SSPC-SP 6 Commercial Blast Cleaning (NACE No. 3) is a standard used for blast cleaning put forth by the Society for Protective Coatings (SSPC) and NACE International Standard. 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. SSPC-SP 6/NACE No. 3 commercial blast cleaning allows for stains or shadows up to 33 percent of each unit area of surface to remain. SSPC-SP 6/NACE No. 3 removes all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and any other foreign matter on the surface.
In reference to the degree of cleanliness for SSPC-SP 6/NACE No. 3 commercial blast cleaning has a higher level of cleaning surfaces than does SSPC-SP 14/NACE No. 8 industrial blast cleaning. However, the degree of cleaning is less than that of SSPC-SP 10/NACE No. 2 near-white blast cleaning or SSPC-SP 5/NACE No. 1 white blast cleaning. Commercial blast cleaning has a lower cost for providing a degree of surface preparation when blast cleaning is necessary.
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 5776 SQ mm or 9 SQ in to best meet the allowed percent of cleanliness per each unit area of the surface.
There are prerequisites that need to be in place prior to applying SSPC-SP 6 commercial blast cleaning. In order to be able to apply commercial blast cleaning be sure that all visible oil, grease, and other contaminant residues are removed. This can be achieved by using standard SSPC-SP 1 Solvent cleaning or other possible methods. 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. Relative humidity should be less than 85% since the higher value can cause moisture condensation on the surface. 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:
Abrasives are used for grinding, polishing, or cleaning hard surfaces. SSPC-SP 6/NACE No. 3 calls for the use of abrasives in the methods listed. 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 size and type of abrasive should be selected based on the blast cleaning system to be used, the surface that requires SSPC-SP 6/NACE No. 3, the finished requirements of the surface, and if recycling of the abrasive is necessary.
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.
Most coating specification requires a surface profile measurement by press-o-film (replica film test) or commercial name as testex tape test. The referenced standard for performing this test is ASTM-4417, method C or ISO-8503-1.
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.
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