Section
2 Structure
2.1 Plans and data submissions
2.1.1 The following additional plans and information are to be submitted:
- General arrangement plans of the drilling plant.
- Drilling derrick structural plans and design calculations.
- Raw water towers’ structural plans and design
calculations.
- Flares structures’ structural plans and design
calculations.
- Structural plans of equipment skids, support stools and design
calculations.
- Structural plans of supports to lifting appliances.
2.2 Materials
2.2.2 Support structures for the drilling plant are to be divided into the
following categories:
- Primary structure.
- Secondary structure.
2.2.3 Main load-bearing members and elements subjected to high tensile or
shear stresses are defined as primary structure. All other structure is considered
to be secondary structure.
2.2.4 Some specific examples of structural elements which are considered as
primary structure are as follows:
- Derrick legs and base plates.
- Derrick principal cross bearing.
- Derrick crown block/water table supports.
- Derrick bolts.
- Support stools (attached to the main/upper deck).
- Main legs, chords and end connections.
- Foundation bolts.
2.3 Supporting structure interfaces
2.3.1 The design loadings for all structures supporting plant, including
equipment skids, support stools, tanks and storage vessels, are to be defined by the
designers/Builders and calculations are to be submitted in accordance with an
appropriate Code or Standard, seePt 12, Ch 1 Recognised Codes and Standards .
2.3.2 The design of supporting structures for drilling facilities is to
integrate with the primary hull under-deck structure.
2.3.4 The BOP frame, lifting points or supports are to meet the requirements of
API RP 2A-WSD.
2.4 Derrick and masts
2.4.2 When the unit is to operate in an area which could result in the
build-up of ice on the drilling derrick, the effects of ice loading are to be
included in the calculations, see
Pt 4, Ch 3 Structural Design. The design criterion for this condition may be taken
as a non-drilling condition with defined setback loading. The environmental criteria
are to be agreed with LR, but in general may be based on five-year return criteria
for the operating location.
2.4.4 Fatigue damage calculations for individual components when required are
to take account of the degree of redundancy and also the consequence of failure.
2.4.5 Where National Administrations give specific requirements with respect
to fatigue design, it is the responsibility of the Owners to comply with such
Regulations.
- The design of the derrick or mast and associated ancillary
equipment is to incorporate features to reduce the risk to personnel during
routine maintenance or operations.
- The design is to allow for suitable and safe access from deck
or installed work platforms for operation, maintenance and inspection
services. All items in the derrick are to be accessible for routine
inspection, without the need for man-riding winches.
- Where direct access to lubrication points such as crown or
deflector sheaves cannot be provided, the use of remote grease lines can be
incorporated.
- Portable equipment such as catwalk samson posts are also to be
fitted with padeyes to allow safe removal and re-location.
- The design is to also allow for extra hang off points for
temporary equipment such as wire line units.
- All padeyes are to be designed, installed and tested to LR
requirements, and all padeyes are to be identified and a record book kept,
allowing for inspection records to be maintained.
- Consideration is to be given to providing access and means to
fight a major fire at the monkey board level. The means to fight a fire at
this level are to include portable and fixed fire-fighting systems.
- Modification to any part of the derrick or mast from original
design will require OEM and LR design approval, followed by trials if
necessary.
- Temporary installed structures, members or fittings are to
undergo an assessment by the dutyholder to confirm they will not affect the
original design; if the design is affected, details are to be submitted for
approval.
- Casing stabbing boards are to comply with the following
requirements:
- The hoisting system is to be designed and constructed
to Codes and Standards approved by LR.
- Permanent safe access to the stabbing board for
operators and maintenance personnel is to be provided.
- Any rack and pinion system is to be designed so that the
working platform will not fall if the rack or pinion should fail,
and a single or common mode failure cannot occur.
- Where winch systems are used, the rope is to spool
evenly on the drum and there are to be at least three full turns of
rope remaining on the drum at all times.
