Rules for Classification and Construction IV Industrial ...rules.dnvgl.com/docs/pdf/gl/maritimerules2016July/gl_iv-6-2_e.pdf · Rules for Classification and Construction IV Industrial

Rules for Classification and Construction IV Industrial Services

6 Offshore Technology

2 Mobile Offshore Units

Edition 2007

The following Rules come into force on June 1st , 2007

Germanischer Lloyd Aktiengesellschaft

Head Office Vorsetzen 35, 20459 Hamburg, Germany

Phone: +49 40 36149-0 Fax: +49 40 36149-200

[email protected]

www.gl-group.com

"General Terms and Conditions" of the respective latest edition will be applicable (see Rules for Classification and Construction, I - Ship Technology, Part 0 - Classification and Surveys).

Reproduction by printing or photostatic means is only permissible with the consent of Germanischer Lloyd Aktiengesellschaft.

Published by: Germanischer Lloyd Aktiengesellschaft, Hamburg Printed by: Gebrüder Braasch GmbH, Hamburg

Table of Contents

Section 1 Scope, Definitions and Procedures

A. Scope, Application ..................................................................................................................... 1- 1 B. Definitions .................................................................................................................................. 1- 1 C. Design Review ........................................................................................................................... 1- 2 D. Supervision of Fabrication and Installation ................................................................................ 1- 6 E. Testing and Commissioning ....................................................................................................... 1- 7

Section 2 Self-elevating Units

A. General ....................................................................................................................................... 2- 1 B. Structure ..................................................................................................................................... 2- 1 C. Stability ...................................................................................................................................... 2- 3

Section 3 Column Stabilized Units

A. General ....................................................................................................................................... 3- 1 B. Structure ..................................................................................................................................... 3- 2 C. Stability ...................................................................................................................................... 3- 4

Section 4 Surface Drilling Units

A. General ....................................................................................................................................... 4- 1 B. Structure ..................................................................................................................................... 4- 2 C. Stability ...................................................................................................................................... 4- 2 D. Drilling Facilities ....................................................................................................................... 4- 2 E. Safety Aspects ............................................................................................................................ 4- 3

Section 5 Pipelaying Units

A. General ....................................................................................................................................... 5- 1 B. Movement and Position Keeping ............................................................................................... 5- 1 C. Structure ..................................................................................................................................... 5- 4 D. Watertight Integrity and Stability ............................................................................................... 5- 4 E. Pipelaying Facility ...................................................................................................................... 5- 5

Section 6 Well Stimulation Units

A. General ....................................................................................................................................... 6- 1 B. Special Safety Aspects ............................................................................................................... 6- 1 C. Position Keeping ........................................................................................................................ 6- 1 D. Well Stimulation Equipment ...................................................................................................... 6- 1

IV - Part 6 GL 2007

Table of Contents Chapter 2Page 3

Section 7 Subdivision, Stability and Load Line

A. General Remarks, Scope ............................................................................................................. 7- 1 B. Righting and Heeling Lever Curves ............................................................................................ 7- 1 C. Intact Stability Criteria ................................................................................................................ 7- 2 1. Standard criteria .......................................................................................................................... 7- 2 D. Inclining Test .............................................................................................................................. 7- 3 E. Subdivision and Damage Stability .............................................................................................. 7- 3 F. Extent of Damage ....................................................................................................................... 7- 4 G. Watertight Integrity ..................................................................................................................... 7- 5 H. Load Line .................................................................................................................................... 7- 6

Section 8 Mooring Equipment

A. General ........................................................................................................................................ 8- 1 B. Temporary Mooring Equipment ................................................................................................. 8- 1 C. Positional Mooring Equipment ................................................................................................... 8- 6

Section 9 Life-Saving Appliances

A. General ........................................................................................................................................ 9- 1 B. Life-Saving Appliances ............................................................................................................... 9- 1 C. Arrangement of Lifeboats and Liferafts ...................................................................................... 9- 2 D. Rescue Boats ............................................................................................................................... 9- 4

Annex A List of Standards, Codes, etc. Quoted

Chapter 2 Page 4

Table of Contents IV - Part 6GL 2007

Index

A Accessories ............................................................................................................................................................ 8-5

Alarm signals ......................................................................................................................................................... 9-1

Anchor lines ........................................................................................................................................................... 8-7

Anchoring systems ................................................................................................................................................. 8-6

Anchors ........................................................................................................................................................... 8-2, 8-7

Application ............................................................................................................................................................ 1-1

B Block coefficient CB .............................................................................................................................................. 1-2

Bottom mat ............................................................................................................................................................ 2-3

Bracing members ................................................................................................................................................... 3-4

Breadth B ............................................................................................................................................................... 1-1

C Chain cable manufacture ...................................................................................................................................... 8-11

Chain cables .................................................................................................................................................... 8-5, 8-8

Chain locker ........................................................................................................................................................... 8-5

Class notation ............................................................................................................. 2-1, 3-1, 4-1, 5-1, 5-2, 6-1, 8-6

Column stabilized units .................................................................................................................... 3-1, 7-5, 7-7, 9-2

Columns, hulls footings ......................................................................................................................................... 3-3

Commissioning ...................................................................................................................................................... 1-7

Construction portfolio ............................................................................................................................................ 1-4

Corrective actions .................................................................................................................................................. 1-7

D Damage .................................................................................................................................................................. 7-4

Definitions ............................................................................................................................................................. 1-1

Depth H .................................................................................................................................................................. 1-1

Design review ........................................................................................................................................................ 1-2

Documents .............................................................................................................................. 1-2, 5-5, 8-1, 8-6, 8-17

Draught T ............................................................................................................................................................... 1-2

Drilling .................................................................................................................................................... 2-1, 3-2, 4-2

Drilling well ........................................................................................................................................................... 4-2

Dynamic position keeping .............................................................................................................. 3-1, 4-1, 5-2, 8-17

E Embarkation stations .............................................................................................................................................. 9-2

Equipment numeral ................................................................................................................................................ 8-2

IV - Part 6 GL 2007

Index Chapter 2Page 5

F Frame spacing a ..................................................................................................................................................... 1-2

H Hazards .................................................................................................................................................................. 1-5

Heeling lever curves .............................................................................................................................................. 7-1

High holding power anchors .................................................................................................................................. 8-2

Hull ....................................................................................................................................................................... 2-1

I Inclining test .......................................................................................................................................................... 7-3

Intact stability ........................................................................................................................................................ 7-2

J Jacking ................................................................................................................................................................... 2-2

L Launching .............................................................................................................................................................. 9-3

Legs ....................................................................................................................................................................... 2-2

Length L ................................................................................................................................................................ 1-1

Lifeboats ................................................................................................................................................................ 9-1

Liferafts ................................................................................................................................................................. 9-2

Life-saving appliances ........................................................................................................................................... 9-1

Lifting appliances ............................................................................................................................. 2-1, 3-1, 4-1, 5-1

Load line ................................................................................................................................................................ 7-6

M Marking ............................................................................................................................................... 1-7, 8-15, 8-17

Materials ................................................................................................................................................................ 8-9

Mooring equipment ............................................................................................................................................... 8-1

O Openings ................................................................................................................................................................ 7-5

Operating manual .................................................................................................................................... 1-4, 5-4, 5-5

P Penetrations ........................................................................................................................................................... 7-5

Personal life saving appliances .............................................................................................................................. 9-2

Pipelaying facility .................................................................................................................................................. 5-5

Pipelaying units ..................................................................................................................................................... 5-1

Pollution prevention .............................................................................................................................................. 1-6

Position keeping ............................................................................................................................................. 5-1, 6-1

Positional mooring equipment .......................................................................................................... 3-1, 4-1, 5-2, 8-6

Preload capability .................................................................................................................................................. 2-3

Production processes ............................................................................................................................................. 1-6

Chapter 2 Page 6

Index IV - Part 6GL 2007

R Rejection repair criteria ....................................................................................................................................... 8-15

Rescue boats .......................................................................................................................................................... 9-4

Righting lever curves ............................................................................................................................................. 7-1

S Safety aspects .......................................................................................................................................... 4-3, 5-1, 6-1

Safety management plan ........................................................................................................................................ 1-5

Safety management system .................................................................................................................................... 1-4

Sea trials .......................................................................................................................................................... 1-7, 5-4

Self-elevating units .......................................................................................................................... 2-1, 7-4, 7-7, 9-2

Stability ..................................................................................................................................... 2-3, 3-4, 4-2, 5-4, 7-1

Storm condition ...................................................................................................................................................... 7-2

Structure ........................................................................................................................................... 2-1, 3-2, 4-2, 5-4

Studs .................................................................................................................................................................... 8-13

Subdivision damage stability ................................................................................................................................. 7-3

Supervision of fabrication ...................................................................................................................................... 1-7

Surface drilling units .............................................................................................................................................. 4-1

Surface units ........................................................................................................................................... 7-4, 7-6, 9-2

T Tanks ..................................................................................................................................................................... 3-3

Temporary mooring equipment .............................................................................................................................. 8-1

Testing ................................................................................................................................................................. 8-14

Testing accessories .............................................................................................................................................. 8-16

Towing .................................................................................................................................................... 2-1, 4-2, 5-2

Towing ballasting ................................................................................................................................................... 3-1

V Valves .................................................................................................................................................................... 7-5

W Waste management ................................................................................................................................................ 1-6

Watertight integrity ................................................................................................................................................ 7-5

Wave clearance ...................................................................................................................................................... 3-2

Well stimulation equipment ................................................................................................................................... 6-1

Well stimulation units ............................................................................................................................................ 6-1

Well stimulation vessels ......................................................................................................................................... 6-1

Winch system ....................................................................................................................................................... 8-17

Wind forces ............................................................................................................................................................ 7-1

Wire ropes .............................................................................................................................................................. 8-5

IV - Part 6 GL 2007

Index Chapter 2Page 7

Chapter 2 Page 8

Index IV - Part 6GL 2007

Section 1

Scope, Definitions and Procedures

A. Scope, Application

1. Scope

1.1 In this Chapter the requirements for the dif-ferent types of mobile offshore units are defined.

1.2 Types of units

− units connected to the sea bed by anchoring (mooring)

− units kept on position by dynamic position-ing/propelling system

− units connected by legs in jacked up condition

1.3 Materials used for construction of the hull

The following materials may be used for the main structure/hull:

− steel, normally

− concrete, in exceptional cases

2. Application

2.1 The following types of employment have to be distinguished:

− drilling/exploration

− self-elevating drilling units

− column stabilized drilling units

− surface drilling units of ship or barge type

− other types of drilling units

− production, e.g. oil/gas

− processing/treatment

− storage or loading on/off

− research, measurements

− construction / pipelaying

2.2 Manning

Only units continuously manned in operation mode are considered.

B. Definitions

1. Mobile offshore unit

A mobile offshore unit is any mobile offshore struc-ture or vessel, whether designed for operation afloat or supported by the sea bed, built in accordance with these Rules and classed by GL and includes the entire structure and components covered by these Rules.

2. Drilling unit

A drilling unit is any unit intended for use in offshore drilling operations for the exploration or exploitation of the subsea resources.

3. Selfpropelled unit

A self-propelled unit is a unit which is designed for unassisted passage. All other units are considered as non-self-propelled.

4. Length L

4.1 Shiptype units

The length L is the distance in metres on the summer load waterline from the fore side of the stem to the after side of the rudder post, or the centre of the rudder stock, if there is no rudder post. L is not to be less than 96 % and need not be greater than 97 % of the ex-treme length of the summer load waterline. In units with unusual stern and bow arrangement, the length L will be specially considered.

4.2 Other units

The length L means 96 % of the total length on a waterline at 85 % of the least moulded depth H meas-ured from the top of the keel, or the length from the foreside of the stem to the axis of the rudder stock on that waterline, if that be greater. In units designed with a rake of keel, the waterline on which this length is measured shall be parallel to the designed waterline.

5. Breadth B

The breadth B is the greatest moulded breadth of the unit.

6. Depth H

The depth H is the vertical distance, at the middle of the length L, from the base line to the top of the deck beam at side of the uppermost continuous deck.

IV - Part 6 GL 2007

Section 1 Scope, Definitions and Procedures Chapter 2Page 1–1

B

In way of effective superstructures the depth is to be measured up to the superstructure deck for determin-ing the unit’s scantlings.

Effective superstructures are extending into the range of 0,4 L admidship and their length exceeds 0,15 L.

7. Draught T

The draught T is the vertical distance at the middle of the length L from base line to freeboard marking for summer load waterline.

8. Block coefficient CB

The moulded block coefficient CB at load draught T, based on the length L is defined as:

3

Bmoulded volume of displacement [m ] atC =

⋅ ⋅T

L B T

9. Frame spacing a

The frame spacing a will be measured from moulding edge to moulding edge of frames.

10. Further definitions

For further definitions see Chapter 1, Section 1, B.

C. Design Review

1. Extent of review

Examination or verification of the following will be undertaken: − design documents, such as load assessment and

stress analyses (as far as applicable), reports on model tests, design drawings

− practical qualifications of manufacturing firms and personnel

− suitability of the materials used − erection procedure of the structure on land and at

the port − transportation procedures and jack-up procedure,

if applicable − critical review of safety management system, see

4.

2. Documents for approval

2.1 General

2.1.1 All documents have generally to be submitted to GL in German or English language.

2.1.2 The general scope of documents is defined in 2.2 to 2.6, the detailed scope will be defined case by case. GL reserve the right to demand additional docu-

mentation if that submitted is insufficient for an as-sessment of the unit or essential parts thereof. This may especially be the case for plants and equipment related to new developments and/or which are not tested on board to a sufficient extent.

2.1.3 Once the documents submitted have been approved by GL they are binding on the execution of the work. Subsequent modifications and extensions require the approval of GL before becoming effective.

2.2 Plans for the hull and design data

General specifications with an indication of the in-tended use, design life, location and environment, place(s) and period of construction and the main stages of construction up to final assembly and/or installation at sea.

Plans showing the scantlings, arrangements and details of the principal parts of the hull are to be submitted for approval before construction commences. These draw-ings have to clearly indicate the scantlings, types and grades of materials, joint details and welding, or other methods of connection. These plans are to include the following, where applicable:

− general arrangement

− specification of the assumed loads

− inboard and outboard profile

− summary of distributions of fixed and variable weights

− plan indicating design loads for all decks

− transverse sections showing scantlings

− longitudinal sections showing scantlings

− decks including helicopter deck

− framing

− shell plating

− watertight bulkheads and flats

− structural bulkheads and flats

− tank boundaries with location of overflows

− structure in way of jacking or other elevating ar-rangements

− hulls, pontoons, legs, footings, pads or mats

− superstructures and deckhouses

− arrangement and details of watertight doors and hatches

− anchor handling arrangements, mooring system

− welding details and procedures, pre- and post-treatments

− lines or offsets

− curves of form or equivalent data

Chapter 2 Page 1–2

Section 1 Scope, Definitions and Procedures IV - Part 6GL 2007

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− wind heeling moment curves or equivalent data

− capacity plan

− corrosion control arrangements

− methods and locations for non-destructive testing, manufacturer’s quality control methods and test procedures

− where appropriate, general arrangement of equip-ment including calculations associated with the transfer/installation mode

In addition an arrangement plan of watertight com-partments shall be submitted as early in the design stage as possible, for review of damage stability. This drawing is to indicate the watertight bulkheads, decks and flats and all openings therein. Doors, hatches, ventilators, etc. and their means of closure, are to be indicated. Piping and ventilation systems shall be shown in sufficient detail to evaluate their effects on the watertight integrity after incurring damage.

2.3 Plans for machinery and electrical equip-ment and design data

Plans are to be submitted showing the arrangement and details of:

− general arrangement of machinery installations and equipment

− general arrangement and design details of propul-sion system

− auxiliary machinery

− steering gear

− boilers and pressure vessels

− general arrangement and particulars of the electri-cal installation

− jacking system including description

− bilge and ballast systems

− fire extinguishing systems

− other pumps and piping systems

− working gear as far as it has been agreed to be included in the design review

2.4 Safety aspects

− hazardous areas plan

− arrangement plans of safety devices and equip-ment, e.g. fire extinguishing plan, escape routes, life-saving appliances, structural fire protection

− operating instructions, as far as related to safety

− safety management plans, where applicable

2.5 Calculations

2.5.1 The following data and calculations are to be submitted in conjunction with the scantling plans, as may be applicable:

− structural analysis for relevant loading conditions as agreed with GL

− resultant forces and moments from wind, waves, current, mooring and other environmental loading taken into account in the structural analysis

− effect of icing on structural loading, stability and windage area

− stability calculations, both intact and damaged, over the appropriate range of drafts, including the transit conditions

− significant operational loads from drilling derrick and associated equipment, industrial items, etc, and other significant loadings

− calculations substantiating adequacy of structure to transmit forces between legs and hull through the jacking or other elevating systems

− evaluation of the ability to resist overturning while bearing on the sea bed

2.5.2 Submitted calculations are to be suitably referenced. Results from relevant model tests or dy-namic response calculations may be submitted as alternatives or as substantiation for the required calcu-lations.

2.5.3 The choice of computer programs according to the “State of the Art“ is free. It is recommended to use computer programs which are approved by GL in advance as appropriate to solve the actual problems. If the computer programs to be used are not known to GL, they may be checked by GL through comparative calculations with predefined test examples. Reference applications, already achieved approvals by other institutions and other relevant information shall be provided in advance. A generally valid approval for a computer program is, however, not given by GL.

The calculations have to be compiled in a way which allows to identify and check all steps of the calcula-tions with regard to input and output in an easy way. Handwritten, easily readable documents are accept-able.

Comprehensive quantities of output data shall be pre-sented in graphic form. A written comment to the main conclusions resulting from the calculations has to be provided.

2.6 Further details

The necessary documentation is indicated in further detail in the relevant Chapters and Sections.

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2.7 Distribution of documents

The distribution of design documents according to 2.2 – 2.6 will be agreed upon in each individual case, depending on the organization on Owner's, contrac-tor's and/or fabricator’s side, and the mandatory re-quirements of responsible Administrations.

For the needs of GL, general descriptions, calculations and test reports have to be submitted in duplicate, structural plans, detail drawings and building/testing specifications in triplicate, one copy of each being returned to the remitter with the approval or review notation.

3. Operating instructions

3.1 Operating Manual (Booklet)

An Operating Manual or equivalent is to be placed on board of each unit. The booklet shall include the fol-lowing information, as applicable in the particular case, so as to provide suitable guidance to the operat-ing personnel with regard to safe operation of the unit:

− general description / main characteristics

− pertinent data for each approved mode of opera-tion, including design and variable loading, envi-ronmental conditions for the execution of certain operations, e.g. jacking, drilling, etc.

− minimum anticipated atmospheric and sea tem-peratures

− assumed seabed conditions and their control, scouring, etc.

− admissible draft, or required distance of certain parts from the water surface

− general arrangement showing watertight compart-ments, closures, vents, allowable deck loading, etc.; if permanent ballast is used, the weight, loca-tion and substance used are to be clearly indicated

− hydrostatic curves or equivalent data

− capacity plan showing capacities of tanks, centres of gravity, free surface corrections, etc.

− instructions for operation, including precautions to be taken in adverse weather, changing mode of operations, any inherent limitations of operations, etc.

− plans and description of the ballast system and instructions for ballasting

− hazardous areas plan

− light unit data on the results of an inclining ex-periment, etc.

− stability information in the form of maximum KG draught curve, or other suitable parameters based upon compliance with the required intact and sta-bility criteria

− representative examples of loading conditions for each approved mode of operation, together with means for evaluation of other loading conditions

− details of emergency shutdown procedures

− identification of the helicopter used for the design of the helicopter deck and procedure for helicopter operations

− safety checks and maintenance work to be carried through

− emergency procedures and rescue operations

− operating booklet for helicopter operation, includ-ing helicopter data on which design is based

3.2 Construction Portfolio (Booklet)

A set of plan copies showing the exact location and extent of application of different grades and strengths of structural materials, together with a description of the material and welding procedures involved, is to be placed on board. Any other relevant construction in-formation is to be included in the booklet, including restrictions or prohibitions regarding repairs or modi-fications.

3.3 The operating instructions will be subject to examination within the design review procedure only insofar as they are related to the specified loads and load cases to be applied, and to other safety matters covered by these Rules.

