Difference Between Standard Container and Offshore Container

Container is a kind of transportation equipment, which was produced in the United Kingdom and developed in the United States. According to the regulations of the International Organization for Standardization Container Technology Committee (ISO/TC 104), the container should meet the following conditions:

(1) It has sufficient strength and can be used repeatedly for a long time;

(2) It is suitable for one or more modes of transportation and is transshipped There is no need to reload the goods in the box;

(3) It is suitable for special fast loading and unloading and handling devices, which is convenient for switching from one mode of transportation to another mode of transportation;

(4) It is convenient for filling and unloading of goods;

With the rapid development of marine engineering, offshore containers as supporting equipment have also developed rapidly, and offshore containers have gradually evolved from standard containers. A standard container refers to a 20-foot or 40-foot container with a maximum total mass of 20,000 ft, generally made of steel, and used for shipping general cargo. Offshore container refers to a mobile unit capable of transporting and operating in wave-high seas with a total mass of no more than 1. This unit is frequently used for the transportation and hoisting of goods or equipment between fixed or floating facilities and ships.

1. Operating environment and lifting method

Standard containers are generally transported port-to-port by container liner. If the standard container is placed in the liner cabin, the box guide column in the cabin can be used to prevent the box from moving; if the standard container is placed on the deck and needs to be stacked in several layers, the upper and lower containers should be fixed by stacking The fittings are connected, and the corner fittings of the container are tightened with the tie rings on the deck through tie rods.

In the port terminal, the hoisting of the standard container usually adopts the shore container crane or the station container crane, and uses the twist lock device of the crane to connect with the four top corner pieces of the container and lift it vertically. Because the port climate is generally mild, there is no collision when standard containers are hoisted, so the operating environment is relatively safe.

Offshore containers are usually placed on the deck of supply ships in the offshore oil industry without tying them up and are directly exposed to the marine environment. Offshore containers are hoisted at a single point, and are often hoisted to oil platforms under harsh sea conditions. Each part of the box is subject to a large impact, and it is easy to collide with adjacent boxes or hulls. Therefore, the structural strength requirements for offshore containers are relatively high. , Generally, the spreader is permanently assembled on the box body, and certain protective devices are required.

Offshore containers usually have no corner fittings, and even if they have corner fittings, they are not allowed to be used for offshore lifting operations. During transportation, offshore containers are not allowed to be stacked on ships, but only on offshore and onshore facilities, and generally no more than 2 layers.

2. Design Requirements

2.1 Cabinet structure requirements

Standard containers are generally 20-foot and 40-foot containers, which are used to ship common dry goods; the box body is made of steel frame, full vertical corrugated side panels and front wall panels, pressed blind corrugated roof panels, wooden floors, hinged movable corrugated doors and conforming to ISO standard corner fittings can be divided into door end, front end, side wall, bottom frame and top plate according to the parts; the functions of each structure are the same, there is no distinction between primary and secondary, and there is no specific regulation on the thickness of the material, as long as it meets the relevant rigidity test Just ask.

Offshore containers are only applicable to the global offshore industry. There are no strict standards for their dimensions and functions. The box structure and box type are mainly designed according to the purpose. The box structure can be divided into main structure and secondary structure according to its function. The main structure plays the main bearing and supporting role, which can be subdivided into key main structures and non-key main structures: key main structures include top and bottom side beams, end top beams, end bottom beams, corner columns, fork grooves and lifting lugs, etc. It can transfer the load generated by the loaded goods to the hook or forklift; the non-critical main structure includes the bottom plate, guide plate and stacking plate, etc. Secondary structures include door panels, side panels and roof panels, etc., which do not play a major bearing role and can be omitted in strength analysis. Offshore containers generally have spreaders permanently attached to the container body. Spreader refers to a comprehensive device connecting offshore containers and lifting equipment, including slings (such as wire rope slings, chain slings, etc.), shackles, connecting rings, etc.

When designing the offshore container structure, the following requirements should also be met: (1) Fully consider the local impact load generated by the impact of the container on the adjacent container or the rigid part of the hull during the hoisting process.

