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C1-C6 Salt Spray Test Levels: Environmental Requirements, Test Duration & Service Life Correlation | ISO 12944 Guide
Understand ISO 12944 C1-C6 salt spray test levels: corrosion environments, test methods (NSS/AASS/CASS), duration (240-3000h), and accelerated life calculation. For engineers & quality control.
1. Salt Spray Classification & Environments
| Level | Corrosivity | Typical Application Scenes |
|---|---|---|
| C1 | Very Low | Temperature-controlled indoor |
| C2 | Low | Rural outdoor, low-humidity buildings |
| C3 | Medium | Urban/industrial outdoor |
| C4 | Medium-High | Coastal industrial, polluted cities |
| C5 | High | Offshore marine, heavy industry (C5-I/M) |
| C6 | Extreme | Severe chemical/coastal exposure |
Keywords: Marine corrosion resistance, industrial coating standards, C5-M certification
2. C1-C6 Test Parameters Comparison
| Level | Method | Duration | Temp | pH | Key Evaluation Criteria |
|---|---|---|---|---|---|
| C1 | NSS (5% NaCl) | 240h | 35±2°C | 6.5-7.2 | Blistering/peeling |
| C2 | NSS (5% NaCl) | 240h | 35±2°C | 6.5-7.2 | Surface rust ≤5% |
| C3 | NSS (5±1% NaCl) | 480h | 35±2°C | 6.5-7.2 | Rust area ≤15% |
| C4 | NSS/AASS/CASS | 720h | 35±2°C | 6.5-7.2 | Adhesion loss ≤level 2 (ISO 4624) |
| C5 | CASS/ASS | 1440h | 35/50°C | 6.5-7.2 | Zero blistering (ISO 12944-6) |
| C6 | NSS (ISO 9227) | ≥3000h | 35°C | 6.5-7.2 | Zero substrate corrosion |
Critical Notes:
C5-M requires CASS/ASS ≥1440h
C4/C5 need 3-5 parallel samples with pretreatment documentation
3. Accelerated Test ⇨ Real Service Life
1 Standard Cycle =
-
-
2h NSS + 22h drying (Lab conditions)
-
48h mixed gas (10ppm NO₂ + 5ppm SO₂, 95% RH, 25°C)
Total = 1 Week
-
Life Expectancy Chart:
| Lab Duration | Real Service Life |
|---|---|
| 1 Week | ≈ 3 Years |
| 2 Weeks | ≈ 8 Years |
| 3 Weeks | ≈ 14 Years |
Formula based on ISO 9227 accelerated corrosion modeling.
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