4. Safety management system

4.1 Safety management procedures 1, may be subject to review by GL either

− based on an agreement with the Owner/Operator, or

− due to authorization and request by the competent national Administration.

4.2 Safety management may be related to

− personal safety of operating personnel, i.e.

− accident prevention

− protection against exposure to toxic, radioactive or otherwise harmful substances

− general preventive and health control measures (alcohol, drugs control, etc.)

− protection of the environment (sea, sea floor, at-mosphere surrounding the installation)

–––––––––––––– 1 See IMO ISM (International Safety Manage-ment) procedures, to be introduced for mobile off-shore units from 1 July 2002



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− operational safety/operability of the technical installations/systems on board

Obviously, an inter-relation exists with the operating manual according to 3., see also 4.4 and 4.6.

4.3 Safety Management Plan

4.3.1 Safety management procedures shall be pre-sented in the form of a Safety Management Plan (SMP), to be set up in each individual case, bearing in mind the particular operational and environmental conditions to be expected as well as the applicable legislation and regulations.

4.3.2 Preparation of a SMP will essentially consist in an assessment of all foreseeable risks emerging from the planned activities, and in providing measures and procedures to minimize these risks. The assess-ment will be based on existing experience and statisti-cal information regarding similar installations and activities. Proven methods of risk and failure analysis including e.g. Fault-Tree or Event-Tree diagrams may be used.

4.3.3 Corrective measures and amendments to the plan may be required following experience gathered during the initial service period, see also 4.4.

4.3.4 The SMP should take into account separately all relevant operational phases and situations and their specific risks, such as

− initial (start-up, test) period(s), also following important changes

− normal ("routine") operations

− operations under restricting conditions, e.g.

− due to extreme environmental impact

− during repairs, conversions, etc.

− periods following an accident or failure

4.4 Essential elements of a SMP

4.4.1 The SMP shall clearly show, through ade-quate procedures and organizational provisions, that

− routine controls, checks, measurements etc. are provided in order to ensure that physical properties and chemical processes remain stable and within prescribed limits, e.g. critical gas concentrations, exposure limits, pressures, ppm values; function-ing of alarms

− information and training of personnel is ensured, taking into account also possible language prob-lems, like information on danger zones, “hazard-ous areas“, alarms; handling of fire fighting and rescue equipment, etc.

− national regulations have been considered

− any (new) hazards becoming known, not taken into account or not sufficiently covered in the

original plan, will be evaluated and duly incorpo-rated in a revised SMP

− communication between operating personnel and responsible company management is ensured, in-cluding immediate and reliable information on special/ abnormal incidents or events defined in the SMP, see 4.4.2. In relevant cases information to Authorities and GL is ensured.

− for any abnormal situations, e.g. repairs requiring operational restrictions, the necessary additional precautions are taken and any person possibly in-volved is aware of the existing danger

4.4.2 The SMP shall indicate follow-up measures and procedures for each case of failure or incident considered. Responsibilities shall be clearly attributed to members of the crew/installation personnel within each contingency procedure, and the paths or chains of information clearly stated for the different cases.

4.4.3 For the unit in service, it shall be guaranteed by regular, and possibly additional, unprecedented, checks, audits etc., that the measures provided by the SMP are actually being observed.

Relevant documentation is to be kept on board and/or in the Operator’s headquarters for a period to be de-fined by the Administration, but not less than 5 years.

4.5 Types of hazards

Among aspects to be considered in assessing risks are the following:

4.5.1 Hazards to personnel

− explosion, fire

− exposure (through contact, inhalation, ingestion) to toxic, irritant or otherwise harmful gases, liq-uids, chemicals etc.

− accidents due to operations with lifting gear/ ap-pliances and machinery or tools

− accidents due to environmental influences (icing, unit’s motions, bad visibility etc.)

− noise/vibrations exceeding given ("tolerable") limits

4.5.2 Hazards to the environment:

− spills/loss of polluting (toxic or otherwise harmful) substances during "normal" - e.g., drilling - opera-tions to the sea or sea floor, see 4.6.2

− spills of hydrocarbons, chemicals etc. during trans-port/conveyance operations, see 4.6.1

− collision and grounding hazard, depending on weather and traffic conditions

− release of polluting (e.g. exhaust) gases to the atmosphere, see 4.6.2

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− dropping of objects (e.g. wastes) to the sea/sea floor, see 4.7

− noise exceeding prescribed limits; may be relevant in certain cases, e.g. in sensitive, protected areas

4.6 Pollution prevention during production and transport activities

4.6.1 Transport/conveyance and storing opera-tions

4.6.1.1 Loading and unloading operations, e.g. using transport (supply) vessels and cargo handling equip-ment, shall be carried out observing weather imposed restrictions, see "operating instructions", and applica-ble safety and environment protection regulations.

4.6.1.2 For the conveyance of oil/hydrocarbon prod-ucts from a production unit to a (shuttle) tanker, using articulated piping, swivels, flexible hoses etc., special precautions - e.g., emergency shutdown and spill ar-resting devices - may be necessary, depending on environment conditions and regulations applicable to the location.

For import/export flow lines (hydrocarbons produc-tion) see also 4.6.2.

4.6.1.3 Any harmful substances subject to controlled handling shall be allocated to defined, properly shel-tered and marked spaces. Liquids or substances capa-ble of releasing harmful liquids under certain condi-tions shall be stored in such a way that spills are pre-vented.

4.6.1.4 Reception/receiving, use/consumption and return/unloading of harmful or polluting substances shall be constantly controlled and their volumes or weight noted.

4.6.2 Production and treatment processes

4.6.2.1 Suitable controls using measuring and moni-toring techniques shall be provided to ensure safe conveyance of hydrocarbons and other polluting sub-stances to and from the offshore unit, through flow lines, risers, hoses, etc.

4.6.2.2 For safe conveyance/transport of liquid and gaseous substances on board of the production unit, between the different processing stations, the provi-sions of Chapters 5 and 6 have to be observed (mate-rial selection, design requirements, safety, monitoring and alarm devices, etc.).

4.6.2.3 Waste water, in connection with the produc-tion process, shall be either collected in storage tanks and discharged via auxiliary vessels or pipeline, or – if allowed by the competent Authority - pumped to the sea after prescribed treatment/purification and under controlled conditions (monitoring of ppm values).

4.6.2.4 Release of gaseous substances to the atmos-phere, including flaring operations, shall occur under controlled conditions and according to the applicable

regulations. Unintentional escape of gases (leakage), particularly in hazardous areas and to accommodation spaces, shall be avoided by precautions such as suit-able arrangement of piping, ducts and exhaust open-ings/ intakes, sensors/measuring devices and alarms, pressurizing, according to the Rules, see Chapter 5 and 6.

4.7 Waste management

4.7.1 For sewage waste water the same applies as stated under 4.6.2.3 for waste water originating from the production process. The sewage residues shall be discharged or transported to corresponding installa-tions onshore.

4.7.2 Generally, no solid wastes whatsoever (sani-tary, food processing, production auxiliary materials such as for cleaning, etc.) shall be dumped from an offshore unit. Crew information and strict adherence shall be ensured by suitable measures such as publica-tion (posters), regular instruction and supervision.

D. Supervision of Fabrication and Installation

1. General

1.1 Supervision of the fabrication of individual components and of the installation of the hull will generally take the form of inspections by the author-ized GL Surveyor to the extent considered necessary by GL at any given time.

1.2 GL branch (inspection) offices will receive, for their supervisory work, previously examined, documents from the Head Office, see C.2.7. Addition-ally all technical documents connected with the rele-vant construction project shall be made available to the Surveyors on request.

1.3 GL will assess the production facilities and procedures of the yard and other fabricators as to whether they meet the requirements of GL Rules. In general, approvals based on such assessments are conditional for acceptance of products subject to test-ing.

1.4 Materials, components, appliances and instal-lations subject to inspection are to comply with the relevant rule requirements and be presented for in-spection and/or construction supervision by GL Sur-veyors, unless otherwise provided as a result of special approvals granted by GL.

1.5 It shall be the duty of the fabricator to inform the competent inspection office of the completion of important stages of the construction or of trials and inspections due.

1.6 In order to enable the Surveyor to fulfil his duties, he is to be given free access to the unit and the



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workshop, where parts requiring approval are fabri-cated, assembled or tested. For performance of the tests required, the yard or fabricators are to give the Surveyor every assistance by providing the staff and equipment necessary for such tests.

2. Supervision of fabrication

2.1 Aim of supervision

During the phase of fabrication of an unit GL will ensure by surveys and inspections that:

− parts for hull and machinery and/or special equip-ment requiring approval have been constructed in compliance with the approved drawings and par-ticulars

− all tests and trials stipulated by GL Rules are per-formed satisfactorily

− workmanship is in compliance with current engi-neering standards and/or GL Rule requirements

− welded parts are produced by qualified welders having undergone tests

− test Certificates have been presented for compo-nents requiring approval (the fabricator will have to ensure that any parts and materials requiring approval will only be delivered and installed, if the appropriate test Certificates have been issued)

− where no individual Certificates are required, type-tested appliances and equipment are employed in accordance with rule requirements

2.2 Marking and attestation of individual components

2.2.1 Insofar as it is necessary to identify materials or components during the fabrication process or possi-bly also after commissioning, e.g. because of special properties of the material, a permanent mark is to be made by means of a stamp.

2.2.2 The construction supervision, survey and/or final inspection of materials, parts supplied or installa-tion components, corresponding to the relevant speci-fications and GL Rules, will be attested by the Sur-veyor concerned on special forms, or informally, as agreed in the individual case.

3. Industrial equipment

Regarding working gear and special equipment, su-pervision of construction and testing will be agreed upon from case to case.

E. Testing and Commissioning

1. Program

An overall test or commissioning program including the complete, combined function of the unit as well as partial tests of the different systems has to be estab-lished. The detailed requirements for the overall func-tion and the functioning of the different systems are defined in the following Chapters and Sections. The test program has to be approved by GL.

2. Tests at fabricators

As far as practicable, machinery and equipment will be subjected to operational trials on the fabricator's test bed to the scope specified in the Construction Rules. This applies also to engines produced in large series. Where the machinery, equipment or electrical installations are novel in design or have not yet suffi-ciently proved their efficiency under actual service conditions on board ships or units , GL may require performance of a trial under particularly severe condi-tions.

Upon completion of work, compartments, decks, bulkheads, etc. are to be tested as specified in the following Chapters and Sections.

3. Sea trials

Upon completion of the unit and/or the system/ equipment to be classed, all structure/hull, machinery and electrical installations will be subjected to opera-tional trials in the presence of the GL Surveyor, prior to and during the sea trial. This will comprise, e. g.:

− tightness, operational and load tests of tanks, cov-ers, shell ports, ramps, etc.

− operational and/or load tests of the machinery and installations (propulsion plant, electrical installa-tions, steering gear, anchor equipment, etc.) of im-portance for safe operation

During a final survey, checks will be made to ensure that any deficiencies found, for instance during the sea trial, have been eliminated.

4. Report

A test or commissioning report has to be established by the fabricator or Owner and to be agreed with the GL Surveyor.

5. Corrective actions

If the tests according to the established test program, see 1., are partially or totally not satisfactory to the GL Surveyor, corrective actions have to be provided by the fabricator or Owner and the relevant part of the tests repeated until a satisfactory result has been reached.

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Section 2

Self-elevating Units

A. General

1. Definition

Self-elevating units have hulls with sufficient buoy-ancy to safely transport the unit to the desired loca-tion, after which the hull is raised to a predetermined elevation above the sea surface on its legs, which are supported on the sea bed. Equipment and supplies may be transported on the unit, or may be added to the unit in its elevated position. The legs of such units may penetrate the sea bed, may be fitted with enlarged sections or footings (spud cans) to reduce penetration, or may be attached to a bottom pad or mat. Self-elevating units are also known as Jack-up units.

The Class Notation SELF ELEVATING UNIT will be assigned for this type, see Chapter 1, Section 2, C.2.3.

2. Scope

2.1 This Section covers those specific design criteria and features of self-elevating mobile offshore units which are not dealt with in the special Sections as referred to in the following.

2.2 Subdivision and watertight integrity

Subdivision and watertight integrity are dealt with in Section 7. Regarding stability see C.

2.3 Machinery and electrical installations

Machinery and electrical installations shall be de-signed according to Chapters 5 and 6, respectively, as far as applicable. For the jacking installation, see Chapter 5, Section 9 and Chapter 6, Section 12, I.

2.4 Auxiliary installations and equipment

Special (auxiliary) installations and equipment are to be designed according to the specific Sections as far as applicable. See also Chapter 1, Section 1, D.2.

2.5 Lifting appliances

For the interaction of lifting appliances with the unit, its foundations, etc. Chapter 4, Section 8.

The requirements for offshore cranes and other lifting appliances themselves are defined in the GL Rules VI – Additional Rules and Guidelines, Part 2 – Life Sav-ing Appliances, Lifting Appliances, Accesses, Chapter 2 – Guidelines for the Construction and Survey of Lifting Appliances.

2.6 Towing and elevating

Conditions for towing, for the elevating and lowering procedures and for operating phases while standing on the sea floor, shall be clearly indicated in the Operat-ing Manual, compare Section 1, C.3.1.

2.7 Drilling

Drilling derricks shall be designed according to recog-nized codes/standards and/or applicable national regu-lations. The rated capacity for each reeving shall be included in the Operating Manual.

Permanently installed piping systems for drilling op-erations are to comply with recognised standard or code.

These Rules do not include requirements for the drill-ing of subsea wells or procedures for their control. Such drilling operations are subject to control by the coastal state.

B. Structure

1. General

1.1 The buoyant main structure (hull) of a self- elevating unit shall be designed to resist the loads and stresses arising in the floating condition and while elevated. Chapter 4, Sections 1 to 4 apply.

1.2 The unit is to be designed for a clearance of either 1,2 m, or 10 % of the combined storm tide, astronomical tide and height of the maximum wave crest above the mean low water level, whichever is less, between the underside of the hull in the elevated position and the crest of the design wave. This crest elevation is to be measured above the level of the combined astronomical and storm tides. See also Chapter 4, Section 2, B.4.10.

1.3 Classification or Certification will be based upon the designer’s assumptions regarding the sea bed conditions. These assumptions shall be recorded in the Operating Manual. It is the responsibility of the Op-erator to ensure that actual conditions do not impose more severe loading on the unit.

2. Hull

2.1 Structural elements such as the outer shell, decks, bulkheads and girders shall be dimensioned according to the principles outlined in Chapter 4, Section 3. The GL Rules I – Ship Technology, Part 1 –

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Seagoing Ships, Chapter 1 – Hull Structures may be used as a basis where applicable, e.g. dimensioning of tank boundaries.

2.2 The hull is to be considered as a complete structure having sufficient strength to resist all in-duced stresses while in the elevated position and sup-ported by all legs. All fixed and variable loads are to be distributed, by an accepted method of rational analysis, from the various points of application to the supporting legs. The scantlings of the hull are then to be determined consistent with this load distribution, but are not to be less than those required by the Rules defined in 2.1. Scantlings of units having other than rectangular hull configurations will be subject to spe-cial consideration.

2.3 Deckhouses located near the boundary of the unit shall be designed to resist the possible impact of sea wash during conveyance.

Deckhouses are to have sufficient strength for their size, function and location and are to be constructed to approved plans. Their general scantlings are to be as indicated in the Rules according to 2.1. Where they are close to the side shell of the unit, their scantlings may be required to conform to the requirements for bulkheads of unprotected deckhouse fronts.

2.4 Special attention is to be paid to the founda-tions and fastening of drilling derrick(s) and cranes, also with regard to transit conditions.

3. Structure in way of jacking

3.1 Load carrying members which transmit loads from the legs to the hull are to be designed for the maximum design loads and are to be arranged that loads transmitted from the legs are properly distrib-uted into the hull structure.

3.2 For the elevated position, special attention is to be paid to the distribution of the loads from the supporting points (legs) into the hull structure, taking account also of possible load redistributions resulting from lack of support at one leg.

The structure surrounding the legs (points of support) shall be designed with particular regard to the intro-duction of local concentrated forces; main loadbearing elements should be continuous in the vertical direc-tion.

Regarding the maximal force to be transmitted, pre-loading of the legs shall be considered, see 4.5 below.

3.3 For loose elements, e.g. bars, rods, bolts, pins, serving for transmission of forces to support the unit, special requirements may be imposed regarding dimensioning (safety factors) and testing.

4. Legs

4.1 Leg types

Legs may be either shell type or truss type. Shell type legs may be designed as either stiffened or unstiffened shells. According to the sea bed conditions envisaged, the legs may be designed with fixed or detachable footings, or bottom mats.

4.2 Lower end

Where footings or mats are not fitted, proper consid-eration shall be given to the leg penetration of the sea bed and the corresponding end fixity of the legs. De-pending on the mat and type of connection, a rota-tional restraint of the leg may exist also in this case.

4.3 Dimensioning

4.3.1 The legs of self-elevating units shall be de-signed to resist the forces and bending moments re-sulting from the following operational conditions. The safety factors according to loading condition 2 accord-ing to Chapter 4, Section 3, C. and D. apply. Fatigue may have to be specially considered, particularly for legs of truss type. For fatigue criteria, see Chapter 4, Section 3, G.

4.3.2 Ocean transit condition

Legs shall be designed for acceleration and gravity moments resulting from the motions in the most se-vere anticipated environmental transit conditions, together with corresponding wind moments. Calcula-tion or model test methods, acceptable to GL, may be used. Alternatively, legs may be designed for a bend-ing moment resulting from a 15° single amplitude of roll or pitch at a 10 second period, plus 120 % of the gravity moment caused by the legs' angle of inclina-tion (minimum design criteria).

For ocean transit conditions, it may be necessary to reinforce or support the legs, or to remove sections of them. The approved condition is to be included in the Operating Manual.

4.3.3 Field transit condition

Legs are to be designed for a bending moment result-ing from a 6° single amplitude of roll or pitch at the natural period of the unit, plus 120 % of the gravity moment caused by the legs' angle of inclination.

The legs are to be investigated for any proposed leg arrangement with respect to vertical position during field transit moves, and the approved positions are to be specified in the Operating Manual.

Such investigation should include strength and stabil-ity aspects.


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Field transit moves may only be undertaken when the predicted weather is such that the anticipated motions of the unit will not exceed the design condition. The duration of a field transit move may be for a consider-able period of time and should be related to the accu-racy of weather forecasting in the area concerned. Such a move should not normally exceed a twelve hour voyage between protected locations, or locations where the unit may be safely elevated; however, dur-ing any portion of the move, the unit is not normally to be more than a six hour voyage away form a pro-tected location or a location where the unit may be safely elevated. The approved condition is to be in-cluded in the Operating Manual.

4.3.4 Condition while lowering legs

Legs are to be designed to withstand the dynamic and current loads which may be encountered along their unsupported length just prior to touching bottom, and also to withstand the shock of touching bottom while the unit is afloat and subject to motions caused by waves and wind.

The maximum design motions, water depth, bottom conditions and sea state while lowering legs are to be clearly indicated in the Operating Manual, and the legs are not to be permitted to touch bottom when the site conditions exceed the allowable.

4.3.5 Condition while elevating the unit

The legs are to be designed to withstand the loads acting on both, the unit’s hull and the legs themselves, during the elevating procedure. The environmental conditions are the same as foreseen for lowering of the legs (4.3.4).

The analysis may have to be done for several interme-diate positions of the hull.

4.3.6 Elevated (working) condition

The largest possible overturning moments shall be considered, using the most adverse combination(s) of applicable variable and environmental and gravity loadings. Forces and moments due to lateral frame deflections of the legs are to be taken into account.

Eccentricity of support or partial restraint of the lower leg ends may have to be considered (e.g. for spud can design), depending on the soil conditions. The analysis will usually have to be carried through for several water depths and corresponding site and environ-mental conditions.

4.4 Bottom mat

4.4.1 If the sea bed conditions are characterized by very soft mud and silt, the lower ends of the legs are to be attached to a mat. Particular attention is to be given to the attachment and the framing and bracing of the mat, in order that the loads are properly distributed.

