Service life of galvanized steel pipes

Process Determines the Lifespan of Galvanized Steel Pipes

The longevity of galvanized steel pipes is closely tied to the galvanizing process used during manufacturing. Two common methods—hot-dip galvanizing and cold-dip (electro) galvanizing—differ significantly in protection performance.

Hot-Dip Galvanized Steel Pipes: Built to Last

Hot-dip galvanizing involves immersing steel pipes into a bath of molten zinc. Through a series of metallurgical reactions, a strong alloy layer forms between the steel substrate and the zinc coating, creating a tightly bonded protective layer. According to the GB/T 13912 standard, the zinc coating thickness should be ≥85μm. This thick layer acts as a robust shield, giving hot-dip galvanized pipes exceptional corrosion resistance. In salt spray tests, they can resist corrosion for over 72 hours, and in dry indoor environments, their service life can exceed 50 years. Even in outdoor conditions exposed to wind, rain, and sunlight, these pipes can last 20 to 50 years.

Cold-Dip Galvanized Steel Pipes: Limited Protection

Cold-dip galvanizing, or electro-galvanizing, uses an electrochemical process to apply a zinc coating directly onto the steel surface. However, this method results in a much thinner layer—only 8–15μm thick. This light coating offers minimal resistance to environmental factors and is more susceptible to corrosion, often showing signs of rust within a year.

The “Invisible Killer” of Environmental Corrosion

1. Climate Conditions

The surrounding environment plays a crucial role in the corrosion resistance of galvanized steel pipes. In dry, well-ventilated indoor spaces, these pipes are in a relatively safe setting, free from moisture, salt, and other corrosive agents. Here, the zinc layer performs optimally, potentially lasting up to 50 years. In humid or coastal environments, however, the service life drops significantly to 10–15 years, with noticeable rust or even perforation appearing within that time.

2. Soil Characteristics

For buried steel pipes, soil properties are a determining factor in their lifespan. In neutral soils, the zinc layer faces less chemical aggression, allowing pipes to remain functional for 25–50 years. But in acidic or saline-alkaline soils, aggressive ions (e.g., hydrogen or salt compounds) accelerate the breakdown of the zinc layer. Without additional protection, the lifespan of galvanized steel pipes in such environments can fall to less than 10 years.

The “Life-Extension Formula” for Maintenance

1. Regular Inspections

Routine checks are essential for assessing the integrity of the zinc layer. A magnetic thickness gauge is a convenient tool to measure zinc coating thickness. If any area measures below 70μm, the protective capability is significantly compromised, and prompt maintenance or replacement is recommended.

Welded joints also require close attention. High temperatures during welding often damage the zinc coating, turning the weld into a corrosion-prone weak spot. Regularly inspect these areas, and if damage is detected, apply a zinc-rich primer to restore protection.

2. Enhanced Anti-Corrosion Measures

Beyond inspections, certain treatments can enhance the corrosion resistance of galvanized pipes:

Passivation treatment: Forms a rainbow-like protective film over the zinc surface, improving resistance to moisture and chemicals.

Cathodic protection: Especially useful for buried pipelines, this technique uses a sacrificial anode, typically made of magnesium alloy. Because magnesium is more reactive than zinc, it corrodes first, thereby protecting the steel pipe from damage.