Surface preparation
EVALUATION OF THE QUALITY OF SURFACE PREPARATION FOR PAINTING
Initial Surface Estimation
The following four degrees of corrosion have been established:
A – the surface of the steel, covered to a large extent by firmly adhering mill scale, but practically free of rust;
B – the surface of the steel that has begun to rust, and from which the mill scale begins to lag behind;
C is the surface of the steel from which the mill scale has rusted away or from which it can be removed, and on which uniform corrosion is observed over a large area under normal consideration;
D is the surface of the steel from which the mill scale has disappeared as a result of rusting, and on which general and pitting corrosion is observed under normal consideration
Evaluation of the degree of cleaning of the surface of the new metal
The method of surface preparation is indicated as follows:
Sa – abrasive blasting (shot blasting) cleaning;
St – cleaning with a manual or mechanized tool.
The degrees of abrasive blasting are characterized as follows:
Sa1 – Easy cleaning. When viewed without magnification, the surface must be free of visible oil, grease, dirt, and loosely adhering scale, rust, paint, and foreign particles.
Sa2 – Thorough cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, as well as most of the mill scale, rust, paint and foreign particles. Any remaining contaminants must adhere firmly.
Sa 2 ½ – Very thorough cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, as well as from mill scale, rust, paint and foreign matter. Any remaining traces of contamination should only appear as light staining in the form of spots or streaks.
Sa3 – Cleaning to visual clean steel. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, as well as from mill scale, rust, paint and foreign matter. It should have a uniform metallic color.
Degrees of cleaning by hand and mechanized tools are characterized as follows:
St2 – Thorough cleaning. When viewed without magnification, the surface shall be free from visible oil, grease, dirt, and ill-adhering mill scale, rust, paint, and foreign particles.
St3 – Very thorough cleaning. As St 2, but the surface must be treated more carefully to achieve a metallic finish.
