Service Life of Galvanized Steel Pipes

Process determines the life span gene
 
The service life of galvanized steel pipes depends largely on the galvanizing process. Common galvanizing processes include hot-dip galvanizing and cold-dip galvanizing, which have significant differences. Hot-dip galvanized pipes are placed in hot-dip galvanized tanks, and through a series of chemical reactions, the iron matrix reacts with the molten metal to form an alloy layer, thereby closely combining the substrate with the plating layer. According to the GB/T 13912 standard, its zinc layer thickness is ≥85μm. This thick zinc layer is like strong armor, giving hot-dip galvanized tubes excellent corrosion resistance and can last for more than 72 hours in salt spray resistance tests. In dry indoor environments, its service life can reach more than 50 years; even when outdoors, it can maintain a service life of 20-50 years in the face of wind, rain, sun and rain.
Cold-dip galvanized pipes mainly use electrochemical principles to directly coat the outer wall of the steel pipe with a layer of zinc. However, its zinc layer is only 8-15μm, and this thin zinc layer has weak protection, just like a thin film, which is difficult to resist external erosion, and is usually prone to rust within 1 year.
 
"Invisible Killer" of Environmental Corrosion
 
1. Climate conditions
The climatic environment in which galvanized steel pipes have a profound impact on their service life. In a dry and well-ventilated indoor environment, galvanized steel pipes are like being put into a "safe" and the corrosion factors are difficult to get close to. There are no excessive moisture, salt and other corrosion factors here. The galvanized layer can play a protective role steadily, so its service life can reach 50 years. In humid environments, the service life of galvanized steel pipes is greatly reduced, typically only 10-15 years. For example, some coastal buildings have seen obvious rust in less than 15 years, and even perforations have occurred in severe areas.
 
2. Soil characteristics
Soil is the "survival environment" of buried galvanized steel pipes, and its characteristics have a key impact on the life of galvanized steel pipes. In neutral soil, the acid-base degree is moderate and the corrosion resistance of the galvanized layer is weak. Galvanized steel pipes can work relatively "stable" and their service life is generally between 25-50 years. But if it is acidic or saline-alkali soil, it is a different scene. Hydrogen ions in acidic soil and salt in saline-alkali soil will react chemically with the galvanized layer, accelerating the loss of the zinc layer. In this case, the life of galvanized steel pipes will plummet to less than 10 years without additional protection.
 
The "Life-Extended Law" for Maintenance
 
1. Regular testing
For zinc layer thickness, it is recommended to use a magnetic thickness gauge for measurement. This instrument is easy to operate and can quickly obtain results. According to relevant standards, when the thickness of the local zinc layer is less than 70μm, it means that the protection capacity of the zinc layer is greatly reduced. At this time, it is necessary to perform timely replacing the steel pipes and re-paint "protective armor" to ensure that it can continue to effectively resist external erosion.
The welded parts are also the focus of inspection. During the welding process, high temperature will destroy the integrity of the galvanized layer, making the welding point a "weak link" of the steel pipe and easily subject to corrosion. Therefore, carefully check the welds every time they are tested. Once the zinc layer is found to be damaged, a zinc-rich primer should be applied immediately.
 
2. Anti-corrosion strengthening
In addition to regular inspections, some anti-corrosion strengthening measures can be used to further improve the service life of galvanized steel pipes. Passivation treatment is one of the effective methods, which can form a rainbow-colored passivation film on the surface of the galvanized layer. For buried galvanized steel pipes, cathode protection technology is a magic weapon to "spend life". It is usually used with a magnesium alloy sacrificial anode. The metal activity of magnesium alloy is stronger than zinc. In soil electrolytes, it will preferentially lose electrons, thereby protecting the galvanized steel pipe from corrosion.

Read more: Seamless Steel Tubes VS Galvanized Steel Pipes in Terms of Corrosion Prevention