4.4.2 The envelope plating of tanks which are not vented freely to the sea is not to be less in thickness than would be required by the rules for tanks, using a head to the design water level taking into account the astronomical and storm tides, see 2.1.

4.4.3 The effects of scouring on the bottom bearing surface should be considered. The effects of skirt plates, where provided, have to be especially consid-ered.

4.4.4 Mats are to be designed to withstand the loads encountered during lowering including the shock of touching bottom while the unit is afloat and subject to wave motions.

4.4.5 Provisions for ballasting and de-ballasting the mat have to be installed. These may be pipelines run-ning down each leg into the mat to vent off trapped air during ballasting or to induce air for displacing the water and thus de-ballasting the mat. These pipelines may also be used to blow air under the bottom of the mat with the aim of facilitating the lifting of the mat from the bottom of the sea.

4.5 Preload capability For units without bottom mats, all legs are to have the capability of being preloaded to the maximum appli-cable combined gravity plus overturning load. The approved pre-load procedure shall be included in the Operating Manual.

Regarding the preloading capability of the elevating machinery, see Chapter 5, Section 9.

C. Stability

1. General The general requirements for stability are defined in Section 7. Additional aspects are given in the follow-ing.

2. Overturning Stability

2.1 The unit, when resting on the sea bed, is to have sufficient downward gravity loading on the sup-port footings or mats to withstand the overturning moment of the combined environmental forces from any direction, for each design loading condition. The overturning safety, defined as the sum of the restoring moments divided by the sum of the overturning mo-ments, should not be less than:

− 1,5 for loading condition 2

− 1,3 for loading condition 3 according to Chapter 4, Section 3, C.

2.2 It is assumed that noticeable inclinations of the unit will not occur or will be corrected immedi-ately, and that the effects of any dangerous changes of the sea bed will be kept under control. Corresponding instructions shall be contained in the Operating Man-ual.

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Section 3

Column Stabilized Units

A. General

1. Definition

Column stabilized units depend upon the buoyancy of widely spaced columns for floatation and stability for all afloat modes of operation or in the raising or low-ering of the unit, as may be applicable. The columns are connected to an upper structure supporting e.g. drilling equipment or accommodation quarters. Lower hulls or footings may be provided at the bottom of the columns for additional buoyancy or to provide suffi-cient area to support the unit on the sea bed. Bracing members of tubular or structural sections may be used to connect the columns, lower hulls or footings, and to support the upper structure.

Operations may be carried out in the floating condi-tion, in which condition the unit is described as a Semi-Submersible Unit, or when the unit is supported by the sea bed, in which condition the unit is described as a Submersible Unit. A Semi-Submersible Unit may be designed to operate either floating or supported by the sea bed, provided each type of operation has been found to be satisfactory and suitable.

The Class Notation COLUMN STABILIZED UNIT will be assigned for this type, compare Chapter 1, Section 2, C.2.3.

2. Scope

2.1 This Section covers those specific design criteria and features of column stabilized mobile off-shore units which are not dealt with in other Sections, as referred to in the following.


Subdivision and watertight integrity are dealt with in Section 7. Regarding stability see C.


Machinery and electrical installations shall be de-signed according to Chapters 5 and 6, respectively, as far as applicable. For ballast and bilge pumping ar-rangements see Chapter 5, Section 13e, H. and I. and Chapter 6, Section 12, J.

Propulsion installations, designed for conveyances under own power or for towage assistance, and/or for positioning, shall also be designed according to Chap-ters 5 and 6 and according to the GL Rules I – Ship Technology, Part 1 – Seagoing Ships, Chapters 2 and 3, as applicable.

2.4 Positional mooring equipment

Mooring equipment for position keeping at the work-ing location is defined in Section 8, C.

2.5 Dynamic position keeping

Dynamic position keeping at the working location means maintaining a desired position within the nor-mal excursions of the control system and under de-fined environmental conditions. The required position tolerances during drilling operations have to be de-fined by the Owner/Operator.

The complete dynamic positioning system requires the following sub-systems:

− power system

− thruster system

− control system

Thrusters used as sole means of position keeping shall provide a level of safety equivalent to that provided for mooring arrangements to the satisfaction of GL.

The Class Notations DP 1 to DP 3 will be assigned if the unit is equipped with such a system, compare Chapter 1, Section 2, C.2.7.

Further details are defined in the Chapter 5, Section 6, E.

2.6 Auxiliary installations and equipment

Special (auxiliary) installations and equipment are to be designed according to the specific Sections as far as applicable. See also Chapter 1, Section 1, D.2.


For the interaction of lifting appliances with the unit, their foundations, etc. see Chapter 4, Section 8.

Each elevator cabin in a column shall provide for an emergency exit with an escape ladder in the hoistway.


2.8 Towing and ballasting

Conditions for towing, for ballasting and deballasting procedures and for mooring operations shall be clearly indicated in the Operating Manual, compare Section 1, C.3.1.

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2.9 Drilling

Drilling derricks shall be designed according to recog-nized codes/standards and/or applicable national regu-lations. The rated capacity for each reeving shall be included in the Operating Manual.

Permanently installed piping systems for drilling op-erations are to comply with an recognised standard or code.


B. Structure

1. General

1.1 Structural design shall be based on the prin-ciples described in Chapter 4, Sections 1 to 4, see also 1.4. Particular attention should be given to structural details in critical areas such as connections of bracing members, where high local loads are acting, see also 3.7 and Chapter 4, Section 3, B. and Section 4, B. – D.

1.2 For the dimensioning of ship-like structural members such as decks, bulkheads, deck houses, gird-ers and pillars, the GL Rules I – Ship Technology, Part 1 - Seagoing Ships, Chapter 1 – Hull Structures may be used as a design basis.

1.3 Wave clearance

1.3.1 Afloat condition

Unless deck structures are designed for wave impact, to the satisfaction of GL, reasonable clearance be-tween the deck structures and the wave crests is to be ensured for afloat modes of operation, taking into account the predicted motion of the unit relative to the surface of the sea. Calculations, model test results or reports on past operating experience with similar con-figurations showing that adequate provision is made to maintain this clearance are to be submitted.

1.3.2 On-bottom condition

The unit is to be designed for a clearance of either 1,2 m, or 10 % of the combined storm tide, astronomical tide and height of the maximum wave crest above the mean low water level, whichever is less, between the underside of the hull in the elevated position and the crest of the design wave. This crest elevation is to be measured above the level of the combined astronomi-cal and storm tides. See also Chapter 4, Section 2, B.4.10.

1.4 Stress and motion analysis

1.4.1 As the design of column stabilized units is governed by both, structural and motion behaviour, calculations will have to be presented for approval covering both aspects. The investigation shall be car-ried out for a sufficient number of draughts and envi-ronmental conditions in order to determine the most severe cases of stressing and the associated motions, and vice versa.

Model tests may serve as additional basis for design.

1.4.2 For units of this type, the highest stresses may be associated with less severe environmental conditions than the maximum specified by the Owner/designer. Where considered necessary by GL, account shall be taken of the consequent increased possibility of encounter of significant stress levels, by either or both of the following:

− suitable reduction of the allowable stress levels for combined loading defined in Chapter 4, Section 3, D.

− detailed investigation of fatigue properties

Particular attention shall also be given to the details of structural design in critical areas such as bracing members, joint connection, etc.

1.5 Structural redundancy

1.5.1 When assessing structural redundancy for column stabilized units, the following assumed dam-age conditions shall apply:

1.5.1.1 The unit’s structure shall be able to withstand the loss of any slender bracing member without caus-ing overall collapse of the unit’s structure.

1.5.1.2 Structural redundancy will be based on the applicable requirements of Chapter 4, Sections 2 to 4, except:

− maximum calculated stresses in the structure re-maining after the loss of a slender bracing member are to be in accordance with Chapter 4, Section 3, D. These criteria may be exceeded for local areas, provided redistribution of forces due to yielding or buckling is taken into consideration.

− When considering environmental factors, a one year return period may be assumed for intended areas of operations, see Chapter 4, Sections 2.

1.5.2 The structural arrangement of the upper hull is to be considered with regard to the structural integ-rity of the unit after the failure of any primary girder.

2. Upper structure

2.1 The scantlings of the upper structure are not to be less than those required by the Rules mentioned above, in association with the loading indicated on the deck loading plan. In addition, when the upper struc-


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ture is considered to be an effective member of the overall structural frame of the unit, the scantlings are to be sufficient to withstand actual local loading plus any additional loading superimposed due to frame action, within the stress limitations given in Chapter 4, Section 3, D.

2.2 When an approved mode of operation or damage condition in accordance with the stability requirements allows the upper structure to become waterborne, special consideration shall be given to the resulting structural loading.

2.3 Tanks

2.3.1 Tanks for fresh water or fuel oil, or other tanks which are not intended to be kept entirely filled in service, are to have divisions or deep swashes as may be required to minimize the dynamic stress on the structure. Tight divisions and boundary bulkheads of all tanks are to be constructed in accordance with the Rules according to 1.2. The arrangement of all tanks, together with their intended service, and the height of the over-flow pipes are to be clearly indicated on the plans submitted for approval. Consideration is to be given to the specific gravity of the liquid in the tank.

2.3.2 Tanks are to be tested in accordance with the Rules and/or specifications.

2.4 Deckhouses fitted to the upper structure are to be designed in accordance with the Rules defined in 1.2, with due consideration given to their location and to the environmental conditions in which the unit will operate.

2.5 Local structures in way of fairleads, winches, etc., forming part of the positional mooring system, shall be designed to the breaking strength of the moor-ing line.

2.6 Special attention is to be paid to the founda-tions (supporting structure) and fastening of drilling derrick(s), cranes (see also Chapter 4, Section 8) and similar installations.

3. Columns, lower hulls and footings

3.1 Main stability columns and lower hull or footings may be designed as either framed or un-framed shells. In either case, framing, ring stiffeners, bulkheads or other suitable elements used are to be sufficient to maintain shape and stiffness under all the anticipated loading.

3.2 Where columns, lower hulls or footings are designed with stiffened plating, framing, girders, etc., may be determined in accordance with the require-ments for tanks. Where an internal space is a void compartment, the design head used is not to be less than that corresponding to the maximum allowable waterline of the unit in service. In general, the scant-

lings are not to be less than required for watertight bulkheads in association with a head equivalent to the maximum waterline in damaged condition; for all areas subject to wave immersion, a minimum head of 6,0 m shall be used.

3.3 Where columns, lower hulls or footings are designed as shells, either unstiffened or ring stiffened, the minimum scantlings of shell plating and ring stiff-eners are to be determined on the basis of established shell analysis using the appropriate safety factors and the design heads as given in 3.2, see also Chapter 4, Section 3, G.4.

3.4 Openings in columns, like portlights or win-dows, including those of the non-opening type, or other similar openings are not to be fitted in columns.

Regarding openings in external and internal walls, bulkheads, etc. see also Section 7, G.

3.5 Scantlings of columns, lower hulls or foot-ings as determined according to 3.2 and 3.3 are mini-mum requirements for hydrostatic pressure loads. Where wave and current forces, or bottom contact pressure in case of units resting on the sea bed are superimposed, the local structure of the shell is to be increased in scantlings as necessary, to meet the strength requirements mentioned in 1.1 above. Scant-lings in tanks are to be determined for both, full and empty conditions.

3.6 When the column, lower hull or footing is an effective member of the overall structural frame of the unit, the scantlings are to be sufficient to meet the requirements of this paragraph plus any additional stress superimposed due to frame action, within the stress limitations of Chapter 4, Section 3, D.

3.7 Particular consideration is to be given to structural details, reinforcements, etc., in areas subject to high local loading, or to such loading that may cause shell distortion, for example:

− sloshing in partially filled tanks

− bracing connection forces

− loads due to mooring operations

− wave impact

− bottom bearing loads, where applicable

3.8 Consideration shall be given to objects falling down from the platform onto the lower hull or footing. The size of objects and the potential area where ob-jects may fall down has to be determined under special consideration of crane operations. From there the following angles of fall direction may be assumed:

− in air, unit floating: 10°

− in air, unit supported on seabed: 5°

− in water: 15 °

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The endangered main structural elements of the lower hull determined in this way have to be reinforced to withstand the impact energy of fallen objects.

3.9 When a unit is designed for operations while supported by the seabed, the footings shall be de-signed to withstand the shock of bottom contact due to wave action on the hull. Such units shall also be evaluated for the effects of possible scouring action (loss of bottom support). The effect of skirt plates, where provided, shall be given special consideration.

4. Bracing members

4.1 Arrangement of braces

Where braces are essential for the structural integrity of the unit, see 1.5, they should be so arranged that they are protected as far as possible against boat im-pact (collisions) and other forces resulting from nor-mal operations.

4.2 Bracing members are to be designed to transmit loading due to environmental and inertia forces acting on the structure. When the unit is sup-ported by the sea bed, the possibility of uneven bear-ing loads shall also be considered. Although designed primarily as brace members of the overall structure under the designated loading, the bracing must also be investigated, if applicable, for superimposed local bending stresses due to buoyancy, wave and current forces.

4.3 Where relevant, consideration is to be given to local stresses due to wave impact.

4.4 When bracing members are of tubular sec-tion, ring frames may be required to maintain stiffness

and roundness of shape. The necessary buckling in-vestigation has to consider axial stresses and stresses caused by hydrostatic pressure, where applicable, see Chapter 4, Section 3, G.4.

4.5 Where braces are designed to be buoyant, they shall be designed to prevent collapse from hydro-static pressure. They shall be accessible for internal inspection, or else adequate means should be provided in order to detect leakage at an early stage.

C. Stability

1. General

The general requirements for stability are defined in Section 7. Additional aspects are given in the follow-ing.

2. Stability of units resting on the sea bed

Units designed to rest on the sea bed are to have suffi-cient downward gravity loading on the support foot-ings or lower hull to withstand the overturning mo-ment of the combined environmental forces from any direction, for each applicable design loading condi-tion.

The overturning safety factor, defined as the sum of the restoring moments divided by the sum of the over-turning moments, should not be less than:



according to Chapter 4, Section 3, C.


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Section 4

Surface Drilling Units

A. General

1. Definition

As surface drilling units are to be understood:

1.1 Ship type drilling units

Ship type drilling units are seagoing ship-shaped units having a displacement-type hull or hulls, of the single, catamaran or trimaran types, which have been de-signed or converted for drilling operations in the float-ing condition. Such types have propulsion machinery.

The Class Notation DRILLING VESSEL will be assigned for this type, compare Chapter 1, Section 2, C.2.3.

1.2 Barge type drilling units

Barge type drilling units are seagoing units having a displacement type hull or hulls, which have been de-signed or converted for drilling operations in the float-ing condition. These units have no propulsion machin-ery.

The Class Notations PONTOON EQUIPPED FOR DRILLING will be assigned for this type, compare Chapter 1, Section 2, C.2.3 and C.2.9.

1.3 Other types of surface drilling units

Units which are designed as mobile offshore drilling units and which do not fall into the categories accord-ing to 1.1 and 1.2 will be treated on an individual basis and be assigned an appropriate Classification designa-tion.

2. Scope

2.1 This Section covers those specific design criteria and features of surface drilling units which are not dealt with in other Sections, as referred to in the following.


Subdivision and watertight integrity of surface drilling units are dealt with in Section 7. Regarding stability see C.


Machinery and electrical installations shall be de-signed according to Chapter 5 and 6 respectively, as applicable.


An arrangement drawing for the mooring system has to be submitted. Mooring forces and permissible mooring directions are to be defined.

In the drawings for the hull structure the foundations for the mooring winches and the fairleads have to be shown. As maximum mooring forces the breaking strength of the mooring cables defined in the mooring arrangement has to be assumed.

Mooring equipment for position keeping at the work-ing location is defined in Section 8, C.

2.5 Dynamic position keeping

Dynamic position keeping at the drilling location means maintaining a desired position within the nor-mal excursions of the control system and under de-fined environmental conditions. The required position tolerances during drilling operations have to be de-fined by the Owner/Operator.

The complete dynamic positioning system requires the following sub-systems:

− power system

− thruster system

− control system


The Class Notations DP 1 to DP 3 will be assigned if the unit is equipped with such a system, compare Chapter 1, Section 2, C.2.7.

Further details are defined in the GL Rules I – Ship Technology, Part 1 – Seagoing Ships, Chapter 15 – Dynamic Positioning Systems.


Drawings showing the location and support of founda-tions for cranes and davits have to be submitted. The forces to the hull structure have to be defined.

For the interaction of lifting appliances with the unit, their foundations, etc. see Chapter 4, Section 8.


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2.7 Towing

If the unit is towed by tugs, a general arrangement drawing of the towing system has to be submitted. Towing forces and permissible towing directions are to be defined.

In the drawings of the hull structure the measures to transfer the towing forces into the hull have to be shown. As maximum towing forces the breaking strength of the towing ropes or cables defined in the towing arrangement has to be assumed.

Conditions for towing shall be clearly indicated in the Operating Manual, compare Section 1, C.3.1.

B. Structure

1. General

Scantlings of the hull structure are to meet the GL Rules I – Ship Technology, Part 1 – Seagoing Ships, Chapter 1 – Hull Structures. For barge types according to A.1.2 especially Section 31 – Barges and Pontoons has to be observed.

Special consideration however is to be given to items which may require some deviation or additions to these Rules, in particular the items indicated in 2. - 5.

2. Drilling well

2.1 The required strength of the unit shall be maintained in way of the drilling well and particular attention shall be given to the transition between fore-and-aft members so as to maintain continuity of the longitudinal material. Stress concentrations have to avoided by a favourable structural detailed design. In addition, the plating of the well is to be suitably stiff-ened to prevent damage due to foreign objects which may become trapped in the well when the unit is in transit.

2.2 The drilling well is to be surrounded by cof-ferdams. Such cofferdams may temporarily be used also as tanks for liquids related to drilling operations, if they can be easily emptied for inspection.

3. Deck area

3.1 The deck area in way of large hatches is to be suitably compensated where necessary to maintain the strength of the unit.

3.2 The structure in way of heavy concentrated loads resulting from the drilling derrick, pipe rack, set back, drilling mud storage, etc., is to be suitably rein-forced.

3.3 The local structure in way of elements of the position mooring system and of the towing system, if applicable, has to be reinforced accordingly, compare A.2.4 and A.2.7.

C. Stability

Stability according to the requirements defined in Section 7 has to be investigated for the three occurring modes of operation:

− drilling operation under defined environmental conditions

− severe storm conditions

− transit conditions between different drilling loca-tions

D. Drilling Facilities

1. Scope


2. Drawings to be submitted

The planned interaction of the drilling systems with hull has to be clearly documented, e.g. by:

− drawings showing the arrangement of the drilling derrick including weights and moments

− drawings showing the pipe storage and handling

− drawings showing mud tanks, cement silos, etc.

3. Operating manual

The rated capacity for each reeving shall be included in the Operating Manual.

4. Drilling equipment

4.1 Drilling derricks shall be designed according to recognized codes/standards and/or applicable Na-tional Regulations.

Permanently installed piping systems for drilling op-erations are to comply with a recognised standard or code.

4.2 Requirements for drilling systems are con-tained in Chapter 5, Section 11.


Section 4 Surface Drilling Units IV - Part 6GL 2007

D

E. Safety Aspects

1. Hazardous areas

The general classification in hazardous and non-hazardous areas is contained in Chapter 5, Section 2, whereas the area classification requirements to be observed for drilling are defined in Chapter 5, Section 11, B.2.

The requirements for explosion protection of electrical equipment in hazardous areas are defined in Chapter 6, Section 13.

2. Fire protection

The requirements for structural fire protection and means of escape are defined in Chapter 5, Section 10, B.

3. Fire detection and extinguishing

The requirements for fire detection and alarm systems are defined in Chapter 5, Section 10, J. The require-ments for fire extinguishing systems and equipment are summarized in Chapter 5, Section 10, C. – I.

4. Life-saving appliances

The number, size and arrangement of life-saving ap-pliances for the complete crew shall follow the re-quirements defined in Section 9 of this Chapter.

IV - Part 6 GL 2007

Section 4 Surface Drilling Units Chapter 2Page 4–3

E

Section 5

Pipelaying Units

A. General

1. Definition

As pipelaying vessels are to be understood:

1.1 Pipelaying vessels

Pipelaying vessels are seagoing ship-shaped units having a displacement-type hull or hulls, of the single or catamaran types, which have been designed or converted for pipe laying. Such types have propulsion machinery and a dynamic positioning system or posi-tional mooring equipment.

