Structural steel components are used in many industries, including construction, shipbuilding, and the production of all kinds of heavy duty vehicles, trucks, railway vehicles, agricultural implements or construction equipment. From the construction of bridges, building of ships or production of equipment that must withstand heavy loads, steel is selected for its strength and durability.
To live up to its full potential and prevent premature failure, the steel must be guarded against corrosion with a protective coating. Shot blasting plays an indispensable role in preparing the steel surface for such coatings. Partnering with a shot blasting expert such as Rosler Metal Finishing can help you determine the shot blasting equipment, blast media, and process required for your structural steel components.
In a series of blog posts, we’ll answer the most common questions about the surface preparation and coating of structural steel.
We begin with a basic question: Why do structural steel components need to be prepared for protective paint coating?
The answer, in short, is for best coating results and longevity.
Goals of Surface Preparation
If not covered with a suitable, protective coating, structural steel components are prone to rust quickly and fail with potentially catastrophic consequences.
The effective life of a coating of anti-corrosive paint applied to steel surface is largely dependent on how thoroughly the surface has been prepared prior to painting.
Structural steel components requiring protective coatings include:
- Beams (I‐beams, H‐beams, channels, angles, etc.).
- Steel plates.
- Round bars and pipes.
Preparing and coating the surfaces effectively increases their durability and improves their appearance.
Issues to Watch For
A variety of factors can create surface issues necessitating proper preparation before coating such as the steel rolling process itself and prolonged exposure to wind, water, or chemicals.
Specific surface factors in need of attention include:
- The presence of rust or mill scale.
The presence of surface contaminants.
Surface profile or roughness.
The presence of mill scale, rust, or any other contaminants on the steel surface can cause premature coating failure. Painting a surface with the wrong surface profile/roughness can also lead to premature failure or drastically increase the paint consumption.
To achieve good coating adhesion, the surface profile generally must become somewhat rougher, increasing the overall surface area.
Tools of the Trade
While numerous cleaning techniques, including hand and power tool cleaning, high-pressure water jetting, and degreasing, are used for surface preparation, dry shot blasting is the most common industrial paint preparation method for structural steel components.
This method utilizes ferrous metallic abrasives and can be used in combination with other methods.
For example, pre-cleaning steps are frequently required before the shot blasting process.
Surface issues for structural steel components vary greatly. Fortunately, users can rely on detailed standards describing the visual evaluation of surfaces and procedures regarding the correct surface preparation for coating and painting.
The most commonly used standards address different surface characteristics of steel components and the respective preparation requirements.
- ISO 8501 – Visual assessments of surface cleanliness, rust, and preparation grades of uncoated steel substrates
- ISO 8502 – Tests for the assessment of surface cleanliness
- ISO 8503 – Evaluates surface roughness characteristics of blast‐cleaned steel substrates
- ISO 8504 – Methods for abrasive blast cleaning
- SSPC – Preparation grades created by the Society for Protective Coatings
- NACE – Preparation grades created by the National Association of Corrosion Engineers
- ASTM D 2200 - Standard practice for use of pictorial surface preparation standards and guides for painting steel surfaces created by the American Society for Testing and Materials
The Rosler Way
Whatever your structural steel needs are, you can count on Rosler Metal Finishing to help you find a better way. Contact us today to discuss your unique challenges.
The complete Structural Steel Series includes:
- Part 1 – Why Surface Preparation is Necessary.
- Part 2 – Methods of Surface Preparation.
- Part 3 – Evaluating Rust and Mill Scale Pre- and Post-Blast.
- Part 4 – Evaluating the Presence of Dust.
- Part 5 – Assessing Surface Profile.
- Part 6 – Blast Media’s Influence on Surface Profile.
- Part 7 – Comparing Commonly Used Blast Machines.
- Part 8 – Are All Turbines Created Equal?
- Part 9 – Removing Residual Blast Media and Dust.
- Part 10 – Blast Rooms for Touch-Ups.
- Part 11 – Preservation Lines.
- Part 12 – Material Handling Options.
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Post written by
Rosler Metal Finishing, USA
Technical Sales Specialist – Shot Blasting