PPGI vs PPGL Which is better for coastal environments?

I. Core Differences. PPGIand PPGL are intrinsically different materials in terms of the metal coating. This difference can directly influence their corrosion resistance mechanisms and how they adapt to the environmental situation. PPGI, short for pre-painted galvanized steel, puts a pure zinc (Zn) coating on the substrate. It takes advantage of a “sacrificial anode protection mechanism” — after you damage the coating, the zinc layer starts corroding and protects the plate beneath. This protective technique works well in standard inland settings, but in a coastal environment with very high salt spray, the zinc layer is used up very quickly. PPGL, which refers to pre-painted galvalume steel, has a 55% aluminum, 43.4% zinc, and 1.6% silicon alloy coating on the steel surface.

Its dual mechanism is barrier protection + auxiliary sacrificial protection. As a "protective shield", the aluminum element forms a dense, stable aluminum oxide film on the surface to prevent the penetration of corrosive media, such as chloride ions and moisture; the zinc element serves as a type of sacrificial shield when local damage to the coating is caused, thus enhancing its protective effect. The addition of silicon enhances adhesion between coating and substrate, preventing the coating from peeling.

II. Performance Comparison. In terms of the special corrosive environment of coastal areas, we compared PPGI and PPGL based on key performance indicators such as corrosion resistance, heat and weather resistance, service life, and economic efficiency:

Corrosion Resistance. Its corrosive risk is most prevalent in coastal regions; chloride ions in salt spray penetrate the electrolyte with high efficiency and can destroy the passivation film on the metal in an instant. Experimental data shows that the salt spray resistance of PPGL's aluminum-zinc alloy coating is 2-4 times that of PPGI's pure zinc coating. In areas with high corrosion within 500 meters of the coastline, the pure zinc layer of PPGI is very easy to corrode, and the aluminum oxide barrier of PPGL effectively resists chloride ion erosion, significantly reducing the corrosion rate. Particularly in weak points like welds and cut edges, although cut edge corrosion resistance is moderate in PPGL's case, it can be achieved through simple surface sealing paint treatment and the overall corrosion resistance advantage is still very high.

Heat and Weather Capability. Coastal regions are subjected to high temperature and frequent intense ultraviolet radiation in the summer weather, which can result readily in deterioration, fading, and deformation of coated steel sheets. In low heat environments, PPGI offers limited resistance and thus can only tolerate stable operation ≤80℃. The coating softens and becomes prone to performance failure, especially at high temperatures. In contrast, PPGL is capable of sustaining high temperatures at 315℃ over prolonged periods, while it has a higher heat reflectivity, thus reducing panel temperature, preventing structural stress resulting from thermal expansion and contraction which can reduce the aging rate of the coating. It is also relatively color stable in harsh ultraviolet conditions.

Length of Operation and Economic Effectiveness. Meanwhile, with respect to service life, PPGI may last for 10-15 years in normal inland habitats and for a shorter period of 7-10 years in harmful coastal sites. PPGL, however, is sustainable for 20-25 years in coastal environments, and certain PPGL with high-weatherability PVDF coatings may resist application for over 30 years. Economically, PPGI has a lower cost to purchase, but because of its short service life and continuous maintenance and replacement, the long-term maintenance costs are high. PPGL has a higher upfront purchase cost of 10%-20% as compared to PPGI, but its longer service life and lower maintenance requirements result in a lower total life cycle cost. Moreover, the PPGL aluminum-zinc alloy is less dense, creating a surface area per ton at least 2-3% larger than PPGI, resulting in further transportation and installation cost savings.

III. Relevant Scenarios in Coastal Regions. According to the performance of the two and regional coastal environment characteristics, it may be considered to a sufficient extent how a material choice of the two is in the following cases:

In what are known scenarios PPGL works best.

Architectural applications: Long term exposures in buildings at coastal areas (e.g., roofs, exterior walls, enclosure structures of seaside villas, port terminals, coastal commercial complexes);

Industrial applications: Coastal industrial park factories, warehouses, and auxiliary facilities, wind power operation and maintenance platforms, and port machinery components;

For higher-end use: Use in projects with design life of ≥15 years, projects that prefer low maintenance bills, high-end buildings with very high requirements of appearance and color stability.