The Class Notation PIPE-LAYING VESSEL will be assigned for this type, compare Chapter 1, Section 2, C.2.3.

1.2 Pipelaying barges

Pipelaying barges are seagoing units having a dis-placement type hull or a semi-submersible configura-tion, which have been designed or converted for pipe laying. These units have no propulsion machinery, but may have positional mooring equipment, adequate tug assistance or dynamic positioning.

The Class Notations PONTOON EQUIPPED FOR PIPELAYING will be assigned for this type, com-pare Chapter 1, Section 2, C.2.3 and C.2.9.

2. Scope

2.1 This Section covers those specific design criteria and features of pipelaying units which are not dealt with in other Sections, as referred to in the fol-lowing.


Machinery and electrical installations shall be de-signed according to Chapter 5 and 6 respectively, as applicable.


2.3.1 Drawings showing the location and support of foundations for cranes and davits have to be sub-mitted. The forces to the hull structure have to be defined.

Rules for the interaction of lifting appliances with the unit, their foundations, etc. are defined in Chapter 4, Section 8.

2.3.2 If the lifting appliances shall be included into the Certification or Classification by GL, the require-ments for offshore cranes and other lifting appliances are defined in the GL Rules VI – Additional Rules and Guidelines, Part 2 – Life Saving Appliances, Lifting Appliances, Accesses, Chapter 2 – Guidelines for the Construction and Survey of Lifting Appliances.

3. Safety aspects

3.1 Hazardous areas

The general classification in hazardous and non-hazardous areas is contained in Chapter 5, Section 2.

The requirements for explosion protection of electrical equipment in hazardous areas are defined in Chapter 6, Section 13.

3.2 Fire protection

The requirements for structural fire protection and means of escape are defined in Chapter 5, Section 10, B.

3.3 Fire detection and extinguishing

The requirements for fire detection and alarm systems are defined in Chapter 5, Section 10, J. The require-ments for fire extinguishing systems and equipment are summarized in Chapter 5, Section 10, C. – I.

3.4 Life-saving appliances

The number, size and arrangement of life-saving ap-pliances for the complete crew shall follow the re-quirements defined in Section 9 of this Chapter.

B. Movement and Position Keeping

1. Possibilities

For the movement and position keeping of the unit during pipelaying the following possibilities may be established:

− positional mooring with cables and anchors

− dynamic positioning by a greater number of thrusters on the unit

− combination of mooring and dynamic positioning

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Section 5 Pipelaying Units Chapter 2Page 5–1

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2. Dynamic analysis of the pipelaying system

A dynamic analysis has to be submitted to GL, which has to consider:

− arrangement of positional mooring system consid-ering elasticity of cables, if applicable

− function of dynamic positioning system, if appli-cable

− influence of the laid pipe and forces at the tension-ers

− influence of seastate, wind and current conditions, see Chapter 4, Section 1

3. Positional mooring equipment

3.1 If the Class Notation “EQUIPPED WITH POSITION MOORING SYSTEM” will be as-signed, such a system consisting of:

− heavy anchors belonging to the unit and regularly changed in position by anchor handling tugs

− safe stowage of the anchors on the unit and appli-ances to hand them over to the tugs

− anchor cables as wire ropes or chain cables from the anchors to fairleads and winches on the unit including accessories like shackles, quick release devices, wire rope terminations, etc.

− a winch or windlass for each anchor cable includ-ing tension control and measuring of cable length paid out

− central control of all winches to keep position and allow forward movement of the unit on the planned track

has to be provided, see also Chapter 1, Section 2, C.2.9.

3.2 An arrangement drawing for the mooring system has to be submitted. Mooring forces and per-missible mooring directions are to be defined. An example for a mooring system with 10 anchors is shown in Fig. 5.1 and Fig. 5.2 for the two phases of starting of the operation and after a travel of abt. 600 m.

3.3 In the drawings for the hull structure the foundations for the mooring winches and the fairleads have to be shown. The acting forces on the founda-tions are to be calculated for 100 % of the nominal breaking load of the mooring cables. For the support-ing structure under this equipment 100 % of the mini-mum yield stress ReH is to be observed as acceptance criterion in the calculation.

3.4 The mooring equipment for position keeping on the pipeline track is defined in Section 8, C.

4. Dynamic position keeping

4.1 Dynamic position keeping at the pipelaying route means maintaining a desired position within the normal allowance of the control system and under defined environmental conditions. The required posi-tion tolerances during pipelaying operations have to be defined by the Owner/Operator.


4.2 The complete dynamic positioning system requires the following sub-systems:

− power system

− thruster system

− control system

4.3 The Class Notations DP 1 to DP 3 will be assigned if the systems complies with the require-ments of the GL Rules I – Ship Technology, Part 1 – Seagoing Ships, Chapter 15 – Dynamic Positioning Systems, see also Chapter 1, Section 2, C.2.7.

5. Combination of positional mooring sys-tems with dynamic positioning

5.1 Also a combination of the positional mooring system according to 3. with a dynamic positioning system according to 4. may be established, if it is of advantage for a special task.

5.2 It must be secured that all elements of the combined system are operated from one control sta-tion overlooking the unit and the mooring area.

5.3 The detailed requirements for such a combi-nation will be defined case by case.

6. Towing

6.1 If the unit is towed by tugs, a general ar-rangement drawing of the towing system has to be submitted. Towing forces and permissible towing directions are to be defined.

6.2 Towing arrangements and procedures shall be such as to reduce to a minimum any danger to person-nel during towing operations. The design and ar-rangement of towing fittings shall have regard to both normal and emergency conditions.

6.3 In the drawings of the hull structure the measures to transfer the towing forces into the hull have to be shown. As towing forces 100 % of the nominal breaking load of the towing lines have to be considered. For the supporting structure under this equipment 100 % of the minimum yield stress ReH is to observed as acceptance criterion in the calculation.


Section 5 Pipelaying Units IV - Part 6GL 2007

B

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IV - Part 6 GL 2007


B

7. Operating manual

For the positioning and towing systems the following aspects have to be included in the Operating Manual, compare Section 1, C.3.1:

− principal functioning and co-operation of the dif-ferent elements of the system

− procedure for the start of pipelaying

− procedure for normal pipelaying operation with advancing unit

− stopping or finishing the pipelaying operation with disconnecting and abandoning of the pipeline

− towing conditions

− procedures in the event of failure of the systems

− emergency measures

8. Sea trials

8.1 A schedule for the proposed tests of the posi-tioning and towing systems has to be submitted for approval to GL Head Office in due time before the sea trials.

8.2 All procedures defined in the Operating Manual have to be tested as far as practicable in this stadium.

8.3 The trials have to be executed in presence of a GL Surveyor who will sign a detailed trials protocol to be prepared by the builder, if the tests are success-ful. The duplicate of this protocol has to be sent to GL Head Office for final approval.

C. Structure

1. General design

Scantlings of the hull structure are to meet the GL Rules I – Ship Technology, Part 1 – Seagoing Ships, Chapter 1 – Hull Structures. For barge types according to A.1.2 especially Section 31 – Barges and Pontoons has to be observed.

Special consideration however is to be given to items which may require some deviation or additions to these Rules, in particular the items defined in the fol-lowing.

2. Loads

The loads established in the dynamic analysis of the pipelaying system according to B.2. have to be con-sidered.

3. Special aspects for the hull structure

The following requirements, which are characteristic for pipelaying, have to be considered for the design of the hull structure, e.g.:

− slot in the rear part of the main deck to lead the pipe with the necessary bending radius to the stinger

− transmission of the forces from the stinger to the stern of the unit and of the forces from the A-frame for holding the stinger back and adjusting the inclination of it to the main deck

− transmission of the pipeline forces pulling the (two) tensioners horizontally to the stern into the midship section of the hull

− considerable mooring forces from different direc-tions at stern and bow

− various loads from the pipelaying facility as de-scribed in E.

D. Watertight Integrity and Stability

1. Watertight integrity

For subdivision into watertight compartments see Section 7, E.

2. Stability

2.1 Load cases

The following load cases have to be considered:

2.1.1 Standard load cases

− normal pipelaying operation up to defined envi-ronmental limit conditions

− severe storm and seaway conditions with pipe disconnected and abandoned at the seabed

2.1.2 Special load cases

− ocean towage for long distances without or with stinger, if applicable

− field towage for short distances with stinger

− inspection or repair of existing pipelines by lifting up a part of the pipeline from the seabed to the units side

− influences from crane operation and positional mooring have to be considered

2.1.3 Other load cases

Depending on the type of pipelaying unit and the method of operation other load cases may be consid-ered case by case.


Section 5 Pipelaying Units IV - Part 6GL 2007

D

2.2 Stability criteria

2.2.1 Intact stability

Concerning stability criteria the Code of Intact Stabil-ity for All Types of Ships Covered by IMO Instru-ments Resolution A.749(18) as amended by resolution MSC 75(69) shall be applied 1.

Special considerations shall be given to an unusual arrangement of units, which also may lead to addi-tional stability criteria.

2.2.2 Damage stability

The criteria of the Code of Safety for Special Purpose Ships acc. to IMO Res.A.543(13) and of the Code for the Construction and Equipment of Mobile Offshore Drilling Units (MODU Code) shall be used as far as applicable.

E. Pipelaying Facility

1. Scope

In general the facility directly used for pipe storage, fabrication of the pipe connections, pipe fixing and delivering/recovering to/from the sea bed are not sub-ject to Classification or Certification by GL. But the characteristics of the facilities, which influence:

− overall design of the unit

− overall safety of the unit

− weights and forces on all foundations

− floating and stability behaviour, etc.

will be considered by GL. Therefore GL has to be fully informed by the documents defined in 2.

2. Documents to be submitted

A complete set of documentation to define the influ-ences on the unit has to be submitted by the builder/Operator of the facility, consisting of e.g.:

–––––––––––––– 1 In addition the criteria of the Code of Safety for Special Pur-

pose Ships acc. to IMO Res.A.543(13) and of the Code for the Construction and Equipment of Mobile Offshore Drilling Units (MODU Code) shall be used as far as applicable.

− general arrangement of the pipelaying facility and description of the main functions, definition of the environmental conditions up to which the facility is able to operate

− facilities for lifting the pipes from the supply ves-sels to the storage area and pipe transport on the unit defining all created moments and forces

− plans showing the arrangement of the pipe stor-age/racks, the maximum weights and the intended foundations on the upper deck

− plans defining the foundation forces of the facility for pipe connections

− plans showing the arrangement of the pipe ten-sioners and the maximum tension forces

− plans showing the support arrangement on the pipe ramp and the maximum forces to be experienced

− plans showing the integration of the stinger at the stern of the hull and definition of the forces to be transferred into the hull, if applicable

− plans showing the stinger including length varia-tion , if applicable and its floating support, if ap-plicable

− plans showing the A-frame for variation of the stinger inclination, if applicable

− GL reserve the right to ask for any other documen-tation necessary to define the interaction of the fa-cility with the unit

3. Operating Manual

The Operating Manual of the unit, compare Section 1, C.3.1, shall include all safety aspects created by the facility and has also to be submitted to GL. This man-ual shall include e.g.:

− functions of the pipelaying facility including repair of existing pipelines, if applicable

− influence of pipelaying on unit operation

− special hazards to the unit

− emergency measures if a failure happens in the pipelaying facility, etc.

IV - Part 6 GL 2007


E

Section 6

Well Stimulation Units

A. General

1. Definition

Well stimulation vessels or units are self-propelled ship-type vessels equipped for intervention at subsea wells with the aim to improve the operational well performance.

The Class Notations WELL STIMULATION VESSEL or WELL STIMULATION UNIT will be assigned for this type, compare Chapter 1, Section 2, C.2.3.

2. Stimulation service

The service of well stimulation vessels/units may be distinguished in:

− stimulation of subsea wells using various operat-ing procedures

− stimulation of subsea wells including handling and storage of well fluids

3. Scope

In this Section the overall and special aspects for this type of vessel/unit are summarized and references are given to the different Chapters and Sections of the Rules where the detailed requirements are defined.

B. Special Safety Aspects

1. Area classification

For all types of vessels/units hazardous and non-hazardous areas have to be investigated and a com-plete area classification has to be performed, as far as needed. For the relevant criteria of such a classifica-tion see Chapter 5 – Machinery Installations, Section 2.

2. Fire protection

Special attention shall be given to fire protection and measures for fire fighting. Relevant methods are summarized in Chapter 5 – Machinery Installations, Section 10.

3. Emergency shut down

For all vessels/units an emergency shut down and quick well disengagement concept has to be developed distinguishing different shutdown levels according to the used procedures of well stimulation. The require-ments for relevant safety systems are defined in Chapter 5 – Machinery Installations, Section 17.

4. Evacuation

If the stimulation procedures fail and the crew will be in extreme danger the equipment for a quick and smooth evacuation shall be available. The require-ments for such equipment are defined in Section 9.

5. Documentation

All safety aspects have to be clearly defined in written form, such as a Safety Management Plan, and shall be included in the Operating Manual of the vessel/unit, compare Section 1, C.3.1.

C. Position Keeping

1. As the well stimulation vessel/unit has to stay near or above the well within a very restricted location allowance, the position keeping will be a major pre-requisite.

2. Position keeping may be established by the following methods:

− positional mooring with anchors, cables and moor-ing winches according to Section 8 and Chapter 5 – Machinery Installations, Section 8, C.

− dynamic positioning with propulsion systems according to Chapter 5 – Machinery Installations, Section 6, E. For this type of vessel/unit the re-quirements for Class Notation DP 2 are recom-mended.

D. Well Stimulation Equipment

1. The foundations for such equipment have to be integrated into the structure of the vessel/unit con-sidering extreme loads likely to occur during the stimulation process.

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Section 6 Well Stimulation Units Chapter 2Page 6–1

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2. Well stimulation equipment is in general not subject to Classification by GL. Nevertheless this equipment shall be designed and built according to recognized regulations and safety standards.

3. Especially equipment to be installed in haz-ardous areas shall meet the necessary safety standards. For electrical installations reference may given to Chapter 6 – Electrical Installations, Section 13.


Section 6 Well Stimulation Units IV - Part 6GL 2007

D

Section 7

Subdivision, Stability and Load Line

A. General Remarks, Scope

1. This Section refers to the subdivision, stabil-ity and load line requirements for mobile offshore units and covers, essentially, the relevant regulations of the IMO "Code for the Construction and Equipment of Mobile Offshore Drilling Units (MODU Code)", as amended.

2. Any additional National Regulations should be observed, where applicable.

3. Regarding the effects of (maximum) angles of inclination on machinery installations see Chapter 5, Section 1, C. and Chapter 6, Section 1, E.

B. Righting and Heeling Lever Curves

1. Curves of righting levers and of wind heeling levers similar to Figure 7.1 with supporting calcula-tions shall be prepared covering the full range of oper-ating draughts including those in transit conditions, taking into account the maximum deck cargo and equipment in the most unfavourable position applica-ble. The righting lever curves and wind heeling lever curves shall be related to the most critical axes. Ac-count shall be taken of the free surface of liquids in tanks.

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2. Where equipment is of such a nature that it can be lowered and stowed, additional wind heeling lever curves may be required; such data shall clearly indicate the position of such equipment.

3. The curves of wind heeling levers shall be drawn for wind forces calculated by the following formula:

[ ]2S HF 0,5 C C v A N= ⋅ ⋅ ⋅ ρ ⋅ ⋅

F = wind force [N]

CS = shape coefficient depending on the shape of the structural member exposed to the wind, see Table 7.1 [–]

CH = height coefficient depending on the height above sea level of the structural member exposed to wind, see Table 7.2 [–]

ρ = air mass density (1,25) [Ns²/m4]

v = wind velocity [m/s]

A = projected area of all exposed surfaces in either the upright or the heeled condition [m²].

4. Wind forces shall be considered from any direction relative to the limit and the value of the wind velocity shall be as follows:

4.1 In general a minimum wind velocity of 36 m/s (70 knots) for offshore service shall be used for normal operating conditions and a minimum wind velocity of 51,5 m/s (100 knots) shall be used for the severe storm conditions. Loading conditions 2 and 3, respectively see Chapter 4, Section 3, C.

Table 7.1 Values of the coefficient CS

Shape CS

Spherical 0,4

Cylindrical 0,5

Large flat surface (hull, deckhouse, smooth under deck areas) 1,0

Drilling derrick 1,25

Wires 1,2

Exposed beams and girders under deck 1,3

Small parts 1,4

Isolated shapes (cranes, beams, etc.) 1,5

Clustered deckhouses or similar structures 1,1

IV - Part 6 GL 2007

Section 7 Subdivision, Stability and Load Line Chapter 2Page 7–1

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Table 7.2 Values of coefficient CH

Height above sea level [m] CH 1

0 – 15,3 1,00

15,3 – 30,5 1,10

30,5 – 46,0 1,20

46,0 – 61,0 1,30

61,0 – 76,0 1,37

76,0 – 91,5 1,43

91,5 – 106,5 1,48

106,5 – 122,0 1,52

122,0 – 137,0 1,56

137,0 – 152,5 1,60

152,5 – 167,5 1,63

167,5 – 183,0 1,67

183,0 – 198,0 1,70

198,0 – 213,5 1,72

213,5 – 228,5 1,75

228,5 – 244,0 1,77

244,0 – 256,0 1,79

Above 256 1,80 1 The higher value of CH has to be used.

4.2 Where a unit is to be limited in operation to sheltered locations (protected inland waters such as lakes, bays, swamps, rivers, etc.) consideration may be given to a reduced wind velocity of not less than 25,8 m/s (50 knots) for normal operating conditions.

4.3 In calculating the projected areas to the verti-cal plane the area of surfaces exposed to wind due to heel or trim, such as deck undersides, etc., shall be included using the appropriate shape factor. Open truss work may be approximated by taking 30 % of the projected block area of both the front and back section, i.e. 60 % of the projected area of one side.

5. In calculating the wind heeling moments the lever of the wind overturning force shall be taken vertically from the centre of pressure of all surfaces exposed to the wind to the centre of lateral resistance of the underwater body of the unit. The unit shall be assumed floating free of mooring restraint.

6. The wind heeling levers shall be calculated for a sufficient number of heel angles to define the curve. For ship shaped hulls the curve may be as-sumed to vary as the cosine function of unit heel.

7. Wind heeling moments derived from wind tunnel tests on a representative model of the unit may be considered as alternatives to the method given in 3. to 5. Such heeling moment determination shall include lift and drag effects at various applicable heel angles.

C. Intact Stability Criteria

1. Standard criteria

1.1 The stability of a unit in each mode of opera-tion shall meet the following criteria, see also Fig. 7.1.

1.2 For surface (ship-like) and self-elevating units the area under the righting lever curve to the second intercept or downflooding angle, whichever is less, shall be not less than 40 % in excess of the area under the wind heeling lever curve to the same limit-ing angle.

1.3 For column stabilized units the area under the righting lever curve to the angle of downflooding shall be not less than 30 % in excess of the area under the wind heeling lever curve to the same limiting angle.

1.4 The righting lever curve shall be positive over the entire range of angles from upright to the second intercept.

2. Severe storm condition

Each unit shall be capable of sustaining a severe storm condition in a period of time consistent with meteoro-logical conditions. The procedures recommended and the approximate length of time required, considering both operating conditions and transit conditions, shall be contained in the Operating Manual. It shall be pos-sible to achieve the severe storm condition without the removal or relocating of solid consumables or other variable loads. However, on application and with agreement of GL, loading a unit past the point at which solid consumables would have to be removed or relocated to go to severe storm condition may be permitted under the following conditions, provided the allowable KG requirement is not exceeded:

− in a geographic location where weather conditions annually or seasonally do not become sufficiently severe to require a unit to go to severe storm con-dition, or

− where a unit is required to support extra deck-load for a short period of time that is well within the bounds of a favourable weather forecast

− geographic locations, weather conditions and load-ing conditions when this is permitted shall be iden-tified in the Operating Manual.


