DNV OSH Rule

DET NORSKE VERITAS AS

The electronic pdf version of this document found through http://www.dnv.com is the officially binding version

OFFSHORE STANDARD

DNV-OS-H206

Loadout, transport and installation of subsea objects

(VMO Standard - Part 2-6)

SEPTEMBER 2014

Det Norske Veritas AS September 2014

Any comments may be sent by e-mail to [email protected]

This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this document, and is believed to reflect the best ofcontemporary technology. The use of this document by others than DNV is at the user's sole risk. DNV does not accept any liability or responsibility for loss or damages resulting fromany use of this document.

FOREWORD

DNV is a global provider of knowledge for managing risk. Today, safe and responsible business conduct is both a licenseto operate and a competitive advantage. Our core competence is to identify, assess, and advise on risk management. Fromour leading position in certification, classification, verification, and training, we develop and apply standards and bestpractices. This helps our customers safely and responsibly improve their business performance. DNV is an independentorganisation with dedicated risk professionals in more than 100 countries, with the purpose of safeguarding life, propertyand the environment.

DNV service documents consist of among others the following types of documents:

Service Specifications. Procedural requirements.

Standards. Technical requirements.

Recommended Practices. Guidance.

The Standards and Recommended Practices are offered within the following areas:

A) Qualification, Quality and Safety Methodology

B) Materials Technology

C) Structures

D) Systems

E) Special Facilities

F) Pipelines and Risers

G) Asset Operation

H) Marine Operations

J) Cleaner Energy

O) Subsea Systems

U) Unconventional Oil & Gas


Offshore Standard DNV-OS-H206, September 2014

CHANGES CURRENT Page 3

CHANGES CURRENT

General

Det Norske Veritas AS, company registration number 945 748 931, has on 27th November 2013 changed itsname to DNV GL AS. For further information, see www.dnvgl.com. Any reference in this document toDet Norske Veritas AS or DNV shall therefore also be a reference to DNV GL AS.

This is a new document.

General

This is a new document in a series of documents replacing the DNV Rules for Planning and Execution ofMarine Operations (1996/2000); this standard replaces Pt.2 Ch.6. Extensive revisions and/or amendments havebeen made, with the following main changes:

Sec.2 General Requirements is new, combining new content with some original text from Section 4 of theprevious Rules.

The simplified method for estimation of dynamic lift loads and relevant soil force/capacities is covered inDNV-RP-H103 and the items covering these parts in section 2 and 3 in the Rules are hence omitted.

Section 2 and 3 are now section 3 and 7 respectively and they have been considerably re-written. Three (3) new sections have been added:

1) Sec.4 Loadout and transport

2) Sec.5 Subsea lifting

3) Sec.6 Installation of pipelines, risers, cables and umbilicals.



Contents Page 4

CONTENTS

CHANGES CURRENT ................................................................................................................... 3

1 Introduction ............................................................................................................................... 8

1.1 Application .................................................................................................................................................... 8

1.1.1 General ............................................................................................................................................... 81.1.2 Complementary standards ................................................................................................................. 81.1.3 Conditions for use .............................................................................................................................. 8

1.2 References....................................................................................................................................................... 8

1.2.1 Numbering and cross references ........................................................................................................ 8

1.3 Definitions..................................................................................................................................................... 10

1.3.1 Verbal forms..................................................................................................................................... 101.3.2 Terminology..................................................................................................................................... 101.3.3 Abbreviations ................................................................................................................................... 101.3.4 Symbols............................................................................................................................................ 11

2 General requirements ............................................................................................................. 12

2.1 Planning ........................................................................................................................................................ 12

2.1.1 General ............................................................................................................................................. 122.1.2 Operation period............................................................................................................................... 122.1.3 Environmental conditions ................................................................................................................ 122.1.4 Critical design parameters................................................................................................................ 122.1.5 Installation site survey ..................................................................................................................... 132.1.6 Route survey..................................................................................................................................... 132.1.7 Risk management ............................................................................................................................. 13

2.2 Documentation ............................................................................................................................................. 13

2.2.1 General ............................................................................................................................................. 132.2.2 Design documentation...................................................................................................................... 132.2.3 Operation manual ............................................................................................................................. 14

2.3 Lifting appliances......................................................................................................................................... 14

2.3.1 Crane ................................................................................................................................................ 142.3.2 Other lifting appliances .................................................................................................................... 14

2.4 Load and motion limiting systems.............................................................................................................. 15

2.4.1 General ............................................................................................................................................. 152.4.2 Active heave compensation systems................................................................................................ 152.4.3 Passive heave compensation systems .............................................................................................. 16

2.5 Lifting equipment ........................................................................................................................................ 17

2.5.1 General ............................................................................................................................................ 172.5.2 Design considerations ...................................................................................................................... 172.5.3 Wet-storage of lifting equipment ..................................................................................................... 182.5.4 Custom-made lifting equipment....................................................................................................... 182.5.5 Lifting tools ...................................................................................................................................... 182.5.6 Test lift ............................................................................................................................................. 18

2.6 Guiding and positioning systems................................................................................................................ 19

2.6.1 General ............................................................................................................................................. 192.6.2 Control of lift.................................................................................................................................... 192.6.3 Guide lines/guide wires.................................................................................................................... 192.6.4 Bumpers and guides ......................................................................................................................... 19

2.7 Installation aids ............................................................................................................................................ 20

2.7.1 General ............................................................................................................................................. 202.7.2 Design considerations ...................................................................................................................... 202.7.3 Design factor .................................................................................................................................... 20

2.8 Miscellaneous systems ................................................................................................................................. 20

2.8.1 Dynamic positioning systems .......................................................................................................... 202.8.2 Ballasting systems............................................................................................................................ 212.8.3 Atmospheric diving systems ............................................................................................................ 21

2.9 ROV operations............................................................................................................................................ 22

2.9.1 Planning............................................................................................................................................ 222.9.2 Schedule and contingency................................................................................................................ 222.9.3 Maintenance and tests ...................................................................................................................... 222.9.4 ROV Tools ....................................................................................................................................... 232.9.5 Operation.......................................................................................................................................... 232.9.6 Navigation ........................................................................................................................................ 23



Contents Page 5

2.9.7 Launching restrictions...................................................................................................................... 232.9.8 Monitoring........................................................................................................................................ 242.9.9 Deep water ROV operations ............................................................................................................ 24

2.10 Operational requirements........................................................................................................................... 24

