The salt spray test is a standard testing method that involves placing samples in a sealed chamber filled with salt spray to evaluate a material’s rust resistance through accelerated corrosion.
Color coated steel sheet are used in building exteriors, roofing, home appliances, and billboards, where they are constantly exposed to humid conditions, acid rain, and salt-laden environments. Rust resistance equals service life, and the salt spray test is the most direct and universal “health check.”
Three Common Test Methods
| Method | Abbreviation | Solution | Severity | Application |
|---|---|---|---|---|
| Neutral Salt Spray | NSS | 5% NaCl | Basic | General coatings |
| Acetic Acid Salt Spray | AASS | Salt + Acetic acid | Medium | Plated coatings |
| Copper Accelerated | CASS | Salt + Acetic + Copper | Most severe | Chrome-plated parts |
There is not just one type of salt spray test; they are categorized into three levels based on severity. For testing the rust resistance of color-coated steel coils, the most commonly used method is the Neutral Salt Spray (NSS) test. Typical test conditions include a 5% sodium chloride solution, a chamber temperature of 35°C, and continuous spraying.
How to Interpret the Results?
The core of the salt spray test is not to see “how long it takes for the sheet to rust,” but to assess the extent of coating degradation. When evaluating, focus on two areas:
- Sheet surface (unscored area): Check for blistering, rust, or coating peeling; the closer the rating is to 0, the better.
- At the scratch mark: This simulates notches caused by transportation impacts or installation cutting. Check how many millimeters (mm) the corrosion has spread from the scratch mark in both directions; the less spread, the better.
Note: Results are typically expressed as a combination of “panel surface rating + scratch spread value,” such as “1,000 h neutral salt spray, panel surface Ri0, scratch spread ≤ 2 mm”.
What Factors Influence Salt Spray Test Results?
| Factor | Influence Mechanism | Recommendation |
|---|---|---|
| Substrate Coating | Zinc layer acts as a sacrificial barrier. | Select high zinc (Z275+). |
| Coating Type | Resistance: PVDF > HDP > PE. | Choose HDP / PVDF. |
| Coating Thickness | Thicker coatings delay penetration. | Standard ≥ 20μm. |
Quick Reference to Standards
- GB/T 10125: Salt spray test (China)
- ISO 9227: International corrosion tests
- ASTM B117: American standard
- ISO 4628: Evaluation of degradation
- GB/T 12754: Organic coated steel product standard
To understand this test report, just remember three points:
- Method: For Color Coated Steel Plate, focus on the NSS test.
- Results: Read both the surface rating (Ri) and the cross-spread (mm) together.
- Comparison: Compare products under the same conditions; do not directly convert test duration into service life.
Post time: Sep-01-2026
