News

The Battle Against Corrosion: Choosing the Right Metallic and Organic Coatings

Unprotected carbon steel oxidizes rapidly when exposed to atmospheric moisture, industrial sulfur, or marine salt-spray. To extend the service life of steel building components, modern metallurgy relies on metallic sacrificial coatings (Hot-Dip Galvanizing, Galvalume) and multi-layer organic coating systems (PPGI, PPGL). Selecting the correct substrate and paint system ensures a structural lifespan ranging from 15 to over 30 years without premature perforation.

1. Hot-Dip Galvanized Steel (GI): The Classic Sacrificial Barrier

Hot-dip galvanized steel is produced by continuously passing cold-rolled steel coils through a bath of molten zinc at approximately 450°C. The zinc layer provides cathodic galvanic protection, corroding sacrificially to protect the underlying base steel.

• Coating Mass Designation: Commonly specified from Z60 (60 g/m² total both sides) for indoor dry use, up to Z275 (275 g/m² / G90) for external structural environments.
• Surface Appearance: Available in Zero Spangle (smooth finish for automotive/appliance use) or Regular/Minimised Spangle (traditional crystalline appearance for construction purlins and ducting).
• Best For: Ventilation ducting, cable trays, agricultural silos, and general fabrication.

2. Galvalume / Aluzinc Steel (GL): Enhanced Thermal & Atmospheric Defense

Galvalume features an alloy coating composed of approximately 55% Aluminum, 43.4% Zinc, and 1.6% Silicon. This unique microscopic formulation combines the passive barrier protection of aluminum oxide with the electrochemical cathodic protection of zinc.

• Performance Advantage: Delivers 2 to 4 times greater atmospheric corrosion resistance than standard GI of equivalent coating thickness in general outdoor exposure, alongside excellent heat reflectivity (resisting continuous temperatures up to 315°C).
• Coating Mass: Standard grades range from AZ50 to AZ150 (150 g/m²).
• Application Note: Avoid direct contact with wet concrete or highly alkaline environments where aluminum alloys degrade faster.

3. Pre-Painted Steel Coils (PPGI & PPGL): Aesthetic Versatility & Dual Protection

Pre-painted coils apply a multi-tier protective structure: Base Steel + Metallic Coating (GI/GL) + Chemical Pre-treatment + Primer Coat (5-7 µm) + Top Finish Coat (15-25 µm), with a protective backer coat on the reverse side.

• Regular Modified Polyester (PE): Cost-efficient, standard color retention for general warehousing and interior partitions.
• High-Durability Polyester (HDP): Enhanced UV and weather resistance, ideal for sub-tropical roofing applications.
• Silicon Modified Polyester (SMP): Superior surface hardness and abrasion resistance.
• Polyvinylidene Fluoride (PVDF): Industry gold standard for commercial facades, coastal projects, and heavy industrial chemical environments, providing 20+ years against chalking and fading.

Summary Matrix for Specifiers

For standard industrial warehouses located inland, Z140-Z275 GI or AZ100 GL substrate with HDP paint offers the optimal balance between initial investment and maintenance longevity. For coastal installations within 5km of seawater, specify AZ150 Galvalume or Z275 GI with minimum 20µm PVDF topcoat systems.