2.10.1 Application....................................................................................................................................... 242.10.2 Operation criteria ............................................................................................................................. 242.10.3 Pre-installation surveys ................................................................................................................... 252.10.4 Testing.............................................................................................................................................. 252.10.5 Organization .................................................................................................................................... 252.10.6 Safety and contingency .................................................................................................................... 25

3 Loads and structural design ................................................................................................... 26

3.1 Loads ............................................................................................................................................................. 26

3.1.1 General ............................................................................................................................................. 263.1.2 Loadcases and analysis .................................................................................................................... 26

3.2 Vessel motions and accelerations................................................................................................................ 26

3.2.1 General ............................................................................................................................................. 263.2.2 Characteristic vessel motions generated by wind seas..................................................................... 273.2.3 Characteristic vessel motions generated by swell ............................................................................ 27

3.3 Loads ............................................................................................................................................................. 27

3.3.1 Weight and buoyancy....................................................................................................................... 273.3.2 Hydrostatic loads.............................................................................................................................. 273.3.3 Environmental loads......................................................................................................................... 283.3.4 Accidental loads ............................................................................................................................... 283.3.5 Pull-down and pull-in loads ............................................................................................................. 283.3.6 Off-lead, side-lead forces and horizontal offset ............................................................................... 283.3.7 Loads during positioning.................................................................................................................. 283.3.8 Other loads ....................................................................................................................................... 29

3.4 Structural design.......................................................................................................................................... 29

3.4.1 General ............................................................................................................................................. 293.4.2 Object ............................................................................................................................................... 293.4.3 Bumpers and Guides ........................................................................................................................ 293.4.4 Rigging lay down and securing........................................................................................................ 293.4.5 Seafastening and supporting structures ............................................................................................ 293.4.6 Inspection ......................................................................................................................................... 29

4 Loadout and transport ............................................................................................................ 31

4.1 General.......................................................................................................................................................... 31

4.1.1 Application....................................................................................................................................... 31

4.2 Submerged towing ....................................................................................................................................... 31

4.2.1 General ............................................................................................................................................. 314.2.2 Submerged tow of objects attached to installation vessel ................................................................ 314.2.3 Submerged tow of objects attached to towed buoy.......................................................................... 314.2.4 Surface or sub-surface tow of long slender elements....................................................................... 324.2.5 Loads and analyses........................................................................................................................... 32

4.3 Bundles.......................................................................................................................................................... 32

4.3.1 General ............................................................................................................................................. 324.3.2 Load-out of bundles ......................................................................................................................... 334.3.3 Towing of bundles............................................................................................................................ 33

4.4 Pipelines, risers, cables and umbilicals ..................................................................................................... 34

4.4.1 General ............................................................................................................................................. 344.4.2 Load out by lifting............................................................................................................................ 344.4.3 Load-out by spooling ....................................................................................................................... 344.4.4 Sea transport..................................................................................................................................... 34

4.5 Pipe joints ..................................................................................................................................................... 35

4.5.1 General ............................................................................................................................................. 354.5.2 Load out by lifting............................................................................................................................ 354.5.3 Sea Transport ................................................................................................................................... 354.5.4 Offshore pipe loading....................................................................................................................... 35

5 Subsea lifting............................................................................................................................ 36

5.1 General.......................................................................................................................................................... 36

5.1.1 Application....................................................................................................................................... 36

5.2 Loads and analysis ....................................................................................................................................... 36

5.2.1 Loads ................................................................................................................................................ 365.2.2 Combination of loads ...................................................................................................................... 36



Contents Page 6

5.2.3 Lift analysis - General ...................................................................................................................... 365.2.4 Simplified method for estimation of hydrodynamic forces acting on submerged objects............... 37

5.3 Acceptance criteria ..................................................................................................................................... 38

5.3.1 Acceptance criteria Simplified method......................................................................................... 385.3.2 Acceptance criteria - Alternative .................................................................................................... 38

5.4 More accurate estimation of hydrodynamic forces .................................................................................. 39

5.4.1 General ............................................................................................................................................. 395.4.2 Documentation ................................................................................................................................. 39

5.5 Lifted object.................................................................................................................................................. 39

5.5.1 General ............................................................................................................................................. 395.5.2 Pipelines, risers, cables and umbilicals ............................................................................................ 405.5.3 Spools ............................................................................................................................................... 405.5.4 Retrieval of damaged objects ........................................................................................................... 40

5.6 Operational aspects ..................................................................................................................................... 40

5.6.1 General ............................................................................................................................................. 405.6.2 Installation tolerances....................................................................................................................... 415.6.3 Wet parking...................................................................................................................................... 415.6.4 Safety and contingency .................................................................................................................... 42

5.7 Deep water ................................................................................................................................................... 42

5.7.1 Deep water lowering operations....................................................................................................... 42

6 Installation of pipelines, risers, cables and umbilicals ......................................................... 43

6.1 General.......................................................................................................................................................... 43

6.1.1 Application....................................................................................................................................... 436.1.2 Risk management ............................................................................................................................. 43

6.2 Operational planning................................................................................................................................... 44

6.2.1 General ............................................................................................................................................. 446.2.2 Operation period............................................................................................................................... 446.2.3 Continuous operations...................................................................................................................... 446.2.4 Safety and contingency .................................................................................................................... 446.2.5 Operation manual ............................................................................................................................. 44

6.3 Installation spread, aids and ancillary equipment.................................................................................... 44

6.3.1 Installation spread ............................................................................................................................ 446.3.2 Calibration and testing .................................................................................................................... 456.3.3 Installation aids and ancillary equipment......................................................................................... 456.3.4 Abandonment and recovery system ................................................................................................. 456.3.5 In-line and termination structures .................................................................................................... 466.3.6 (Platform) Pull-in winch systems..................................................................................................... 46

6.4 Loads and design.......................................................................................................................................... 46

6.4.1 Loads ................................................................................................................................................ 466.4.2 Load effects ...................................................................................................................................... 476.4.3 Limit states ....................................................................................................................................... 476.4.4 Failure modes ................................................................................................................................... 47

6.5 Installation - General................................................................................................................................... 48

6.5.1 General ............................................................................................................................................. 486.5.2 Initiation .......................................................................................................................................... 486.5.3 Laying ............................................................................................................................................. 486.5.4 Lay monitoring................................................................................................................................. 486.5.5 Lay-down ......................................................................................................................................... 496.5.6 Shore pull ......................................................................................................................................... 49

6.6 Product specific installation requirements ................................................................................................ 50

