Den Norske Veritas (DNV) is a Norwegian classification society established in 1864 to provide rules for assessing the risks of insuring individual vessels. When oil was found in the North Sea, DNV was well suited to take on a regulatory role and provide supervision and inspecting for the offshore assets, such as the platforms, rigs, and supply vessels used to explore and drill for oil. In its regulatory role, DNV began issuing lists of standards for certifications that manufacturers and offshore assets would need to meet to pass inspection and become certified. These certifications cover a broad range of topics related to things like the construction of the vessels, passenger safety, and handling hazardous or dangerous goods and chemicals.When working with offshore modules, the Den Norske Veritas regulatory society, most commonly known as DNV, has two certifications - DNV 2.7-1 and DNV 2.7-2.
DNV 2.7-1- Offshore Containers
The Standard for Certification No. 2.7-1 applies for transport and lifting-related requirements for offshore containers. DNV 2.7-1 is based upon European standard EN 12079 and is globally accepted for the offshore lifting of containers at sea. These requirements ensure the safety of the crews who work with the containers, the environment, and the vessel and installation the containers are moved to or from. The standard covers the materials, design review, manufacturing, testing, certification, marking, and periodic inspection.
For the standard, an offshore container is considered to be “a portable unit used for repeatable use in the transportation of goods or equipment, handled in open seas, to, from or between fixed and/or floating installations and ships.” The units are then broken into three categories: offshore freight containers, offshore service containers, or an offshore waste skip. Offshore modules such as Specialist Services Red Guard’s G4 series modules and the FLEX series of accommodation modules fall under the offshore service container category. Red Guard’s offshore modules are DNV 2.7-1 certified for safe transportation and lifting at sea.
Usually, there are three categories of offshore containers.
Offshore freight containers
An offshore container built for the transport of goods, which can include general cargo containers, cargo baskets, special containers, boxes and gas cylinder racks. Offshore portable tanks are also included in this category. These are used to transport dangerous goods used offshore, and must also meet the International Maritime Dangerous Goods Code.
Offshore service containers
These units are designed for specific purposes which are usually temporary. For instance, workshop cabins, control stations, power plants, labs, mess cabins, and accommodation cabins.
Offshore waste skip
These containers are usually used for holding waste which can be open or closed. All the above-mentioned units are designed and built as per the international regulations.
Offshore containers are also commonly called “skids” in the offshore oil and gas industry, they are often used to transport large components to drilling and production rigs. These can be as simple as frames that hold the contents. The skid, along with its contents, is sometimes referred to as a “skid package.”
DNV 2.7-3-Portable Offshore Units
According to DNVGL-ST-E273 Section 1.4.3, a POU (portable offshore unit) is a package or unit intended for repeated or single offshore transport and installation/lifting which may also be designed for sub sea lifting.
Although the definitions may seem to be similar, it’s important to understand the primary differences. This is especially important for design engineers as the design approach is fundamentally different between the two standards. DNVGL-ST-E271 adheres to a “design by code” philosophy, while DNVGL-ST-E273 is a “design by analysis” approach.
Design by code is a fairly straightforward process. Basically, if the offshore container falls within specified categories, then you apply the designated design criteria. The inherent structure of the code limits subjective decision making of the design engineer, which results in a more streamlined review process by DNVGL. This results in a faster and less expensive design review cycle.
Design by analysis puts more responsibility on the design engineer for defining the design basis including limits of operation, load case scenarios, and selecting and/or defining proper acceptance criteria. Since the design engineer assumes more ownership of the design process, the engineering review phase of the certification process is more in depth and requires a longer review cycle and is usually more expensive than the design review for 2.7-1.
Universal Engineering Services has more than a decades experience in the pressure vessel design for clients in UAE, Oman, Qatar, Kuwait, Bahrain, Saudi Arabia, and many more countries all over the world. UES work to many ASME standards to design and validate pressure vessels, boiler, fittings and piping systems. We are also experts in Stress analysis of piping, structural design, ASME Joint review, Design of Storage tanks, code calculations, FEA/FEM, and spotless service on design management.
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