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METAL SURFACE PREPARATION STANDARDS
Surface preparation standards that are most frequently used have been developed by:
– The National Association of Corrosion Engineers (NACE)
– The Society of Specialists on Protective Coatings (SSPC)
– The Swedish Standards Association (Sa, St)
The surface preparation standards were initially developed by the Swedish Institute for Corrosion Problems, and later on approved by the Society of Specialists on Protective Coatings (SSPC) and other organizations.
International Standard (ISO)
ISO Standards
To determine to what a degree a steel surface is free from rust and cleaned International Standards ISO 8501-01-1988 and ISO 8504-1992 are used.
For scale ISO 8501-01 is used and sets the following corrosion contamination levels:
A — The steel surface is covered, to a greater degree, with the scale, but, to a lesser degree or not in the least, affected by the rust.
B — The steel surface has begun to corrode, and the scale to shed therefrom.
C — The scale has fallen off the steel surface and may be removed therefrom, but there are slightly visible pits thereon.
D — The scale has fallen off the steel surface, but there are snaked-eyed pits thereon.
Preliminary surface preparation degrees
ISO sets seven surface preparation degrees ISO-St Manual and electromechanical processing:
ISO-St —Manual and electromechanical processing: scraping, scrubbing, brushing and polishing. After cleaning the surface shall be free of flaking paint and dust.
ISO-St2 — Extensive manual and electromechanical cleaning. After cleaning a substrate shall look free of visible trace oil, grease and mud, and flaking scale, rust, paint and foreign matters.
ISO-St3 — Highly extensive manual and electromechanical cleaning. The same as for St2, by the substrate shall be cleaned by far more extensively, until metallic luster is achieved.
ISO-Sa — Sandblasting. Before sandblasting the substrate shall be made free of thick rust layers by chipping, visible oily and greasy contaminations, and mud. After sandblasting the substrate must be free of dust and rubbish.
ISO-Sa1 — Light Sandblasting. When examined with the naked eye, the surface must look free of visible oily/greasy stains, mud and flaking scale, rust, paint and other foreign matters.
ISO-Sa2 — Extensive Sandblasting. When examined with the naked eye, the surface must look free of visible oily/greasy stains, mud and much of scale, rust, paint and other foreign matters. Each residual contamination must bear against.
ISO-Sa2,5 — Highly Extensive Sandblasting. When examined with the naked eye, the surface must look free of visible oily/greasy stains, mud and much of scale, rust, paint and other foreign matters. All residual trace contaminations must appear only as hardly visible stains and stripes.
ISO-Sa3 — Sandblasting, until a visible bare metal is reached. When examined with the naked eye, the surface must look free of visible oily/greasy stains, mud and much of scale, rust, paint and other foreign matters. The surface must have uniform metallic luster.
Surface roughness after sandblasting
Rz — average projection against a plain level=abrasive profile,
Rt — maximum projection against a plain level,
Ra — average distance to an imaginary central line that may be drawn between tops and plains (ISO3274).
Abrasive Profile (Rz)-4 to 6 times C.L.A. (Ra) Direct measurement of the TCC of primers for steels exposed to sandblasting up to the thickness of 30μm is significantly inaccurate. For dry layer thickness of 30μm and more the primer gives an average thickness instead of that on tops. When Rz Abrasive Profile is mentioned in specifications, ISO –Sa2.5 Sandblasting must be achieved using mineral sand, unless otherwise specified. Over Ra at 17 μm (R Abrasive Profile at TCC =100 μm) it is recommended to use an additional primer coat to conceal roughness. If highly corroded steels are exposed to sandblasting, the profile of over 100 μm is frequently achieved.