6.6.1 Pipeline system installation.............................................................................................................. 506.6.2 Riser, umbilical and cable installation ............................................................................................. 506.6.3 J-tube pull-in of flexible risers, flexibles pipelines, umbilicals and cables ..................................... 506.6.4 Bundle and pipe string installation................................................................................................... 516.6.5 Tie-in of pipe strings and bundles ................................................................................................... 51

6.7 Tie-in operations .......................................................................................................................................... 51

6.7.1 Application ...................................................................................................................................... 516.7.2 General ............................................................................................................................................. 51

7 Soil and foundations ................................................................................................................ 52

7.1 Soil capacity and on bottom stability ......................................................................................................... 52

7.1.1 General ............................................................................................................................................. 527.1.2 Stability calculations ........................................................................................................................ 527.1.3 Material factors ................................................................................................................................ 52



Contents Page 7

7.2 Loads and installation aspects .................................................................................................................... 52

7.2.1 Positioning loads .............................................................................................................................. 527.2.2 Installation effects on the soil .......................................................................................................... 527.2.3 Penetration and levelling of skirted foundations.............................................................................. 53

7.3 Miscellaneous ............................................................................................................................................... 53

7.3.1 Effects of conductor installation and shallow well drilling ............................................................. 537.3.2 Retrieval of object ............................................................................................................................ 54



Sec.1 Introduction Page 8

SECTION 1 INTRODUCTION

1.1 Application

1.1.1 General

1.1.1.1 This standard, DNV-OS-H206 - Loadout, transport and installation of subsea objects, providesrequirements, recommendations and guidance for loadout, transport and installation of subsea objects.

1.1.1.2 The standard applies to subsea objects being lowered to their final position on the seabed by cranes orother means, or pulled down or ballasted from the sea surface. Typical objects covered are subsea structures,pipelines, umbilicals, bundles, cables and risers.

1.1.2 Complementary standards

1.1.2.1 DNV offshore standards covering marine operations, i.e. DNV-OS-H101, DNV-OS-H102 and DNV-OS-H201 through DNV-OS-H206, are collectively referred to as the VMO Standard.

Guidance note:

The VMO Standard supersedes and replaces DNV - Rules for Planning and Execution of Marine Operations. See

also Table 1-2.

---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

1.1.2.2 General recommendations for planning, loads associated with and the design of marine operations aregiven in DNV-OS-H101 and DNV-OS-H102.

1.1.2.3 Complementary guidance and recommendations for lifting operations in air are given in DNV-OS-H205.

1.1.2.4 For positioning and station keeping of installation vessels, relevant requirements in DNV-OS-H203should be considered.

1.1.3 Conditions for use

1.1.3.1 The objectives of this Standard are stated in DNV-OS-H101 Sec.1 A.

1.1.3.2 The general conditions for use of this Standard are stated in DNV-OS-H101 Sec.1 B200.

1.2 References

1.2.1 Numbering and cross references

1.2.1.1 Table 1-1 defines the numbering system used throughout this standard, in comparison with thatadopted in some of the DNV-H series of offshore standards, published to date. See Table 1-2.

1.2.1.2 The text in this standard includes references to the documents listed in Table 1-2. If indicated wherethe references are given, the referenced text shall be considered as part of this standard.

1.2.1.3 Requirements herein are based on the document revisions listed in Table 1-2; however the latestrevision shall normally be applicable, unless otherwise agreed.

Guidance note:

The agreement should be made (normally through contracts) between the parties involved, typically Company,

Contractors and MWS.


Table 1-1 Numbering

Level Numbering Numbering in some published DNV-H standards

Sections 1 Sec. 1, 2, 3

Sub-Sections 1.1 A., B., C..

Paragraphs 1.1.1 A 100, A 200, A 300

Items 1.1.1.1 101, 102.., 201, 202.., 301, 302




1.2.1.4 The documents listed in Table 1-3 include information that through references in this text, clarify andindicate acceptable methods of fulfilling the requirements given in this standard.

1.2.1.5 The latest revision of the informative references should normally be considered.

Table 1-2 Normative references

Reference Revision Title

DNV-OS-E407 Oct 2012 Underwater Deployment and Recovery Systems

DNV-OS-F101 Oct 2013 Submarine Pipeline Systems

DNV-OS-F201 Oct 2010 Dynamic Risers

DNV-OS-H101 Oct 2011 Marine Operations, General (VMO Standard Part 1-1)

DNV-OS-H102 Jan 2012 Marine Operations, Design & Fabrication (VMO Standard Part 1-2)

DNV-OS-H201 Apr 2012 Load Transfer Operations (VMO Standard Part 2-1)

DNV-OS-H202 See note Sea Transport (VMO Standard Part 2-2)

DNV-OS-H203 Feb 2012 Transit and Positioning of Offshore Units (VMO Standard Part 2-3)

DNV-OS-H204 Nov 2013 Offshore Installation Operations (VMO Standard Part 2-4)

DNV-OS-H205 Apr 2014 Lifting Operations (VMO Standard Part 2-5)

Note: Publication of the complete DNV-OS H-series is planned during the period October 2011 - January 2015. Each OS will enter into force on the date of publication. Until the OS is published the relevant requirements in DNV - Rules for Planning and Execution of Marine Operations shall be considered governing.

Table 1-3 Informative references

Reference Title

DNV-RP-H101 Risk Management in Marine- and Subsea Operations

DNV-RP-H102 Marine Operations during Removal of Offshore Installations

DNV-RP-H103 Modelling and Analysis of Marine Operations

DNV-RP-C205 Environmental Conditions and Environmental Loads

DNV-RP-A203 Qualification Procedure for New Technology

DNV-RP-J301 Subsea Power Cables in Shallow Water Renewable Energy Applications

DNV-RP-H201 Subsea Lifting (Planned issued October 2014)

DNV 2.7-3 DNV Standard for Certification No 2.7-3 Portable Offshore Units

DNV Ship Rules DNV Rules for Classification of Ships

DNV-OS-E303 Offshore Fibre Ropes

DNV CN30.4 DNV Classification Note 30.4 Foundations

ND/0029 GL Noble Denton Guidelines for Submarine Pipeline Installation

ND/0035 GL Noble Denton Guidelines for Offshore Wind Farm Infrastructure Installation

IMO MSC/ Circ. 645 Guidelines for vessels with dynamic positioning systems

NORSOK U-102 Remotely Operated Vehicle (ROV) Services

IMCA AODC 032 Remotely Operated Vehicle Intervention During Diving Operations

IMCA D 014 International Code of Practice for Offshore Diving

ISO-13628-2 Design and operation of subsea production systems - Part 2: Unbonded flexible pipe systems for subsea and marine applications

ISO-13628-5 Design and operation of subsea production systems - Part 5: Subsea umbilicals

ISO-13628-11 Design and operation of subsea production systems - Part 11: Flexible pipe systems for subsea and marine applications

API 17E Specification for Subsea Umbilicals, Fourth Edition (ISO 13628-5:2009, Identical Adoption)

API 17J Specification for Unbonded Flexible Pipe

API 17B Recommended Practice for Flexible Pipe




1.3 Definitions

1.3.1 Verbal forms

1.3.1.1 Verbal forms of special importance are defined as indicated below in this standard.

1.3.2 Terminology

1.3.2.1 Terms of special importance are defined as indicated below in this standard. See also DNV-OS-H101for general terms and DNV-OS-H205 for lifting related terms.

