Differences Between GI, GL and ZAM

Abstract

Galvanizing is a common coating used for pipe fittings. There are different kinds of galvanized products, including GI (pure zinc coating), GA (zinc-iron alloy coating), GL (55% Al-Zn coating), 5% AL-Zn (Galfan coating), aluminizing (pure aluminum coating and aluminized silicon coating), and ZAM (zinc-aluminum-magnesium coating). Here let’s review the differences between GI, GL and ZAM.

Table of Contents

1. Coating Differences
2. Corrosion Resistance
3. Appearance
4. Application Differences
5. Cost
6. Key Questions
7. Conclusion
8. Coating Difference

GI is applied with a pure zinc coating; galvalume coating consists of 55% aluminum, 43.4% zinc, and 1.6% silicon by weight. While zinc-aluminum-magnesium steel is a new type of high corrosion-resistant steel. The coating mainly consists of zinc, plus 1.5%-11% aluminum, 1.5%-3% magnesium, and a trace amount of silicon.

2. Corrosion Resistance

In the same environment, the corrosion resistance of ZAM is the best, which is much better than that of GI and GL. The galvalume steel has better corrosion resistance compared to a galvanized coil of the same thickness. However, the hot dip GI sheet is  economical anti-corrosion coating.

The corrosion resistance of GL coating is mainly due to the protective function of aluminum. When the zinc is worn away, the aluminum forms a dense layer of aluminum oxide, preventing further corroding the interior. But its alkali corrosion resistance is poor. In addition, the protection performance of the Al-Zn coating on the cutting area is much worse than that of the GI coating. In comparison, ZAM steel has strong chlorine resistance (salt/seawater/soil) and alkali corrosion resistance. Besides, Mg offers ZAM coating with high corrosion resistance and high cutting-edge protection performance. It has a self-healing function, which can guarantee no red rust for 20-30 years.

For pipe fittings, since they are usually exposed to damp, chemical substances or soil environments, corrosion resistance is of  importance. GI pipe fittings are suitable for general water supply systems with low corrosion risks, while GL may perform poorly in alkaline drainage pipes. ZAM pipe fittings, due to their  tolerance to chlorine and alkali, are highly suitable for coastal areas, industrial wastewater pipes, or underground networks.

3. Appearance

In the field of pipe fittings, for exposed installations, appearance can be very important. The brightening variations of GI (normal, minimum, zero) offer flexibility to meet different aesthetic requirements, while the uniform brightening of GL and the smooth surface of ZAM are more favored in commercial or public areas for visible pipe systems.

Hot-dip galvanized steel has normal spangles, spangles, and zero spangles. While galvalume steel also has spangles, which are more even and beautiful. The zinc-aluminum-magnesium steel looks finer and smoother.

4. Application Differences

Due to the difference in performance, the application scenarios of GI, GL and ZAM are also different.

GI steel is widely used in construction, furniture, machinery manufacturing and other fields. For example: roofs, walls, pipes, furniture shells and supporting structures, etc.

In pipe fitting, GI is commonly used for indoor water pipes, drainage pipes in low-corrosion environments, and structural pipe supports due to its cost-effectiveness.

GL steel is often used in occasions that require high corrosion resistance and high temperature resistance, such as chemical equipment, high-temperature furnaces, etc.

ZAM steel can replace materials such as color steel, stainless steel and aluminum plates, and is mainly used in various fields such as photovoltaic industry, home appliance manufacturing, high-speed rail, large substations and automobile manufacturing.

ZAM fittings are particularly suitable for harsh environments: water supply pipelines in coastal areas, seawater desalination systems, underground sewage pipelines, and industrial pipelines transporting alkaline or highly chlorinated liquids. This is because they possess long-term corrosion resistance and self-repairing capabilities.

5. Cost

The cost of GI is the cheapest, followed by GL and ZAM. But as for their corrosion resistance and service life, ZAM is the best, followed by GL and GI. You can choose a suitable material according to the use purpose, the use environment, and your budget.

For pipe fitting installation projects, for large-scale installations with a low risk of corrosion, GI pipe fittings are cost-effective option. GL products can meet the needs of users with moderate corrosion resistance requirements. Although ZAM is more expensive, it reduces the long-term maintenance costs of pipeline systems in harsh environments.

6. Key Questions

• What are the core differences in coating compositions between GI, GL, and ZAM?

GI is a pure zinc coating. GL consists of 55% aluminum, 43.4% zinc, and 1.6% silicon by weight. ZAM is zinc-based, containing 1.5%-11% aluminum, 1.5%-3% magnesium, and a trace amount of silicon. One of the notable differences is that ZAM contains magnesium, while GI and GL do not have this component.

• What accounts for the fact that ZAM exhibits corrosion resistance far superior to that of GI and GL?

The coating of ZAM is characterized by a specific compositional feature. It contains magnesium in a proportion ranging from 1.5% to 3%. This magnesium content serves a dual purpose. On one hand, it enhances the overall corrosion resistance of the coating. On the other hand, it improves the coating’s advanced protective performance.

7. Conclusion

There are significant differences among pure zinc coating (GI), 55% aluminum-zinc coating (GL), and zinc-aluminum-magnesium coating (ZAM) in terms of coating composition, corrosion resistance, appearance, application, and cost. When applied to pipe fitting engineering, various characteristics of different coatings need to be comprehensively considered, and selection and adaptation should be made based on the environment.