Surface preparation can account for up to 40 percent of structural steel painting and repainting jobs. As ALFA LASER’s Structural Steel FAQ series has already established, the life of anti‐corrosion coatings on a steel surface depends to a large extent on how thoroughly the surface has been prepared for painting.

Properly evaluating the surface of structural steel surfaces for coating before and after Laser blasting will help balance the cost of preparing, repairing, and monitoring structural steel throughout its impressive lifespan.

This installment of our Structural Steel FAQ series will answer How are rust and mill scale evaluated pre‐ and post‐ Laser blasting?

The Standards

Widely used standards were developed to visually assess the initial surface conditions and the quality of the required surface preparation relative to the initial steel surface conditions.

The dominant standards for evaluating rust and mill scale are ISO 8501‐1:2007, SSPC Vis 1‐89, and NACE. While different in some minor details, these standards are practically identical.

Rust Grades

The standards identify four initial rust grades based on visual evaluation as described below and shown in these examples:

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

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

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

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

Preparation Grades

After Laser cleaning, the standards define four preparation grades. The appearance of the laser blasted surface must correspond to one of the following descriptions and standards:

The cost to achieve longevity of each grade varies and should be considered based on initial cost as well as lifetime costs based on your structural steel’s uses and expected lifespan.

• Brush‐off – After light laser blast cleaning, loose mill scale, rust, and foreign matter are removed. Despite being the least expensive grade of the four, brush-off preparation may not hold paint and coatings as the other grades and may require more frequent resurfacing.

• Commercial – Thorough laser blast cleaning removes almost all mill scale, rust, and foreign matter. This grade is normally adequate in a non-corrosive atmosphere and is more labor and cost intensive than brush-off preparation.

• Near White – Very thorough Laser cleaning removes mill scale, rust, and foreign matter to the extent that the only remaining traces are light stains in the form of spots and stripes. This grade is fully acceptable for most somewhat corrosive environments. It is the most common preparation grade for ship building.

• White Metal – Laser cleaning reveals pure metal. This grade is very expensive through old methods like Sandblast, Grinding, Dry Ice, Waterjet, Chemicals and typically reserved for applications where the costs of coating failure are catastrophic, for example, Heavy Equipment, Trucks, and many more industries.

Preparation grade examples based on ISO 8501/SIS

The different preparation grades depend on the initial rust grade. ISO 8501/SIS standard grades are presented below to provide visual examples. SSPC Vis 1/89 and NACE incorporate similar visual comparisons.

The ALFA LASER Way

Whatever your pre- and post-blast goals are for structural steel, you can count on ALFA LASER to help you find a better way. Contact us today to discuss your unique challenges.

Laser cleaning is a innovative method that uses laser beams to remove mill scale by vaporization. It is clean, safe, and environmentally friendly, as it does not produce any secondary waste, noise, or emissions. It can also preserve the substrate, improve the adhesion, and create surface textures. Laser cleaning is suitable for high-quality and high-value applications, such:

Industries

• Automotive Solutions & Autoparts

• Process & Production

• Military & Defense

• Shipbuilding & Ship Repair

• Aerospace & Air Transport

• Steel & Metal Manufacturing

• Building Restoration & Conservation

• Oil & Gas Industries

• Finishing Plants

• Construction

• Hydro Power

• Infrastructure

• MRO

• Mining

• Marine

• Heavy Equipment

• Remanufacturing

• Aluminium Manufacturing

• Stainless Steel Manufacturing

• Transportation & Mobility

• Energy

• Railway

• Cleaning Services

Alfa Laser Cleaning machine is a product of Alfa Laser, a company that specializes in laser cleaning solutions. It is a portable and versatile device that can remove mill scale from steel structures using a fiber laser source. It has a user-friendly interface, a flexible arm, and a fume extraction system. It can operate in different modes, such as continuous, pulse, or burst, and adjust the power, frequency, and speed according to the application. Alfa Laser Cleaning machine is a reliable and efficient tool for mill scale removal.

Sandblasting Alternative: The GreenBlast™

The GreenBlast is a powerful, hand-held sandblasting alternative that:

• Easily and effectively removes corrosion, mill scale and coatings

• Generates an anchor profile from 1 mils up to 4.7 mils

• Creates a surface cleanliness equivalent to [ Nace No.1 ] [SSPC-SP 5, white metal blast cleaning) [ ISO Sa 3 ]

• Is environmentally friendly. Alfa Laser Cleaning Machine Blasting does not use or produce hazardous materials

• Doesn’t require an expensive or timely clean up after operation

Conclusion

A novel method for metal surface preparation to remove mill scale, rust & residues for the production and finishing of metal surfaces is the Laser Cleaning through ALFA LASER machines.