1.3.3 Abbreviations

1.3.3.1 The list below defines abbreviations used within this standard:

Table 1-4 Verbal forms

Term Definition

Shall Verbal form used to indicate requirements strictly to be followed in order to conform to the document.

Should Verbal form used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred but not necessarily required.

May Verbal form used to indicate a course of action permissible within the limits of the document.

Table 1-5 Terms

Term Description

Characteristic condition: A condition which has a defined probability of being exceeded within a defined time period, see also DNV-OS-H101 Sec.3 A300.

Characteristic load: The reference value of a load to be used in the determination of load effects. See also DNV-OS-H102, Table 3-1.

Design load: The design value of a load found by combining the relevant characteristic load(s) multiplied by the appropriate load factor(s).

Design sea state: The short term wave condition which forms a basis for the design and design verification.

Object: The structure handled during the marine operation, typically a structure, pipeline, cable, riser, umbilical etc. that will be permanently installed subsea.

Product: This is used as a collective term for the various objects covered in Sec.6.

Short term wave condition:

A wave condition where significant wave height and zero crossing wave period are assumed constant in the duration time, typically 3 hrs.

Significant wave height: Four times the standard deviation of the surface elevation in a short term wave condition (approximately equal to the average wave height associated with the highest third of all waves).

Snap force: Short-duration dynamic force associated with sudden changes in velocity of a lifted object, or sudden tensioning of a slack cable system, e.g. in the case of uncontrolled lift-off from a supply vessel or sea-bed, and/or during uncontrolled deployment/recovery through the splash-zone.

Zero crossing wave period:

Average wave period, i.e. average time interval between upward or downward crossings of the still water level by the water surface.

ADS Atmospheric diving systems

AHC Active heave compensating

ALS Accidental limit state, see DNV-OS-H102

CoB Centre of buoyancy

CoG Centre of gravity

DAF Dynamic amplification factor

DAFconv Converted DAF, i.e. DAF calculated as a function of weight in air (m g) of the object

DP Dynamic positioning

FMEA Failure mode effect analysis

HAZOP Hazard and operability study

MBL Minimum breaking load

MPI Magnetic particle inspection

PHC Passive heave compensating

ROV Remotely operated vehicle




1.3.4 Symbols

1.3.4.1 The list below defines symbols used within this standard:

TLP Tension leg platform

ULS Ultimate limit state, see DNV-OS-H102

UT Ultrasonic testing

VIV Vortex induced vibration

AROV Projected cross sectional area of ROV.

dcab Diameter of (submerged) cable.

Fcur Horizontal current force on ROV

Fhyd Characteristic hydrodynamic load.

Fpd Forces on object when pulled down in lock-in position.

Fsnap Characteristic snap load

Fstatic Static submerged weight of object.

Fstatic-min Minimum static submerged weight

Fstatic-max Maximum static submerged weight

Ftotal Total (static + hydrodynamic) characteristic load on the object

g Acceleration due to gravity.

Hs Significant wave height of design sea state.

K Stiffness of hoisting system.

lcab Projected length of submerged cable.

m Mass of object in air.

TR Operation reference period, see DNV-RP-H101.

vcur Maximum current velocity.

ct Characteristic single amplitude vertical motion of crane tip.



Sec.2 General requirements Page 12

SECTION 2 GENERAL REQUIREMENTS

2.1 Planning

2.1.1 General

2.1.1.1 Subsea operations shall be planned and documented according to the requirements and philosophiesgiven in DNV-OS-H101 Sec.2.

2.1.1.2 Operational requirements/restrictions, see [2.10], shall be duly considered in the planning phase.

2.1.2 Operation period

2.1.2.1 The required operation reference period TR (defined in DNV-OS-H101 Sec.4 B200) should bethoroughly evaluated at an early stage.

2.1.2.2 The start and end points for subsea installation operations shall be Safe Conditions. The SafeConditions and point(s) of no return, if any, should be clearly defined. Safe Condition is defined in DNV-OS-H101 Sec.2 A102 Guidance Note. See [6.2.3] for continuous operations.

Guidance note:

The time expected for the removal of seafastening should normally be included in the operation reference period. Thestart of seafastening removal will normally be defined as a point of no return unless equipment and procedures forreinstatement of seafastening has been planned and accounted for in the operation reference period.


2.1.3 Environmental conditions

2.1.3.1 Subsea installation operations will normally be weather restricted; planning should include a thoroughevaluation of the expected environmental conditions to ensure that there will be adequate weather windows forthe planned operations.

Guidance note:

A subsea installation operation could comprise several sub-operations, each with different limiting environmentalcriteria.


2.1.3.2 All possible environmental conditions (see DNV-OS-H101 Sec.3) shall be evaluated and consideredduring planning.

2.1.4 Critical design parameters

2.1.4.1 When evaluating a subsea operation, the parameters listed below should as found relevant, be takeninto account prior to establishing the operation and design criteria (see also DNV-OS-H101 Sec.4 B).

a) water depth

b) tide

c) on bottom visibility

d) accuracy of survey equipment

e) available current data

f) wave/wind statistics for area in question

g) the expected operation reference period

h) expected time to reverse the operation

i) type of operation

j) contingency procedures, e.g. retrieval or abandonment of object

k) type of installation vessel/equipment

l) weather forecast and monitoring uncertainties

m) vessel response characteristics

n) deck handling/over-boarding restrictions

o) type of lifting gear

p) crane capacity and specifications

q) weight of crane wire (in deep water)




r) crane tip motion

s) crane hoisting/lowering speed

t) hydrostatic and hydrodynamic effects (air filled structure or not)

u) entrapped air

v) submerged weight

w) tugger line forces

x) operational restrictions on tugger line disconnection

y) guide wire forces and winch speed limitations

z) soil conditions and soil properties

aa) seabed topography

ab) load reducing systems (heave compensation capacities)

ac) vessel DP capability /position keeping systems

ad) ROV station keeping capability

ae) ROV working range

af) complexity of ROV tasks (e.g. ROV Interfaces on structure).

