Condensation in Containers: Detailed Analysis of Causes and Solutions
This article presents the most comprehensive guide to the issue of condensation in shipping and storage containers. It offers detailed definitions of key terms, an analysis of physical processes, causes and specific consequences of condensation. Emphasis is placed on proven and modern prevention methods and real‑world examples. The article builds on the latest findings in logistics, container manufacturing and the experience of specialist companies (e.g., ThoMar OHG).
What is condensation in containers?
Condensation is a physical phenomenon in which water vapor contained in the air inside a sealed container turns into liquid form on interior surfaces (walls, ceiling) as the temperature drops – it forms water droplets. This occurs when the temperature of the interior surface of the container falls below the dew point of the internal air.
Why is condensation a problem?
Condensation is a major risk to the safety and quality of goods during both sea and land transport. It causes losses amounting to tens of billions of crowns each year (globally up to 10 % of shipped goods are damaged by moisture). The greatest damage occurs with moisture‑sensitive cargo such as electronics, food, paper, wood, bulk materials, chemicals, construction products, etc.
Key terms and technical definitions
| Term | Definition & relevance in logistics |
|---|---|
| Condensation | Conversion of water vapor to liquid when temperature falls below the dew point |
| Container rain | “Container rain” – intensive dripping of condensed water from the ceiling onto the cargo |
| Container sweat | “Container sweat” – formation of water droplets on walls/ceiling during sudden cooling |
| Cargo sweat | “Cargo sweat” – condensation on the surface of goods when air heats up faster than the cargo |
| Dew point | Temperature at which air is 100 % saturated with water vapor and condensation begins |
| Moisture content | Percentage of water in a material (wood, pallets, packaging, goods, air) |
| Relative humidity | Ratio of current to maximum possible humidity at a given temperature (in %) |
| Hygroscopic materials | Materials that absorb and release moisture from the environment (wood, paper, textile, food) |
| Breathing of the container | Cyclic air exchange caused by expansion/contraction during temperature changes |
Detailed types of condensation (according to ThoMar OHG)
- Container rain – droplets of condensed water fall from the container ceiling onto the cargo. Occurs after prolonged water accumulation on metal walls/ceiling, usually due to large temperature swings between day and night or when crossing climate zones.
- Container sweat – water condenses on the interior side of the container, especially during rapid cooling of the walls (e.g., night‑time temperature drop or winter transport).
- Cargo sweat – condensation forms on the surface of the cargo itself – typically when moving from a colder to a warmer environment, causing the air to heat faster than the goods.
Physical causes of condensation in containers
1. Temperature fluctuations
- Metal walls of the container heat up and cool down quickly according to external conditions (sun, night, rain, wind).
- During the day wall temperatures can exceed 60 °C, at night they may fall below 0 °C.
- Critical periods: ocean voyages, mountain routes, or storage in extreme conditions (e.g., desert vs. sea).
- Result: Warm interior air holds more moisture; when walls cool below the dew point, massive condensation occurs.
2. Presence of moisture in cargo and packaging
- Hygroscopic materials: wood, paper, textile, leather, some foods – strongly influence the internal micro‑climate.
- Wooden pallets: new pallets can contain up to 15 L of water (depending on weight and wood moisture).
- Cardboard packaging: can absorb large amounts of water during rain, outdoor storage, or poor handling.
- Cargo: foods, raw materials, chemicals and other products often contain “hidden” moisture that is released during transport.
3. Breathing of the container
- Day/night cycle: heating expands and expels air; cooling draws in fresh (often humid) outside air.
- Repeated cycles increase the total moisture amount inside the container on long journeys.
4. Inadequate or poorly designed ventilation
- Standard containers have only small ventilation holes (usually in the upper corners).
- These openings are insufficient for air exchange, so moisture remains “trapped” and condenses cyclically during temperature swings.
5. Empty space (free air volume)
- The more free space in a container (e.g., partially filled loads), the more air = more capacity for moisture accumulation and subsequent condensation.
