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Surface Preparation Standards

Surface Preparation Standards


Surface Preparation Pan Abrasives


Surface preparation standards are stipulated by various bodies throughout the world to designate the cleanliness condition of blasted steel, prior to applying a protective coating.The applicable cleanliness standard is usually called for by either the protective coating manufacturer or the owner of the structure to be painted.

 

The most commonly referred to standards are SSPC, NACE, and Swedish Standards.

 

Each standard is divided into four standards of cleanliness, broadly described as follows; brush off, commercial, near white metal, white metal. Whilst each standard may differ slightly in requirements and terminology the following cross reference chart indicates the close approximation of each level of cleanliness for each standard.

  BRUSH OFF COMMERCIAL NEAR WHITE METAL WHITE METAL
SSPC SP 7 SP 6 SP 10 SP 5
NACE No.4 No.3 No.2 No.1
SWEDISH Sa.1 Sa.2 Sa.2.5 Sa.3

 

A brief description of each of the four levels of cleanliness is as follows:

  • Brush Off - Loose mill scale, loose rust and foreign particles are removed.

  • Commercial - Mill scale, rust and foreign particles are substantially removed and grey metal is visible.

  • Near White Metal - Mill scale, rust and foreign particles are removed to the extent that only traces remain in the form of spots or stripes. The cleaned surface will show varying shades of grey.

  • White Metal - Visible mill scale, rust and foreign particles are entirely removed. The cleaned surface should have a uniform metallic colour but may show varying shades of grey when viewed at different angles.

 

The appearance of steel after blasting will vary greatly and is subject to, amongst other things, the condition and appearance of the steel prior to blasting. Other factors that influence the post blasting appearance include, type and size of abrasive used, angle of blast and profile height.

 

The intial condition of the steel, prior to blasting, can be divided into one of four categories: (As per AS1627.4-1989)

  • Condition A. Steel surface covered completely with adherent mill scale and with little if any, rust.

  • Condition B. Steel surface which has begun to rust and from which the mill scale has begun to flake.

  • Condition C. Steel surface on which the mill scale has rusted away, or from which the mill scale can be scraped, but having little pitting visible to the naked eye.

  • Condition D. Steel surface on which the mill scale has rusted away, and on which considerable pitting is visible to the naked eye.

The following pictorial table illustrates the variations in surface appearance after blasting, depending on the intial condition of the steel prior to blasting.

 

Little Rust - Unblasted Steel

Condition A

Unblasted

Little Rust - Blasted Steel Sa1

Condition A

Blasted Sa.1

Little Rust - Blasted Steel Sa2

Condition A

Blasted Sa.2

Little Rust - Blasted Steel Sa2.5

Condition A

Blasted Sa.2.5

Little Rust - Blasted Steel Sa3

Condition A

Blasted Sa.3

Slight Rust - Unblasted Steel

Condition B

Unblasted

Slight Rust - Blasted Steel Sa1

Condition B

Blasted Sa.1

Slight Rust - Blasted Steel Sa2

Condition B

Blasted Sa.2

Slight Rust - Blasted Steel Sa2.5

Condition B

Blasted Sa.2.5

Slight Rust - Blasted Steel Sa3

Condition B

Blasted Sa.3

Medium Rust - Unblasted Steel

Condition C

Unblasted

Medium Rust - Blasted Steel Sa1

Condition C

Blasted Sa.1

Medium Rust - Blasted Steel Sa2

Condition C

Blasted Sa.2

Medium Rust - Blasted Steel Sa2.5

Condition C

Blasted Sa.2.5

Medium Rust - Blasted Steel Sa3

Condition C

Blasted Sa.3

Heavy Rust - Unblasted Steel

Condition D

Unblasted

Heavy Rust - Blasted Steel Sa1

Condition D

Blasted Sa.1

Heavy Rust - Blasted Steel Sa2

Condition D

Blasted Sa.2

Heavy Rust - Blasted Steel Sa2.5

Condition D

Blasted Sa.2.5

Heavy Rust - Blasted Steel Sa3

Condition D

Blasted Sa.3