2.1.5 Installation site survey

2.1.5.1 The planning process shall incorporate information gathered from site surveys to account for prevailingsoil conditions, see [2.1.4.1] item z) and aa).

2.1.5.2 In general, installation site surveys should be carried out as described in DNV-OS-H204 Sec.2 [4.3].

Guidance note:

The below listed aspects could be of relevance for subsea installations and the survey should hence give adequateinput to evaluate properly these aspects:

a) Limiting set-down velocity. I.e. to estimate soil-structure interaction effects due to installation impact loads.

b) Suction forces (reverse end bearing) during rapid pull-out.

c) Off-target position of object, both due to alternative permanent positions and due to contingency set-down.

d) Scour/build-up caused by current.


2.1.6 Route survey

2.1.6.1 For pipelines, umbilicals, flexibles, cables and submerged tows, route surveys shall be carried outalong the total length of the planned route to provide sufficient data for design and installation related activities.

Guidance note:

More information regarding route surveys and their purpose can be found in the following documents/sections:

For pipelines: DNV-OS-F101 Sec.3.

For subsea cables: DNV-RP-J301 [3.4]

Submerged pipeline towing: DNV-OS-F101 Sec.10 F500

Bundles: [4.3.3.3]


2.1.7 Risk management

2.1.7.1 Operational risk should be evaluated and handled in a systematic way see DNV-OS-H101 Sec.2 C.

2.2 Documentation

2.2.1 General

2.2.1.1 General requirements for documentation are given in DNV-OS-H101 Sec.2 B.

2.2.2 Design documentation

2.2.2.1 Depending on type of structure the following design documentation is normally required as a minimum:

Design load evaluations/calculations/analysis including motion response characteristics for installationvessel(s).




Structural strength analysis and stability calculations for the object. Strength and capacity calculations for all equipment and (temporary) structures. Technical specifications, certificates and test reports for equipment. Documentation of soil characteristics. Vessel data, stability and strength verifications.

Guidance note:

For lifting appliances the design documentation should normally be given in the form of certificates - however, seealso [2.3.2].


2.2.2.2 If monitoring is used as a means of operational control, expected target monitoring results should bedocumented by calculation. Target monitoring values and acceptable tolerances on them should be clearlydefined.

2.2.3 Operation manual

2.2.3.1 An operation manual shall be prepared, see DNV-OS-H101 4 G200.

2.2.3.2 The items listed below should be adequately covered in the manual. A clear reference to the documentswhere this information could be found may normally be considered as adequately covered.

a) Operational organisation chart(s) and responsibilities of key personnel.

b) Description of limiting operational environmental criteria and requirements for weather forecasting andwind/wave/current monitoring.

c) Detailed operation schedule and weather window requirements, ref. DNV-OS-H101 Sec.4 B.

d) Pre-launch/deployment checklists ensuring that all required preparations have been carried out.

e) Clearly defined and measurable installation tolerances.

f) Target position of the object and vessels during all phases of the operation.

g) Procedures for handling of possible contingency situations (see [2.10.6]).

h) Object limiting structural criteria (e.g. max allowable tension, min. allow. tension, MBR, etc.)

i) Description of equipment limitations.

j) Detailed description of operational steps, supported by relevant drawings and sketches.

2.3 Lifting appliances

2.3.1 Crane

2.3.1.1 Crane and crane vessel shall comply with the requirements in DNV-OS-H205 [2.2].

2.3.2 Other lifting appliances

2.3.2.1 The capacity and quality of underwater deployment and recovery systems should generally bedocumented as adequate according to the principles described in DNV-OS-E407.

2.3.2.2 If a winch is chosen for deployment of structures to the seabed, the winch shall be regarded as a liftingappliance.

Guidance note:

Documented capacity and load-testing as for a crane, see e.g. DNV 2.22, of deployment winches are mandatory. Otherrequirements to cranes e.g. to monitoring and alarm systems can be evaluated on a case by case basis.


2.3.2.3 Structures, such as A-frames, forming part of a lifting appliance intended for subsea lifts shouldnormally fulfil the design, fabrication and test requirements applicable to cranes; see DNV-OS-H205 [2.2].

Guidance note:

Alternatively, it can be acceptable to define these parts as structures, see DNV-OS-H205 Sec.5. Normally thisapproach would apply to temporary lifting appliances, used for specific operation(s). Note also Table 5-1 in DNV-OS-H205.


2.3.2.4 If traction winches are used for deep water installations, due considerations shall be made to thepossible failure modes of the rope.




Guidance note:

System performance will depend on the type of rope and winch design. Discard criteria for the rope should beestablished based on relevant failure modes identified. See DNV-OS-E303 Offshore fibre ropes (ConditionManagement Program).


2.4 Load and motion limiting systems

2.4.1 General

2.4.1.1 Load and motion limiting systems are devices used to minimise relative motions and dynamic loadsexperienced by a lifted object, during subsea lifting operations.

Guidance note:

Load and motion limiting systems can consist of active or passive heave compensation systems, shock absorbers, softsprings and fenders. Heave compensating systems are generally described DNV-RP-H201 App.C.


2.4.1.2 Load and motion limiting systems shall be designed, fabricated, installed and tested in accordance withrelevant recognised codes and standards, see DNV-OS-H101 Sec.1 B305.

2.4.1.3 Adequate capacity and functionality for the intended use shall be documented. A thorough descriptionof the system and its use during the planned lifting operation shall be provided.

Guidance note:

Typical elements to be evaluated are structural capacity, hydraulic capacity, sufficient stroke length, power supply,adequate cooling etc.


2.4.1.4 Unless adequate reliability can be documented, contingency cases considering malfunction of the load/ motion limiting system shall be investigated. Calculations may be carried out assuming accidental limit state(ALS).

Guidance note:

Adequate reliability implies a documented risk of catastrophic failure less than 1/10,000 per operation. Hence, if therisk of malfunction is greater than 1/10.000 the possible consequence of malfunction, which could be catastrophicfailure, should be analysed. All possible failure modes of load limiting systems should be identified using applicablerisk identification techniques and methods as described in DNV-OS-H101 Sec.2 C200. It should be documented thatthe installation can be safely completed or abandoned at all times, without jeopardizing the integrity of the object.


