Containers with open tops are designed for over-height cargo or cargo that can only be loaded from the top. The tops for these containers are available in two basic configurations, a tarpaulin top (soft) or a solid steel top (hard).
Considered a variation of the General Purpose shipping container, there are no readily available statistics available on the number of open top containers in use, or the percentage of them when compared with the total number of intermodal containers in use. It is interesting to note that, as of 2012, there were 20.5 million intermodal containers in the world. While about 60% of the world’s cargo is moved by intermodal containers, most of the remaining cargo is transported by ships built for transportation of bulk solid, liquid, or gaseous cargo. While break bulk cargo still exists, it is slowly giving way as shippers figure out ways to utilize containers for shipping even the most challenging cargo.
Open top containers provide a shipping container configuration that can accommodate top-loaded machinery and cargo that is over-height. This type of container is also used for transporting loads that must be top loaded, such as solid bulk or loose cargo.
Open top containers are built with two different types of tops, which are as follows:
HARD – Solid Metal Top – This is a removable roof that allows top-loading of cargo. Once the cargo is loaded, the metal top is secured in place.
SOFT – Tarp with Bows – Bows lock into place and the tarp lies over top of them. The tarp is secured with a rope and hooks system.
Each container is manufactured to meet or exceed the ISO specifications for intermodal containers. Open top containers are based on the closed box model, minus the top. Like other intermodal containers, they are built using Corten® steel, a weathering steel alloy that uses copper, chromium, and nickel to create an insoluble oxide layer that protects the steel underneath.
The side, front, and back panels are assembled and welded together while the base is being made. Once all of the components are ready, they are moved to the final assembly area where a team of workers sets each panel in place, welding them together. After final assembly is complete, the container is sent to shot blasting, where it is prepared for priming.
The primer coat is applied and allowed to dry. Next, several applications of a water-based coating are applied and allowed to dry. The use of epoxy paints is in decline, due to environmental concerns.
Once painting is finished, the container is tested for leaks. If any are found, they are repaired before sending the container to labeling, where all identification codes will be applied.
Finally, a treated plywood floor is installed using self-tapping screws to fasten them to the cross members underneath.
Stacking and Handling
Open top containers are stackable, unless cargo height prevents that. Each container has castings at the top and bottom of the corner posts that make it possible to stack and lock the containers together. To ensure safe, stable stacking, there are rules that must be followed. Shipping containers longer than 20ft (6 meters), can be stacked on the 20ft (6 meter) containers, so long as there are two in a row, but 20ft (6 meter) containers can never be stacked on longer containers. All containers longer than 40ft (12 meters) stack at the 40ft (12 meter) coupling width.
Containers are transferred using a variety of equipment, including cranes, reach stackers, forklifts, and straddle carriers. ISO standard containers can be lifted and handled in a variety of ways by their corner fixtures, but the 45ft (13.7 meters) type-E containers have limits on how they can be lifted and handled.
Security and Load Securement
A variety of materials and means are utilized to safely secure cargo inside of containers. Polyester strapping, dunnage bags, wood blocks, and other items are used to stabilize cargo against shifting and movement during transport. For high-value cargo, containers are equipped with a panel and various alarm systems, including a radio signal that can alert security guards if a container is broken into. Currently, there are new technologies being developed to further improve high value cargo security including laser-etched seals, tamper-evident seals with RFID and real-time GPS location, along with changes in logistics planning to make it much more difficult for thieves to steal loads through the use of forged seals and documents.
Creative use of containers is a long-standing practice, the most common of which is storage. Containers no longer used for transportation of goods are ready-made storage units, and can be used almost anywhere. In recent years, another trend has emerged, with people building homes out of used shipping containers, which is environmentally friendly and cost-effective. People have made a variety of buildings out of shipping containers, including cafes, shops, mobile data centers, and man caves. When it comes to repurposing, there is no limit to what a person can do with a used shipping container. While there may be no limit to the possibilities for containers, there are some limitations to how containers can be used. When using them to build a multi-level home, make sure they have the proper structural support. Failure to do this could result in catastrophic failure, causing part of the home to collapse. Also, while the sides of a container are designed to withstand the stresses of oceangoing passage, they are not suitable for subterranean installation. The sides are not designed to withstand the lateral forces of soil pushing against them, making a container vulnerable to collapse. The same goes for the roof. If a container were buried in the ground, the roof would likely give way, unable to support the weight of the soil on top of it. Before building anything with containers, take the time to carefully research how to do this safely.
How Open Top Containers Improved Shipping
Open top containers made it possible to easily and efficiently handle over-height machinery, small shipments of solid materials, and loose bulk cargo. This made it easier for businesses to get the machinery they needed much faster. These containers also made it possible to ship much smaller quantities of solid bulk materials and loose bulk cargo in a much more efficient timeframe.