Metal surface treatment and coating
1. Steel Structure Preparation
2. Degreasing
3. Abrasive Media Selection
4. Sandblasting
**Steel Structure Preparation**
To ensure optimal coating performance, the steel surface must be properly prepared before sandblasting. Any imperfections such as air holes, incomplete welds, or sharp edges should be corrected. Sharp edges and flame-cut surfaces should be ground to a radius of at least R ≥ 2 mm. Welds must be smooth, free from spatter, and even in texture to provide a uniform base for coating.
**Degreasing**
Before blasting, all grease or residues from inspection films must be removed using the SSPC-SP1 "solvent cleaning" method. This step is essential to ensure proper adhesion of the coating and avoid contamination that could lead to premature failure.
**Abrasive Media Selection**
The abrasive used for blasting must be dry, clean, and free from debris that might compromise the coating’s integrity. It should meet the requirements of ISO 11126 1–8 and be tested according to ISO 11127 1–7. River sand is not permitted for sandblasting due to its inconsistent quality. The abrasive size should be chosen to achieve the required surface roughness for the specific coating system. Surface roughness is measured according to ISO 8503. During blasting, care must be taken to prevent oil or water from contaminating the steel surface. A water separator must be installed on the air compressor to maintain dry air. Unless authorized, abrasive materials cannot be reused.
**Surface Preparation Standards**
The steel surface should be blast-cleaned to ISO 8501-1 Sa? grade with a surface roughness of Rz 50–70 microns or a "moderate (G)" grade as per ISO 8503-2. After blasting, the surface must remain clean, dry, and free from grease until the first coat of paint is applied. All dust must be thoroughly removed, and the dust level should not exceed 3 levels as per ISO 8502-3. Painting must be completed within 4 hours after treatment to prevent the steel from re-rusting or becoming contaminated. If visible rust, moisture, or contamination occurs, the surface must be re-cleaned to the required standard.
**Special Surface Treatments**
For non-carbon steel surfaces such as flanges, galvanized layers, and aluminum, follow detailed construction instructions. When painting a galvanized surface, it should be sandblasted to ensure proper adhesion.
**Maintenance Procedures**
In maintenance scenarios, the surface should be treated to achieve an SSPC SP2 grade using an appropriate method.
Editor: Hardware Business Network Information Center
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