NACE International recently published five new companion wet abrasive blast (WAB) standards. The NACE/SSPC: The Society for Protective Coatings (SSPC) joint standards define the processes for preparing a carbon steel (CS) surface to a specified degree of surface cleanliness using a WAB cleaning method. Each WAB standard represents one of five levels of cleanliness achievable by WAB, which include near-white metal, white metal, commercial, industrial, and brush off.
WAB cleaning is a process using a mixture of water and abrasive that can produce various levels of surface cleanliness and surface profile (roughness) similar to those obtained with dry abrasive blast cleaning. WAB cleaning may be specified when dust suppression is desired, and also may be a means for reducing soluble salt contamination.
The standards include descriptions of the WAB cleaning methods, as well as sections with additional technical considerations, such as flash rust as defined in the NACE/SSPC joint standards for waterjetting. Also, there are sections that describe various aspects of the cleaning process, such as procedures to follow prior to WAB cleaning, abrasive blast cleaning materials, and procedures that immediately follow WAB cleaning before the coating is applied. Additionally, three nonmandatory appendixes are included: explanatory notes, procedures and process controls, and methods for assessing the degree of flash rust.
“The wet abrasive blast cleaning standards are written for specific end results, not specific equipment. The definitions and substrates are defined within the more conventional dry abrasive blast cleaning standards, with cautions for flash rust that is formed while the water is drying. The cleaned substrates will be profiled and look very similar to conventional substrates,” says Lydia Frenzel, executive director of the Advisory Council (Vancouver, Washington) and chair of NACE Task Group (TG) 350, “Surface Preparation by Wet Abrasive Blast Cleaning.”
The standards are limited to requirements for visible surface contaminants, and are intended for use by coating or lining specifiers, applicators, inspectors, and others whose responsibility is to define a standard degree of surface cleanliness for CS surfaces to be achieved by WAB cleaning.
NACE WAB-2/SSPC-SP 10 (WAB), “Near-White Metal Wet Abrasive Blast Cleaning” (NACE SP0615-2015)
Joint standard NACE WAB-2/SSPC-SP 10 (WAB) defines the process for preparing a CS surface to the near-white metal degree of surface cleanliness using a WAB method of cleaning. Near-white metal WAB cleaning provides a greater degree of cleaning than commercial WAB cleaning (NACE WAB-3/SSPC-SP 6 [WAB]) but less than white metal WAB cleaning (NACE WAB-1/SSPC- SP 5 [WAB]). Near-white metal WAB cleaning is used when the objective is to remove all rust and other corrosion products, coating, and mill scale, but when the extra effort required to remove all stains from these materials is determined to be unwarranted. Near-white metal WAB cleaning allows staining on no more than 5% of each unit’s surface area, while commercial WAB cleaning allows staining on no more than 33% of each unit’s surface area. White metal WAB cleaning does not permit any staining to remain on the surface.
NACE WAB-1/SSPC-SP 5 (WAB), “White Metal Wet Abrasive Blast Cleaning” (NACE SP0175-2015)
Joint standard NACE WAB-1/SSPC-SP 5 (WAB) defines the process for preparing a CS surface to the white metal degree of surface cleanliness using a WAB method of cleaning. White metal WAB cleaning is used when the objective is to remove all rust and other corrosion products, coating, mill scale, and other foreign matter from the surface. White metal WAB cleaning provides a greater degree of cleaning than near-white metal WAB cleaning (NACE WAB-2/SSPC-SP 10 [WAB]). White metal WAB cleaning does not permit any staining to remain on the surface. Near-white metal WAB cleaning allows staining on no more than 5% of each unit’s surface area.
NACE WAB-3/SSPC-SP 6 (WAB), “Commercial Wet Abrasive Blast Cleaning” (NACE SP0815-2015)
Joint standard NACE WAB-3/SSPC-SP 6 (WAB) defines the process for preparing a CS surface to the commercial degree of surface cleanliness using a WAB method of cleaning. Commercial WAB cleaning provides a greater degree of cleaning than industrial WAB cleaning (NACE WAB-8/SSPC-SP 14 [WAB]), but less than near-white metal WAB cleaning (NACE WAB-2/SSPC-SP 10 [WAB]). Commercial WAB cleaning is used when the objective is to remove all rust, coating, and mill scale, but when the extra effort required to remove all stains from these materials is determined to be unwarranted. The WAB cleanliness level specified should be the same as the corresponding degree of cleaning specified if dry abrasive blast cleaning were the process being used.
NACE WAB-8/SSPC-SP 14 (WAB) “Industrial Wet Abrasive Blast Cleaning” (NACE SP0915-2015)
Joint standard NACE WAB-8/SSPC-SP 14 (WAB) defines the process for preparing a CS surface to the industrial degree of surface cleanliness using a WAB cleaning method. Industrial WAB cleaning provides a greater degree of cleaning than brush-off WAB cleaning (NACE WAB-4/SSPC-SP 7 [WAB]), but a lesser degree of cleaning than commercial WAB Cleaning (NACE WAB-3/SSPC-SP 6 [WAB]). Industrial WAB cleaning allows tightly adherent paint, mill scale, and rust to remain on no more than 10% of each unit’s surface area. Brush-off WAB cleaning allows all tightly adherent paint, mill scale, and rust to remain on the surface. Commercial WAB cleaning allows staining to remain on no more than 33% of each unit’s surface area, but requires removal of all coating, mill scale, and rust.
NACE WAB-4/SSPC-SP 7 (WAB) “Brush-Off Wet Abrasive Blast Cleaning” (NACE SP1015-2015)
Joint standard NACE WAB-4/SSPC-SP 7 (WAB) defines the process for preparing a CS surface to the brush-off degree of surface cleanliness using a WAB method of cleaning. Brush-off WAB cleaning provides a lesser degree of cleaning than industrial WAB cleaning (NACE WAB-8/SSPC-SP 14 [WAB]). The difference between an industrial WAB cleaning and a brush-off WAB cleaning is that the objective of a brush-off WAB cleaning is to allow as much of an existing adherent coating to remain as possible and to roughen the surface before coating application. Industrial WAB cleaning allows tightly adherent paint, mill scale, and rust to remain on no more than 10% of each unit’s surface area.
These standards are available in the NACE Store. NACE International members can download these at no charge.
Contact Trudy Schreiner, NACE International Technical Activities staff editor—e-mail: trudy.schreiner@nace.org.