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what is the polishing standard SA2.5 ?

Release time:

2025-10-23

The SA 2.5 is a surface preparation standard defined by ISO 8501-1 and commonly used in the field of steel surface preparation before painting or coating. It specifically refers to a level of cleanliness achieved during abrasive blasting (sandblasting or similar techniques) and is part of a set of standards for surface cleanliness known as Swedish Standard (SS 05 59 00).

SA 2.5 (Near White Metal Blast Cleaning)

Description: SA 2.5 is the second-highest grade of surface cleanliness, known as Near White Metal Blast Cleaning. This standard is often used for surfaces that will be coated in environments with high demands for protection, such as offshore platforms, bridges, and tanks.

Visual Appearance: The surface should appear nearly free from contaminants. The visible rust and mill scale are removed to a significant extent, leaving only a slight amount of residues.

Surface Characteristics:

The steel surface should be mostly free from visible oil, grease, dirt, and other contaminants.

Any rust, mill scale, or old coatings should be almost completely removed.

No more than 5-10% of the surface area may show slight traces of rust or mill scale.

There should be no visible pitting, and the surface should have a slightly rough texture suitable for the application of the coating.

Preparation Process:

Abrasive blasting (using materials like sand, steel grit, or shot) is commonly employed to reach this cleanliness level.

The blasting process removes contaminants, oxides, and old coatings, creating a textured surface to which new coatings will better adhere.

Key Features of SA 2.5 Surface Preparation:

No Oil or Grease: The surface should be completely free of any oil or grease.

Minimal Rust or Scale: No more than 5-10% of the surface may show slight traces of rust or scale.

Visible Pitting: There should be no pitting or other damage to the surface. Any defects like corrosion pits should be minimal or absent.

Surface Roughness: The surface should have a rough profile (anchor pattern) that helps the new coating bond properly.

Clean Appearance: The surface should look almost completely clean, leaving only faint remnants of mill scale or rust.

Visual Comparison with Other Grades:

SA 3 (White Metal Blast Cleaning): The highest grade of surface cleanliness, where the surface is nearly completely free of any contaminants (visible surface rust, scale, etc.).

SA 2 (Industrial Blast Cleaning): This is a lower grade than SA 2.5, where the surface has more rust and mill scale than SA 2.5 but is still prepared for coating.

Applications:

Heavy Duty Coating: Used when a high level of surface preparation is required for protective coatings in harsh environments.

Offshore and Marine Structures: Often required for ships, oil rigs, and underwater pipelines.

Bridges: Especially when protective coatings are needed for long-lasting corrosion resistance.

Storage Tanks and Industrial Equipment: Used in environments prone to corrosion due to chemicals or extreme weather conditions.

Advantages:

Better Adhesion: The rough surface left by abrasive blasting enhances the bonding between the metal surface and the protective coating.

Corrosion Protection: Ensures coatings will last longer, offering better protection against rust and corrosion.

Durability: Ideal for applications where the surface will be exposed to harsh conditions (marine, industrial, or high-moisture environments).

Would you like to dive deeper into the methods used to achieve SA 2.5 or explore how it compares to other standards like SA 3 or SA 2?