SSPC-SP 7: Brush-Off Blast Cleaning

Abstract

Surface preparation is a crucial step in ensuring the longevity and performance of industrial coatings. Among the standards set by the Society for Protective Coatings (SSPC), SSPC-SP 7 Brush-Off Blast Cleaning provides an efficient and economical solution for removing loosely adhered contaminants while maintaining tightly adhered material. This standard is particularly useful for applications where minimal preparation is required, yet a clean and stable surface is essential for proper coating adhesion. This article explores the SSPC-SP 7 standard, its requirements, applications, and best practices.

Introduction to SSPC-SP 7

SSPC-SP 7 Brush-Off Blast Cleaning is a surface preparation standard designed to remove visible loose rust, mill scale, paint, and other contaminants. Unlike more aggressive methods such as SSPC-SP 5 (White Metal Blast Cleaning) or SSPC-SP 10 (Near-White Blast Cleaning), SSPC-SP 7 leaves tightly adhered materials intact and does not aim to achieve a uniform surface profile. This makes it an ideal method for less demanding applications where a light cleaning is sufficient to prepare the substrate for coatings.

Key Requirements of SSPC-SP 7

To comply with SSPC-SP 7, the surface must:

1. Be free of all visible loose mill scale, rust, and coatings.
2. Retain tightly adhered mill scale, rust, and coatings that cannot be removed by lifting with a dull putty knife.
3. Exhibit minimal surface alteration, as SSPC-SP 7 does not aim to create a specific surface profile.
4. Be free of visible dust, dirt, grease, oil, and other contaminants, typically addressed by SSPC-SP 1 Solvent Cleaning prior to blasting.

The standard is equivalent to NACE No. 4, ensuring alignment with global surface preparation standards.

The SSPC-SP 7 Process

1. Tools and Equipment

SSPC-SP 7 utilizes abrasive blasting equipment, but with lower pressure or intensity compared to more aggressive blasting standards. Common abrasives include:

• Crushed Glass: Provides light cleaning without excessive material removal.
• Aluminum Oxide: Suitable for non-ferrous surfaces.
• Steel Shot or Grit: Effective for steel surfaces requiring light preparation.

2. Technique

The process focuses on lightly blasting the surface to remove loose contaminants without extensively altering the substrate. Operators should maintain consistent blasting distance and pressure to avoid excessive removal of tightly adhered materials.

3. Pre-Cleaning

SSPC-SP 1 Solvent Cleaning is often performed before SSPC-SP 7 to remove grease, oil, and other soluble contaminants, ensuring a cleaner surface for blasting.

Applications of SSPC-SP 7

1. Maintenance Painting

SSPC-SP 7 is widely used in maintenance scenarios where existing coatings are still largely intact but require light cleaning to remove surface contaminants. This ensures compatibility and adhesion of new coatings.

Example: Repainting structural steel components on bridges or industrial facilities.

2. Marine and Offshore Projects

For ship hulls, decks, and offshore structures, SSPC-SP 7 provides sufficient preparation for touch-up coatings or secondary layers without removing tightly adhered material.

Example: Preparing ship decks for anti-slip coatings.

3. Industrial and Commercial Equipment

Machinery and equipment with minor rust or loose coatings can be prepared using SSPC-SP 7 to ensure adhesion of protective or aesthetic coatings.

Example: Refurbishing storage tanks or machinery in manufacturing plants.

4. Temporary Protective Coatings

SSPC-SP 7 is an effective method for preparing surfaces for temporary coatings, such as primers or rust inhibitors, used during transit or storage.

Advantages of SSPC-SP 7

1. Cost-Effective
   SSPC-SP 7 is less labor-intensive and requires less abrasive material compared to more stringent blasting standards, making it a cost-effective choice.
2. Quick Turnaround
   The light cleaning process ensures rapid preparation, reducing project downtime.
3. Preservation of Substrate
   Tightly adhered materials are left intact, minimizing substrate damage and unnecessary material removal.
4. Environmental Benefits
   Produces less dust and waste than more aggressive blasting methods, making it suitable for environmentally sensitive areas.

Limitations of SSPC-SP 7

1. No Surface Profile
   SSPC-SP 7 does not create a measurable surface profile, limiting its use for high-performance coating systems that require strong adhesion.
2. Limited Cleaning Power
   This method cannot remove tightly adhered mill scale, rust, or coatings, making it unsuitable for heavily corroded surfaces.
3. Not for Critical Applications
   SSPC-SP 7 is not recommended for environments where maximum cleanliness and performance are required, such as chemical plants or subsea structures.

Comparison with Other SSPC Standards

• SSPC-SP 1 (Solvent Cleaning): Removes grease, oil, and other soluble contaminants but does not address rust or mill scale.
• SSPC-SP 2 (Hand Tool Cleaning): Removes loose contaminants manually, but less efficiently than SSPC-SP 7.
• SSPC-SP 10 (Near-White Blast Cleaning): Removes almost all contaminants, leaving very light shadows or staining.
• SSPC-SP 5 (White Metal Blast Cleaning): Provides the highest level of cleanliness, leaving no visible contaminants.

Check out our full guide to industrial coating applications.

Best Practices for SSPC-SP 7

1. Pre-Clean Thoroughly
   Always perform SSPC-SP 1 Solvent Cleaning prior to blasting to remove grease, oil, and other contaminants.
2. Use Appropriate Abrasives
   Select abrasives that match the substrate and cleaning requirements to avoid excessive material removal.
3. Inspect During and After Cleaning
   Regularly inspect the surface to ensure all loose contaminants have been removed while tightly adhered materials remain intact.
4. Pair with Compatible Coatings
   Choose coatings that do not require a specific surface profile for optimal adhesion and performance.

Industrial Coating Systems for SSPC-SP 7

SSPC-SP 7 is commonly used in conjunction with:

• Primer Coatings: Provides a base layer for subsequent protective coatings.
• Maintenance Coatings: Ensures adhesion of new coatings applied over old ones.
• Rust Inhibitors: Temporary coatings that protect surfaces during transit or storage.

Conclusion

SSPC-SP 7 Brush-Off Blast Cleaning is a practical and cost-effective standard for light surface preparation in industrial, marine, and commercial settings. While it does not achieve the level of cleanliness or surface profile required for high-performance applications, its ability to quickly and efficiently prepare surfaces makes it a valuable tool for maintenance painting and touch-up work.

For more information about SSPC standards or to determine if SSPC-SP 7 is the right choice for your project, contact us.

• Category: Coatings Application, SSPC Standards