All abrasive blasting is done in accordance with Australia Standards AS 1627.4-2005 (r2017) Metal finishing—Preparation and pretreatment of surfaces Part 4: Abrasive Blast Cleaning of Steel and conforms to Queensland and Worksafe Code of Practice – Abrasive Blasting – 2020.
Initial Surface Assessment as per AS 1627.4-2005
The surface of hot rolled steel may be defined according to one of four initial rust grades defined and illustrated in AS 1627.9 (and as shown by the approximate examples below) depending on the relative amounts of mill scale and rust. The worst grade that is evident on the steel surface to be treated shall be recorded.
GRADE A
Steel surface covered completely with adherent mill scale and with little if any rust.
GRADE B
Steel surface, which has begun to rust and from which the mill scale has begun to flake.
GRADE C
Steel surface on which the mill scale has rusted away or from which it can be scraped, but with little pitting visible to the naked eye.
GRADE D
Steel surface on which the mill scale has rusted away and on which considerable pitting is visible to the naked eye.
Classes of Blast Cleaning as per AS 1627.4-2005
The Australian Standard defines four classes of surface preparation achievable by abrasive blast cleaning, identical to those described and pictured in AS 1627.9 (and as shown by the approximate examples below). The definitions are:
Sa 1 (Brush Blast)
Light blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter. The appearance corresponds to the prints designated Sa 1 in AS 1627.9.NOTE: Mill scale, rust or paint coating is considered to be poorly adhering if it can be removed by lifting with a blunt putty knife.
Sa 2 (Commercial Blast)
Thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and shall be free from most mill scale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering (see note to Sa 1). It corresponds to the appearance of the prints designated Sa 2 in AS 1627.9.
Sa 2½ (Near White Metal)
Very thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and shall be free from mill scale, rust, paint coatings and foreign matter. Any remaining contamination shall show only as slight stains in the form of spots or stripes and correspond to the prints designated Sa 2½ in AS 1627.9.
Sa 3 (White Metal)
Blast cleaning to visually clean steel. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and shall be free from mill scale, rust, paint coating and foreign matter. It shall then have a uniform metallic colour and correspond to the prints designated Sa 3 in AS 1627.9.
Note: The images shown above are indicative only, for the abrasive blasting of Grade C rusted steel surfaces.
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