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 General, the following additional plans and information are to
be submitted:
- General arrangement plans.
- General arrangement plans of drilling derrick and
equipment.
- Structural plans of drill floor, drilling derrick supports,
substructure, drilling equipment supports, pipe rack and supports.
- Structural arrangements in way of drilling wells.
- Movable drilling cantilevers and skid beams.
- Hull supporting structures.
- Hull structural plans of mud compartments, mud tanks and
pump-rooms.
- Deckhouses and modules.
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 drilling structures and applied
equipment weights and forces introduced by the drilling operations. Attention should
be paid to loads resulting from hull flexural effects at support points. For surface
type units, see also Pt 3, Ch 1, 1 Rule Application.
2.2.2 The design loadings for the strength of the drill floor and substructure
are to be defined by the designers/Builders and calculations are to be
submitted.
2.2.3 Strength calculations are to be submitted for moveable drilling
cantilevers, skid beams and their supports. The clearances between the cantilever
support claw and the skidding guides is the responsibility of the
designers/Builders.
2.2.4 The maximum reaction forces from the drilling derrick are to be
determined from an acceptable National Code or Standard and should take into account
the load effects from vessel motions, the drillpipe setback, hook load, rotary table
and tensioning equipment, see
Pt 3, Ch 7 Drilling Plant Facility.
2.2.5 When the unit is to operate in an area which could result in the
build-up of ice on the drilling derrick and other structures, the effects of ice
loading is to be included in the calculations, see
Pt 4, Ch 3, 4 Structural design loads.
2.2.6 The local structure should be reinforced for the component forces from
drilling equipment and tensioner forces, and the design loadings are to be
determined in accordance with Pt 3, Ch 7 Drilling Plant Facility.
2.3 Well structure
2.3.1 The primary hull strength of the unit is to be maintained in way of
drilling wells and other large deck openings and suitable compensation is to be
fitted as necessary. For surface type units the minimum hull modulus in way of the
drilling well is to satisfy the Rule requirements for longitudinal strength.
2.3.2 Arrangements are to be made to ensure continuity of strength at the ends
of longitudinal and well side bulkheads. In general, the design should be such that
the bulkheads are connected to bottom and deck girders by means of large, suitably
shaped brackets arranged to give a good stress flow at their junctions with both the
girders and bulkheads.
2.3.3 The boundary bulkheads of drilling wells are to be designed for the
maximum forces imposed by the drilling operations. The minimum scantlings of well
bulkheads are to comply with the requirements for tank bulkheads in Pt 4, Ch 6, 7 Bulkheads using the load head measured to the top
of the well, but in no case is the well plating to have a thickness less than 9,0
mm.
2.4 Permissible stresses
2.5 Mud tanks
2.5.1 The scantlings of structural mud tanks are not to be less than those
required for tanks in Pt 4, Ch 6, 7 Bulkheads using the design density of the mud. In
no case is the relative density of wet mud to be taken less than 2,2 unless
otherwise agreed with LR.
2.5.2 Divisions in mud tanks or pits are to be designed for one-sided loading
and the scantlings are to comply with the requirements for tanks in Pt 4, Ch 6, 7 Bulkheads
2.6 Deckhouses and modules
2.6.2 Offshore containers are to comply with Pt 3, Ch 4, 2.4 Offshore
containers.
2.7 Pipe racks
2.7.1 The pipe rack is to be designed for the following normal operating loads
as applicable:
- Gravity loads.
- Maximum dynamic loads due to wave-induced unit motions.
- Direct wind loads.
- Ice and snow loads.
2.7.2 The pipe rack supports are also to be designed for an emergency
condition as defined in Pt 3, Ch 8, 1 General.
2.7.3 In general, the pipe rack supports are to be aligned with the primary
under-deck structure. Where this is not practicable additional under-deck supports
are to be fitted. Deck girders and under-deck supports are to comply with Pt 4, Ch 6, 4 Decks
2.7.4 In the emergency condition arrangements are to be made to restrain the
pipes in their stowed position and details are to be submitted for approval.
2.8 Bulk storage vessels
2.8.2 The deck supports under free standing bulk storage vessels are to comply
with the requirements for local structure in Pt 4, Ch 6 Local Strength, taking into account the maximum design reaction
forces.
2.8.3 Where bulk storage vessels penetrate watertight decks and can be
subjected to external hydrostatic pressure due to progressive flooding in hull
damage conditions, the bulk storage vessel is to be suitably reinforced and the
permissible stress is not to exceed the code stress in accordance with Pt 3, Ch 8, 4 Pressure vessels and bulk storage.
2.9 Watertight and weathertight
integrity
2.9.1 The general requirements for watertight and weathertight integrity are
to be in accordance with Pt 4, Ch 7.
2.9.2 The integrity of the weather deck is to be maintained. Where items of
plant equipment penetrate the weather deck and are intended to constitute the
structural barrier to prevent the ingress of water to spaces below the deck, their
structural strength is to be equivalent to the Rule requirements for this purpose.
Otherwise such items are to be enclosed in superstructures or deckhouses fully
complying with the Rules. Full details are to be submitted for approval.
2.9.3 Where items of plant equipment or pipes penetrate watertight boundaries,
the watertight integrity is to be maintained and full details are to be submitted
for approval.
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