Surface Preparation Grades of Blast Cleaned Steel

Assessment of degree of removal of rust, mill scale and other visual contaminants (inspected without magnification).

Important Note: Surface cleanliness is not a measure of surface profile – see the following pages for notes on surface profile.

Explanatory Details

Rust Grade A

Steel 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 B

Steel 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 C

Rusty 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 D

Very 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.

NOTE: All blasting preparation grades must be free of oil, grease and dirt.
blast cleaned steel spread

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’.