Introduction

Rust removal and protective coating are critical processes in ensuring the durability, safety, and longevity of steel structures. Whether used in construction, energy, or industrial manufacturing, proper surface preparation and coating application directly impact corrosion resistance and overall performance.

This guide provides a comprehensive, standards-based overview of steel structure rust removal and painting processes, aligned with international best practices and optimized for industrial applications.

1. Rust Removal and Coating Requirements

Steel structure surface treatment and coating must comply with recognized standards such as:

• GB/T 50025-2020 – Acceptance Standard for Construction Quality of Steel Structures

• GB/T 8923 – Rust Grades and Preparation Grades of Steel Surfaces Before Painting

These standards define surface cleanliness, rust removal grades, and coating system requirements.

1.1 Surface Preparation (Rust Removal)

Key Requirements:

• Rust removal and coating must be carried out only after structural inspection approval and proper component identification.

• All contaminants must be removed prior to treatment, including:

• Oil and grease

• Welding slag and spatter

• Burrs and sharp edges

• Surface defects such as weld undercuts, pores, arc craters, and missed welds must be repaired before blasting.

Recommended Method: Abrasive Blasting (Sa2.5)

• Steel surfaces should be treated using shot blasting or sandblasting.

• Required cleanliness level: Sa2.5, ensuring:

• Complete removal of rust, scale, and contaminants

• Clean metallic appearance

Critical Timing:

• Apply the first primer within 4 hours after rust removal

• Maximum interval:

• 12 hours (indoor or low humidity conditions)

1.2 Coating Application Requirements

Coating should only proceed after rust removal inspection is approved.

Areas NOT to be Coated:

• Anchor bolts and base plates

• High-strength bolt friction surfaces

• Surfaces embedded in concrete

• Field welding zones (±100 mm)

General Coating Guidelines:

• Follow design specifications for:

• Coating type

• Color

• Number of layers

• Film thickness

• Use only certified coatings with:

• Product certificates

• Technical datasheets

Thinner Usage (Maximum Ratios):

2. Steel Structure Rust Removal Process

2.1 Selection of Rust Removal Methods

Three common methods are used:

Recommended Approach:

• Main structures: Shot blasting

• Corners / complex areas: Sandblasting or power tools

• Secondary treatment: Power tools

2.2 Shot Blasting Equipment ParametersMax width: 2.5 m

• Max height: 4.0 m

• Conveyor speed: 0.8–2.4 m/min

• Blasting angle: -60° to 60°

Abrasive Material:

• Use steel shots, tested for:

• Cleanliness

• Chloride content

2.3 Key Process Control Points

• Maintain relative humidity below 85%

• Ensure steel surface temperature is ≥3°C above dew point

• Clean surface thoroughly before blasting

• Remove dust and residual abrasives after blasting

3. Steel Structure Coating Process

3.1 Coating Environment

• Temperature: 5°C – 38°C

• Humidity: ≤85%

• Avoid:

• Rain, snow, fog

• Strong wind or dust

3.2 Preferred Coating Method: Airless Spray

Advantages:

• High efficiency: up to 500 m²/hour

• Smooth, dense, high-quality coating

• Better adhesion and longer service life

• Saves 20–30% paint consumption

3.3 Coating Workflow

1. Surface preparation

2. Pre-coating (edges, welds)

3. Primer application

4. Intermediate coating

5. Final coating

3.4 Application Best Practices

• Spray distance: ~30 cm

• Use brush for hard-to-reach areas

• Ensure uniform coating—no sagging or bubbling

• Follow recoat intervals strictly

• Clean surface before each layer

4. Inspection and Quality Control

4.1 Pre-Coating Inspection

• Verify rust removal grade and roughness

• Check environmental conditions

• Inspect coating materials

4.2 In-Process Inspection

• Measure wet film thickness

• Ensure no defects:

• Peeling

• Pinholes

• Air bubbles

4.3 Final Inspection

• Visual inspection: smooth, uniform, defect-free

• Thickness measurement using dry film thickness gauge

• Adhesion test (cross-cut method, ≤ Grade 1)

5. Coating Protection and Handling

• Avoid contact before full curing

• Protect coated surfaces during lifting and transport

• Use soft materials (rubber, wood) for support

• Repair damaged coatings immediately

6. Packaging and Transportation of Steel Components

Packaging Methods:

1. Box Packaging – Small, loose components

2. Bulk (Loose) Loading – Large structural elements

3. Bundled Packaging – Standardized smaller components

Transportation Requirements:

• Use appropriate trailers (flatbed or stake trailers)

• Equip vehicles with GPS tracking

• Ensure real-time communication for logistics safety

Conclusion

Proper rust removal and coating of steel structures are not just procedural steps—they are critical quality control measures that determine the durability and safety of industrial assets.

By adopting Sa2.5 surface preparation, airless spray coating, and strict inspection standards, manufacturers can significantly improve coating performance, extend service life, and reduce long-term maintenance costs.

Keywords: steel structure coating, rust removal process, shot blasting, sandblasting, Sa2.5 surface preparation, airless spray painting, industrial coating systems, corrosion protection, steel fabrication coating, protective coatings for steel structures