2.4.2 Active heave compensation systems

2.4.2.1 A subsea lifting operation that relies on an active heave compensation (AHC) system shall be carefullydesigned, ensuring that the operation is carried out in accordance with the systems operational limitations andoperating procedures.

Guidance note:

Consideration of an accidental case (as described in [2.4.1.4]) will normally be required. As a base case therefore, itis recommended to calculate hydrodynamic loads without considering AHC systems.

For sub-operations mentioned in [2.4.2.3] it is normally acceptable to take into account the motion (and if applicableload) reducing effect of an AHC system. The AHC function should be checked before the sub-operation andcontingency procedures in case of an unsuccessful check should be established in order to fulfil the requirement in[2.4.1.4].


2.4.2.2 Efficiency of the heave compensator (in terms of stroke length and /or max pay out/in speed) shallgenerally not be taken higher than 80% of the theoretical operational values.

Guidance note 1:

A safety factor of 0.9 on the stated and documented efficiency reduction factor is recommended, i.e. if the heave compsystem has 90% stated / documented efficiency, the maximum efficiency factor should be 0.9 0.9 0.8, or 80%.





Guidance note 2:

The test results and operational records used to derive the efficiency factor should be based on data from operationswhere the environmental conditions, depth, weight of object and other effects influencing the performance of theheave compensation system are comparable with those of the planned operation.


2.4.2.3 The motion (and if applicable, load) reducing effect of an AHC system should normally be appliedduring sub-operations of limited duration only, e.g. final landing, final positioning or initial phase of retrievalof a subsea object.

Guidance note:

Acceptable duration of AHC operations should be evaluated based on the criticality of the operation and the reliabilityrecord of the AHC.


2.4.2.4 Characteristics and performance of AHC systems shall be documented (see [2.4.1.3]). Performancemay be documented by testing and relevant operational records.

Guidance note:

Guidelines for performance of AHC systems are presented in DNV-RP-H201 App.C.


2.4.2.5 If there is a high risk of significant suction forces and/or soil friction, the appropriate crane mode andits limitations should be duly considered as indicated below:

AHC mode shall only be used in combination with measures to avoid excessive loads.

Guidance note:

Lifting off in AHC mode can give the crane operator control of the lifting speed. There is however a risk of excessiveloading.


Tension Control mode shall be used only in combination with measures to avoid excessive speed.

Guidance note:

Whilst lifting off in Tension Control mode can provide the crane operator with tension control, there is a risk ofexcessive lifting speeds.


2.4.3 Passive heave compensation systems

2.4.3.1 The effect of passive heave compensation (PHC) systems (e.g. spring/damper devices) may beaccounted for in hydrodynamic load calculations.

Guidance note:

The dynamics of PHC systems can be calculated following the guidelines in DNV-RP-H103 Sec.5. The effect of suchsystems may also be implemented as soft springs in snap load calculations (see DNV-RP-H103 [4.7]).


2.4.3.2 The characteristics and performance of the PHC system shall be documented (see [2.4.1.3]). Theperformance of the system can be documented by testing and/or operational records.

Guidance note 1:

Guidelines for performance of PHC systems are presented in DNV-RP-H201 App.C


Guidance note 2:

PHC systems can be set up in different ways e.g. with full stroke available to resist loads above the threshold settingor with the stroke divided so that both load increases and reductions can be absorbed (within the available part-strokelengths).


Guidance note 3:

If the rigging includes multiple PHC systems the stability of the system should be demonstrated.


2.4.3.3 If relevant, efficiency of the heave compensator in terms of stroke length and /or max pay out/in speedshould generally not be taken higher than 80% of the theoretical operating range.




Guidance note:

To use an efficiency factor of 80%, system performance of 90% of theoretical values should be documented.


2.5 Lifting equipment

2.5.1 General

2.5.1.1 See DNV-OS-H205 Sec.4 for general definitions and requirements.

Guidance note:

This sub-section includes clarifications and additional recommendations regarding use of lifting equipment for subseaoperations.


2.5.1.2 Subsea lifting equipment materials must be carefully selected to take account of the potential failuremechanisms that may be caused or accelerated by the environment such as galvanic corrosion, stress corrosioncracking or the effects of cathodic protection systems.

2.5.2 Design considerations

2.5.2.1 Lifting equipment shall be verified for the worst combination of dynamic hook load and all reasonablyforeseeable load effects (including unintentional ones).

2.5.2.2 Lift points should be configured such that the risk of damage and/or accidental release of slings (dueto possible impact loads) are negligible.

2.5.2.3 Lift point layout and rigging design shall ensure adequate stability and acceptable tilt of the objectduring all phases.

Guidance note 1:

If adequate lift stability is not obvious by inspection, the risk of overturning should be evaluated, documented andmitigated. Adequate stability of the object should be ensured considering:

all possible unfavourable combinations of sling loads, buoyancy, CoB and CoG (CB and CG), see also DNV-RP-H103 [3.6] and [5.6.1.6]

vertical wave loads

horizontal (differential) wave loads

current loads

lift dynamics.


Guidance note 2:

Due to buoyancy, the tilt of the lifted object can change when being submerged. This should be considered whendefining the optimal tilt in air and water.


2.5.2.4 Lifting equipment should be designed with attention given to the planned subsea release/connection ofthe rigging.

2.5.2.5 Lift points and exposed areas of the lifted object should be designed to allow slackening of lifting wiresand release and controlled recovery of rigging items without snagging.

2.5.2.6 All lifting equipment shall as a minimum incorporate one safety barrier / retention mechanism (safetylatch, split-pin/cotter-pin etc.), itself being adequately secured and protected against accidental release.

Guidance note:

These safety barriers / mechanisms should not be affected by lifting or external loads.


2.5.2.7 For lifting operations with dynamic forces that are large relative to the static weight of the object, it isconsidered normal practise to incorporate a minimum of two safety barriers, again suitably protected againstaccidental release. The primary safety barrier should have adequate strength to accommodate any possible loaddirection.




Guidance note:

ROV spring safety latch hooks should be avoided if there is any possibility of slack slings/snap forces. This becauseeven if the latch has a secondary release barrier the hook may come out of position and the latch take the load whichit is not dimensioned for.


2.5.2.8 Lifting equipment containing hydraulic, pneumatic or other remotely operated release mechanisms,shall be designed to fail safe.

2.5.2.9 Structural lifting elements, like spreader bars, lifting frames, etc. should preferably be free flooding. Ifnot, free flooding maximum depth rating to be calculated and marked on the equipment, see [3.3.2.1].