Section 7 Subdivision, Stability and Load Line IV - Part 6GL 2007

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3. Alternative stability criteria

Alternative stability criteria may be accepted provided an equivalent level of safety is maintained, and if they are demonstrated to afford adequate positive initial stability. The acceptability of such criteria will be determined considering at least the following and taking into account, as appropriate:

− Environmental conditions representing realistic winds (including gusts) and waves appropriate for world wide service in various modes of operation.

− Investigate dynamic response of the unit. The analysis shall include the results of wind tunnel tests, wave tank model tests, and non-linear simu-lation, where appropriate. Any wind and wave spectra used shall cover sufficient frequency ranges to ensure that critical motion responses are identified.

− Potential for flooding taking into account dynamic responses in a seaway.

− Susceptibility to capsizing considering the unit’s restoration energy and the static inclination due to the mean wind speed and the maximum dynamic response.

− An adequate safety margin to account for uncer-tainties.

D. Inclining Test

1. An inclining test shall be carried out with the first unit of a design, when as near to completion as possible, to determine accurately the light ship data (weight and position of centre of gravity).

2. For successive units which are identical by design, the light ship data of the first unit of the series may be accepted in lieu of an inclining test, provided the difference in light ship displacement or position of centre of gravity due to weight changes and minor differences in machinery, outfitting or equipment, confirmed by the results of a deadweight survey, are less than 1 % of the values of the light ship displace-ment and principal horizontal dimensions as deter-mined for the first of the series.

Particular care shall be given to the detailed weight calculation and comparison with the original unit of a series of column stabilized semi-submersibles as these, even though identical by design, are recognized as being unlikely to attain an acceptable similarity of weight or centre of gravity to warrant a waiver of the inclining test.

3. The results of the inclining test, or dead-weight survey and inclining experiment adjusted for weight differences, shall be indicated in the Operating Manual.

4. A record of all changes to machinery, struc-ture, outfit and equipment that affect the light ship data, shall be maintained in the Operating Manual, or a light ship data alterations log, and be taken into account in daily operations.

5. For column stabilized units, a deadweight survey shall be conducted at intervals not exceeding five years. Where the deadweight survey indicates a change from the calculated light ship displacement in excess of 1 % of the operating displacement, an inclin-ing test shall be conducted.

6. The inclining test or deadweight survey shall be carried out in the presence of a GL Surveyor.

E. Subdivision and Damage Stability

1. Surface and self-elevating units

1.1 The unit shall have sufficient freeboard and be subdivided by means of watertight decks and bulk-heads to provide sufficient buoyancy and stability to withstand in general the flooding of any one com-partment in any operating or transit condition consis-tent with the damage assumptions set out in F.

1.2 The unit shall have sufficient reserve stability in a damaged condition to withstand the wind heeling moment based on a wind velocity of 25,8 m/s (50 knots) imposed from any direction. In this condition the final waterline, after flooding, shall be below the lower edge of any downflooding opening.

2. Column stabilized units

2.1 The unit shall have sufficient freeboard and be subdivided by means of watertight decks and bulk-heads to provide sufficient buoyancy and stability to withstand a wind heeling moment induced by a wind of velocity of 25,8 m/s (50 knots) imposed from any direction in any operating or transit condition, consid-ering:

− The angle of inclination after the damage set out in F.3. shall not be greater than 17°.

− Any opening below the final waterline shall be made watertight, and openings within 4 m above the final waterline shall be made weathertight.

− The righting lever curve after damage as set out above shall have, from the first intercept to the lesser of the extent of weathertight integrity re-quired above and the second intercept, a range of at least 7°. Within this range the righting lever curve shall reach a value of at least twice the wind heeling lever curve, both being measured at the same angle, see Fig. 7.2.

IV - Part 6 GL 2007


E

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Fig. 7.2 Righting and heeling lever curves for damage stability

2.2 The unit shall provide sufficient buoyancy and stability to withstand, in any operating or transit condition, the flooding of any watertight compartment wholly or partially below the waterline in question, which is a pump room, a room containing machinery with a salt water cooling system or a compartment adjacent to the sea, considering:

− The angle of inclination after flooding shall not be greater than 25°.

− Any opening below the final waterline shall be made watertight.

− A range of positive stability shall be proven, be-yond the calculated angle of inclination in this condition, of at least 7°.

3. All types of units

3.1 The requirements of 1.1 and 1.2 shall be determined by calculations which take into considera-tion the proportions and design characteristics of the unit and the arrangements and configuration of the damaged compartments. In making these calculations, it shall be assumed that the unit is in the worst antici-pated service condition as regards stability and is floating free of mooring restraints.

3.2 The ability to reduce heeling angles by pump-ing out or ballasting compartments, or by application of mooring forces etc., shall not be considered as alle-viating the requirements.

F. Extent of Damage

1. Surface units

1.1 In assessing the damage stability of surface units, the following extent of damage shall be assumed between effective watertight bulkheads:

− horizontal penetration: 1,5 m

− vertical extent: from the base line upwards without limit

1.2 The distance between effective watertight bulkheads or their nearest stepped portions, which are positioned within the assumed extent of horizontal penetration, shall be not less than 3 m. Where there is a lesser distance one or more of the adjacent bulk-heads shall be disregarded.

1.3 Where damage of a lesser extent than given in 1.1 results in a more severe condition, such lesser extent shall be assumed.

1.4 All piping, ventilation systems, trunks, etc., within the extent of damage referred to in 1.1 shall be assumed to be damaged. Positive means of closure shall be provided at watertight boundaries to preclude the progressive flooding of other spaces which are intended to be intact.

2. Self-elevating units

2.1 In assessing the damage stability of self-elevating units, the following extent of damage shall be assumed between effective watertight bulkheads:

− horizontal penetration: 1,5 m

− vertical extent: from the base line upwards without limit

Where a bottom mat is fitted, assumed damage pene-tration simultaneous to both the mat and the upper hull need only be considered when the lightest draught allows any part of the mat to fall within 1,5 m verti-cally of the waterline, and the difference in horizontal dimension of the upper hull and mat is less than 1,5 m in any area under consideration. If damage of a lesser extent results in a more severe final equilibrium condi-tion, such lesser extent shall be assumed.

2.2 The distance between effective watertight bulkheads or their nearest stepped portions, which are positioned within the assumed extent of horizontal penetration, shall be not less than 3 m. Where there is a lesser distance one or more of the adjacent bulk-heads shall be disregarded.

2.3 Where damage of a lesser extent than given in 2.1 results in a more severe condition, such lesser extent shall be assumed.

2.4 All piping, ventilation, systems, trunks, etc. within the extent of damage referred to in 2.1 shall be assumed to be damaged.

2.5 Positive means of closure shall be provided at watertight boundaries to preclude the progressive flooding of other spaces which are intended to be intact. In addition, the compartments adjacent to the bottom shell are also to be considered flooded indi-vidually.



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2.6 The recessed ends and sides of the drilling slot need not be subject to horizontal penetration if warning signs be posted on each side of the vessel stating that no boats be allowed inside the drilling slot. Instructions to this effect should be included in the Operating Manual.


3.1 In assessing the damage stability of column stabilized units, the following extent of damage shall be assumed.

3.2 Only those columns, underwater hulls and braces on the periphery of the unit shall be assumed to be damaged, and the damage shall be assumed in the exposed portions of the columns, underwater hulls and braces.

3.3 Columns and braces shall be assumed to be flooded by damage having a vertical extent of 3 m occurring at any level between 5 m above and 3 m below the draughts specified in the Operating Manual. Where a watertight flat is located within this region, the damage should be assumed to have occurred in both compartments above and below the watertight flat in question. Lesser distances above or below the draughts may be applied to the satisfaction of GL, taking into account the actual operating conditions. However, the extent of required damage region should be at least 1,5 m above and below the draughts speci-fied in the Operating Manual.

3.4 No vertical bulkhead shall be assumed to be damaged, except where bulkheads are spaced closer than a distance of one eighth of the column’s perime-ter at the draught under consideration, measured at the periphery, in which case one or more of the bulkheads shall be disregarded.

3.5 Horizontal penetration of damage shall be assumed to be 1,5 m.

3.6 Underwater hulls or footings shall be as-sumed to be damaged while the unit is operating in a transit condition, in the same manner as indicated in 3.2, 3.3, 3.5 and having regard to their shape, either 3.4 or between effective watertight bulkheads.

3.7 If damage of a lesser extent results in a more severe damage equilibrium condition, such a lesser extent shall be assumed.

3.8 All piping, ventilation systems, trunks, etc., within the extent of damage shall be assumed to be damaged.

3.9 Positive means of closure shall be provided at watertight boundaries to preclude the progressive flooding of other spaces which are intended to be intact.

G. Watertight Integrity

1. Openings and penetrations

The number of openings in watertight subdivisions shall be kept to a minimum compatible with the design and proper working of the unit. Where penetrations of watertight decks and bulkheads are necessary for ac-cess, piping, ventilation, electrical cables, etc., ar-rangements shall be made to maintain the watertight integrity of the enclosed compartments.

2. Valves

2.1 Where valves are provided at watertight boundaries to maintain watertight integrity, these valves shall be capable of being operated from a pump-room or other normally manned space, a weather deck, or a deck which is above the final wa-terline after flooding. In the case of a column stabi-lized unit this will be the central ballast control sta-tion. Valve position indicators shall be provided at the remote control station.

2.2 For self-elevating units the ventilation system valves required to maintain watertight integrity shall be kept closed when the unit is afloat. Necessary ven-tilation in this case shall be arranged by alternative approved methods.

3. Internal openings

3.1 The means to ensure the watertight integrity of internal openings shall comply with the following requirements:

− Doors and hatch covers which are used during the operation of the unit while afloat shall be remotely controlled from the central ballast control station and shall also be operable locally from each side. Open/shut indicators shall be provided at the con-trol station.

− Doors or hatch covers which are normally closed while the unit is afloat are to be provided with an alarm system (e.g. light signals) showing person-nel both locally and at the central ballast control station whether the doors or hatch covers in ques-tion are open or closed. A notice shall be affixed to each such door or hatch cover to the effect that it is not to be left open while the unit is afloat.

3.2 The means to ensure the watertight integrity internal openings which are kept permanently closed during the operation of the unit, while afloat, shall comply with the following requirements:

− A notice shall be affixed to each such closing appliance to the effect that it is to be kept closed while the unit is afloat, except that manholes fitted with close bolted covers need not be so marked.

− On self-elevating units, an entry shall be made in the official log book or tour report, as applicable,

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to the effect that all such openings have been wit-nessed closed before the unit becomes waterborne.

4. External openings

4.1 All downflooding openings, the lower edge of which are submerged when the unit is inclined to the first intercept between the righting lever and wind heeling lever curves in any intact or damaged condi-tion, shall be fitted with a suitable watertight closing appliance, such as closely spaced bolted covers.

4.2 Where flooding of chain lockers or other buoyant volumes may occur, the openings to these spaces shall be considered as downflooding points for calculating intact stability.

H. Load Line

1. General requirements

1.1 The requirements of the 1966 Load Line Convention, as amended shall in principle apply to all units. The minimum freeboard of units which cannot be computed by the normal methods laid down by that Convention shall be determined on the basis of meet-ing the applicable intact stability, damage stability and structural requirements for transit conditions and drill-ing operations while afloat. The freeboard shall not be less than that computed from the Convention where applicable.

1.2 The requirements of the 1966 Load Line Convention with respect to weather tightness and water tightness of decks, superstructures, deckhouses, doors, hatchway covers, other openings, ventilators, air pipes, scuppers, inlets and discharges, etc., shall be taken as a basis for all units in the afloat condition.

1.3 In general, heights of hatch and ventilator coamings , air pipes, door sills, etc., in exposed posi-tions and their means of closing shall be determined by consideration of both intact and damage stability requirements.

1.4 All downflooding openings which may be-come submerged, before the angle of inclination at which the required area under the intact righting arm curve is achieved, shall be fitted with weathertight closing appliances.

1.5 With regard to damage stability, the require-ments in E.2.1 (2nd item), E.2.2 and G.4.1 shall apply.

1.6 Special consideration shall be given to the position of openings which cannot be closed in emer-gencies, such as air intakes for emergency generators, having regard to the intact righting arm curves and the final waterline after assumed damage.

1.7 Special consideration shall be given to small hatches with an opening area of 2,5 m² or less at the exposed deck over the forward 0,25 L on seagoing units of length 80 m or more, that are contracted on or after 1st January 2004, where the height of the exposed deck in way of the hatch is less than 0,1 L or 22 m above the summer load waterline, whichever is the lesser. For design details see GL Rules I – Ship Tech-nology, 1 – Seagoing Ships, Chapter 1 – Hull Struc-tures, Section 17, D.2.

1.8 Special consideration shall be given to air pipes, ventilator pipes and their closing devices at the exposed deck over the forward 0,25 L on seagoing units of length 80 m or more, that are contracted on or after 1st January 2004, where the height of the exposed deck in way of the pipes is less than 0,1 L or 22 m above the summer load waterline, whichever is the lesser. For design details see GL Rules I – Ship Tech-nology, 1 – Seagoing Ships, Chapter 1 – Hull Struc-tures, Section 21, E.5.

2. Surface units

2.1 Load lines shall be assigned to surface units as calculated under the terms of the 1966 Load Line Convention and shall be subject to all the conditions of assignment of that Convention.

2.2 Where it is necessary to assign a greater than minimum freeboard to meet intact or damage stability requirements, or due to any other restriction, seasonal marks above the centre of the ring shall not be marked, and any seasonal marks below the centre of the ring shall be marked.

2.3 Where moonpools are arranged within the hull in open communication with the sea, the volume of the moonpool shall not be included in calculation of any hydrostatic properties. An addition shall be made to the geometric freeboard, if the moonpool has a larger cross-sectional area above the water line at 0,85 H than below, corresponding to the lost buoyancy (H = depth). This addition for the excess portion above 0,85 H shall be made as prescribed for well/recesses below. If an enclosed superstructure contains part of the moonpool, deduction shall be made for the effec-tive length of the superstructure.

Where open wells/recesses are arranged in the free-board deck, a correction equal to the volume of the well/recess up to the freeboard deck divided by the waterplane area at 0,85 H shall be made to the free-board obtained after all other corrections except bow height correction have been made. Free surface effects of the flooded well/recess shall be taken into account in stability calculations.



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2.4 The procedure described in 2.3 shall also apply in cases of small notches or relatively narrow cut-outs at the stern of the unit.

2.5 Narrow wing extensions at the stern of the unit shall be considered as appendages and excluded for the determination of length L and for the calcula-tion of freeboards.

3. Self-elevating units

3.1 Load lines shall be assigned to self-elevating units as calculated under the terms of the 1966 Load Line Convention taking into account 2.2 to 2.5. When floating or when in transit from one operational area to another, units shall be subject to all the conditions of assignment of that Convention unless specifically excepted, e.g. from Reg. 39 (minimum bow height).

However, these units shall not be subject to the term of that Convention while they are supported by the seabed or are in the process of lowering or raising their legs.

For the consideration of moonpools see 2.3.

3.2 The minimum freeboard of units which due to their configuration cannot be computed by the nor-mal methods laid down by the 1966 Load Line Con-vention shall be determined on the basis of meeting applicable intact stability, damage stability and struc-tural requirements in the afloat condition.

3.3 Some self-elevating units utilize a large mat or similar supporting structure which contributes to the buoyancy when the unit is floating. In such cases the mat or similar supporting structure shall be ig-nored in the calculation of freeboard. The mat or simi-lar supporting structure shall, however, always be taken into account in the evaluation of the stability of

the unit when floating since its vertical position rela-tive to the upper hull may be critical. See also Section 2 – Self Elevating Units.


4.1 The hull form of this type of unit makes the calculation of geometric freeboard in accordance with the provisions of Chapter III of the 1966 Load Line Convention impracticable. Therefore the minimum freeboard of each column stabilized unit shall be de-termined by meeting the applicable requirements for

− the strength of unit’s structure

− minimum clearance between passing wave crests and deck structure, see Section 3, B.1.3.

− intact and damage stability requirements

4.2 The minimum freeboard shall be marked in appropriate locations on the structure.

4.3 The enclosed deck structure of each column stabilized unit shall be made weathertight.

4.4 Windows, sidescuttles and portlights, includ-ing those of the non-opening type, or other similar openings shall not be located below the deck structure of column stabilized units.

4.5 Special consideration shall be given to the position of openings which cannot be closed in emer-gencies, such as air intakes for emergency generators, having regard to the intact righting arm curves and the final waterline after assumed damage.

5. Pipelaying units

For the special requirements for watertight integrity and stability of pipe laying units see Section 5, D.

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Section 8

Mooring Equipment

A. General

1. Definitions

1.1 Temporary mooring equipment

Temporary mooring equipment in the context of this Section is the mooring equipment consisting of an-chors, cables, winches etc. intended to be used while the mobile offshore unit is not in a working condition but during voyages and location moves, and for an-choring within harbours or in sheltered areas. The equipment is to be designed to hold a unit in position when exposed to moderate environmental loads.


Positional mooring equipment in the context of this Section is a system for position keeping on the work-ing location. The system is intended to keep the unit in position, i.e. maintaining the prescribed limits of movement during the work envisaged and preventing the unit or other floating bodies from drifting under all anticipated sea and weather conditions.

2. Scope

2.1 As a condition of Class and for assigning the Class Notation , the unit is to be provided with temporary mooring equipment complying with the provisions of B. Deviations from this general require-ment will be stated in the Class Certificate.

2.2 Positional mooring equipment, usually pro-vided for ship type and column stabilized units, is to comply with the provisions of C. An appropriate Nota-tion may be affixed to the Character of Classification, see C.1.2.

2.3 When separate temporary mooring equipment is not fitted, consideration will be given to accepting the positional mooring equipment as equivalent to the rule requirements for temporary mooring equipment, if the provisions of B. are complied with.

2.4 Where positioning of the unit on the working location is achieved by a dynamic positioning system, the Notation DP will be affixed to the Character of Class, see C.7. In that case separate temporary moor-ing equipment according to B. will be required.

3. Documents to be submitted

Plans showing the arrangement and complete details of the anchoring system, including anchors, shackles, anchor lines consisting of chain, wire or rope, together with details of fairleads, windlasses, winches and any other components of the anchoring system and their foundations are to be submitted to GL.

B. Temporary Mooring Equipment

1. General

1.1 Temporary mooring equipment fitted in ac-cordance with the provisions of this Section is to be designed for quick and safe operation in all foresee-able service conditions and for holding the unit at anchor.

Note:

1. Temporary mooring equipment is, therefore, not intended to hold a unit off fully exposed coasts in rough weather or to stop a unit which is moving or drifting. In this condition, the loads on the mooring equipment increase to such a degree that its compo-nents may be damaged or lost owing to the high en-ergy forces generated, particularly for large units.

2. In good holding ground the temporary moor-ing equipment required by this Section is intended to hold a unit in conditions such as to avoid dragging of the anchor. In poor holding ground, the holding power of the anchors will be significantly reduced.

3. The Equipment Numeral formula for the temporary mooring equipment required in this Section is based on an assumed current speed of 2,5 m/sec, a wind speed of 25 m/sec, and a scope of chain cable between 6 and 10, the scope being the ratio between length of chain paid out and water depth.

1.2 The temporary mooring equipment shall consist of anchors, chain cables, windlass or winches, chain stoppers, chain lockers (if chains are fitted) and wire ropes.

The equipment of anchors and chain cables is to be determined from Table 8.1.

1.3 The anchors are to be effectively stowed and secured to prevent any movement at sea. If the an-chors are stowed at the shell, the shell plating is to be increased in thickness and the framing may have to be strengthened.

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Section 8 Mooring Equipment Chapter 2Page 8–1

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1.4 The arrangements are to be such as to provide an easy lead of chain cable/wire rope from the anchor to the windlass/winch and to ensure that the anchor can be dropped by its own weight without assistance.

1.5 Dimensioning

1.5.1 For the supporting structure under wind-lasses, chain stoppers, fairleads, sheaves and any other items of equipment subjected to loads from the anchor cables as determined in accordance with the provi-sions of 1.5.2 or 1.5.3, the following permissible stresses are to be observed:

− axial, bending stress: σb ≤ 0,8 ⋅ ReH

− shear stress: τ ≤ 0,5 ⋅ ReH

− equivalent stress: 2 2eq b eH3 Rσ = σ + ⋅ τ ≤

1.5.2 Where chain cables are led through hawse pipes, the acting forces are to be taken as 80 % or 45 % of the rated breaking load of the chain cable, i.e.

