Section 2 Structure

2.1 Plans and data submission

2.1.1 In addition to the structural plans and information as required by Pt 3, Ch 1, 2 Information required and Pt 4, Ch 1, 4 Information required, the following additional plans and information are to be submitted as applicable:

Structural plans of the accommodation including deckhouses and modules.
Design calculations for containerised modules.
Module support frames or skids and details of attachments.
Structural arrangements and supports under diving installations.
Structural arrangements in way of crane supports.

2.2 General

2.2.1 The general hull strength is to comply with the requirements of Pt 4 Steel Unit Structures, taking into account the applied weights and forces due to the accommodation, diving installations and cranes, and the local structure is to be suitably reinforced. Attention should be paid to loads resulting from hull flexural effects at support points.

2.2.2 The scantlings of structural deckhouses are to comply with Pt 4, Ch 6, 9 Superstructures and deck-houses.

2.2.3 The strength of containerised modules which do not form part of the main hull structure will be specially considered in association with the design loadings.

2.3 Watertight and weathertight integrity

2.3.1 The general requirements for watertight and weathertight integrity are to be in accordance with Pt 4, Ch 7 Watertight and Weathertight Integrity and Load Lines.

2.4 Offshore containers

2.4.1 Definition. For the purposes of this sub-Section, offshore containers are defined as portable units for repeated use in the transport of goods or equipment handled in open seas to, from and between fixed and/or floating installations and ships. Offshore containers are subdivided into three categories:

Offshore freight containers
An offshore container built for the transport of goods. Examples of offshore freight containers are:
1. General cargo container. A closed container with doors;
2. Cargo basket. An open top container for general or special cargo;
3. Tank container. A container for the transport of dangerous or non-dangerous fluids. Tote tanks are considered tank containers;
4. Bulk container. A container for the transport of solids in bulk;
5. Special container. A container for the transport of special cargo e.g. garbage containers, equipment;
6. Boxes and gas cylinder racks.
Offshore service containers
An offshore container built and equipped for a special service task, usually as a temporary installation e.g. laboratories, workshops, stores, power plants and control stations.
Offshore waste skip
An open or closed offshore container used for the storage and removal of waste.

2.4.2 Offshore containers are to be certified to IMO MSC/Circ.860 as supported by BS EN 12079-1:2006 Offshore containers and associated lifting sets. Design, manufacture and marking or an equivalent recognised Standard. The containers are to be certified by an IMO classification body certified for such services on their ISO 17020 accreditation scope. Containers may be certified using LR’s Container Certification Scheme.

2.4.3 Additional requirements are required for offshore portable tanks which store dangerous fluids e.g. aviation fuel and pipeline pre-commissioning chemicals. These require the certifying body to hold the applicable regulatory approvals (e.g. for the International Maritime Dangerous Goods Code and additionally for aviation fuel CAP 437 Standards for Offshore Helicopter Landing Areas).

2.4.4 In-service, offshore containers are required to be inspected as per the offshore standards at a maximum duration of every 4 years, and with a visual inspection performed annually. The inspection body is required to be accredited (e.g. to ISO 17020) for such activities. Any NDT undertaken is to comply with the standard requirements (e.g. NDT operators to Level 2 of ISO 9712 for EN 12079-2). The inspection reports are to be submitted to LR. Where it is intended to keep a container on-board for more than one year, it is to be located with sufficient access to allow inspection and repair of the container in-situ, including load testing of the lifting sets where applicable.

2.4.5 Offshore portable tanks used as bulk storage vessels associated with the drilling plant or process plant are additionally to comply with the requirements of Pt 3, Ch 7, 4 Bulk storage wet and dry systems or Pt 3, Ch 8, 4 Pressure vessels and bulk storage, as applicable.

2.4.6 When offshore containers can be subjected to wave loading or protect openings leading into buoyant spaces, the scantlings are not to be less than required by Pt 3, Ch 4, 2.2 General 2.2.3.

2.4.7 The deck connections and supporting structure for offshore containers are to be designed to the load cases in Pt 4, Ch 3, 4.3 Load combinations for all operating and transit conditions for the applicable loads defined in Pt 4, Ch 3, 4 Structural design loads. The permissible stress levels are to be in accordance with Table 5.2.1 Factors of safety for the combined load cases in Pt 4, Ch 5, 2 Permissible stresses.

2.4.8 The deck connections and supporting structure for offshore containers are additionally to be designed for an emergency static condition with the unit inclined to the following angle:

Column-stabilised and tension-leg units:
25° in any direction.
Surface type units:
22,5° heel, port and starboard, and trimmed to an angle of 10° beyond the maximum normal operating trim.
Self-elevating units:
17° in any direction in transit conditions only.

These angles may be modified by LR in particular cases as considered necessary. In no case is the inclined angle for the emergency static condition to be taken as less than the maximum calculated angle in the worst damage condition in accordance with the appropriate damage stability criteria. The permissible stress levels are to be in accordance with load case (d) in Table 5.2.1 Factors of safety for the combined load cases in Pt 4, Ch 5, 2 Permissible stresses. The maximum operating weights of the offshore containers are to be assumed. Where applicable, ice and snow loads are to be included. Wind loads need not be considered to be acting during this emergency condition.

2.4.9 Container securing arrangements for stowage on exposed decks are to comply with the applicable requirements of Pt 3, Ch 14, 5 Container securing arrangements for stowage on exposed decks without cell guides of Rules and Regulations for the Classification of Ships, July 2022.