Various steel surface preparation standards are used throughout the world, so it can be confusing to know how each standard relates to the other – and the practical implications for surface cleanliness. At KUE Group, we operate under the ISO 8501-1:2007 standards, which provide an internationally recognised set of four visual cleanliness grades, based on the level of blast cleaning required to reach that standard.
The three main alternatives to ISO 8501-1:2007 are:
1. National Association of Corrosion Engineers / NACE International (NACE), USA: The National Association of Corrosion Engineers started life as a regional professional association in Texas, but has since expanded its scope into a truly international association, with accredited members across the world (including KUE Group here in the UK). NACE issues a well-defined set of surface cleanliness categories that operate alongside their ISO equivalents.
2. Society for Protective Coatings (SSPC), USA: The SSPC is a professional association of surface treatment businesses specialising in industrial and marine equipment. The SSPC’s SP surface cleanliness standards overlap in considerable ways with the NACE standards, with which they are closely associated, and direct equivalents can be drawn with the ISO standards. Unlike the NACE standards, which are used widely throughout the world, the SSPC standards are predominantly used by businesses in North America.
3. Swedish Standards Institution, Sweden: The Swedish Standards Institution is the author of the influential ‘Sa’ surface cleanliness standards, which were designed to clarify slight differences between the ISO and US standards regarding dry abrasive blasting, creating a bridge between the two. The Sa grades are used extensively in Europe, and are often given priority to, or used interchangeably with, their equivalent ISO grade. While the Sa grades are well understood in the US market, the preferred standards in the Americas are ISO, NACE and SSPC.
What Is Meant By Cleanliness?
Cleanliness for a carbon steel surface before treatment is defined by the visible level of rust and mill scale. As we’ve discussed in a previous article from July 2019, surface cleanliness can be roughly divided into four rust grades, ranging from the least soiled to the most.
A – Extensive mill scale coverage but little or no rust.
B – Mill scale has begun to peel away and the beginnings of rust is evident.
C – Mill scale has largely rusted away, revealing a slightly pitted surface to the naked eye.
D – Mill scale has entirely rusted away, leaving general pitting which is visible under normal conditions.
The surface preparation standards describe the visual condition of the carbon steel surface after a certain intensity of blast cleaning is applied. Following the ISO 8501-1:2007 standards;
Light blast cleaning – results in a surface that is visibly largely free from dirt, grease and oil, and from poorly adhering rust, paint, mill scale and contaminants.
Thorough blast cleaning – results in a surface from which all visible grease, oil and dirt has been removed, along with most mill scale and rust. Ingrained and firmly adhered rust and contaminants may still be visible.
Very thorough blast cleaning – results in a surface completely free from grease, dirt, mill scale, rust and paint. Contamination may remain in the form of visible stains, stripes and patches.
Blast cleaning to visually clean steel – the treated surface has no visible contaminants, mill scale, rust or stains, and has a uniformly metallic appearance.
The table below shows how the ISO 8501-1:2007 standards relate to their Swedish and American counterparts.
| ISO 8501 -1 | Sa | SSPC | NACE | Alternative NACE/SSPC designation |
| Light blast cleaning | Sa1 | SP7 | 4 | Brush blast |
| Thorough blast cleaning | Sa2 | SP6 | 3 | Commercial blast |
| Very thorough blast cleaning | Sa 2½ | SP10 | 2 | Near white blast |
| Blast cleaning to visually clean steel | Sa3 | SP5 | 1 | White blast |
Find Out More
To find out more about steel surface cleanliness standards, and how the various standards relate to our work here at KUE Group, or to discuss your project requirements, please call 01274 721188 today.