− for chain stoppers: 80 %

− for windlasses: 80 % where no chain stoppers are fitted

− for windlasses: 45 % where chain stoppers are fitted

1.5.3 Where hawse pipes are not installed and the chain cables are guided by fairleads and sheaves, the acting forces are to be taken as 100 % or 50 % of the rated braking load of the chain cable, i.e.

− for chain stoppers: 100 %

− for windlasses: 100 % where no chain stoppers are fitted

− for windlasses: 50 % where chain stoppers are fitted

2. Equipment numeral

The equipment numeral Z is to be calculated as fol-lows:

2 / 3WZ D f= +

D = moulded displacement [t] in seawater having a density of 1,025 t/m³ when at anchor

fW = projected area of all surfaces above the water line [m²] perpendicular to the wind direction when at anchor

The masking effect of structures located behind each other is normally not to be taken into ac-count.

However, upon case-by-case consideration a reduced projected area of leeward structures may be accepted.

Reduction factors on account of the particular shape of structures are normally not to be ap-plied.

3. Anchors

3.1 Number

Two rule power anchors according to Table 8.1 are to be connected to their chain cables and positioned on board ready for use. It is to be ensured that each an-chor can be stowed in the hawse and hawse pipe in such a way that it remains firmly secured in seagoing conditions.

3.2 Construction

3.2.1 The anchors are to be made of materials and are to be tested as required in accordance with the GL Rules II - Materials and Welding, Part 1 - Metallic Materials, Chapter 4 - Equipment, Section 1.

3.2.2 The anchors must be of approved design. The mass of the heads of patent anchors (stockless an-chors), including pins and fittings, must comprise not less than 60 % of the total mass of the anchor.

3.2.3 In case of stock anchors, the total mass of the anchor including the stock must comply with the val-ues given in Table 8.1. The weight of the stock should be approximately 20 % of this total mass.

3.2.4 The mass of each individual anchor may deviate from the tabular mass by up to 7 % as long as the total mass of the anchors fitted and attached to the chain cables is not less then twice the tabular mass of one anchor.

3.3 High holding power anchors

3.3.1 Where anchors with increased holding power are intended to be used, a special approval procedure is required, as described in 3.4. The following reduced masses may be admitted:

− for ‘High Holding Power’ (HHP) anchors: 75 % of the tabular mass

− for ‘Very High Holding Power’ (VHHP) anchors: 50 % of the tabular mass

3.3.2 The dimensions of the chain cable and wind-lass are to be based on the tabular anchor mass as given in Table 8.1.


Section 8 Mooring Equipment IV - Part 6GL 2007

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Table 8.1 Definition of anchors and chain cables

2 stockless bower

anchors Stud link chain cables

Diameter Number. for.

Reg. Equipment numeral Z

Mass per anchor Total length

d1 1 D2 d3

[−] [−] [kg] [m] [mm] [mm] [mm]

120 720 – 780 2280 467,5 48 42 36 121 780 – 840 2460 467,5 50 44 38 122 840 – 910 2640 467,5 52 46 40 123 910 – 980 2830 495 54 48 42 124 980 – 1060 3060 495 56 50 44 125 1060 – 1140 3300 495 58 50 46

126 1140 – 1220 3540 522,5 60 52 46 127 1220 – 1300 3780 522,5 62 54 48 128 1330 – 1390 4050 522,5 64 56 50 129 1390 – 1480 4320 550 66 58 50 130 1480 – 1570 4590 550 68 60 52

131 1570 – 1670 4890 550 70 62 54 132 1670 – 1790 5450 577,5 73 64 56 133 1790 – 1930 5610 577,5 76 66 58 134 1930 – 2080 6000 577,5 78 68 60 135 2080 – 2230 6450 605 81 70 62

136 2230 – 2380 6900 605 84 73 64 137 2380 – 2530 7350 605 87 76 66 138 2530 – 2700 7800 632,5 90 78 68 139 2700 – 2870 8300 632,5 92 81 70 140 2870 – 3040 8700 632,5 95 84 73

141 3040 – 3210 9300 660 97 84 76 142 3210 – 3400 9900 660 100 87 78 143 3400 – 3600 10500 660 102 90 78 144 3600 – 3800 11100 687,5 105 92 81 145 3800 – 4000 11700 687,5 107 95 84

146 4000 – 4200 12300 687,5 111 97 87 147 4200 – 4400 12900 715 114 100 87 148 4400 – 4600 13500 715 117 102 90 149 4600 – 4800 14100 175 120 105 92 150 4800 – 5000 14700 742,5 122 107 95

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Table 8.1a Definition of anchors and chain cables (Continuous)

2 stockless bower

anchors Stud link chain cables

Diameter Number. for.

Reg. Equipment numeral Z

Mass per anchor Total length

d1 1 D2 d3

[−] [−] [kg] [m] [mm] [mm] [mm]

151 5000 – 5200 15400 742,5 124 111 97 152 5200 – 5500 16100 742,5 127 111 97 153 5500 – 5800 16900 742,5 130 114 100 154 5800 – 6100 17800 742,5 132 117 102 155 6100 – 6500 18800 742,5 120 107

156 6500 – 6900 20000 770 124 111 157 6900 – 7400 21500 770 127 114 158 7400 – 7900 23000 770 132 117 159 7900 – 8400 24500 770 137 122 160 8400 – 8900 26000 770 142 127

161 8900 – 9400 27500 770 147 132 162 9400 – 10000 29000 770 152 132 163 10000 – 10700 31000 770 137 164 10700 – 11500 33000 770 142 165 11500 – 12400 35500 770 147

166 12400 – 13400 38500 770 152 167 13400 – 14600 42000 770 157 168 14600 – 16000 46000 770 162

d1 = chain diameter Grade K1 (ordinary quality) d2 = chain diameter Grade K2 (special quality) d3 = chain diameter Grade K3 (extra quality)

1 not recommended for offshore use

3.4 Approval procedure

3.4.1 For approval as a "High Holding Power An-chor", satisfactory tests are to be made on various types of bottom and the anchor is to have a holding power at least twice that of a patent anchor ("Admi-ralty Standard Stockless") of the same mass. The mass of anchors to be tested should be representative of the full range of sizes intended to be manufactured. The tests are to be carried out on at least two sizes of an-chors in association with the chain cables appropriate to the weight. The anchors to be tested and the stan-dard stockless anchors should be of approx. the same mass.

3.4.2 The chain length used in the tests should be approx. 6 to 10 times the depth of water.

3.4.3 The tests are normally to be carried out from a tug, however, alternative shore based tests (e.g. with suitable winches) may be accepted.

Three tests are to be carried out for each anchor and type of bottom. The pull shall be measured by means of a dynamometer or recorded by a recording instru-ment. Measurements of pull based on rpm/bollard pull curve of the tug may be accepted. Testing by compari-son with a previously approved HHP anchor may be accepted as a basis for approval.



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3.4.4 The maximum mass of an anchor thus ap-proved may be 10 times the mass of the largest size of anchor tested.

3.5 Positional anchors

Anchors used as positional anchors in accordance with C., which must be specially laid the right way up or which require flukes and profile to be adjusted to meet sea bed conditions, will not normally be approved for temporary mooring purposes.

4. Mooring chain cables and accessories

4.1 The chain cable diameters given in Table 8.1 apply to chains complying with the requirements of the GL Rules II – Materials and Welding, Part 1 – Metallic Materials, Chapter 4 - Equipment, Section 2, where

− Grade K 1 (ordinary quality)

− Grade K 2 (special quality)

− Grade K 3 (extra special quality)

are defined.

4.2 Grade K1 chain cable should not be used for offshore applications. Where the installation of off-shore quality mooring chains is intended, the provi-sions of C.4. apply.

4.3 Grade K 2 and K 3 chain cables must be post production quenched and tempered and shall be pur-chased only from recognized manufacturers.

4.4 Chain cables or wire ropes, if fitted, are to be made of materials and tested in accordance with the GL Rules mentioned under 4.1.

4.5 Where the total mass of anchors is divided into three or four anchors, see 3.1, the chain cable diameter and lengths are to be determined from Table 8.1 for the mass of the anchor actually fitted. The chain cable length is to be determined by dividing the tabular length by two and then multiplying by the number of anchors actually fitted, unless specified otherwise by the Owner/Operator.

4.6 Accessories

4.6.1 Anchor shackles shall be of an approved type and the material(s) shall conform to the GL Rules mentioned under 4.1. Kenter-type shackles are rec-ommended.

4.6.2 A forerunner with swivel is to be fitted be-tween anchor and chain cable. In lieu of a forerunner with swivel, an approved swivel shackle may be fitted. However, swivel shackles are not to be connected directly to the anchor shank unless specially approved.

4.6.3 Where a spare anchor is fitted, see 3.1, a sufficient number of suitable spare shackles is to be

kept on board to facilitate fitting of the spare anchor at any time.

4.7 Attachment of cable ends

4.7.1 The inboard ends of the chain cables are to be secured to the structure. The attachment is to be able to withstand a force not less than 15 % nor more than 30 % of the rated breaking load of the chain cable.

4.7.2 The attachment of the inboard ends of the chain cables to the unit’s structure is to be provided with suitable means to permit, in case of emergency, an easy slipping of the chain cables to sea from an accessible position outside the chain locker.

4.8 Wire ropes

Where wire ropes are fitted in lieu of chain cables, the following applies:

− The length of ropes is to be equal to 1,5 times the corresponding tabular chain cable length.

− The ropes’ breaking strength is not to be less than the breaking strength of the tabular Grade K 1 chain cable. Strength according to Grade K 2 chains is recommended.

− A short length of chain cable is to be fitted be-tween anchor and wire rope. Wire rope winches are to be fitted which comply with the rules for windlasses, see Chapter 5, Section 8, A.

5. Chain locker

5.1 The chain locker is to be of adequate capacity and depth to facilitate an easy direct lead of the cables through the chain pipes and to permit self-stowing of the cables. The chain locker is to be provided with internal divisions so that the chain cables may be fully and separately stowed.

The minimum required stowage capacity without mud box for the two bower anchor chains is as follows:

21,1 dS100000

⋅ ⋅= [m3]

d = chain diameter [mm] according to Table 8.1

= total length of stud link chain cable according to Table 8.1

The total stowage capacity is to be distributed on two chain lockers of equal size for the port and starboard chain cables. The shape of the base areas shall as far as possible be quadratic with a maximum edge length of 33 ⋅ d. As an alternative, circular base areas may be selected, the diameter of which shall not exceed (30 – 35) ⋅ d.

Above the stowage of each chain locker in addition a free depth of H = 1500 [mm]

is to be provided.

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5.2 The chain locker boundaries and their access openings are to be watertight to prevent flooding of adjacent spaces, where essential installations or equipment are arranged, in order to not affect the proper operation of the unit after accidental flooding of the chain locker.

5.3 Where the chain locker boundaries are also tank bulkheads, the scantlings of plating and stiffeners are to be determined as for tanks.

5.4 Special requirements to minimize the in-gress of water

5.4.1 Spurling pipes and cable lockers are to be watertight up to the weather deck.

5.4.2 Where means of access is provided, it is to be closed by a substantial cover and secured by closely spaced bolts.

5.4.3 Spurling pipes through which anchor cables are led are to be of suitable diameter and shall be pro-vided with permanently attached closing appliances to minimize water ingress.

5.5 Adequate drainage facilities are to be pro-vided.

C. Positional Mooring Equipment

1. General

1.1 All units, except self-elevating units and submersible units, should be provided with positional mooring equipment designed to maintain the floating unit on station in all design conditions valid for its intended area(s) of operation.

1.2 Units provided with positional mooring equipment in accordance with 1.1 will be eligible to the special optional Class Notation "EQUIPPED WITH POSITION MOORING SYSTEM" added to the Character of Classification in accordance with the GL Rules, see Chapter 1, Section 2, C.2.9.

1.3 Units provided with thrusters serving (also) for position keeping will be eligible for the special Notations DP1 to DP3, see 7.

2. Anchoring systems

2.1 Approval documents

2.1.1 Plans showing the arrangement and complete details of the anchoring system, including anchors, shackles, anchor line components, wires, together with details of fairleads, windlasses, winches, controls and instrumentation, as well as any other components of the anchoring system and its foundations, are to be submitted to GL for approval.

2.1.2 An analysis of the anchoring arrangements expected to be utilised during the unit’s operation is to be submitted to GL. Among items to be addressed are:

− design environmental conditions: waves, wind, currents, tides, and ranges of water depth

− anchor holding capacities for various seabed soil conditions

− air and sea temperature

− ice conditions, if applicable

− description of analysis method

2.1.3 Plans showing the towing arrangement(s) and equipment are to be submitted for information.

2.2 Design conditions, safety factors

2.2.1 Redundancy

The anchoring system should be designed such that a sudden failure of any single anchor line will not cause progressive failure of the remaining lines.

2.2.2 Loads

Anchoring system components should be designed utilizing adequate safety factors and a design method-ology suitable to identify the most severe loading condition for each component. In particular, sufficient numbers of heading angles together with the most severe combination of wind, current, and waves are to be considered, usually from the same direction, to determine the maximum tension in each mooring line.

When a particular site is being considered, any appli-cable cross sea conditions are also to be taken into account in the event that they might induce higher mooring loads.

2.2.3 Quasi static methods

When the Quasi static method is applied, the tension in each anchor line is to be calculated at the maximum excursion for each design condition defined in 2.2.4, combining the following steady state and dynamic responses of the unit: a) Steady mean offset due to the defined wind, cur-

rent, and steady wave forces. b) Most probable maximum wave induced motions of

the moored unit due to wave excitation.



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For relatively deep water, the effect from damping and inertia forces in the anchor lines is to be considered in the analysis.

The effects of slowly varying motions are to be in-cluded for column stabilized units when the magni-tudes of such motions are considered to be significant.

2.2.4 When the Quasi Static Method outlined in 2.2.3 is applied, the minimum factors of safety at the maximum excursion of the unit for a range of head-ings should be considered according to Table 8.2

Table 8.2 Minimum factors of safety

Design condition Safety factor

Operating 2,7

Severe storm 1 1,8

Operating – one line failed 1,8

Severe storm – one line failed 1 1,25

1 see Chapter 4, Section 3, C.: Extreme environmental loads

Safety factor = B

max

PT

Tmax = characteristic tension in the anchor line, equal to the maximum value obtained according to 2.2.2 and 2.2.3

PB = minimum rated breaking strength of the anchor line

2.2.4.1 Operating

For the most severe design environmental condition for normal operations as defined by the Owner or Designer see Chapter 4, Section 3, C.4.2.

2.2.4.2 Severe Storm

For the most severe design environmental condition for severe storm as defined by the Owner or Designer see Chapter 4, Section 3, C.4.3.

2.2.4.3 Operating - One Line Failed

Situation which follows a failure of any one mooring line in the operating condition.

2.2.4.4 Severe Storm - One Line Failed

Situation which follows a failure of any one mooring line in the severe storm condition.

2.2.5 Dynamic analysis

When a dynamic analysis is employed, other safety factors may be considered to the satisfaction of GL.

The defined operating and severe storm conditions are to be the same as those identified for the design of the

unit, unless GL is satisfied that lesser conditions may be applicable to specific sites.

2.2.6 In general, the maximum wave induced mo-tions of the moored unit about the steady mean offset should be obtained by means of model tests. GL may accept analytical calculations provided that the pro-posed method is based on a sound methodology which has been validated by model tests.

Wind loads shall be determined according to the prin-ciples shown in Chapter 4, Section 1, B. and Section 2, B.2. The results of wind tunnel tests, as well as other recognized criteria, may be considered.

2.2.7 GL may accept different analysis methodolo-gies provided that a level of safety equivalent to the one obtained by 2.2.3 and 2.2.4 is ensured.

2.2.8 GL may give special consideration to an arrangement where the anchoring systems are used in conjunction with thrusters to maintain the unit on station, see 1.3 and 7.

3. Anchors

3.1 General

Type/design, materials, manufacture and testing of anchors used for position mooring shall comply with the GL Rules mentioned under B.3., if Certification by GL is requested.

Anchors specially designed for position mooring are normally not to be used for temporary mooring, see B.3.5.

3.2 Testing

Anchors shall be subjected to load tests according to the Rule requirements, in approved testing installa-tions. After application of the test load, it must be shown that the anchor is free of any defects/ deforma-tions resulting from testing, and fully operable.

Test loads are shown in Table 8.3. For anchors with increased holding capacity, the following test loads have to be applied:

HHP anchors: A load corresponding to 1,33 × mass of anchor.

VHHP anchors: A load corresponding to 2 × mass of anchor.

3.3 Anchors are to be securely stowed on board to prevent movement during transit/towage.

4. Anchor lines (mooring chain cables)

4.1 General requirements

4.1.1 GL are to be ensured that the anchor lines are of a type/composition that will satisfy the design con-ditions of the anchoring system. In general anchor

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cables may be of wire, rope, chain or any combination thereof. For wire ropes see B.4.8.

4.1.2 Means are to be provided to enable the an-chor lines to be released from the unit after loss of main power.

4.1.3 Means are to be provided for measuring an-chor line tensions.

4.1.4 Anchor lines are to be of adequate length to prevent uplift of the anchors under the maximum design load condition for the anticipated area(s) of operation.

4.2 Offshore mooring chain cables - material requirements

4.2.1 General Requirements

4.2.1.1 Scope

These Rules apply to the materials, design, manufac-ture and testing of offshore mooring chains and acces-sories intended to be used for applications such as: mooring of mobile offshore units, mooring of floating production units, mooring of offshore loading systems and mooring of gravity based structures during fabri-cation.

Mooring equipment covered are common links, con-nection common links (splice links), enlarged links, end links, detachable connecting links (shackles), and shackles, swivels and swivel shackles.

4.2.1.2 Chain cable grades

Depending on the nominal tensile strength of the steels used for manufacture, chain cables are to be subdivided into three grades, i.e.: GL-R3, GL-R3S, GL-R4.

4.2.1.3 Approval of chain cable manufacturers

4.2.1.3.1 Offshore mooring chain cables are to be manufactured only by works approved by GL. For this purpose approval tests are to be carried out, the scope of which is to include proof and breaking load tests, measurements and mechanical tests including fracture mechanic tests.

4.2.1.3.2 Manufacturers are to submit for review and approval the sequence of operations from receiving inspection to shipment, and details of the following manufacturing processes:

a) Bar heating and bending including method, tem-perature control and recording.

b) Flash welding including current, force, time and dimensional variables as well as control and re-cording of parameters.

c) Flash removal including method and inspection.

Table 8.3 Test loads for anchors 1

Mass [kg]

Test load [kN]

Mass [kg]

Test load [kN]

2200 2300 2400 2500

2600 2700 2800 2900

3000 3100 3200 3300

3400 3500 3600 3700

3800 3900 4000 4100

4200 4300 4400 4500

4600 4700 4800 4900

5000 5100 5200 5300

5400 5500 5600 5700

5800 5900 6000 6100

6200 6300 6400 6500

6600 6700 6800 6900

7000 7200 7400 7600

367 388 401 414

427 438 450 462

474 484 495 506

517 528 537 547

557 567 577 586

595 604 613 622

631 638 645 653

661 669 677 685

691 699 706 713

721 728 735 740

747 754 760 767

773 779 786 794

804 818 832 845

7800 8000 8200 8400

8600 8800 9000 9200

9400 9600 9800

10000

10500 11000 11500 12000

12500 13000 13500 14000

14500 15000 15500 16000

16500 17000 17500 18000

18500 19000 19500 20000

21000 22000 23000 24000

25000 26000 27000 28000

29000 30000 31000 32000

34000 36000 38000 40000

42000 44000 46000 48000

861 877 892 908

922 936 949 961

975 987 998 1010

1040 1070 1090 1110

1130 1160 1180 1210

1230 1260 1270 1300

1330 1360 1390 1410

1440 1470 1490 1520

1570 1620 1670 1720

1770 1800 1850 1900

1940 1990 1030 1070

2160 2250 2330 2410

2490 2570 2650 2730

1 Intermediate values can be determined by linear interpolation



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d) Stud insertion method.

e) Heat treatment including furnace types, means of specifying, controlling and recording of tempera-ture and chain speed and allowable limits, quench-ing bath and agitation, cooling method after exit.

f) Proof and break loading including method/ ma-chine, means of horizontal support, if applicable, method of measurement recording.

g) Non-destructive examination procedures.