2.5.2.10 If trunnion-type lift points are used, slings should be mechanically secured against significantdisplacement and unintended release during phases of variable sling load.

2.5.2.11 The lifting arrangement should have sufficient length to allow crane hook to be connected at decklevel in order to avoid working at height on board the installation vessel/barge.

Guidance note:

If not possible e.g. due to lifting height a proper plan for the hooking on including if required physical means asrigging platforms, etc. needs to be in place.


2.5.3 Wet-storage of lifting equipment

2.5.3.1 Lifting and other temporary equipment stored on the seabed shall have adequate resistance against allpossible mechanisms of degradation - material properties shall be justified and documented accordingly.

2.5.3.2 If storage periods beyond normal inspection intervals are anticipated, the means for satisfying anyformal and regular inspection requirements should be agreed.

2.5.3.3 The destructive effect of cyclic loading shall be considered for equipment subject to such loadingduring wet-storage (e.g. pick-up lines connected to buoys).

2.5.4 Custom-made lifting equipment

2.5.4.1 Lifting equipment designed for case-specific usage shall comply with requirements in DNV-OS-H205[5.1.5].

2.5.5 Lifting tools

2.5.5.1 Lifting tools shall comply with requirements in DNV-OS-H205 [4.3.3].

Guidance note:

A lifting tool in this sub-section is defined as a hydraulic tool, internally or externally connected to a tubularreceptacle.


2.5.5.2 It shall be documented that the tool cannot accidentally release due to varying loads (typically lowtension) in the lift system.

2.5.5.3 Lifting tools designed for remote subsea release shall have a back-up release mechanism.

2.5.6 Test lift

2.5.6.1 The need to perform test lifts shall be considered.

Guidance note:

An onshore test-lift is recommended. The actual rigging configuration and lifted load should be used to confirm thatsling lengths and tilt are within specified tolerances and that slings / loose gear can be hooked-up and laid down, safelyand without damage.


2.5.6.2 If the required tolerance on tilt of a submerged object is small (e.g. due to the need to engage with guideposts), a subsea test-lift should also be considered.




Guidance note:

The main purpose of this test is to find the tilt of the object in submerged condition. See also [2.5.2.3] GN 2. Theevaluation of need for testing should consider possible corrective action based on test results and the level ofconfidence in CoG/CoB positions.


2.6 Guiding and positioning systems

2.6.1 General

2.6.1.1 General requirements for guiding and positioning systems are given in DNV-OS-H101 Sec.6 C.Requirements for the operational control of lifts in-air can be found in DNV-OS-H205 [2.3.2]. This sectionclarifies some of the requirements in these documents and where appropriate should be considered tosupplement their requirements.

2.6.2 Control of lift

2.6.2.1 Adequate control of any lift shall be ensured during all phases. See DNV-OS-H205 [2.3.2] forrequirements relating to the lifting in-air phase.

2.6.2.2 In cases where the retrieval of a lifted object to deck is necessary, the following should be considered:

anticipated weight increase and instability due to the effects of entrapped water, debris and drainage duringlifting

available deck space guides and bumpers tugger wire system reinstatement of seafastening.

Guidance note:

The above is also applicable for retrieval/backloading of heavy rigging, spreaderbars, installation tools etc.


2.6.2.3 Subsea disconnection of tugger lines should be suitably planned. If ROVs are to be used fordisconnecting tugger lines, consideration should be given to the limitations and recommendations in [2.9.1].

2.6.3 Guide lines/guide wires

2.6.3.1 Guide wires should be used to prevent rotation of the lifted object during installation. It will normallybe sufficient to prevent rotation during only the final stages of lowering. Other means of preventing rotationcan be acceptable.

2.6.3.2 If guide/pull-down lines fixed to a pre-installed subsea template or similar require a fixed vesselheading, the weather criteria specified for the operation should reflect this.

2.6.3.3 Guide wire tension shall be adjusted to suit the weight of the installed object and possible current forceson the object/lifting gear.

2.6.3.4 If guide wire winches are used to provide wire tension, the weight of the guide wire shall be accountedfor when defining the required winch tension/capacity.

2.6.3.5 Guide wire winch speed shall be considered when defining the operational limiting criteria for theoperation.

2.6.3.6 Capacity of guide-wire attachment points on subsea structures shall satisfy the structural strengthrequirements given in DNV-OS-H102.

2.6.3.7 The guide-wire system shall include a weak link. The capacity of the weak link shall not exceed thedesign load of the guide-wire attachment, or 80% of the system MBL, whichever is less.

2.6.4 Bumpers and guides

2.6.4.1 If a guide system on a subsea structure incorporates more than one guidepost, the use of guide posts ofdiffering length should be considered to facilitate landing of the object.

2.6.4.2 If a guide system consists of guide funnels or similar, the connection of the guide receptacle to thestructure should be designed with consideration given to installation loads (e.g. overload / impact) that coulddamage the integrity of primary structural elements of the object.




2.6.4.3 The design of guiding systems should consider contingency cases and should not limit retrieval of theobject.

2.6.4.4 Due consideration shall be paid to the possibility of the object/structure becoming jammed in the guidesystem.

Guidance note:

Primary and a secondary guiding systems can be required to install structures with smaller tolerances than can besafely achieved (e.g. without risk of jamming) by one system alone. Two independent guiding systems can also berequired in cases where large motions are expected. The primary system should be designed according [2.6.4.1] and[2.6.4.2]; the secondary guiding system being designed to resist residual forces and achieve final alignment/installation.


2.6.4.5 Design requirements for bumpers and guides are given in [3.4.3].

2.7 Installation aids

2.7.1 General

2.7.1.1 General requirements for system and equipment design are given in DNV-OS-H101 Sec.6 A.

Guidance note:

Installation aids are defined herein as purpose-built equipment, used to assist and control a specific phase of a liftingoperation, in turn making it safer and more efficient.


2.7.2 Design considerations

2.7.2.1 Installation aids should be located such that they are not damaged during preceding operations, e.g.lifting of structures, handling of piles, opening/closing of hatches, etc.

2.7.2.2 Temporary attachments having the potential to damage the structure or other equipment should beremoved after final use without undue delay.

2.7.2.3 The use of surface-supplied gas/hydraulic power to connect/lock the object to a pre-installed seabedunit should be avoided. If used, the risk of sustaining of mechanical damage during lowering/positioningshould be assessed and minimised; a sufficient back up system can be necessary to mitigate undue risk.

2.7.2.4 Subsea sheaves, blocks and other equipment that require lubrication during operation should haveclosed or pressure-compensated lubrication systems.

