Galvanized steel pipes are commonly used in our daily lives, produced by treating steel strips with galvanization technology. To enhance corrosion resistance and prolong the lifespan of the pipes, a layer of zinc coating is added to the surface through galvanization, effectively isolating the steel from corrosive media. While the chemical properties of these pipes are relatively stable, issues such as alkali rusting over time can occur, necessitating attention to prolong their preservation. Here are some causes and precautions:
Causes of Alkali Rust (White Rust, Black Spots):
1. Formation Mechanism: When galvanized products are tightly stacked in humid air, the lack of airflow on the surface triggers electrochemical corrosion of the zinc layer, leading to the formation of white rust. Condensed water on the zinc layer surface combines with gases like oxygen, carbon dioxide, hydrogen sulfide, sulfur dioxide, and oxides to create a corrosive solution, resulting in the formation of an electrolyte. This electrolyte corrodes the zinc layer, resulting in visible white powdery substances (zinc oxide), known as white rust. Secondary and tertiary oxidation products form black spots on the surface, collectively referred to as alkali rust.
2. Effects: White rust can appear extensive and severe due to the considerable volume increase when metallic zinc transforms into zinc oxide or zinc hydroxide, impacting the appearance of the zinc layer. However, these formations only result in minimal zinc loss on the surface.
3. Treatment: While extensive white rust may occur on the surface of
galvanized steel pipes, it does not necessarily indicate severe zinc layer damage. Upon white rust formation, galvanized products should be spread out to allow rapid surface drying, as this phenomenon is typically influenced by weather, transportation, and storage conditions during summer. As long as the zinc layer corrosion remains within standard values, it does not affect product lifespan.
Precautions:
1. All galvanized products are susceptible to white rust in humid, high-temperature, or poorly ventilated environments. Products prone to white rust include angle steel, flat iron, square and rectangular tubes, and round tubes tightly sealed in packages, especially when accumulated water inside causes moisture retention in hot and humid weather.
2. Upon arrival, galvanized products should be stored in well-ventilated warehouses, avoiding areas with harmful gases and excessive dust.
3. In case of slight white rust or spots on the surface, disassemble and air dry the products immediately, brushing off the white rust with a brush once it turns powdery.
4. Store galvanized products indoors in well-ventilated, dry conditions, avoiding direct contact with moist soil during stacking.
5. While galvanized products are resistant to high temperatures, humidity, and concentrated stacking, they are susceptible to corrosion when all three conditions are present simultaneously, such as in humid, hot, and densely stacked environments.
Location: Galvanized products are typically purchased in bulk, requiring attention to storage locations. Common scenarios include outdoor storage, storage under color steel sheds, and warehouse storage. Outdoor storage is least favorable due to exposure to rain and snow, leading to surface oxidation (alkali rust) and reduced lifespan. Color steel sheds offer partial protection against rain and snow, allowing sunlight exposure for drying, thereby aiding in product preservation. Warehouse storage, with its dry environment, offers optimal protection against rain and snow, ensuring galvanized products remain dry even in damp conditions.
Ground Conditions: Ground conditions for storage typically include soil, concrete, and brick. Soil surfaces are the least favorable, as moisture evaporation post-rainfall leads to dampness and increased humidity, detrimental to galvanized product storage. Concrete surfaces reduce natural ground moisture, facilitating quicker natural drying even when wet, making them suitable for galvanized product storage. Brick surfaces, while more absorbent, can be improved by sprinkling lime to lower air humidity, maintaining a dry storage environment.
Placement Conditions: Placement conditions vary depending on store setups, with common methods including direct ground placement, placement on sleepers, concrete pillars, or steel racks. Direct ground placement is the least favorable, as it allows steel pipes to come into direct contact with the ground, preventing rapid water evaporation and promoting electrolytic corrosion. Sleepers and concrete pillars maintain a distance between the steel and ground, allowing better air circulation to reduce pipe moisture. Steel rack placement, common in retail settings, suspends steel pipes, ensuring maximum airflow and dryness.