- The rope is to remain captive with the drum and sheave
systems under all service conditions, including slack rope
conditions.
- Upper and lower-level limit switches are to ensure that
the hoist system does not operate beyond its specified range.
- Casing stabbing boards is to be clearly marked ‘SUITABLE
FOR CARRYING PEOPLE’ and with the number of people they can
carry.
- Casing stabbing boards and other working platforms that
are raised and lowered by a powered or manually operated system are
to provide users with a secure and safe means of travel and support
at the point of work.
- The working platform is to be positively guided by rails
or runners. The guidance system is to ensure that the platform
remains captive to its rails or runners under all circumstances,
including any wheel or roller failure or failure of the primary
hoisting system.
- Rails/runners are to be securely attached to their
supports and are to not open up under static operations, travelling
or other dynamic operations, overload testing or operation of the
secondary control/braking system.
- The working platform is to have non-slip standing
surfaces, handrails, mid-rails and edge protection.
- The platform is to also have anchorage points for
inertia-type safety harnesses.
- Control of the primary lifting system is to provide
smooth movement of the working platform. The control lever is to
spring to neutral on release, effectively braking the primary
hoisting system.
- Where a manual system of raising or lowering the
platform is used, a positive locking system such as a
ratchet-and-pawl mechanism is to be provided in addition to the
service brake.
- A secondary, inertia-type brake, acting at the rails, is
to be provided in case there is any failure in the primary hoisting
system. The secondary brake is to act independently of the primary
brake and not require any power source (hydraulic, electrical or
pneumatic) for its operation.
- Each braking system is to be capable of holding the full
rated capacity of the loaded stabbing board plus allowances for
dynamic effects. It is not to be possible to lower the working
platform by brake operation only. Two locking devices are to be
provided, such that one locking device operates when the lifting
handle is at neutral and the other one operates if the hoist
mechanism fails. Each device is to be independent.
- A speed controlling device is to prevent the raising
and lowering speed of the platform exceeding tripping speed.
- Adequate safety gear of the progressive type is to be
provided, designed to engage within freefall conditions.
- The platform is to be equipped with a latch lock
mechanism which secures it when not in motion.
2.5 Water towers
2.5.1 Water towers on self-elevating units are to be designed in accordance
with a recognised Code or Standard, modified to take into account the unit’s motions
and marine environmental aspects, see
Pt 12, Ch 1 Recognised Codes and Standards. Provisions for effective securing of
towers when the unit is in transit is also to be similarly designed. The design
conditions defined in Pt 3, Ch 7, 1.4 Plant design characteristics are to be complied with.
2.5.3 Where National Administrations give specific requirements with respect to
fatigue design, it is the responsibility of the Owners to comply with such
Regulations.
2.5.4 For slender structures and components, the effects of wind induced
cross-flow vortex vibrations are to be assessed.
2.6 Flares structures
2.6.2 The flare structures are also to be designed for the imposed loads due to
handling the structure and when in the stowed position.
2.6.4 The structural design of flare structures is to include the effect of
fatigue loading and the thermal loads during flaring, see
Pt 4, Ch 5 Primary Hull Strength.
2.6.5 Where National Administrations give specific requirements with respect to
fatigue design, it is the responsibility of the Owners to comply with such
Regulations.
2.6.6 For slender structures and components, the effects of wind induced
cross-flow vortex vibrations are to be assessed.
2.7 Lifting appliances
2.7.1 Lifting appliances shall, as a minimum, meet the requirements of the
following Standards and are to comply with LR’s Code for Lifting Appliances in a Marine Environment, July 2022 or LR’s Invalid hyperlink [GUID-6B56846B-6DA0-451C-9822-A3F2B665F6A6],
as appropriate, and where applicable, PUWER Reg 4 and LOLER Reg 5. See also
Pt 3, Ch 11 Lifting Appliances and Support Arrangements.
