Almost everything you can find in the neighbourhood grocery store has touched a trailer during at least one leg of the supply chain, proving that the transport industry is the engine behind the world’s economy, ensuring a high quality of life.
But, it’s not just the standard, curtain-sided semi that is making sure shop shelves are filled up at any given time. Liquid tankers ensure that the milk you have with your morning tea is picked up from the farm and bottled; and that the service station around the corner is stocked up on petrol so you get to work on time. Even the road you drive on and the house you live in have been built with the help of a modern road tanker.
Today, tankers are used to transport anything from petrol and diesel to milk, water, concrete and even industrial chemicals. They can be constructed of various materials, depending on the cargo they are hauling and the region and climate they work in. Most commonly, you will find a mix of aluminium, mild steel, stainless steel and fiberglass reinforced plastic (FRP). In petroleum transport, the most popular material is aluminium as it can prevent sparking in the event of a rollover. Aluminium is also a popular choice because it weighs less, and can therefore haul more payload than a steel alternative.
Some tanks, articulated or rigid, are able to carry multiple products at once due to the segmentation into different compartments. That “compartmentation” is also used to balance out the load as liquid cargo can be delicate to transport.
The first motorised oil tanker truck was developed in 1905 by a subsidiary of US company Standard Oil, known as Anglo-American. The trucks this company developed were used in the transportation of fuel products from railroad tankers to substations. Though these trucks were common in urban settings by 1910, rural areas continued using horses into the following decade.
Only when manufacturing capability and pumps improved, did industry see the true potential of transporting liquids in bulk as opposed to many small barrels. By the end of World War I, the tanks – initially round and sometimes rectangular – were reconfigured to be cylindrical or elliptical, as US truck journalist Stan Holtzman pointed out in a 1997 retrospective.
It was this turning point that gave birth to the modern day road tanker. Today, we see tanker manufacturers taking the original simple concept of a big can on wheels and continuously refining it to be more efficient, economic and safe.
Every day, trillions of litres of liquids are transported and manufacturers across the globe work hard to service an industry that growing at a rapid pace.
The key challenge to consider in designing a modern liquid tanker is the liquid’s interaction with the construction material, compliance to local road and design rules to control the minimum standard required for the safety and well being of the community – and its style. Today, especially oil tanks can often resemble moving billboards, displaying the name of the company whose product they were hauling.
According to automotive journalist Jon Robinson, style has become a viable aspect in the manufacture and sale of a tanker. But, although a new tank may appear to be a manufacturing work of art to the average citizen, to the industry professional the key factors are efficiency, flow and utilisation.
As a result, the simple barrel tanker has become quite complicated in design. Take two innovative designs that are now commonly used.
Firstly, the stepped shape to allow a typical skid plate height with a bigger tank volume rearward of the truck drive. A seemingly obvious way to increase volume, but the transition from a one-size barrel to a larger one at a more highly stressed part of the tank was not easy at the time of design.
The second design innovation is the elliptical tank that became popular after World War I, and its latest evolution, the cylindrical-elliptical tank. Basically, it is another way to increase volume as it can reduce trailer length and still maintain the same volume as a longer tanker. With the elliptical tank design, the bottom of the tank typically has a larger radius than the top half. The result is a flat looking bottom that blends into a round top section.
More adventurous manufacturers have also couple the tank with a flat platform, creating a trailer that is a road tanker on one leg of the trip and a standard semi-trailer with the load on top for the return leg. While the potential is endless – fuel in, ore out; chemicals in, paper out; milk in, cheese out; glue in, timber out – the concept further developed by Finnish company Saalasti has not been embraced by the market.
In contrast, the use of aluminium frame brackets is a development that has attracted attention around the globe. Prior to that, the connection of steel frame brackets to aluminium chassis has been be problematic, so the advent of an aluminium solution has improved reliability across the board.
For unloading purposes, liquid tanks usually have drain valves with quick shut-off capabilities, located in several areas on their underbelly. The load can be discharged using a pump, or by mere force of gravity. Some tanks are lightly pressurized to enable quicker unloading.
While large-scale manufacturers have developed their own discharge systems in-house, small operators and transport companies that use various tanker manufacturers and wish to standardise fittings across the fleet prefer to use dedicated suppliers such as international company, Liquip International.
Liquip specialises in the design, development and manufacture of equipment for the bulk handling of fuels and related chemicals, including tank truck loading, discharge and venting equipment.
On the component front, a major development has been that of vapour recovery systems, designed to trap environmentally harmful vapours, preventing them from seeping into the atmosphere. Previously, these dangerous vapours were simply released into the air. As companies have oriented themselves toward environmentally responsible practices, spill and vapour prevention has also become an important issue.
In regard to suspension systems, transport companies tend to opt for the best compromise between weight and resilience, depending on country of operation and the load they haul.
Apart from the construction of the tank, it is the load itself that has to be considered. The type of liquid being transported affects the combination’s overall weight and therefore the amount of fuel that can be transported.
Aviation fuel, for instance, weighs less than standard petrol; while jet fuel is heavier than automobile fuel. Diesel weighs even more, naturally restricting the overall volume that can be transported.
According to Holtzman, it takes a different kind of savvy to cart liquid cargo such as milk and oil. “Unlike properly loaded solid cargo (…) liquid cargo freely sloshes and moves around within the (…) tank. This becomes immediately apparent when a driver tries to stop or turn too quickly, because centrifugal force attempts to keep the fluid moving, which can cause the truck to continue moving. For this very reason, hauling liquids can a tricky task, at best.”
To tackle the issue, modern tanks are equipped with baffles and bulkheads to minimise the surge effects of the liquids during cornering, braking, and accelerating. “The baffles, which are essentially large plates spanning from side to side within the tank, have holes in them to allow the fluids to flow within the tank, but a greatly reduced speed, thus greatly reducing surge forces,” says Holtzman.
In addition, the very nature of load has to be considered as well. While petrol is classified as a dangerous good, for instance, milk tankers have to comply to strict food transport regulations. That’s why tank trailers are required to display a placard to indicate their cargo’s level of hazard; a lower number is indicative of a more hazardous material. This system, known as the HazMat Code System, is applicable in any country around the globe.
While modern road tanker, including the diamond shaped HazMat sign, have long become a common sight on the road, most people don’t know that it is much more than just a barrel on wheels. The combination of a “dynamic” load that is prone to movement and a vast catalogue of regulations make the design of a tanker one of the most challenging tasks in the industry.