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y1, ._ SSPC-SP 5
<br /> ` March 1, 1985
<br /> A. Appendix SSPC-vis 1, "Pictorial Surface Preparation Standards
<br /> A.1 FUNCTION —White Metal Blast.Cleaning(SSPC- for Painting Steel Surfaces," provides color photographs
<br /> SP 5) provides a greater degree of cleaning than Near- for the various grades of surface preparation as a function
<br /> White Blast Cleaning (SSPC-SP 10). It should be used of the initial condition of the steel.The following table lists
<br /> where the highest degree of blast cleaning is required.The the pictorial standards for this specification that are ap-
<br /> primary functions of blast cleaning before painting are: (a) plicable to the rust grades given.
<br /> to remove material from the surface that can cause early Adherent Mill Rusting Mill Pitted and
<br /> failure of the coating system, and (b) to obtain a suitable Rust Grade Scale Scale Rusted Rusted
<br /> surface roughness. Pictorial
<br /> A.2 ABRASIVE SELECTION — Types of metallic and Standards A Sa 3 B Sa 3 C Sa 3 D Sa 3
<br /> non-metallic abrasives are discussed in the Surface Many other visual standards are available and are
<br /> Preparation Commentary (SSPC-SP COM). It is important described in Section 7 of the Commentary(SSPC-SP COM).
<br /> to recognize that blasting abrasives may become embed- A.5 SURFACE IMPERFECTIONS — Surface imperfec-
<br /> ded in or leave residues on the surface of the steel during tions can cause premature failure when the service is
<br /> preparation. While normally such embedment or residues severe. Coatings tend to pull away from sharp edges and
<br /> are not detrimental, care should be taken (particularly if projections, leaving little or no coating to protect the
<br /> the prepared steel is to be used in an immersion environ- underlying steel.Other features which are difficult to prop-
<br /> ment) to assure that the abrasive is free from detrimental erly cover and protect include crevices, weld porosity,
<br /> amounts of water soluble, solvent soluble, acid soluble,or laminations, etc. The high-dost of the methods to remedy
<br /> other such soluble materials. the surface imperfections requires weighing the benefits
<br /> A.3 SURFACE PROFILE — Surface profile is the of edge rounding, weld spatter removal, etc., versus a
<br /> roughness of the surface which results from abrasive blast potential coating failure.
<br /> cleaning. The profile depth (or height) is dependent upon Poorly adhering contaminants, such as weld slag
<br /> the size,type,and hardness of the abrasive, particle veloci- residues, loose weld spatter, and some minor surface
<br /> ty and angle of impact, hardness of the surface, amount of laminations, may be removed during the blast cleaning
<br /> recycling,and the proper maintenance of working mixtures operation. Other surface defects (steel laminations, weld
<br /> of grit and/or shot. porosities, or deep corrosion pits) may not be evident until
<br /> The allowable minimumimaximum height of profile is the surface preparation has been completed. Therefore,
<br /> usually dependent upon the thickness of the paint to be proper planning for such surface repair work is essential
<br /> applied. Large particle sized abrasives (particularly since the timing of the repairs may occur before,during,or
<br /> metallic) can produce a profile which may be too deep to after the blast cleaning operation. Section 4 of the Com-
<br /> be adequately covered by a single thin film coat. Accord- mentary (SSPC-SP COM) contains additional information
<br /> ingly, it is recommended that the use of larger abrasives be on surface imperfections.
<br /> avoided in these cases. however, larger abrasives may be A.6 CHEMICAL CONTAMINATION — Steel contam-
<br /> needed for thick film coatings or to facilitate removal of r
<br /> inated with soluble salts (i.e,, chlorides and sulfates)
<br /> heavy mill scale or rust. If control of profile (min- develops rust-back rapidly at intermediate and high
<br /> imumlmaximum) is deemed to be significant to coatings humidities.These soluble salts can be present on the steel
<br /> performance, it should be addressed in the procurement
<br /> surface prior to blast cleaning as a result of atmospheric
<br /> documents (project specification).
<br /> contamination. In addition, contaminants can be de-
<br /> Typical maximum profile heights achieved with com•
<br /> mercial abrasive media are shown in Table 8 of the Surface posited on the steel surface during blast cleaning
<br /> Preparation Commentary (SSPC-SP COM). Methods (i.e., whenever the abrasive is contaminated. Therefore, rust-
<br /> comparators, replica tape, depth micrometers) are back can be minimized by removing these salts from the
<br /> steel surface, preferably before blast cleaning, and
<br /> available to aid in estimating the profile of surfaces blast eliminating sources of recontamination during and after
<br /> cleaned with sand, steel grit, and steel shot.
<br /> blast cleaning. Identification of the contaminants along
<br /> AA VISUAL STANDARDS — Note that the use of with their concentrations may be obtained from laboratory
<br /> visual standards in conjunction with this specification is and field tests.A number of tests for soluble salts are now
<br /> required only when they are specified in the procurement under study by the SSPC,ASTM, Maritime Administration,
<br /> documents (project speciflcation) covering the work. It is and ISO.
<br /> recommended, however, that the use of visual standards A.7 RUST-BACK— Rust-back(rerusting)occurs when
<br /> be made mandatory in the procurement documents (proj- freshly cleaned steel is exposed to conditions of high
<br /> ect specification)
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