How to Prevent Rust and Moisture from Condensation in Container Shipping?

In today's increasingly frequent international logistics, container shipping is an essential part of almost all foreign trade companies. However, anyone who has exported, especially metal, machinery, or electronic products, has likely encountered a problem: goods arrive at the destination port undamaged, but upon opening the container, the cardboard boxes are wet, the wooden pallets are blackened, and the metal parts are rusted. These problems seem to have no apparent cause, but most are actually related to a deeply hidden factor—condensation in the container, commonly known as "container rain." In long-distance sea transport, it can be a factor affecting cargo transport and metal rusting.

Why are containers prone to rust? Where does condensation actually come from?

If you've ever left a chilled drink on a table on a rainy day, you'll see a layer of water droplets quickly form on the bottle. This is the most typical example of "condensation." The same thing happens in containers, only on a larger scale and with more severe effects. During sea transport, containers may be shipped from the cold, dry season in northern China, navigating the extreme temperature fluctuations of day and night at sea before arriving in the humid and hot regions of Vietnam, the Philippines, Malaysia, and Thailand. The temperature and humidity changes throughout this journey are extremely drastic. When humid air encounters cold metal surfaces, the moisture condenses into water droplets, eventually dripping onto the cargo as "rain."

The danger of condensation lies in the fact that it can cause damage even in small amounts. Metal parts, when combined with moisture and oxygen in the air, can begin to oxidize within a day or two; cardboard boxes, after absorbing water, lose their protective strength and are prone to collapse during handling; wooden pallets become moldy and blackened when damp; and electronic equipment can suffer internal malfunctions or even short circuits due to moisture. Worse still, all of this often occurs after the goods have been loaded onto the ship, making it impossible to address the issue on-site.

What products should be used for moisture protection?

To reduce humidity inside containers, many factories used to use ordinary desiccants, such as silica gel bags and quicklime desiccants. However, these products often fail quickly in the large, high-humidity, and long-term environment of a container. Silica gel has limited moisture absorption and can even become damp again after saturation; quicklime produces a lot of dust and is unsafe to use; and the 30-60 day transport cycle inside a container places too much strain on them.

This is why Shipping Container Desiccant Bag is widely used. Shipping Container Desiccant Bag's moisture absorption capacity is several times that of ordinary desiccants. It continuously absorbs moisture from the air, locking it firmly into a gel-like state, preventing backflow, leakage, and secondary pollution inside the container. More importantly, Shipping Container Desiccant Bag is specifically designed for large spaces and can operate from the moment of loading until the goods arrive at the customer's warehouse.

Installation of Shipping Container Desiccant Bag is also quite simple; it is simply hung on hooks on the inner wall of the container, taking up little space and volume, and does not affect the stacking of goods. Depending on the humidity of the cargo, container loading, and the environment of the destination country, the number of desiccants used typically varies, ranging from 6 to 12. In regions like Vietnam, Malaysia, and the Philippines, where humidity levels are consistently above 80%, customers generally fill a 40HQ container with 10-12 desiccants, virtually eliminating condensation inside the container.

CVCI has received excellent feedback from customers exporting to Southeast Asia. Many customers, after a year of use, tell us that complaints about humidity issues, which used to be frequent, are now almost nonexistent, and costs have decreased due to reduced rework, claims, and re-production losses. It's fair to say that Shipping Container Desiccant Bag has become an indispensable moisture-proof and rust-proof product for long-haul shipping.

Besides placing desiccants in the container, what other protection is needed for the product itself?

Shipping Container Desiccant Bag can control environmental humidity, but if the product itself is susceptible to corrosion, simply reducing humidity is insufficient. This is especially true for metal products, whose sensitivity to humidity is far higher than you might imagine. Ferrous metals begin to corrode when air humidity approaches 60%; at 80%, many metal surfaces show significant oxidation; and in salt spray environments, the rate of corrosion increases exponentially.

This is why we strongly recommend using VCI anti-rust film, VCI anti-rust bags, VCI anti-rust paper, or anti-rust liquid coatings. The key feature of VCI is that it doesn't require oiling or large-area coatings, yet it forms an invisible molecular protective layer that is stable, uniform, and automatically covers metal surfaces. Whether you have complex hardware structures, parts with gaps, or large machinery, it provides comprehensive coverage, ensuring safe transport.

This combination is particularly popular in Southeast Asia. The hot and humid climate and high salt spray concentrations there mean ordinary packaging simply doesn't last long. Many of our Vietnamese and Philippine clients have experienced excellent overall transport results after using the "VCI + Shipping Container Desiccant Bag" method, and they have repeatedly repurchased this combination.

What other easily overlooked risks exist during transportation?

Actually, container shipping involves more than just condensation. It also involves several small, often overlooked details that can significantly impact the final moisture-proofing effect.

For example:

High ambient humidity on the day of loading traps humid air directly inside the container.

Products not fully dried after washing retain moisture inside the packaging.

Using wooden pallets with high moisture content allows moisture to continuously release during transport.

Poor quality cardboard boxes collapse after absorbing moisture.

These problems can be mitigated through strategies such as using heat-treated pallets, selecting moisture-resistant cardboard boxes, and minimizing the time the container doors are open before loading. However, even with these measures, humidity fluctuations cannot be completely avoided, hence the need for specialized moisture-proofing tools like container desiccant bags.

The moisture problem in container shipping is fundamentally caused by the combined effects of temperature and humidity. It is uncontrollable and unpredictable, but it can be effectively managed. By taking the right measures before shipping, such as using Shipping Container Desiccant Bag to control humidity inside the container, combining this with VCI rust-proof film or bags to protect metal surfaces, and using compliant pallets and suitable packaging materials, most rust and moisture problems can be predicted and addressed in advance.

CVCI's moisture-proof and rust-proof products are currently exported to many countries and regions, with Southeast Asian customers showing particularly strong repeat purchases. The reason is simple: high humidity and numerous product issues in these areas, and our solutions genuinely help customers reduce claims, minimize losses, and improve transportation quality.

If you are troubled by moisture, rust, moldy cartons, or product corrosion during sea freight, please contact us. We can develop a more precise and practical moisture-proof and rust-proof solution based on your product material, shipping route, customer location, and container loading method. We also warmly welcome you to visit the CVCI factory to tour the equipment, learn about the processes, and experience the actual effectiveness of our rust-proof products firsthand.