2.7-3 Portable offshore units
|Publication Date:||1 April 2016|
This standard DNVGL-ST-E273 covers suitable requirements to portable offshore units (POUs), see [1.4.3], with respect to design, manufacturing, testing and certification.
It is the intention that a POU that is certified by DNV GL according to this standard could be safely sea transported and lifted offshore including subsea (see [3.11]) anywhere in the world. Standardized frames/ skids used for sea transport only may also be certified as a POU, see [3.3.3].
This standard covers the POU's main structure, supports for any permanent equipment and features important for the functionality during the transport phase.
The intention is that POUs shall meet the following requirements:
Be safe in use with regard to:
hazard to the vessel/installation.
Be suitable for single or repeated use in applicable cases through choice of:
ease of repair and maintenance.
It shall be noted that this standard covers only the POU design and it is the responsibility of the transport/ installation contractor to ensure that all handling is carried out safely with due consideration to applicable HSE requirements.
Users and use of this standard
This standard is primarily issued to help the industry to design and produce POUs that safely can be handled during the transport phase. It is however assumed that all users of this standard have fundamental knowledge within structural engineering and safety discernment. Owners, designers and manufacturers should have a basic understanding of the requirements and limitations outlined in this standard.
The certification scheme described in this document is the scheme used by DNV GL. Organisations other than DNV GL providing certification services related to this standard may also use this scheme or they may use schemes provided by other parties. DNV GL has however no obligations or responsibility for any services related to this standard delivered by others.
DNV GL has a qualification scheme mandatory to approval engineers and surveyors providing services related to this standard. This ensures that all design approvals and certifications delivered are carried out by well qualified personnel who understand the intention behind the standard, the limitations and the correct interpretations.
The use of this document is at the user's sole risk. DNV GL does not accept any liability or responsibility for loss or damages resulting from any use of this document.
DNV, DNV GL and their respective logos are trademarks of DNV GL AS and shall not be used without prior permission of DNV GL. This includes, but is not limited to the use of these logos and trademarks in branding services associated with the present standard DNVGL-ST-E273, e.g. whereas service providers may refer to the standard, also in the form of "2.7-3", DNV GL has the exclusive right to brand its services in the form of e.g. "DNV 2.7-3" and "DNV GL 2.7-3".
DNV GL currently brands its services in the form of "DNV 2.7-3". The term "DNV GL 2.7-3" is considered synonymous, reflecting the merger referred to in the foreword. DNV GL intends to cease the use of the term "DNV 2.7-3" from 2017-07-01 onwards; thereafter, adherence to and validity of the preceding paragraph will be unaffected.
There are a number of considerations that should be made before establishing design and manufacturing criteria for construction and transport of different types or categories of POUs suitable for transport offshore. Such considerations could be:
Single or reoccurring transport.
Value of product may require special design and fabrication precautions.
Transport phases, e.g. road transport, and transport conditions not adequately covered by the given requirements in this standard.
Specially planned transport events due to size, shape, weight or other special features.
See [3.1] for design considerations.
The requirements in this standard are based on a number of assumptions regarding the handling and operation of POUs:
They are lifted individually by one crane, if not otherwise specified.
The maximum allowable wave height during lifting from vessel to/from vessel/platform is restricted according to the POU's operational class, see [3.3.3].
Any wave restriction for subsea lifting, if applicable, needs to be assessed for each POU.
The handling/lifting is carried out according to the agreed operational procedure, see [1.2.2], if any, see [1.2.1].
The POU is lifted with an adequate lifting set, see e.g. [7.3].
They can be lifted anywhere (world-wide) by any crane(s) with sufficient capacity and speed if not otherwise specified, e.g. due to a single transport.
They are only stacked if they are designed for this and in this case only onshore or on offshore installations where permitted. Stacking during transport on ships is not covered by this standard, see [1.1.5].
Cargo or loose installations are properly secured in the POU.
They are handled according to IMO CSS Code, OSV Code or according to a special made transport procedure.
Handling and operation is in accordance with local regulations.
DNV GL may approve alternative solutions that are found to represent an overall safety standard equivalent to the requirements in this standard. Such approval may be revoked if subsequent information indicates that the chosen alternative is not satisfactory.
Types of portable offshore units
This standard groups the POUs into five types, namely; Type A, B, C, D and E. Examples of types A through E are shown in the sketches in Figure 1-1.
Type A is POUs with a primary structure frame (including skids arranged with crash frames). Type A units typically share many characteristics with Offshore Containers, but deviate from the definition given in DNV 2.7-1, e.g. with MGW > 25 tonnes or because they are intended for a single transport. POUs which for other reasons are not able to comply with the requirements for containers in DNV 2.7-1 may also be accepted as POUs of Type A. Type A units will typically be service packages such as pumps, generation units, coiled tubing units, skid mounted manifolds, pressure vessels or process arrangements of portable nature.
Type B is POUs with skid based installations but without a primary structure frame (skids arranged without crash frames). Type B units could have installations with the same type of main functions as mentioned for Type A units. The reason for omitting the crash frame may be related to the size or shape of the POU or other considerations.
Type C is POUs that lack a dedicated skid or frame. Type C units may be arranged with self-supporting feet, skirts or support points integrated in the units' own structure. Example of this type could be: x-mas trees, reels, manifolds, pressure vessels with stools, etc.
Type D is mainly boxes or units of stress skin design, where the suitability for transport is arranged in the shell through attachments and reinforcements to achieve adequate structural integrity. These types of structures do normally depend on the shell or skin to resist transport generated loads. Examples of the Type D POUs would be control cabins or smaller modules for different services.
Type E is a POU that does neither fall into any of the POU types A through D nor is a DNV 2.7-1 container. It shall be agreed with DNV GL in each case if it is applicable to certify a Type E unit as a POU.