Chemsafe - Asset Integrity & Process Safety

By far the most significant and important method used for the thorough cleaning of mill-scaled and rusted surfaces is abrasive blast cleaning. This method involves mechanical cleaning by the continuous impact of abrasive particles at high velocities on to the steel surface either in a jet stream of compressed air or by centrifugal impellers. The latter method requires large stationary equipment fitted with radial bladed wheels onto which the abrasive is fed.
As the wheels revolve at high speed, the abrasive is thrown onto the steel surface, the force of impact being determined by the size of the wheels and their radial velocity.
Modern facilities of this type use several wheels, typically 4 to 8, configured to treat all the surfaces of the steel being cleaned. The abrasives are recycled with separator screens to remove fine particles. This process can be 100% efficient in the removal of mill scale and rust.
The standard grades of cleanliness for abrasive blast cleaning in accordance with BS EN ISO 8501-1 are:
Sa 1 – Light blast cleaning
Sa 2 – Thorough blast cleaning
Sa 2½ – Very thorough blast cleaning
Sa 3 – Blast cleaning to visually clean steel