brushing, blowing off residue with clean, dry air, and vacuum cleaning. Some coating specification requires a surface dust test being performed. Most coating specification requires a surface profile measurement by Press-O-Film replica test or commercial name as testex tape test.
The amount of surface profile depends on coating specification , but most of the specifications requires 2 thru 3 mils. As mentioned prior, after blast cleaning, be sure to meet all surface standards as presented in the coating specification documents.
Unperfected surfaces may lead to premature paint failure. Also, prior to continuing with the coating, be sure to remove any visible rust that forms on the steel surface after blast cleaning. If the recently blasted surface is exposed to salts, moisture, contamination or a corrosive environment, rust can occur easily.
Therefore, always be certain to remove visible rust prior to continuing with the new coating system. SSPC-SP 5 white metal blast cleaning is preferred to other methods if cleanliness is an important factor. Therefore, fewer imperfections are acceptable with white metal blast cleaning.
As with all standards, it is very important to take the necessary precautions when working with blast cleaning. Return to coating inspection. Did you find this article useful? We will be updating and growing this site with more and more of industrial inspection related articles. Please subscribe to my monthly newsletter so you don't miss a thing. Search this Site! Inspection 4 Industry LLC. Comments Have your say about what you just read!
NACE No. NACE8 sspc sp Item No. It is intended to aid the manufacturer, the consumer, and the general public.
SSPC Surface Preparation Standards
White metal blast cleaning is to be used to clean unpainted or painted steel surfaces prior to applying high-performance protective coating or lining systems. Therefore, it is often better than other blast cleaning as it requires higher standards of a clean surface. Please note random staining, light shadows, discoloration are not allowed to remain on the surface. White metal blast cleaning is also used when immersion service requires the highest level of cleaning. In order to be able to apply white metal blast cleaning be sure that all visible oil, grease, and other contaminant residues are removed.