4.2.1.3.3 Calibration of furnaces shall be verified by measurement and recording of actual link temperature (surface and internal).

4.2.1.4 Approval of quality system at chain cable manufacturers

Chain cable manufacturers are to have a documented and effective quality system approved by GL, e.g. according to ISO 9001.

4.2.1.5 Approval of steel mills for rolled bars

4.2.1.5.1 Bar material intended for chain and accesso-ries are to be manufactured only by works approved by GL. The approval is limited to a nominated sup-plier of bar material. If a chain cable manufacturer wishes to use material from a number of suppliers, separate approval tests must be carried out for each supplier.

Approval will be given only after successful testing of the completed chain cable. The approval will normally be limited to a thickness equal to that of the bars tested.

4.2.1.5.2 The steel maker is to submit a specification of the chemical composition of the bar material, which must be approved by GL and by the chain cable manu-facturer.

For Grade GL-R4 chain cables the steel should con-tain a minimum of 0,20 per cent molybdenum.

4.2.1.5.3 A heat treatment sensitivity study simulating chain cable production conditions shall be applied in order to verify mechanical properties and establish limits for temperature and time combinations.

4.2.1.5.4 The bar manufacturer is to provide evidence that the material is resistant to strain ageing, temper embrittlement and hydrogen embrittlement.

4.2.1.6 Approval of forges and foundries for ac-cessories

4.2.1.6.1 Forges and foundries intending to supply finished or semifinished accessories are to be ap-proved by GL. The scope of approval is to be agreed with GL.

4.2.1.6.2 Manufacturers intending to supply accesso-ries in machined condition (e.g. Kenter type shackles) are to submit detailed drawings for approval.

4.2.2 Materials

4.2.2.1 Scope

These requirements apply to rolled steels, forgings and castings used for the manufacture of offshore mooring chain cables and accessories.

4.2.2.2 Rolled steel bars

4.2.2.2.1 Steel manufacture

The steels are to be manufactured by basic oxygen, electric furnace or such other process as may be spe-cially approved. All steels are to be killed and fine grain treated.

4.2.2.2.2 Chemical composition

For acceptance tests, the chemical composition of ladle samples of each heat is to be determined by the steel maker and is to comply with the approved speci-fication.

4.2.2.2.3 Mechanical tests

.1 Bars of the same nominal diameter are to be presented for test in batches of 50 tonnes or fraction thereof from the same heat. Test specimens are to be taken from material heat treated in the same manner as intended for the finished chain.

.2 Each heat of Grade GL-R3S and GL-R4 steel bars is to be tested for hydrogen embrittlement. In case of continuous casting, test samples representing the beginning and the end of the charge shall be taken. In case of ingot casting, test samples representing two different ingots shall be taken.

Two (2) tensile test specimens shall be taken from the central region of bar material which have been simu-lated heat treated. The specimens shall preferably have a diameter of 20 mm, alternatively 14 mm. One specimen is to be tested within max. 3 hours after machining. For a 14 mm diameter specimen, the time limit is 1,5 hours. Alternatively, the specimen may be cooled to – 60 °C immediately after machining and kept at that temperature for a period of max. 5 days. The other specimen is to be tested after baking at 250 °C for 4 hours, alternatively 2 hours for 14 mm diame-ter specimen.

A slow strain ≤ 0,0003 s-1 must be used during the entire test, until fracture occurs. This means approx. 10 minutes for a 20 mm diameter specimen.

Tensile strength, elongation and reduction of area are to be reported. The requirement for the test is:

1

2

Z0,85

Z≥

Z1 = reduction of area without baking

Z2 = reduction of area after baking

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If the requirement Z1 / Z2 ≥ 0,85 is not met, the bar material may be subjected to a hydrogen degassing treatment after agreement with GL. New tests shall be performed after degassing.

.3 For all grades, one tensile and three Charpy V-notch specimens are to be taken from each sample selected. The test specimens are to be taken at ap-proximately one-third radius below the surface, as shown in Fig. 8.1.

The results of all tests are to be in accordance with the appropriate requirements of Table 8.4.

.4 If the tensile test requirements are not achieved, a retest of two further specimens selected from the same sample shall be permissible. Failure to meet the specified requirements of either or both of the additional tests will result in rejection of the batch represented, unless it can be clearly attributed to im-proper simulated heat treatment.

4.2.2.2.4 Dimensional tolerances

The diameter and roundness shall be within the toler-ances specified in Table 8.5, unless otherwise agreed.

4.2.2.2.5 Non-destructive examination and repair The bars shall be free from pipe, cracks and flakes. Bar material is to be subjected to ultrasonic examina-tion at an appropriate stage of the manufacture.

One hundred percent of the bar material is to be exam-ined by magnetic particle or eddy current methods. The bars shall be free of injurious surface imperfec-tions such as seams, laps and rolled-in mill scale. Provided that their depth is not greater than 1 % of the bar diameter, longitudinal discontinuities may be re-moved by grinding and blending to a smooth contour.

The frequency of non-destructive examinations may be reduced at the discretion of GL provided it is veri-fied by statistical means that the required quality is consistently achieved.

4.2.2.2.6 Marking

Each bar is to be stamped with the steel grade designa-tion and the charge number (or a code indicating the charge number) on one of the end surfaces. Other marking methods may be accepted subject to agree-ment.

4.2.2.3 Forged steels

4.2.2.3.1 Forged steels used for the manufacture of accessories must be in compliance with specifications submitted and approved.

��

��

��

��

Fig. 8.1 Location of test specimens

Table 8.4 Mechanical properties of offshore mooring chain cables

Charpy V-notch impact tests

Yield stress Tensile strength

Elongation A5

Reduction of area 3 Test

temperatureAverage energy

Average energy flash

weld Grade

[N/mm2] minimum

[N/mm2] minimum

[%] minimum

[%] minimum [°C] 2 [J]

minimum [J]

minimum

GL-R3 410 690 17 50 0 - 20

60 40

50 30

GL-R3S 490 770 15 50 0 - 20

65 45

53 33

GL-R4 580 860 12 50 - 20 50 36 1 Aim value of yield to tensile ratio: 0,92 max 2 At the option of Society the impact test of Grade GL-R3 and GL-R3S may be carried out at either 0 °C or minus 20 °C. 3 Reduction of area of cast steel is to be:

− for grades R3 and R3S: min. 40 % − for grades R4: min 35 % - cf. item 4.2.2.3.4



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Table 8.5 Dimensional tolerances of bar stock material

Nominal diameter

[mm]

Tolerance on diameter

[mm]

Tolerance on roundness (dmax - dmin)

[mm] below 25 -0 + 1,0 0,60

25 – 35 -0 + 1,2 0,80 36 – 50 -0 + 1,6 1,10 51 – 80 -0 + 2,0 1,50

81 – 100 -0 + 2,0 1,95 101 – 120 -0 + 3,0 2,25 121 – 160 -0 + 4,0 3,00

4.2.2.3.2 Chemical composition

4.2.2.2.2 applies.

4.2.2.3.3 Heat treatment

Finished forgings are to be properly heat treated in compliance with specifications submitted and ap-proved.

4.2.2.3.4 Mechanical properties

The forgings must comply with the mechanical prop-erties given in Table 8.4, when properly heat treated.


For test sampling, forgings of similar dimensions, that means that diameters do not differ by more than 25 mm, originating from the same heat treatment charge and the same heat of steel are to be combined into one test unit. From each test unit one tensile and three impact test specimens are to be taken and tested. For the location of the test specimens see Fig. 8.1.

4.2.2.3.6 Ultrasonic examination

The forgings are to be subjected to ultrasonic exami-nation at an appropriate stage of manufacture and in compliance with the standard submitted and approved.

4.2.2.3.7 Marking

Marking is to be similar to that specified in 4.2.2.2.6.

4.2.2.4 Cast steels

4.2.2.4.1 Cast steels used for the manufacture of ac-cessories must be in compliance with specifications submitted and approved. 4.2.2.4.2 Chemical composition

4.2.2.2.2 applies.


All castings are to be properly heat treated in compli-ance with specifications submitted and approved.

4.2.2.4.4 Mechanical properties

The castings must comply with the mechanical proper-ties given in Table 8.4.


For test sampling, castings of similar dimensions originating from the same heat treatment charge and the same heat of steel are to be combined into one test unit. From each test unit one tensile and three impact test specimens are to be taken and tested. For the loca-tion of the test specimens see Fig. 8.1.

4.2.2.4.6 Ultrasonic examination

The castings are to be subjected to ultrasonic examina-tion in compliance with the standard submitted and approved.

4.2.2.4.7 Marking

4.2.2.3.7 applies.

4.2.2.5 Materials for studs

The studs are to be made of steel corresponding to that of the chain or in compliance with specifications sub-mitted and approved. In general, the carbon content should not exceed 0,25 per cent if the studs are to be welded in place.

4.2.3 Design and chain cable manufacture

4.2.3.1 Design

Drawings giving detailed design of chain cables and accessories made by or supplied through the chain cable manufacturer are to be submitted for approval. Typical designs are given in ISO 1704: 1991.

In addition, drawings showing the detailed design of the stud shall be submitted for information. The stud shall give an impression in the chain link which is sufficiently deep to secure the position of the stud, but the combined effect of shape and depth of the impres-sion shall not cause any harmful notch effect or stress concentration in the chain link.

Machining of Kenter shackles shall result in fillet radius min. 3 % of nominal diameter.

4.2.3.2 Manufacturing process

Offshore mooring chain cables shall be manufactured in continuous lengths by flash butt welding and are to be heat treated in a continuous furnace; batch heat treatment is not permitted.

The use of joining shackles to replace defective links is subject to the written approval of the end purchaser in terms of the number and type permitted. The use of connecting common links is restricted to 3 links in each 100 m of chain cable.

4.2.3.3 Manufacturing process records

4.2.3.3.1 Documentation

Records of bar heating, flash welding and heat treat-ment shall be made available for inspection by the Surveyor.

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4.2.3.3.2 Bar heating

For electric resistance heating, the heating phase shall be controlled by an optical heat sensor. The controller shall be checked at least once every 8 hours and re-cords made.

For furnace heating, the temperature shall be con-trolled and continuously recorded using thermocou-ples in close proximity to the bars. The controls shall be checked at least one every 8 hours and records made.

4.2.3.3.3 Flash welding

The following welding parameters shall be controlled during welding of each link: a) Platen motion. b) Current as a function of time. c) Hydraulic pressure.

The controls shall be checked at least every 4 hours and records made.


Chain cables shall be austenitized above the upper transformation temperature, at a combination of tem-perature and time within the limits established.

When applicable, chain cables shall be tempered at a combination of temperature and time within the limits established.

Temperature and time or temperature and chain speed shall be controlled and continuously recorded.

4.2.3.4 Mechanical properties

The mechanical properties of finished chain cables and accessories are to be in accordance with Table 8.4. For the location of test specimens see Figs. 8.1 and 8.2.

4.2.3.5 Proof and break load tests

Chain cables and accessories are to withstand the proof and breaking load tests given in Table 8.6.

��

��

��

��

��

��

Fig. 8.2 Location of test specimens

Table 8.6 Formulas for proof and breaking load tests, weight and length over 5 links

Grade GL-R3 Grade GL-R3S Grade GL-R4

Proof test load [kN] Break test load [kN]

0,0148 d2 (44-0,08d) 0,0223 d2 (44-0,08d)

0,0180 d2 (44-0,08d) 0,0249 d2 (44-0,08d)

0,0216 d2 (44-0,08d) 0,0274 d2 (44-0,08d)

Chain weight [kg/m] 0,0219 d2

Length over 5 links Min. [mm] Max. [mm]

22 d

22,55 d



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4.2.3.6 Freedom from defects

All chain cables are to have a workmanship like finish consistent with the method of manufacture and be free from defects. Each link is to be examined in accor-dance with 4.2.4.5 using approved procedures.

4.2.3.7 Dimensions and dimensional tolerances

4.2.3.7.1 The shape and proportion of links and ac-cessories must conform to ISO 1704: 1991 or to the designs specially approved.

4.2.3.7.2 The following tolerances are applicable to links: a) Nominal diameter measured at the crown: up to 40 mm nominal diameter: – 1 mm over 40 up to 84 mm nominal diameter: – 2 mm over 84 up to 122 mm nominal diameter: – 3 mm over 122 mm nominal diameter: – 4 mm

The plus tolerance may be up to 5 % of the nominal diameter. The cross sectional area at the crown shall have no negative tolerance. b) Diameters measured at locations other than the

crown: The diameter is to have no negative toler-ance. The plus tolerance may be up to 5 % of the nominal diameter. The approved manufacturer specification is applicable to the plus tolerance of the flash butt weld.

c) The allowable manufacturing tolerance on a length of five links is + 2,5 %, but may not be negative.

d) All other dimensions are subject to a manufactur-ing tolerance of ± 2,5 %, provided always that all parts fit together properly.

e) Studs must be located in the links centrally and at right angles to the sides of the link. The following tolerances are acceptable provided that the stud fits snugly and its ends lie flush against the inside of the link:

Maximum off-centre distance "X" is 10 % of the nominal diameter, Maximum deviation a" from the 90°- position is 4°.

The tolerances are to be measured in accordance with Fig. 8.3.

4.2.3.7.3 The following tolerances are applicable to accessories: a) Nominal diameter: + 5,0 %, – 0 % b) Other diameters: ± 2,5 %

4.2.3.8 Welding of studs

4.2.3.8.1 A welded stud may be accepted for grade GL-R3 and GL-R3S chains. Welding of studs in grade GL-R4 chains is not permitted unless specially ap-proved.

4.2.3.8.2 Where studs are welded into the links this is to be completed before the chain is heat treated.

4.2.3.8.3 The stud ends must have a good fit inside the link and the weld is to be confined to the stud end opposite to the flash butt weld. The full periphery of the stud end is to be welded unless otherwise ap-proved.

4.2.3.8.4 Welding of studs at both ends is not permit-ted unless specially approved.

�

�

�

�

��

� ��

Fig. 8.3 Tolerances for stud position

4.2.3.8.5 The welds are to be made by qualified weld-ers using an approved procedure and low-hydrogen approved consumables.

4.2.3.8.6 The size of the fillet weld shall as a mini-mum be as per API specification 2F.

4.2.3.8.7 The welds are to be of good quality and free from defects such as cracks, lack of fusion, gross po-rosity and undercuts exceeding 1 mm.

4.2.3.8.8 All stud welds shall be visually examined. At least 10 per cent of all stud welds within each length of chain shall be examined by dye penetrant or magnetic particle after proof load testing. If cracks or lack of fusion are found, all stud welds in that length are to be examined.

4.2.3.9 Connecting common links

4.2.3.9.1 Single links to substitute for test links or defective links without the necessity for re-heat treat-ment of the whole length are to be made in accordance with an approved procedure. Separate approvals are required for each grade of chain cables and the tests are to be made on the maximum size of chain cables for which approval is sought.

4.2.3.9.2 Manufacture and heat treatment of connect-ing common links is not to affect the properties of the adjoining links. The temperature reached by these links is nowhere to exceed 80 % of the tempering temperature.

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4.2.3.9.3 Each link is to be subjected to the appropri-ate proof load and non-destructive examination as detailed in Table 8.6 and 4.2.4.5. A second link shall be made identical to the connecting common link; the link shall be tested and inspected according to 4.2.4.4. and 4.2.4.5.

4.2.3.9.4 Each connecting common link is to be marked on the stud in accordance with 4.2.4.7 plus an unique number for the link. The adjoining links are also to be marked on the studs.

4.2.4 Testing and inspection of finished chain cables

4.2.4.1 General

All chain cables are to be subjected to proof load tests, breaking load tests and mechanical tests after final heat treatment in the presence of a GL Surveyor. Where the manufacturer has a procedure to record proof loads and the Surveyor is satisfied with the ade-quacy of the recording system, he needs not witness all proof load tests. The Surveyor is to satisfy himself that the testing machines are calibrated and maintained in a satisfactory condition.

Prior to test and inspection the chain cable is to be free from scale, paint or other coating. The chain cable shall be sand or shot blasted to meet this requirement.

4.2.4.2 Proof and breaking load tests

4.2.4.2.1 The entire length of chain cable shall with-stand the proof load specified in Table 8.6 without fracture and shall not crack in the flash weld. The load applied shall not exceed the proof load by more than 10 % when stretching the chain cable. Where plastic straining is used to set studs, the applied load is not to be greater than that qualified in approval tests.

4.2.4.2.2 A breaking load test specimen consisting of at least 3 links is to be either taken from the chain or produced at the same time and in the same manner as the chain. The test frequency is to be based on tests at sampling intervals according to Table 8.7 provided that every cast is represented. Each specimen shall be capable of withstanding the break load specified with-out fracture and shall not crack in the flash weld. It shall be considered acceptable if the specimen is loaded to the specified value and maintained at that load for 30 seconds.

If the loading capacity of the testing machine is insuf-ficient, another equivalent method shall be agreed with GL.


4.2.4.3.1 After proof load testing measurements are to be taken on at least 5 per cent of the links in accor-dance with 4.2.3.7.

4.2.4.3.2 The entire chain cable is to be checked for the length, five links at a time. By the five link check the first five links shall be measured. From the next set of five links, at least two links from the previous five links set shall be included. This procedure is to be followed for the entire chain cable length. The meas-urements are to be taken preferably while the chain cable is loaded to 5 – 10 % of the minimum proof load. The links held in the end blocks may be ex-cluded from this measurement.

Table 8.7 Frequency of breaking load and me-chanical tests

Nominal chain diameter

[mm]

Maximum sampling interval

[m] Min - 48 91 49 - 60 110 61 - 73 131 74 - 85 152 86 - 98 175 99 - 111 198 112 - 124 222

4.2.4.4 Mechanical tests

Links of samples detached from finished, heat treated chain shall be sectioned for determination of mechani-cal properties. A test unit shall consist of one tensile and nine impact specimens. The tensile specimen shall be taken at the side opposite the flash weld. Three impact specimens shall be taken across the flash weld with the notch centred in the middle. Three impact specimens shall be taken across the unwelded side and three impact specimens shall be taken from the bend region.

The test frequency is to be based on tests at sampling intervals according to Table 8.7 provided that every cast is represented. Mechanical properties shall be as specified in Table 8.4.

The frequency of impact testing in the bend may be reduced at the discretion of GL provided it is verified by statistical means that the required toughness is consistently achieved.

4.2.4.5 Non-destructive examination

4.2.4.5.1 After proof load testing, all surfaces of every link shall be visually examined. Burrs, irregu-larities and rough edges shall be contour ground. Links shall be free from mill defects, surface cracks, dents and cuts, especially in the vicinity where gripped by clamping dies during flash welding. Studs shall be securely fastened.



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4.2.4.5.2 Magnetic particle procedures shall be em-ployed to examine the flash welded area including the area gripped by the clamping dies. Procedures and equipment in accordance with those approved shall be used. The frequency of examination shall be every link. Link surface at the flash weld shall be free from cracks, lack of fusion and gross porosity.

4.2.4.5.3 Ultrasonic procedures shall be employed to examine the flash weld fusion. Procedures and equip-ment in accordance with those approved shall be used. On-site calibration standards for chain cable configu-rations shall be approved.

The frequency of examination shall be every link.

The flash weld shall be free from defects causing ultrasonic back reflections equal to or greater than the calibration standard.

4.2.4.6 Retest, rejection and repair criteria

4.2.4.6.1 If the length over 5 links is short, the chain cable may be stretched by loading above the proof test load specified provided that the applied load is not greater than that approved and that only random lengths of the chain cable need stretching.

If the length exceeds the specified tolerance, the over length chain cable links shall be cut out and 4.2.4.6.2 shall apply.

4.2.4.6.2 If single links are found to be defective or do not meet other applicable requirements, defective links may be cut out and a connecting common link inserted in their place. The individual heat treatment and inspection procedure of connecting common links is subjected to the GL Surveyor’s approval.