Consequences of condensation and moisture damage
Overview of the most common risks and damages
| Type of damage | Description | Practical examples |
|---|---|---|
| Corrosion / rust | Damage to metal products, sheets, machines, electronics | Rust on steel, severe devaluation of goods |
| Mold / fungi | Growth of mold on organic materials, including packaging | Food, textile, paper – loss of value |
| Material deformation | Warping, cracking and disintegration of wood, paper, textile, plaster | Furniture, musical instruments, packaging |
| Packaging degradation | Wetting of cardboard, label peeling, loss of strength, pallet collapse | Damaged packing, handling problems |
| Odor | Stale moldy smell permeates goods and packaging | Unsellable goods, complaints |
| Bulk materials | Hardening, caking, germination, loss of flowability | Cement, flour, granules, fertilizers |
Statistical data
- Up to 10 % of containerized goods are reported worldwide to be damaged by moisture.
- The highest number of claims concerns: food, electronics, chemicals, pharmaceuticals, construction materials, paper and textile industries.
How to prevent condensation: Proven and modern methods
1. Control and minimize moisture sources
| Measure | Description & recommendation |
|---|---|
| Dry pallets | Always use pallets dried in a kiln (kiln‑dried, below 19 % moisture) or plastic/composite pallets |
| Dry packaging and cargo | Never store packaging or cargo outdoors in rain or humid places; check moisture of incoming raw material |
| Container inspection | Before loading, check dryness of floor and walls, remove any residual water from previous use |
2. Active moisture management – desiccants
Types of desiccants
- Calcium chloride (CaCl₂): most widely used, high absorption capacity, available as bags, rods, blankets.
- Silica gel: lower absorption, suitable for smaller volumes or sensitive applications.
- Modern composites: combination of adsorptive and absorptive components, extended effect.
Calculating required amount
- Follow DIN 55474 – calculation based on container volume, cargo type, transport duration, expected temperature and humidity.
- For a standard 20‑ft container, typically 6–8 kg CaCl₂ are needed; more for highly risky cargo.
- Use manufacturer calculators (e.g., ThoMar SeaDry Calculator) for specific cases.
Placement of desiccants
- Hang bags on walls, in upper corners and between layers of goods.
- Lay special “blankets” on the top layer of cargo.
- Ensure desiccants are evenly distributed, including corners and “dead zones”.
3. Ventilation and structural modifications
- Additional ventilation grilles: larger vents can be installed on stationary or long‑term stored containers.
- Ventilation rule: ventilate only when moving from warm to cold (otherwise you risk increasing moisture).
- Special containers: for demanding applications, use containers with controlled internal ventilation or air‑conditioning.
4. Container insulation
- Sprayed polyurethane foam: creates a continuous insulating layer, preventing rapid temperature changes.
- Polystyrene boards, sandwich panels: slow heat transfer, stabilize interior temperature.
- Container liners: special insulating inserts for the container interior.
- Condensation‑resistant coatings (e.g., Grafotherm): porous layers temporarily absorb condensed water, preventing dripping.
5. Protection of the cargo itself
- Barrier and vapor‑tight packaging: vacuum packs, aluminum foils, combined with miniature desiccant bags.
- Absorptive blankets: capture water droplets falling from the ceiling (container rain), suitable for moisture‑sensitive goods.
6. Monitoring and tracking
- Data loggers: electronic recorders of temperature and humidity (e.g., Sensitech, Tempmate) enable post‑trip condition checks.
- Control labels: humidity indicator cards signal when critical values are exceeded.
Specifics of different condensation phenomena
| Phenomenon | How it forms | Risky situations (examples) | Special measures |
|---|---|---|---|
| Container rain | Long‑term water accumulation on ceiling, then dripping | Long voyages, large temperature swings, extreme storage conditions | Absorptive blankets, coatings, insulation |
| Container sweat | Rapid cooling of walls | Night cooling, transition to cold climate | Desiccants, ventilation |
| Cargo sweat | Rapid heating of air while cargo remains cold | Transfers between zones, transport from cold to warm | Barrier packaging, desiccants |
Standards, recommendations and expert sources
- DIN 55474 – Standard for calculating desiccant quantities in transport packages
- ČSN EN ISO 1496‑1 – Construction requirements and testing of containers
- ČSN EN 12195‑1 – Securing cargo in containers
Practical tips and real‑world examples
- Example 1: Transport of electronics from China to Europe – 10 kg CaCl₂ used in a 40‑ft container, complete barrier packaging, resulting in zero moisture‑related claims.
- Example 2: Transport of food in cardboard boxes – failure because boxes were stored outdoors before loading; moisture from the packaging caused massive mold despite using desiccants.
- Example 3: Long‑term storage of construction material on a building site – no insulation or desiccants led to cement caking and tool rust; after installing ventilation and desiccants the problem disappeared.
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