Anti-Corrosion Grades: Classification Based on Environmental Corrosivity
The anti-corrosion grades for complete electrical assemblies are classified according to ISO 12944 (corrosion protection of steel structures) and IEC environmental standards, ranging from C1 (low corrosivity; dry indoor environments) to C5 (very high corrosivity; coastal industrial or high-humidity environments).
Higher grades entail thicker coating systems and longer service lives regarding corrosion resistance.
Industry experts note that the required anti-corrosion grade is determined by the operating environment: coastal, chemical processing, and high-humidity environments require high anti-corrosion grades (C4/C5), utilizing zinc-aluminum coatings and powder coating, with these requirements specified in the technical agreement.
Anti-Corrosion Grade Classification (ISO 12944)
- C1: Low corrosivity; dry indoor environments (e.g., power distribution rooms);
- C2: Low-to-medium corrosivity; indoor environments with fluctuating temperature and humidity;
- C3: Medium corrosivity;
general industrial areas and coastal inland areas; - C4: High corrosivity; coastal industrial areas, chemical plants, and high-humidity environments;
- C5: Very high corrosivity;
offshore locations or environments with extreme humidity and salt spray.
Key Anti-Corrosion Requirements
First, environmental classification: Select the anti-corrosion grade based on the installation environment (C4+ for coastal areas, C5 for offshore locations).
Second, coating system: Galvanized layer + primer + topcoat (or powder coating), with film thickness meeting grade requirements.
Third, enclosure material: Stainless steel or Al-Zn alloy coated steel sheets are used for high-corrosivity environments.
Fourth, fasteners.
Corrosion-resistant fasteners (stainless steel or galvanized) are used to prevent rust.
The fifth step is verification through testing: salt spray testing (per GB/T 10125) is conducted to verify corrosion resistance and confirm the corresponding performance grade.
Acceptance Criteria
First, grade alignment: the corrosion protection grade must meet the technical agreement (e.g., C4/C5 for coastal projects).
Second, coating inspection: the surface must be free of rust and coating delamination, and film thickness must be spot-checked.
Third, salt spray reports: the test report must correspond to the specific coating system used.
Common Pitfalls
First, “inflated grade ratings”: labeling C2 coatings as C4, leading to rapid rusting in coastal areas.
Second, “cutting corners on coatings”: insufficient film thickness or omission of the primer layer.
Third, “fastener corrosion”: standard fasteners rust in coastal environments;
stainless steel should be selected instead.
Trends and Reminders
Corrosion protection is shifting toward “long-life coating systems”: high-weather-resistance powders and zinc-aluminum-magnesium alloy sheets extend service life, while wind power and offshore applications are driving the adoption of the C5 grade.
For purchasers, the recommendation is to “classify the environment, specify coating film thickness, and verify via salt spray reports.”
Corrosion protection acts as armor against the environment—the right grade ensures a long service life.