Other methods for repair are subject to the written approval of GL and the end purchaser.

4.2.4.6.3 If a crack, cut or defect in the flash weld is found by visual or magnetic particle examination, it shall be ground down no more than 5 % of the link diameter in depth and streamlined to provide smooth contours. The final dimensions must still conform to the agreed standard.

4.2.4.6.4 If indications of interior flash weld defects in reference to the accepted calibration standards are detected during ultrasonic examination, 4.2.4.6.2 shall apply.

4.2.4.6.5 If link diameter, length, width and stud alignment do not conform to the required dimensions, these shall be compared to the dimensions of 40 more links, 20 on each side of the affected links. If a single particular dimension fails to meet the required dimen-sional tolerance in more than 2 of the sample links, all links shall be examined, 4.2.4.6.2 shall apply.

4.2.4.6.6 If a breaking load test fails a thorough ex-amination, with the Surveyor informed in a timely manner, is to be carried out to identify the cause of failure. Two additional breaking test specimens repre-senting the same sampling length of chain cable are to

be subjected to the breaking load test. Based upon satisfactory results of the additional tests and the re-sults of the failure investigation, it will be decided what lengths of chain cable can be accepted. Failure of either or both of the additional tests will result in re-jection of the sampling length of chain represented, and 4.2.4.6.2 shall apply.

4.2.4.6.7 If a link fails during proof load testing, a thorough examination, with the Surveyor informed in a timely manner, is to be carried out to identify the probable cause of failure of the proof load test. In the event that two or more links in the proof loaded length fail, that length is to be rejected.

The above failure investigation is to be carried out, especially with regard to the presence in other lengths, of factors or conditions thought to be causal to failure.

In addition to the above failure investigation, a break-ing load test specimen is to be taken from each side of the one failed link, and subjected to the breaking load test. Based upon satisfactory results of both breaking load tests and the results of the failure investigation, it will be decided what length of chain can be considered for acceptance. Failure of either or both of the break-ing load tests will result in rejection of the proof loaded length.

Replacement of defective links is to be in accordance with 4.2.4.6.2.

4.2.4.6.8 If the tensile test fails to meet the require-ments, a retest of two further specimens selected from the same sample shall be permissible. Failure to meet the specified requirements of either or both of the additional tests will result in rejection of the sampling length of chain cable represented, and 4.2.4.6.2 shall apply.

4.2.4.6.9 If the impact test requirements are not achieved, a retest of three further specimens selected from the same sample shall be permissible. The results shall be added to those previously obtained to form a new average. The new average shall comply with the requirements. Not more than two individual results are to be lower than the required average and not more than one result is to be below 70 per cent of the speci-fied average value.

Failure to meet the requirements will result in rejec-tion of the sampling length represented, and 4.2.4.6.2 shall apply.

4.2.4.7 Marking

4.2.4.7.1 The chain cable shall be marked at the fol-lowing places:

− at each end

− at intervals not exceeding 100 m

− on links next to shackles or connecting common links

All marked links shall be stated on the Certificate, and the marking shall make it possible to recognise lead-

IV - Part 6 GL 2007


C

ing and tail end of the chain. In addition to the above required marking, the first and last common link of each individual charge used in the continuous length shall be adequately and traceably marked.

The marking shall be permanent and legible through-out the expected lifetime of the chain.

The chain cable shall be marked on the link as fol-lows, compare Fig. 8.4:

− chain cable grade

− Test Certificate No.

− GL Surveyor’s stamp

− month and year of test

The Certificate number may be exchanged against an abbreviation or equivalent. If so, this shall be stated in the Certificate.

The chain cable Certificate shall contain information on number and location of connecting common links. The Certificate number and replacement link number may be exchanged against an abbreviation or equiva-lent. If so, this shall be stated in the Certificate.

��

��

��

�� !��"��

#��!��

Fig. 8.4 Stamping of chain cables

4.2.4.8 Documentation

A complete Chain Cable Inspection and Testing Re-port in booklet form shall be provided by the chain cable manufacturer for each continuous chain cable length. This booklet shall include all dimensional checks, test and inspection reports, NDT reports, process records, photographs as well as details of any non-conformity, corrective action and repair work.

Individual Certificates are to be issued for each con-tinuous single length of chain cable.

All accompanying documents, appendices and reports shall carry reference to the original Certificate num-ber.

The manufacturer will be responsible for storing, in a safe and retrievable manner, all documentation estab-lished for a period of at least 10 years.

4.2.5 Testing and Inspection of Accessories

4.2.5.1 General

All accessories are to be subjected to proof load tests, breaking load tests and mechanical tests after final heat treatment in the presence of a Surveyor. Where the manufacturer has a procedure to record proof loads and the Surveyor is satisfied with the adequacy of the recording system, he need not witness all proof load tests. The Surveyor is to satisfy himself that the testing machines are calibrated and maintained in a satisfac-tory condition.

Prior to test and inspection the chain cable accessories are to be free from scale, paint or other coating.

4.2.5.2 Proof and breaking load tests

4.2.5.2.1 All accessories are to be subjected to the proof load specified for the corresponding chain.

4.2.5.2.2 Chain cable accessories are to be tested to the breaking test loads prescribed for the grade and size of chain cable for which they are intended. At least one accessory out of every batch or every 25 accessories, whichever is less, is to be tested.

For individually produced accessories or accessories produced in small batches, alternative testing will be subject to special consideration. Accessories which have been subjected to a breaking load test are to be scrapped.


At least one accessory (of the same type, size and nominal strength) out of 25 is to be checked for di-mensions after proof load testing. The manufacturer is to provide a statement indicating compliance with the purchaser’s requirements.

4.2.5.4 Mechanical tests

Accessories are to be subjected to mechanical testing as described in 4.2.2.3 and 4.2.2.4. For individually produced accessories or accessories produced in small batches, alternative testing will be subjected to special consideration.

4.2.5.5 Non-destructive examination

After proof load testing all chain cable accessories are to be subjected to a close visual examination. Special attention is to be paid to machined surfaces and high stress regions. All non-machined surfaces are to be sand or shot blasted to permit a thorough examination. All accessories are to be checked by magnetic particle or dye penetration methods.

The manufacturer is to provide a statement that non-destructive examination has been carried out with satisfactory results. This statement should include a brief reference to the techniques and to the Operator’s qualification.



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4.2.5.6 Test failures

In the event of a failure of any test the entire batch represented is to be rejected unless the cause of failure has been determined and it can be demonstrated to the Surveyor’s satisfaction that the condition causing the failure is not present in any of the remaining accesso-ries.

4.2.5.7 Marking

Each accessory is to be marked as follows:

− chain cable grade

− Test Certificate No.

− GL Surveyor’s stamp

− month and year of test

All detachable component parts shall be stamped with a serial number to avoid mixing of components. The Certificate number may be exchanged against an ab-breviation or equivalent. If so, this shall be stated in the Certificate.

4.2.5.8 Documentation

A complete Inspection and Testing Report in booklet form shall be provided by the manufacturer for each order. This booklet shall include all dimensional checks, test and inspection reports, NDT reports, process records as well as any non-conformity, correc-tive action and repair work.

Each type of accessory shall be covered by separate Certificates.

All accompanying documents, appendices and reports shall carry reference to the original Certificate num-ber.

The manufacturer will be responsible for storing, in a safe and retrievable manner, all documentation estab-lished for a period of at least 10 years.

5. Winch system

5.1 Winches

The requirements for mooring winches including their controls are defined in Chapter 5, Section 8, C.

5.2 Fairleads and sheaves

Fairleads and sheaves shall be designed to prevent excessive bending and wear of the anchor lines. The attachments to the hull or structure are to be such as to comply with the requirements of B.1.5.

6. Quality control

Details of the quality control of the manufacturing process of individual anchoring system components are to be submitted. Components shall be designed, manufactured, and tested in accordance with recog-nized standards and, if included in the Classification procedure according to 1.2, also in accordance with GL Rules. Equipment so tested shall, insofar as practi-cal, be legibly and permanently marked with GL's stamp and delivered with documentation which re-cords the results of the tests. Concerning details on chain cables see 4.2.

7. Dynamic positioning systems

Thrusters used as a sole means of position keeping shall provide a level of safety equivalent to that pro-vided for anchoring arrangements, to the satisfaction of GL, see also Chapter 5, Section 6, E. and Chapter 6, Section 12, E.

The Class Notations DP1 to DP3 will be assigned if the offshore unit is equipped with such a system, compare Chapter 1, Section 2, C.2.7.

Further details are defined in the GL Rules I – Ship Technology, Part 1 – Seagoing Ships, Chapter 15 – Dynamic Positioning Systems.

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Section 9

Life-Saving Appliances

A. General

1. Scope

1.1 Life-saving appliances shall comply with the relevant applicable International Regulations accord-ing to 2.1 and/or National Regulations and shall be suitable for the type and use of the mobile offshore unit.

1.2 The design and testing of lifeboats, liferafts and rescue boats with their launching appliances is in general not within the scope of Classification of mo-bile offshore units by GL. However, their arrangement in the overall design of the unit and the structure in way of launching appliances taking into account the forces from above appliances are always part of Clas-sification.

1.3 On special request lifeboats and rescue boats and their launching appliances may be approved by GL on the basis of the GL Rules defined in 2.2.

1.4 For the requirements for lifejackets, immer-sion suits, lifebuoys, radio life-saving appliances, distress flares and line-throwing appliances, etc. see B.1.5. These requirements have to follow the regula-tions defined in 2.1.

2. Rules and regulations

2.1 International Regulations

− International Maritime Organisation (IMO): In-ternational Convention for the Safety of Life at Sea (SOLAS), Chapter III - Life-Saving Appli-ances and Arrangements

− IMO: International Life-Saving Appliance Code (LSA Code), Resolution MSC.48(66)

− IMO: Testing and Evaluation of Life Saving Ap-pliances, Resolution MSC.81(70), as amended by MSC.200(80)

− IMO: Code for the Construction and Equipment of Mobile Offshore Drilling Units (MODU Code), Chapter 10

− IMO: Code of Safety for Special Purpose Ships, Resolution A.534(13), Chapter 8

− IMO: 1974 SOLAS Convention, Resolution 6(48), Chapter III

2.2 GL Rules

− GL Rules VI – Additional Rules and Guidelines, Part 2 – Life Saving Appliances, Lifting Appli-ances, Accesses, Chapter 6 – Guidelines for Life-boats and Rescue Boats

− GL Rules VI – Additional Rules and Guidelines, Part 2 – Life Saving Appliances, Lifting Appli-ances, Accesses, Chapter 1 – Guidelines for Live-Saving Launching Appliances

3. Emergency warnings and instructions

3.1 Alarm signals

For alarm and pubic address system see Chapter 6, Section 9.

3.2 Operating instructions

Illustrations and instructions shall be provided on or in the vicinity of lifeboats and liferafts and their launch-ing controls and shall:

− illustrate the purpose of controls and the proce-dures for operating the appliance and give relevant instructions or warnings

− be easily readable under emergency lighting con-ditions

− use symbols in accordance with the recommenda-tions of SOLAS, MODU Code, National Regula-tions, etc.

B. Life-Saving Appliances

1. Type and equipment

1.1 Life-saving appliances shall be suitable for the type and use of the mobile offshore unit.

1.2 The lifeboats shall meet the requirements of the LSA Code, Chapter IV and the Testing Regula-tions defined in A.2.1 and shall be of the following type:

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− totally enclosed lifeboats launched by falls with fire protection and self-contained air support sys-tem considering LSA Code § 4.6, 4.8 and 4.9, or

− free-fall lifeboats with fire protection and self-contained air support system considering LSA Code § 4.7 to 4.9

− if the unit is considered as “special purpose ship”, the reduced requirements according to IMO Reso-lution A.534(13), Chapter 8 may be applied, com-pare A.2.1.

1.3 The liferafts shall meet the requirements for davit-launched liferafts of the LSA Code, Chapter IV and the Testing Regulations defined in A.2.1.

1.4 Lifeboats and liferafts shall be fully equipped as required by the LSA Code, Chapter IV defined in A.2.1. However, for operation in restricted areas items may be dispensed by the Administration of the state of flag or location.

1.5 Personal life saving appliances shall meet the requirements of the LSA Code, Chapter II, of the relevant Administration and of GL considering cli-matic conditions.

2. Number and size

The number and size of life saving appliances has to be defined according to the regulations mentioned in A.2.1.

If not stated otherwise by the responsible Administra-tion, each manned unit should be provided with at least the lifeboats and liferafts listed in the following:

2.1 Mobile surface units

2.1.1 Each unit shall carry on each side, one or more lifeboats of such aggregate capacity as will ac-commodate the total number of persons on board.

2.1.2 In addition, a liferaft or liferafts shall be car-ried, capable of being launched on either side of a unit and of such aggregate capacity as will accommodate the total number of persons on board. If the liferaft or liferafts cannot be readily transferred for launching on either side of a unit, the total capacity available on each side should be sufficient to accommodate the total number of persons on board.

2.1.3 If lifeboats and liferafts are stowed in a posi-tion which is more than 100 m from the stem or stern, in addition to the liferafts as provided in 2.1.2, a lif-eraft shall be stowed as far forward or aft, or one as far forward and another as far as aft, as is reasonable and practicable. Notwithstanding C.3.3 such liferaft or liferafts may be securely fastened so as to permit manual release.

2.2 Self-elevating and column-stabilized units

2.2.1 Each unit shall carry lifeboats, installed in at least two widely separated locations on different sides or ends of the unit. The arrangement of lifeboats should provide sufficient capacity to accommodate the total number of persons on board if:

− all the lifeboats in any one location are lost or rendered unusable, or

− all the lifeboats on any one side, any end or any one corner of the unit are lost or rendered unusable

2.2.2 In addition liferafts shall be carried of such aggregate capacity as will accommodate the total number of persons on board.

2.2.3 In the case of a self-elevating unit where, due to its size or configuration, lifeboats cannot be located in widely separated locations to satisfy 2.2.1 the Ad-ministration of the state of location or flag may permit the aggregate capacity of the lifeboats to accommo-date only the total number of persons on board. How-ever, the liferafts should be served by launching appli-ances.

C. Arrangement of Lifeboats and Liferafts

1. Muster and embarkation arrangements

1.1 If separate, muster stations shall be provided close to the embarkation stations. Each muster station shall have sufficient space to accommodate all persons assigned to muster at that station.

1.2 Muster and embarkation stations shall be readily accessible from accommodation and work areas.

1.3 Muster and embarkation stations shall be adequately illuminated by emergency lighting.

1.4 Alleyways, stairways and exits giving access to the muster and embarkation stations shall be ade-quately illuminated by emergency lighting.

1.5 Davit-launched survival craft muster and embarkation stations shall be so arranged as to enable stretcher cases to be placed in survival craft.

1.6 Survival craft embarkation arrangements shall be so designed that:

− lifeboats can be boarded by their full complement of persons within 3 minutes from the time the in-struction to board is given

− lifeboats can be boarded and launched directly from the stowed position


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− davit-launched liferafts can be boarded and launched from a position immediately adjacent to the stowed position or from a position to which the liferaft is transferred prior to launching in compli-ance with 3.3

− where necessary, means shall be provided for bringing the davit-launched liferaft to struc-ture/hull side and holding it alongside so that per-sons can be safely embarked

2. Stowage

2.1 Each lifeboat and liferaft shall be stowed:

− so that neither they nor their stowage arrange-ments will interfere with the operation of any other lifeboat or liferaft or rescue boat at any other launching station

− as near the water surface as is safe and practicable

− in a state of continuous readiness so that two crew members can carry out preparations for embarka-tion and launching in less than 5 minutes

− as far as practicable, in a secure and sheltered position and protected from damage by fire and explosion

2.2 Lifeboats shall be stowed

− that they are protected from damage by heavy seas

− attached to launching appliances

2.3 Liferafts shall be stowed:

− as to permit manual release from their securing arrangements

− within reach of the lifting hooks, if liferafts are davit-launched; unless some means of transfer is provided which is not rendered inoperable within the limits of trim and list prescribed in Section 7 for any damaged condition or by motion or power failure

− every liferaft, other than those in B.2.1.3, shall be stowed with the weak link of its painter perma-nently attached and with a floatfree arrangement complying with the requirements of the regula-tions defined in A.2. so that the liferaft floats free and, if inflatable, inflates automatically when the unit sinks.

3. Launching and recovery arrangements

3.1 Launching appliances shall be provided for all lifeboats and davit-launched liferafts. They shall meet the requirements defined in Rules and Regula-tion defined in A.2.

3.2 Launching stations shall be in such positions as to ensure safe launching having particular regard to clearance from any exposed propeller, if applicable. Launching stations shall not be located near or even above working stations which would hinder the launching at certain working conditions. The exact position shall be agreed with the Administration and GL.

3.3 Preparation and handling of survival craft at any one launching station shall not interfere with the prompt preparation and handling of any other survival craft or rescue boat at any other station.

3.4 As far as possible, launching stations shall be located so that lifeboats and liferafts can be launched down a straight side of the structure/shell, except for:

− lifeboats and liferafts specially designed for free-fall launching

− lifeboats and liferafts mounted on structures in-tended to provide clearance from lower structures

3.5 Means shall be available to prevent any dis-charge of fluids on to lifeboats or liferafts during abandonment.

3.6 During preparation and launching, lifeboats and liferafts, its launching appliance and the area in the water into which they are to be launched shall be adequately illuminated by emergency lighting.

3.7 Launching and recovery arrangements shall be such that the appliance Operator on the unit is able to observe the survival craft at all times during launch-ing and lifeboats during recovery.

3.8 Falls, where used, shall be long enough for the survival craft to reach the water with the unit un-der unfavourable conditions, such as maximum air-gap, lightest transit or operational condition or any damaged condition as described in Section 7. Only one type of release mechanism shall be used for simi-lar survival craft on board and the opening of the mechanism shall be possible under load from inside the boat.

3.9 In any case of damage defined in the previous Sections, lifeboats with an aggregate capacity of not less than 100 % of persons on board shall, in addition to meeting all other requirements of launching and stowage defined in this Section, be capable of being launched clear of any obstruction.

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D. Rescue Boats

1. Number and requirements

Each unit shall carry at least one fast rescue boat com-plying to the requirements of rules and regulations defined in A.2.

2. Stowage

Rescue boats shall be stowed:

− in a state of continuous readiness for launching in not more than 5 minutes

− in a position suitable for launching and recovery

− so that neither the rescue boats nor their stowage arrangements will interfere with the operation of any lifeboat or raft of another launching station

− in compliance with C.3, if they are lifeboats

3. Embarkation and launching

The rescue boat embarkation and launching arrange-ments shall be such that the rescue boat can be boarded and launched in the shortest possible time.

Launching arrangements shall include a single point hoist and release mechanism and in other aspects comply with C.3.

4. Recovery

Rapid recovery of rescue boats shall be possible when loaded with its full complement of at least six persons and the relevant equipment.


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Annex A

List of Standards, Codes, etc. Quoted

Table A.1 List of Standards, Codes, etc. Quoted

Chapter / Section IACS UR IMO ISO Others

2/1 (D2.2) (D2.1) (D1.6)

ISM – 1 July 2002

2/2 (D.4) (MODU) 2/3 (D.5) (MODU)

2/4 (D.3) (D.6) (D.9)

(MODU)

2/5

A.749(18), MSC.75(69), A.543(13),

MODU

2/6

2/7 (D.3) (D.4) (D.5)

MODU Load Line 66

2/8 (D.3) MODU 1704 9001

2/9

SOLAS Res 6(48) LSA

MSC.48(66) MSC.81(70)

MSC.200(80) A.534(13)

Explanation of abbreviations:

D1 – D12 Requirements concerning Mobile Offshore Drilling Units, Unified Requirements of IACS, 1996 IACS International Association of Classification Societies IMO International Maritime Organization ISM IMO International Safety Management Procedures, 1 July 2002 ISO International Standardization Organization Load Line International Convention on Load Lines 1966 MODU Code for the Construction and Equipment of Mobile Offshore Drilling Units, issued by IMO SOLAS Safety of Life at Sea, issued by IMO (……) reference not explicitly declared in the text

IV - Part 6 GL 2007

Annex A List of Standards, Codes, etc. Quoted Chapter 2Page A–1