API Spec 2C.
Specification for offshore pedestal mounted cranes.
API RP 2D.
Operation and maintenance of offshore cranes.
ASME B30.20.
Below-the-hook lifting devices.
BOP handling systems will meet the minimum requirements of API Spec
7K.
Hoisting appliances are to be located such as to ensure safe operation,
and must be suitably protected if for location in a hazardous area. Protection is to
limit surface temperature to a maximum of 80 per cent of auto-ignition temperature.
This temperature, if unknown, may be taken to be a maximum of 200°C.
Submitted design data for hoisting appliances is to include all load and
hoisting/lowering speed combinations at the rope drum.
Man-riding winches are to be of an approved type and certified for
offshore use, and they are to comply with the following requirements:
- Two fail safe brakes are to be provided, one automatic and the
other manual.
- Hydraulic winches may be provided with a regenerative brake
system with breaking valve, in place of a secondary manual brake.
- The operating lever is to be returned to neutral upon release
in any position.
- Declutching devices are not to be fitted, unless otherwise
agreed by LR, see
Pt 3, Ch 7, 2.7 Lifting appliances 2.7.1.(e).
- ‘Sprag’ type unidirectional bearings
(freewheels) are acceptable subject to regular satisfactory in-service
inspection.
- Lowering under normal operating conditions is to be through
control of the motor.
- Means for prevention of overriding and underriding of the winch
is to be provided, where reasonably practicable.
- Manufacturer’s label indicating operational parameters and
approval for man-riding.
- A sign affixed to the winch, clearly indicating suitability for
man-riding (for example, ‘SUITABLE FOR MANRIDING’).
- The winch operating lever must automatically return to neutral
when released.
- An automatic brake that will engage upon returning the operating
lever to neutral.
- A manual brake.
- A guide for spooling the wire rope onto the drum (manual or
automatic).
- The ability to lower the rider in a controlled manner in the
event of loss of power to the winch.
- An emergency disconnect from the power source (ESD) located
within winch operator’s reach.
2.8 Guard rails and ladders
2.8.1 It is the Owners’ responsibility to provide permanent access
arrangements and protection by means of Ladders and guard rails. It is recommended
that such arrangements are designed in accordance with a recognised Code or
Standard.
2.8.2 Dutyholders should be aware that the hoops of a ladder alone may not be
effective in safely arresting a fall without injury. Dutyholders are therefore
advised to review their risk assessments and consider if additional fall protection
is required or alternative means of access is to be supplied.
Where dutyholders choose to use fall arrest equipment inside a hooped
ladder to arrest a fall, they should be aware that hoops may interfere with the
operation of some types of fall arrest equipment (for example, inertia reel
devices). Dutyholders should contact their manufacturer or supplier for advice on
the performance of such equipment when used in a hooped ladder.
Users of fall arrest equipment inside a caged ladder should also be
aware of the possibility of injury from striking the cage following a fall. The use
of climbing helmets to reduce the risk of injury may need to be considered (refer to
HSE CCID 1-2012).
Where ladders are used as (or part of) an emergency escape route, they
are to be fire resistant to comply with BS 476 part 7, 1989 or equivalent.
Ladders fixed and portable are to be suitable for use in the intended
areas, and the Owner is to conduct risk assessments with regard to the use of wooden
or aluminium ladders in an offshore drilling environment.
2.9 Fire and blast loading
2.9.1 Particular consideration is to be given to the potential effects of fire
and blast impinging on exposed boundary bulkheads of accommodation spaces and/or
temporary refuge. Where boundary bulkheads can be subjected to blast loading, the
scantlings are to comply with Pt 4, Ch 3, 4.16 Accidental loads and Pt 4, Ch 6, 9.1 General 9.1.6.
Other Standards which will apply to fire and blast loading include:
API RP 2FB Recommended practice for design of offshore facilities
against fire and blast loading.
|