Although this phenomenon is well known in theory, it has very real implications for day-to-day operations, particularly when temperatures remain above 30–35°C for prolonged periods and the vehicle is exposed to direct sunlight or waiting in logistics areas.
In the transport of chemical liquids, where safety and precision are critical, understanding this behaviour is not optional but essential.
What Exactly Is Thermal Expansion in Liquids?
Thermal expansion is the tendency of liquids to increase in volume as their temperature rises.
At a molecular level, an increase in temperature causes particles to move faster and occupy more space, reducing the density of the product.
Although this change may appear small, it can have a significant impact when dealing with large volumes, such as those transported in tankers.
How Does the Product Behave Inside a Tanker in Summer?
Under normal conditions, the product is loaded with a safety margin to allow for thermal expansion. However, in extreme heat conditions, situations such as the following may occur:
- A progressive increase in internal tank pressure
- An increase in the volume occupied without any change in the product’s mass
- Activation of pressure relief or safety systems in extreme cases
- Additional stress on valves, seals and system components
This behaviour is particularly relevant when:
- The lorry remains parked in direct sunlight for several hours
- The product has a high coefficient of thermal expansion
- There are significant temperature variations between loading, transport and unloading
Factors That Increase Thermal Expansion in Summer
1. Direct solar radiation on the tanker: The steel tank absorbs heat quickly, increasing the temperature of the product even when the vehicle is stationary.
2. Road surface temperature: Heat reflected from the ground can considerably increase the temperature of the vehicle as a whole.
3. Duration of exposure: A short temperature peak is not the same as several hours of continuous exposure.
4. Type of product being transported: Each liquid has a different coefficient of thermal expansion. More volatile or lighter products are particularly sensitive.
Operational Impact on Tanker Transport
Although thermal expansion is a physical phenomenon, its consequences are very practical:
• Filling management
Loading without taking thermal expansion into account can reduce the available safety margin and increase operational risk.
• Internal tank pressure
The increase in volume can lead to higher pressure levels that need to be controlled through appropriate ventilation and safety systems.
• Unloading behaviour
Temperature differences between the point of origin and the destination can cause variations in the apparent volume of the product.
• Safety during prolonged stops
Unshaded parking areas can become critical points during heatwaves.
Good Practices to Minimise Risks
In professional tanker transport, managing thermal expansion requires a combination of planning, technical measures and monitoring:
✔ Control of filling levels
Always respect the expansion margins established according to the applicable regulations and the type of product.
✔ Avoid prolonged exposure
Whenever possible, park in shaded or well-ventilated areas.
✔ Pressure monitoring
For sensitive products, monitoring internal pressure is essential during transport and while stationary.
✔ Route and time planning
Minimise unnecessary waiting times in high temperatures.
✔ Staff training
Understanding how the product behaves is essential for anticipating potential incidents.
Thermal expansion is an unavoidable phenomenon, but it can be effectively managed when transporting liquids by tanker.
Its impact during summer can be significant if its effects on volume, pressure and product behaviour are not taken into account.
If you would like more information about our dangerous goods transport services or any of the solutions we offer, please do not hesitate to contact us.