The National Association of Corrosion Engineers (NACE)
NАСЕ 1 Cleaning, until a bare metal is reached
NACE 2 Cleaning, until a bare metal is nearly reached
NACE 3 Commercial Cleaning
The Society of Specialists on Protective Coatings (SSPC)
SP-1 Chemical Cleaning
SP-2 Manual Cleaning
SP-3 Mechanical Cleaning
SP-4 Thermal Cleaning
SP-5 Cleaning, until a bare metal is reached
SP-6 Commercial Cleaning
SP-7 Stripping Cleaning
SP-8 Etching
SP-9 Cleaning after sandblasting
SP-10 Cleaning, until a bare metal is nearly reached
The Swedish Standards Association (Sa, St)
St 2 Manual cleaning
St 3 Electromechanical Cleaning
Sa 1 Stripping Cleaning
Sa 2 Commercial Cleaning
Sa 2 1/2 Cleaning, until a bare metal is nearly reached
Sa 3 Cleaning, until a bare metal is reached
SSPC-SP-1
Chemical Cleaning. All foreign particles, oils, greases, contaminations, trace soils, salts, paints and chips and other contaminants accumulating on the steel surface are removed using solvents, emulsions, cleaning compositions or similar materials and methods, where solvents or cleaners are specified for use.
SSPC-SP-2 St2
Manual Cleaning. Roll scale, mill scale, flaking rust and paint are removed using a steel brush, manual sandblasting, manual scraping or other hand tool, and a combination thereof.
After treatment the substrate must have tarnished metallic luster and be free of oil, grease, dust, soil, salts and other contaminations.
SSPC-SP-3 St3
Electromechanical Cleaning. Roll scale, mill scale, flaking rust and paint are removed to prepare for automated cleaning using a wire brush, mechanical tools, automatic polishing and sandblasting or a combination thereof. The substrate must have clear metallic luster and be free of oils, greases, mud, soils, salts and other contaminations. The surface must not be polished and smooth.
SSPC-SP-4
Thermal Cleaning. Loose scale, rust and other contaminations are removed using high temperatures. To do so oxyacetylene burners are used. The surface must be preliminarily cleaned using a metal brush and free of oils, greases, mud, trace soils, salts and other contaminations.
SSPC-SP-5 Sa3 NACE 1
Cleaning, until a bare metal is reached. Mill scale, rust, roll scale, paint and other contaminations are removed using abrasive particles delivered by compressed air or a shotblast rotor onto the surface.
The surface cleaned, until a bare metal is reached, has a grey-white metallic color and roughness, and is ready for paint coating application. The surface must be free of oils, greases, mud, visible mill scale, rust, corrosion products, oxides, paint and other contaminations.
SSPC-SP6 Sa2 NACE 3
Commercial Cleaning. Mill scale, rust, roll scale, paint and other contaminations are removed using abrasive particles delivered by compressed air or a shotblast rotor onto the surface.
After commercial cleaning the surface must be completely free of oils, greases, mud, roll scale, mill scale, old paint and rust. Light shadows, stripes and color changes caused by the rust, mill scale oxides and old paint residues may be allowed. If the surface has indents, small rust or old paint residues may remain at the very bottom of such indents.
SSPC-SP-7 Sa1
Stripping Cleaning. Flaking mill scale, rust and paint are removed to a certain degree using abrasive particles delivered by compressed air or a shotblast rotor onto the surface. It is not a must that the surface is completely free of scale, rust and paint. Mill scale, rust and paint residues must be solid with the surface adequately polished to provide adhesion.
After striping cleaning the surface must be completely free of oils, greases, mud, rust residues, flaking scale, rust and paint coating, while a small mill scale amount, solid rust and paint residues are allowed. Numerous evenly distributed substrate metal stains are to be treated.
SSPC-SP-8
Etching. Mill scale, rust and roll scale are removed using chemicals and electrolysis or a combination thereof. As a result of etching, the surface must be completely free of all residues, rust and other foreign matters. Moreover, the surface must be free of acids and alkaloids that have not yet entered into a reaction.
SSPC-SP-9
Cleaning after sandblasting. All mill scale particles are removed after sandblasting.
SSPC-SP-10 Sa 2 1/2 NACE 2
Cleaning, until a bare metal is nearly reached. 95% of all the surface area must be free of all visible contaminations, while a slight color change may be allowed in the remaining part.
Virtually, all the mill scale, rust, roll scale, paint and other contaminations are removed using abrasive particles delivered by compressed air or a shotblast rotor onto the surface.
As a result of cleaning, until a bare metal is nearly reached, the surface must be free of oils, greases, mud, mill scale, rust, corrosion products, oxides, paint and other foreign matters, while light shadows, stripes and color changes caused by the rust, mill scale oxides and solid old paint residues may be allowed.