Section 1 General

1.1.1 This Chapter outlines the hull structural design requirements of ship units with hull construction in steel engaged in production and/or cargo storage/offloading while permanently moored at offshore locations. For the purposes of this Part, the term ‘cargo’ refers to crude oil, liquefied gas, condensate, methanol, process chemicals including refrigerants and by-products of the production process.

1.1.2 The Rules are also applicable to units which normally operate while moored at offshore locations, but which are disconnectable in order to avoid extreme environmental conditions or hazards, see also Pt 4, Ch 3, 4 Structural design loads.

1.1.3 Units which operate as shuttle tankers will normally be assigned class in accordance with the Rules and Regulations for the Classification of Ships (hereinafter referred to as the Rules for Ships).

1.1.4 Hull strength, scantlings and arrangements for ship units are to comply with Pt 10 SHIP UNITS. Reference is also made to the LR ShipRight Procedure for Ship Units.

1.1.5 All aspects which relate to the specialised offshore function of the unit are to be considered on the basis of this Chapter and the additional requirements related to the design arrangements and functions of drilling and production units given in Pt 3, Ch 2 Drilling Units and Pt 3, Ch 3 Production and Storage Units are to be complied with.

1.1.6 The scantlings and arrangements of units with a limited number of tanks for the storage of flammable liquids having a flash point not exceeding 60°C (closed-cup test) will be specially considered.

1.1.7 The class notations and descriptive notes applicable to units classed in accordance with these Rules are to be in accordance with List of abbreviations andPt 3, Ch 3, 1 General, to which reference should be made.

1.1.8 Additional requirements related to the design function of the unit are given in Pt 3 FUNCTIONAL UNIT TYPES AND SPECIAL FEATURES.

1.1.9 Turret structures, mooring arms and yoke structures, etc. are to comply with the requirements of Pt 10, Ch 1, 9 Mooring structure andPt 3, Ch 13 Buoys, Deep Draught Caissons, Turrets and Special Structures.

1.1.10 Units with a process plant facility which comply with the requirements of Pt 3, Ch 8 Process Plant Facility will be eligible for the assignment of the special features class notation PPF.

1.1.11 Units with a drilling plant facility which comply with the requirements of Pt 3, Ch 7 Drilling Plant Facility will be eligible for the assignment of the special features class notation DRILL.

1.1.12 The structural design of integral tanks for the storage of condensates is to comply with the requirements in this Part outlined for cargo tanks and other tanks designed for liquid filling. The density of the condensate is not to be taken as less than the minimum density values, as defined inPt 10, Ch 2, 1.2 Definitions 1.2.3 in Pt 10, Ch 2 Loads and Load Combinations, for strength and fatigue assessments.

1.1.14 The structural design of independent tanks for the bulk storage of liquid chemicals is to comply with the requirements of Pt 11, Ch 4 Cargo Containment and Pt 10, Ch 1, 1.1 Application 1.1.13 and Pt 10, Ch 1, 1.1 Application 1.1.13.

1.1.15 Ship units engaged in the production, storage and offloading of liquefied gases at a fixed location are to comply with Pt 11 PRODUCTION, STORAGE AND OFFLOADING OF LIQUEFIED GASES IN BULK and other relevant Parts in addition to the requirements of this Part.

1.2.1 General definitions are given in Pt 1, Ch 2, 2 Definitions, character of classification and class notations and Pt 4, Ch 1, 5 Definitions.

1. Delivery voyage. Delivery voyage of a unit along a defined route from a shipyard or field to the operating site at which the OI class notation is assigned. The delivery voyage is typically scheduled for restricted sea states.
2. Restricted service area transit. Transit of a unit at any time across a restricted service area. Voyages of this nature may be carried out by disconnectable units that sail away within a defined service area either to avoid approaching heavy weather and/or to return to a dry dock for inspection.
3. Unrestricted worldwide transit. Transit of a unit at any time across any sea area in the world. Voyages of this nature may be carried out by disconnectable units that sail away either to avoid approaching heavy weather and/or to return to a dry dock for inspection.

1.3.1 All units are to be assessed for the delivery voyage. This is to ensure that the unit arrives fit for entry into class at the operating field where the OI class notation is assigned. The Owner is to define the wave environment and the maximum transit speed for the delivery voyage.

1.3.2 Disconnectable units are to be assessed for unrestricted worldwide transit, in which case the delivery voyage need not be assessed. The Owner is to define the maximum transit speed for disconnected service. For unrestricted worldwide transit, the loads defined in Pt 10, Ch 2, 7 Environmental loads for unrestricted worldwide transit condition are to be used. Alternatively, at the request of the Owner, the unit may be assessed to transit within a restricted service area. In this case, a service restriction will be placed on the unit and recorded in the class notation, see Pt 10, Ch 1, 1.2 Definitions 1.2.5. The Owner is to define the wave environment for the restricted service area.

1.4.1 In general, the Working Stress Design (WSD) method is applied for the assessment of the scantlings in Pt 10, Ch 3 Scantling Requirements. Three sets of acceptance criteria are given that are dependent on the probability level of the characteristic combined loads.

1.4.2 The acceptance criteria set AC1 is applied when the combined characteristic loads are frequently occurring, typically for the static design load combination. This means that the loads occur on a frequent or regular basis. The allowable stress for a frequent load is lower than for an extreme load and takes into account allowance for some dynamics and operational mistakes.

1.4.3 The acceptance criteria set AC2 is typically applied when the combined characteristic loads are extreme values, e.g. typically for the static + dynamic design load combinations. High utilisation of the structural capacity is allowed in such cases because the considered loads are extreme loads with a low probability of occurrence.

1.4.4 The acceptance criteria set AC3 is typically applied for capacity formulations based on plastic collapse models such as those that are applied to address bottom slamming and bow impact loads.