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When assessing the degree of removal of rust, mill scale, and other visual contaminants from steel surfaces, it’s crucial to understand the different grades of rust and the corresponding blast cleaning standards.
Important Note: Surface cleanliness is not a measure of surface profile – see the following pages for notes on surface profile.
Explanatory Details |
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Rust Grade ASteel with the millscale layer intact and very minor, or no rusting |
Blast Class 1 (SP-7/N4)Very light, whip over blast clean with removal of loose surface contaminants. |
Rust Grade BSteel with spreading surface rust, and the millscale commenced flaking. |
Blast Class 2 (SP-6/N3)Substantial blast clean with wide spread, visible contaminant removal and base metal color appearing. |
Rust Grade CRusty Steel with the millscale layer flaked and loose, or lost, but only minor occurrence of pitting. |
Blast Class 2 ½ (SP-10/N2)Intense blast clean leaving shaded grey metal with only tiny, isolated flecks or strips of visible contaminants. |
Rust Grade DVery rusty steel with the millscale layer all rusted and extensive occurrence of pitting. |
Blast Class 3 (SP-5/N1)Complete blast clean with consistent, metal color all over and no visible contaminants. |
DISCLAIMER: The grades of rust and blast cleaned surfaces ‘information’, described and illustrated on these pages are a guide only and do not claim to be approved nor complying nor substitutable for or by any surface preparation standard. It is responsibility of the reader and/or users of this ‘information’ to separately determine and verify the specifications and/or methods and/or assessment of surface preparation as indicated or directed or required by or in any work specifications or standards. Blast-One™ expressly disclaims any liability for the use or misuse of this ‘information’.
Looking for more insights on surface preparation? Check out our detailed guide on Understanding Surface Profile vs. Class of Blast. Learn the key differences between these two essential aspects of blasting and discover how to ensure your project meets specified requirements. Plus, find out about our assessment free tools to help you identify Class of Blast standards on your jobsite. Don’t miss out—click to read more!
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