Contaminants impossible to remove in the chemical treatment before the process of hot-dip galvanizing need to be removed by the Client before delivery. The following list presents the most common contaminants unremovable in degreasing and pickling:
- Paint markings and layers, varnish,
- Tarry substances, lubricants, grease, oil,
- Excess rust and mill scale,
- Welding residues, slag, chips, anti-chip sprays,
- Abrasive blasting residues, sand, pellets, abrasive slag,
- Contaminants of material after NDT examination,
- Products containing carbon in the form of graphite which facilitate the metal forming process,
- Residue chips in holes and burrs after cutting.
Noticing some defects and contaminants on the surface which make proper anti-corrosion protecion impossible cannot be performed before the final stage - galvanizing.
If the contaminants listed above are not removed, while galvanizing the coating can be stretched or may not be formed at all.
Some uneven patches on the steel surface, for example defective rolling, pitting corrosion, mill scale pitting, scales, cracks and other defects, welding craters, welding slag residues, non-metallic inclusion can be recognized and noticed after hot-dip galvanizing.