The longevity and performance of protective coatings in industrial settings, especially in corrosive environments, are heavily influenced by surface preparation quality. The conventional approach relies on abrasive blasting methods, which, though effective, are often impractical in maintenance contexts with limited access. Bristle blasting, a relatively new surface preparation method introduced by International Paint Ltd., presents a promising alternative that combines the efficiency of power tools with a surface profile quality approaching that of traditional abrasive blasting.
The Necessity of Advanced Surface Preparation Methods
Surface preparation in industrial maintenance, especially for offshore and onshore structures exposed to corrosive environments, remains critical to extending the lifespan of protective coatings. Offshore structures, for example, face high maintenance costs that can reach up to 20 times the initial cost if coatings degrade prematurely. For these applications, surface cleanliness and profile are essential to effective coating adhesion. The leading industrial standards, such as SSPC-SP 5 and SP 10, require abrasive blasting; however, in confined or remote areas, this may not be viable, requiring alternatives like SSPC-SP 11. Standard power tools like wire brushes and grinders, while accessible, fail to meet these standards, resulting in polished surfaces prone to adhesion failure and corrosion.
Bristle Blasting Technology: A Technical Overview
Bristle blasting technology introduces an innovative approach by using hardened, sharp bristles attached to a rotary head that scours the surface. Unlike conventional wire brushes, which produce surface striations, the bristles in this method retract upon impact, creating craters and an anchor pattern similar to abrasive blasting. This distinctive surface profile significantly enhances coating adhesion. Furthermore, bristle blasting has demonstrated its capability to approach the cleaning standards of SSPC-SP 5 while achieving profiles close to that of grit blasting—a groundbreaking achievement for power tool-based methods.
Comparative Analysis: Bristle Blasting vs. Conventional Methods
Testing conducted by International Paint Ltd. compared bristle blasting with other power tools and abrasive grit blasting across several conditions, including thermal cycling, continuous condensation, and immersion in seawater. Key findings from these tests underscore the reliability and effectiveness of bristle blasting:
1. Surface Profile and Roughness (Rmax): Using a profilometer, the study recorded the surface roughness and profile depth achieved by each method. For both Rust Grade A and Rust Grade D steel, bristle blasting achieved Rmax values (2.7–4.6 mils) similar to those of grit blasting, significantly outperforming power wire brushing. Higher Rmax values indicate a more textured surface, which is crucial for optimal coating adhesion.
2. Corrosion Resistance: In accelerated ISO 12944-9:2018 cyclic corrosion tests, bristle blasting exhibited superior corrosion resistance. Whereas wire-brushed surfaces showed extensive corrosion creep, bristle-blasted surfaces remained intact with minimal corrosion. Grit blasting outperformed bristle blasting slightly; however, bristle blasting achieved significantly better results than power wire brushing.
3. Adhesion Strength: Adhesion tests performed on coatings over bristle-blasted surfaces showed marked improvement compared to those over wire-brushed surfaces. The adhesion values of coatings over bristle-blasted surfaces approached those over grit-blasted surfaces, reinforcing the bristle blasting method's efficacy in enhancing coating performance under harsh conditions.
4. Thermal Cycling and Sea Water Immersion: Additional tests, including thermal cyclic and seawater immersion tests, evaluated coating performance on bristle-blasted surfaces against those on wire-brushed and grit-blasted surfaces. After six months, no rusting or disbondment was observed for any of the methods, indicating that bristle blasting meets the durability standards for long-term marine exposure.
Advantages and Limitations of Bristle Blasting
Advantages
Bristle blasting excels in its adaptability and ease of use for confined spaces, where traditional blasting techniques may be logistically and financially unfeasible. Its ability to achieve a desirable anchor profile similar to abrasive blasting opens new possibilities for enhancing corrosion protection in previously hard-to-reach areas. Additionally, bristle blasting reduces vibration exposure risks for workers, making it safer than traditional methods like needle gunning.
Limitations
However, bristle blasting has some limitations compared to grit blasting. It is time-intensive and less efficient for large surface areas, making it better suited to maintenance in smaller, localized regions. While the bristle blasting method yields high performance on small-scale projects, grit blasting remains the preferred choice for large industrial surfaces due to its speed and coverage capabilities. However, Bristle blasting provides significant reduction in the carbon footprint, compared to grit blasting.
Application and Future Potential
Given its robust performance in lab tests and field studies, bristle blasting is finding its place in industrial maintenance specifications, particularly in high-corrosion offshore environments. While still emerging, this technique has the potential to support high-performance coating systems, including zinc-rich epoxies that offer extended protection in severe conditions like C5M (offshore) and C5I (onshore) corrosive environments, as per ISO 12944 standards.
Moreover, the industry continues to innovate with bristle blasting technology, exploring further applications in shipyards and oil and gas installations. As this method becomes more widely adopted, additional research and field studies will help refine its capabilities and validate its long-term durability.
Conclusion
For mechanical engineers and maintenance professionals, bristle blasting offers a significant advancement in surface preparation technology. It bridges the gap between power tool convenience and abrasive blasting performance, providing a versatile solution for maintaining industrial coatings in challenging, corrosive environments. Bristle blasting enables higher surface profile standards, enhanced corrosion resistance, and increased coating adhesion, thus contributing to extended maintenance cycles and reduced long-term costs. While it may not replace grit blasting entirely, bristle blasting's niche role in maintenance is already proving indispensable for small, complex, and hard-to-reach areas in the field.
We have based this article on the original paper from Neil Wilds, presented during NACE 2009. You can dowload this here