What are these and which ones are important to the industry? Standardized subjects include requirements for paints, standards for evaluating the qualifications of contractors, surface preparation standards, and other topics. Here is a list and brief summary of the surface preparation standards used in the hot-dip galvanizing industry with a brief summary of each. SSPC-SP1 Solvent Cleaning The method of solvent cleaning is intended to remove all visible oil, grease, soil, drawing and cutting compounds, and all other soluble contaminants from steel surfaces.
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Commercial blast cleaning is to be used for a defined degree of cleaning unpainted and painted steel surfaces prior to protective coating or lining systems. Commercial blast cleaning has a lower cost for providing a degree of surface preparation when blast cleaning is necessary. What Should You Consider? The degree of cleaning for commercial blast cleaning entails the allowed percent of each unit area of the surface to show stains or shadows.
The limit of surface cleaning for SSPC-SP 6 commercial blast cleaning is no more than 33 percent of each unit area of the surface. With commercial blast cleaning, light shadows, slight streaks, or minor discolorations from rust, mill scale, or other types of stains are permitted. Special note should be taken on the coating specified with the degree of surface roughness that is suitable for the coating system of interest.
The unit area that is evaluated should always remain approximately SQ mm or 9 SQ in to best meet the allowed percent of cleanliness per each unit area of the surface. In order to be able to apply commercial blast cleaning be sure that all visible oil, grease, and other contaminant residues are removed.
Some coating specification requires a chloride test being performed before power blasting even before solvent cleaning to identify the amount of deposited soluble salts. Environmental Conditions needed for SSPC-SP 6 Commercial Blast Cleaning 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 document must be met. The coating specification is part of the contract and have established requirements that must be met per project. Therefore, the surface must be free of sharp fins, edges, weld spatter, or burning slag as indicated by the specification prior to performing SSPC-SP 6 commercial blast cleaning.
Commercial blast cleaning can be done by dry abrasive blasting in the following ways: Using compressed air, blast nozzles, or an abrasive Using a closed-cycle, recirculating system with compressed air, blast nozzle, and an abrasive, with or without vacuum for recovery of abrasives and dust. Using a closed-cycle, recirculating system with centrifugal wheels and an abrasive.
Additional methods can be discussed between the contractor and those who established the requirements. 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 commercial blast cleaning should be dry and free of any contaminants, such as oil, grease, etc. The air compressor 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. A surface dust test can be performed to ensure all dust and residue being removed. As mentioned prior, after commercial cleaning, be sure to meet all surface standards as presented in the coating specification.
Unperfected surfaces may lead to premature paint failure. The amount of surface profile depends on coating specification, but most of the specifications require 2 thru 3 mils.
In addition, 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 quickly. Therefore, always be certain to remove visible rust prior to continuing with the new coating system. As with all standards, it is very important to take the necessary precautions when working with blast cleaning.
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. The coating specification also might call for chloride testing to ensure deposited soluble salts are not higher the permissible limit.
SSPC-SP 6 Commercial Blast Cleaning (NACE No. 3)