# What Makes an Offshore Container Different From a Shipping Container

Created on 09.15

Open blue shipping container with doors wide open, revealing an empty, clean interior.

LongTeng Industrial Co., Limited — Technical Insight

Two boxes can stand side by side in the same yard and look almost identical. One is a shipping container. The other is an offshore container.

The difference is not the paint, not the corrugation, and not the name on the door. The difference shows up the first time the offshore container leaves the deck of a supply vessel. Until that moment, no buyer can tell an offshore container from a shipping container.

The offshore container is designed around a different load case

A shipping container is engineered around stacking and static transport. An offshore container is engineered around repeated dynamic lifting — scores, sometimes hundreds, of lifts across a service life measured in decades. That is the load case DNV 2.7-1 was written around, and it is the single fact that separates one product from the other. An offshore container that ignores it is a shipping container wearing the wrong name.

That one difference in load case reshapes every downstream decision on an offshore container: steel grade, member size, weld detail, lifting interface, test regime, marking and inspection cycle. Specify an offshore container against shipping-container rules, and you will receive a shipping container. Specify it against DNV 2.7-1, and you receive an offshore container.

Land lifting and offshore lifting are not the same problem

On land, a lift of an offshore container is close to a static event. The ground is stable, the crane is on a firm footing, and the load arrives where it is placed. Design an offshore container for those conditions and it will look perfectly adequate.

Offshore, the same lift becomes a dynamic event. The vessel rises and falls, the offshore container swings on its sling set, and acceleration compounds the static weight. Land lifting is about holding weight. Offshore lifting is about surviving impact.

So an offshore container is not simply a heavier box. It is a box whose primary structure, sling points and welds were sized for a load case the shipping container was never designed to meet — the load case set out in DNV 2.7-1.

Fatigue matters as much as strength in an offshore container. A weld on an offshore container that survives one lift on land may still fail after three hundred lifts at sea — which is precisely why an offshore container is examined on a cycle that no ordinary shipping container ever faces. DNV 2.7-1 reflects that reality directly: it is the reason the lifting set of an offshore container is certified separately from the offshore container itself.

Nine differences you can see on the drawing

Item	Standard shipping container	Offshore container
Lifting interface	Corner castings only	Sling points or pad eyes welded to the primary structure of the offshore container, plus corner castings
Design case	Static stacking and transport	Repeated dynamic lifting of the offshore container, loaded, as required by DNV 2.7-1
Lifting set	Not part of the product	A certified sling set supplied with the offshore container, with individual component certificates
Welding	Production welding	Qualified procedures, a weld map, and full-penetration welds at every primary load path of the offshore container
Non-destructive testing	Spot checks	Visual, magnetic particle and ultrasonic testing across the primary structure of the offshore container
Proof load	Prototype testing only	A proof load test of the finished offshore container and its lifting set before delivery
Marking	Safety approval plate and identification number	A data plate on the offshore container showing tare, maximum gross mass, payload, test date and certifying body
Service regime	Periodic plate renewal	Periodic examination of the offshore container and its sling set, on a defined cycle
Buyer's first question	How many can we stack?	Under which edition of DNV 2.7-1 has this offshore container been certified?

The whole of DNV 2.7-1 is really that table in nine lines, and every line of it is a promise about the offshore container. A shipping container is a transport product. An offshore container is a lifting product that happens to look like the transport product — and that resemblance is the only reason a buyer can be misled by an offshore container that was not built to the standard.

Why the offshore container became a separate product

For years, offshore cargo moved in boxes designed to land rules — shipping containers doing an offshore container's job. The result was predictable: structures that performed well on a quay, and struggled under the acceleration, impact and repeated lifting of an offshore crane. That is the gap DNV 2.7-1 was created to close for the offshore container.

DNV 2.7-1, the standard introduced for offshore containers in the late 1980s, did not invent a new shape. It introduced a new set of obligations. Dynamic load cases had to be considered. Safety factors had to rise. A proof load test had to be witnessed. Welding on an offshore container had to be qualified, recorded and inspected. For an offshore container built to DNV 2.7-1, non-destructive testing stopped being optional.

Read that list again and notice what it is really saying: an offshore container is not certified because it is strong. It is certified because every step that produced that offshore container can be traced — design assumption, steel certificate, welder, weld, test, name of the inspector who signed it off against DNV 2.7-1.

The documents that should travel with every offshore container

When an offshore container arrives without paperwork, it is not an offshore container. It is a steel box with unknown history.

Ask for the drawing and the load calculation for the offshore container. Ask for the weld map and the procedures behind it. Ask for the non-destructive testing reports. Ask for the proof load certificate and the commissioning record of the sling set supplied with that offshore container. Ask for the coating specification with dry film thickness readings taken across the offshore container. Ask for the DNV 2.7-1 certificate covering the offshore container as delivered.

The DNV 2.7-1 data plate belonging to the offshore container is worth a paragraph of its own — it is the identity card of an offshore container. If the tare figure stamped on it does not match the offshore container on the scale, the payload figure is wrong too — and an offshore container whose payload is wrong is a risk loaded onto a deck.

Where offshore containers fail in service — and why it is rarely the frame

Most offshore container problems we are asked about are not structural failures at the main members. They start smaller:

Sling points and pad eyes

Mixed lifting sets

Tare drift

Coating breakdown at contact points

Door and seal damage

None of these appear on the day the offshore container is delivered. All of them appear in year seven, on a platform, in weather. An offshore container is judged in year seven, not on delivery day.

Why LongTeng Industrial builds offshore containers

LongTeng Industrial Co., Limited has manufactured containers — including the offshore container — for thirteen years from a 50,000 square metre facility with two production lines. Welding, structural preparation and coating happen in our own works rather than across a chain of subcontractors — which is the only way to keep the record of an offshore container intact from the first cut to the final inspection.

In practice, that means the engineering review of an offshore container happens before fabrication, not after. Sling point positions, bottom structure, reinforcement around openings, coating system and marking are agreed against the duty of that specific offshore container and against DNV 2.7-1. Third-party inspection is arranged at the works. The offshore container leaves with a document pack, not with a promise. No offshore container leaves the works without it.

Because we build the offshore container rather than resell it, sizes are also open. A standard offshore container platform covers most offshore duties; a non-standard offshore container is engineered where the deck space, the payload or the handling equipment demands it. Every offshore container we deliver starts from that engineering review, not from a catalogue.

The bottom line

Anyone can build a box that looks like an offshore container. The difference between an offshore container and an ordinary box is not visible in a photograph — it lives in the weld map, the test report, the DNV 2.7-1 data plate and the sling set certificate. All four belong to the offshore container, not to the salesman.

Buy the report, not the paint. The offshore container will then outlive the project it was bought for.

Specifying an offshore container? Send us the intended duty, payload, lifting configuration and destination — LongTeng Industrial will return a configured offshore container proposal with structure, coating system, DNV 2.7-1 certification route and document pack.

LongTeng Group is a private owned enterprise group involves in designing, manufacturing, trading and transporting of ISO dry cargo container, special container and house container, reefer container, tank container. Also provide container spare parts for repairing and manufacturing new container. The group have exported to over 60 countries. The total annual production capacity is 120,000 TEU of ISO Containers.