(2) When arranging the main structure, the effective continuity of the structure should be ensured; the intersection distance between beams (columns) should be as far as possible, and effective measures should be taken to reduce the stress concentration of the web or flange. (3) The box body should have the ability to tilt 30° in any direction. ) Reasonably set the box door, handles, box cover lugs, etc., and take corresponding protective measures to prevent them from being hung on the hooks of the lifting equipment.                                  

Standard containers are mainly used for ocean transportation, which requires high corrosion resistance of materials, so weather-resistant steel such as SPA-H and SS400 are generally used. Weather-resistant steel is made by adding a little copper, chromium, phosphorus, vanadium and other elements to ordinary steel, and its weather resistance and corrosion resistance are 4 to 8 times higher than ordinary steel. This is because the special elements contained in the weather-resistant steel will form a layer of oxide film after contact with the atmosphere. This strong film isolates the steel from the outside world, so that it will not be affected by the climate and achieve the purpose of weather resistance and corrosion resistance. Under the general environment of energy saving and emission reduction and the overall downturn in the shipping industry, high-strength steel is more and more applied to the standard container manufacturing industry, because the use of high-strength steel can reduce the container strength while maintaining the same strength. body weight, thereby increasing the load capacity of standard containers, and the use of high-strength steel has little impact on cost.

Since all offshore containers are lifted at a single point, during the lifting process, various parts of the container body (especially the corner columns, top and bottom side beams, front and rear lintels, and front and rear sills, etc.) will suffer large impacts, and it is very easy to collide with adjacent containers or hulls. ;During transportation, the boxes will collide with each other due to lack of binding. When the temperature decreases, the brittleness of offshore container materials increases and the impact toughness decreases; therefore, Q345D/Q345E low-alloy steel with low-temperature impact energy is generally used as offshore container materials to minimize damage after collision. The design temperature of offshore containers should not be higher than the minimum daily average temperature of the area where they are used, and should not be higher than 20°C, so Q345D low-alloy steel is generally used; The temperature of ℃ is designed, so Q345E low-alloy steel is selected, which still has sufficient strength and impact toughness under low temperature conditions.

In addition, offshore container materials must also meet the following requirements:

(1) For corner posts and bottom beams, the minimum material thickness is , but for offshore containers with a total mass not greater than , the minimum material thickness is ; the minimum material thickness for other primary structures is ; the minimum material thickness for secondary structures is .

(2) To ensure safety, the equivalent stress of the design load is not allowed to exceed 85% of the minimum yield strength of the material used.

(3) In order to prevent brittle fracture, it is not allowed to use high-strength steel with a yield strength greater than that at room temperature.                               

 According to different use environments and lifting methods, standard containers and offshore containers have different test requirements.

3. Certification and production

Compared with standard containers, there are strict regulations on the certification and production of offshore containers. Notice No. 860 of the International Maritime Safety Committee of the International Maritime Organization clearly requires that design calculations and actual verification must be considered when certifying offshore containers. In this regard, it stipulates 6 items that must be considered when designing offshore containers and 4 items that must be carried out test.

The certification of offshore containers takes the following 3 steps.

(1) Evaluation and certification: Calculate and review the structural drawings of offshore containers according to various standards, and evaluate the details of the box material, cargo load, box lifting, and cargo fastening in the box.

(2) Manufacturing process inspection: Certified inspectors authenticate and test raw materials to ensure that welder qualifications, welding processes and non-destructive testing work meet the requirements.

(3) Sample box test: including four-point lifting, two-point lifting, tilt test and drop test, etc.

In the production process of offshore containers, the lifting lugs and the fillet welds connected to them are required to be fully penetrated, and 100% ultrasonic flaw detection should be carried out; the welding of main structures such as load-bearing structural beams, fork grooves and bottom beams should be fully penetrated, certified The inspector can conduct ultrasonic or radiographic flaw detection according to the requirements of 20%. At the same time, the materials of the main structure must be tracked during the whole production process.

4. Conclusion

Based on different functions, use environments and lifting methods, there are many differences between standard containers and offshore containers in terms of box structure, material requirements, test requirements, certification and production; therefore, in the process of container procurement, design, production and operation must be distinguished and identified in order to better carry out offshore container business.