1.What are the core control standards?
**Absolute Safety Line:** Relative Humidity ≤ 60% RH
This is the universal gold standard for rust prevention in steel storage. At this humidity level, the metal corrosion rate is significantly reduced, effectively preventing rust in most environments.
Most industrial dehumidifiers and air conditioning systems use 60% RH as their target control point.
**Ideal Control Range:** 45% ~ 55% RH
For cold-rolled coils with higher requirements (such as those used in automotive exterior panels, high-end home appliances, galvanized or tin-plated substrates), it is recommended to control the humidity within this range.
This range provides a greater safety margin for temperature fluctuations, further inhibiting corrosion and protecting special coatings or surface treatments.
**Danger Warning Line:** Relative Humidity > 65% RH
When humidity remains consistently above 65%, the risk of corrosion increases dramatically. Once the steel plate temperature (e.g., at night or in spring) drops below the air dew point, condensation will inevitably occur, and rust may appear within hours.
2.What is the relationship between temperature and humidity?
The biggest enemy is temperature fluctuation: when there are large temperature differences between inside and outside the warehouse, or between day and night, warm, humid air will condense when it encounters the cooler steel plate surface.
Control strategy: Not only should humidity be controlled, but the temperature inside the warehouse should also be kept as constant as possible to prevent the steel plates from becoming "cold spots." For example, in spring when there are large temperature differences between day and night, even if the humidity is not high during the day, condensation may still occur at night due to the low temperature of the steel plates.
3.How to distinguish based on the surface condition of cold-rolled coils?
Uncoated coils: Most susceptible to corrosion, and the above humidity standards must be strictly followed. Especially for cold-rolled "white-skinned" coils after pickling, they are extremely sensitive to humidity.
Oiled coils: The surface rust-preventive oil provides some protection, and requirements can be slightly relaxed. However, for long-term storage or in humid areas, it is still recommended to keep humidity below 60% to prevent oil film cracking or localized corrosion.
Film-coated/paper-coated coils: The protective film or rust-preventive paper itself can isolate some moisture, but if the environment is too humid, moisture may penetrate the edges or under the film, forming more difficult-to-detect "edge rust" or "under-film rust." Therefore, environmental humidity control remains important.
Zinc (GI)/Al-Zinc (GL) coils: Although the coating provides sacrificial protection, high humidity environments can still cause "white rust" (basic zinc carbonate) to form on the coating surface, affecting appearance and subsequent processing. Humidity control is also necessary.
4.What are the effects of geographical location and seasonal factors?
Coastal and humid southern regions (such as East and South China): Powerful dehumidification systems (such as industrial rotary dehumidifiers) must be installed and operated year-round. The plum rain season (the period of high humidity) is a critical time for prevention and control.
Dry northern regions: Dehumidification may only require ventilation or regular air conditioning during the summer rainy season, but in winter, attention should be paid to condensation caused by indoor and outdoor temperature differences due to heating.
5.How can effective control be achieved?
Monitoring First:
Install temperature and humidity sensors with data logging capabilities in different locations within the warehouse (especially corners, ventilation dead spots, and near the main entrance) for continuous 24-hour monitoring.
Real-time data is essential for risk assessment and verifying the effectiveness of dehumidification measures.
Hardware Configuration:
Industrial Dehumidifiers: The core equipment for active humidity control. Select the appropriate model based on warehouse volume and local climate (refrigeration dehumidifiers are suitable for normal temperature environments; rotary dehumidifiers are suitable for low-temperature environments or environments requiring extremely low humidity).
Sealing and Insulation: Enhance the warehouse's airtightness (doors, windows), and insulate the roof and walls to reduce the impact of external temperature and humidity.
Adequate Ventilation: Ventilate when the outside air is drier than the inside (e.g., on a sunny winter day in northern regions). Ventilation is strictly prohibited in humid weather.
Warehouse Management Operations:
Avoid "Cold Material Entering the Warehouse": Steel coils transported from low-temperature environments should not be immediately placed in warm warehouses. They should first be placed in a transition zone to allow their temperature to rise to near the warehouse temperature, preventing condensation on their surface.
Elevation and Isolation: Steel coils should be placed on wooden pallets to avoid direct contact with the ground (especially if the ground is damp). Maintain a certain distance between coils from different batches to facilitate air circulation.
First-In, First-Out (FIFO): Accelerate inventory turnover and shorten storage time.