SSPC: New Wet Abrasive Blast Standards
Five new joint SSPC-NACE Wet Abrasive Blast Cleaning standards are now available from SSPC: The Society for Protective Coatings.
Wet abrasive blast (WAB) cleaning is primarily specified for suppression of dust in areas that would otherwise be prepared by dry abrasive blast cleaning, the association explains.
An additional benefit of using wet surface preparation methods is that they will reduce the levels of any non-visible water-soluble contaminants, such as soluble salts, that may be present on the surface and adversely affect coating performance, it adds.
Although the definitions of surface cleanliness immediately prior to coating application are the same for both the WAB and dry abrasive blast cleaning standards, the association says, the wet abrasive blast cleaning standards eliminate the need for “customizing” the dry blast cleaning standards to address flash rust levels and other specialized equipment and procedures that must be used with wet cleaning methods.
The newly published joint standards are:
The standards are intended for use by coating or lining specifiers, applicators, inspectors or others whose responsibility is to define a standard degree of surface cleanliness for carbon steel surfaces to be achieved by wet abrasive blast cleaning.
These standards combine elements of the existing standards for dry abrasive blast cleaning with elements of the 2012 SSPC/NACE waterjet cleaning standards, according to SSPC.
The definitions of cleanliness for the steel surface immediately following wet abrasive blast cleaning are identical to the definitions in the five dry abrasive blast cleaning standards. However, because water is used to convey the abrasive onto the surface, a layer of flash rust will form on the cleaned steel as the water evaporates, the association explains.
Due to the varied tolerance of coatings for the presence of flash rust on the surface, contractors must know the maximum permissible level of flash rust that may be present on the steel immediately prior to the application of the protective coating, as well as how to assess how much flash rust has developed.
The WAB cleaning standards define four levels of flash rust: no flash rust, light flash rust, medium flash rust, and heavy flash rust.
These definitions are based on the extent to which the flash rust obscures the underlying steel substrate, the ease with which it can be removed by wiping with a cloth, and the amount of material that appears on the cloth after the surface is wiped, SSPC says.
The new joint standards combine elements of the existing standards for dry abrasive blast cleaning with elements of the 2012 SSPC/NACE waterjet cleaning standards, SSPC says.
As with the waterjetting standards and the dry abrasive blast cleaning standards, the association adds, the WAB cleaning standards also include information on materials and methods used to perform the cleaning process.
For example, the water used must be free of contaminants that would affect the cleanliness of the prepared surface and the functioning of the pumps or other equipment. If the project specification includes specific requirements for non-visible contaminants, the water used for waterjetting must be free of impurities that could prevent the surface from meeting those requirements.
SSPC notes that the new WAB standards are relevant to the following SSPC Training and Certification Programs as well:
More information: http://www.sspc.org/.