2.7.3 Design factor

2.7.3.1 Rigging equipment used for purposes other than lifting should be used with safety factors adequate forthe intended use.

Guidance note:

If the consequence of failure is considered tolerable by all involved parties, a reduced consequence (safety) factor canbe acceptable. E.g. if the rigging is used for pulling/hold-back only and the consequences of rigging failure areregarded as negligible, a lower consequence factor may be applied, see DNV-OS-H205 [4.1.5].


2.8 Miscellaneous systems

2.8.1 Dynamic positioning systems

2.8.1.1 General requirements for the operation of DP (Dynamic Positioning) vessels are given in DNV-OS-H203 Sec.5.

2.8.1.2 DP operations requiring DP equipment class 2 and 3 shall be restricted (planned, see also [2.8.1.3] and[2.8.1.4] below) based on the power/thrust available after worst single failure.

Guidance note:

The worst single failure concept is further described in DNV Ship Rules Pt.6 Ch.7- Dynamic Positioning Systems, andin IMO MSC/Circ. 645.


2.8.1.3 DP capability should be continuously monitored throughout the operation, and the operation should be




safely terminated if the DP-vessel will no longer be able to keep position if the single failure criterionapplicable to the equipment class should occur. In this context deterioration of environmental conditions andthe necessary time to safely terminate the operation should also be taken into consideration. Possible increasein current forces and uncertainty in the weather forecasting (see DNV-OS-H101) shall be accounted for.

Guidance note:

DP capability plots should be used to verify power/thrust availability based on expected environmental conditions.


2.8.1.4 Should a stand-off mode be impossible, preparations for abandoning or retrieval of an object should bemade in due time, prior to reaching the consequence analysis alarm.

Guidance note:

Stand-off mode is defined as a situation where operation is discontinued and vessel/product/object is temporarily heldin a safe condition. The Stand-off mode shall be designed as a safe condition as defined in DNV-OS-H101 Sec.2A102. Adequate planning should be made to accommodate any vessel heading limitations and object handlingrestrictions.


2.8.1.5 Minimum clearances between a DP vessel and any fixed or floating structures shall be definedconsidering the minimum clearances indicated in DNV-OS-H203 Sec.5 C200, see also DNV-OS-H205[2.3.3.5].

2.8.1.6 For complex and/or close proximity DP operations involving one or more DP vessels, a DP operationprocedure shall be presented.

Guidance note:

The DP procedure shall as a minimum include:

a description of the work that is planned performed

weather criteria (force and direction)

minimum distances between vessels

pre-operation DP testing requirements

foot print testing should be included if found relevant based on the required station keeping accuracy

reference systems setup, including evaluation of possible shadow effects on aerials and thrust interference onhydro-acoustic transducers

engine room and switchboards configuration

communication procedures, internally and between vessels

copy of HAZOP/risk analysis findings and risk reducing measures

training/competence level of key DP personnel.


2.8.2 Ballasting systems

2.8.2.1 For operations requiring ballasting of an object, a suitable ballast control and monitoring system shouldbe provided.

2.8.2.2 Ballast systems utilising external umbilical power supply are subject to the same recommendations asin [2.7.2.3]. The ballast system should be designed to fail safe in case of umbilical damage.

2.8.2.3 All ROV operated valves should be clearly marked according to function and with open/shut (O/S)positions. Valve indicators on critical valves can be considered necessary for visual verification purposes.

2.8.2.4 Analogue pressure gauges to be monitored by ROV shall be of adequate size and have easy-to-readindication and figures.

2.8.2.5 Special back-up or monitoring equipment can be required to avoid uncontrolled ballasting and over-pressurisation.

2.8.3 Atmospheric diving systems

2.8.3.1 Atmospheric diving systems (ADS) shall be certified in accordance with recognised standards.

2.8.3.2 The system and operational procedures should be adequate for the intended work scope. IMCA D 014can be consulted for detailed advice and recommendations.

2.8.3.3 ADS should in general incorporate adequate back-up, enabling 24 hours (around the clock) operabilityif required.




2.8.3.4 Operational reliability should be documented through presentation of dive logs, maintenance recordsetc.

2.8.3.5 It should be documented that the ADS system is capable of operating under the given design andoperational criteria.

2.9 ROV operations

2.9.1 Planning

2.9.1.1 ROV systems and tooling should be selected based on the environmental conditions expected at theworksite during the planned and contingency intervention/observation tasks.

2.9.1.2 When planning for a subsea operation, the following ROV limitations and recommendations should benoted:

a) Minimum practical operational depth in the expected wave conditions, also considering possible wake fromvessel thrusters.

b) ROV working range, i.e. maximum horizontal offset vs. available tether length, considering the worstexpected current conditions.

c) Planning and design of the ROV operation shall as far as possible minimise the operational influence of theROV operator's skill and experience.

d) Poor visibility due to e.g. disturbed soil conditions, stirred up by contact or thruster use close to seabed.

e) Access to working site.

2.9.1.3 The station keeping capability and manoeuvrability of the ROV during operation shall be considered.If the ROV is carrying equipment or is equipped with tooling packages/skids, this needs to be accounted for.

Guidance note:

ROV operations involving moving targets should not normally be undertaken and any ROV manipulator or toolingoperation that requires the pilot to actively control the position of the ROV during performance of the task should beavoided.


2.9.1.4 All essential ROV interfaces should have appropriate grab bars or other means for stabilizing ROV.

2.9.2 Schedule and contingency

2.9.2.1 ROV downtime, both planned and possible/unforeseen (see DNV-OS-H101 Sec.4 B300 and B400),should be taken into consideration when establishing the required weather window.

Guidance note:

ROV contingency procedure(s) developed to ensure that one ROV down failure will not (significantly) compromisethe time to safe position may be considered. See also [2.9.2.3].


2.9.2.2 Realistic ROV recovery time, both for planned maintenance and repairs shall be taken into accountduring planning of the operation.

2.9.2.3 Subsea operations, where operation reference period is based on there being at least one operationalROV at all times, should be equipped with at least two independent ROV spreads. The need for backup ofessential ROV tools should be assessed and if applicable the time needed to switch ROV tools/skids betweenROVs should be accounted for in the planning.

2.9.2.4 The ROV crew should be sufficient to provide 24 hours (around the clock) operability.

Guidance note:

Time/schedule critical ROV operations always implies 24hrs coverage, but such coverage may be deemed notnecessary on some ROVs and OBSROVs.


2.9.3 Maintenance and tests

2.9.3.1 Prior to acceptance of ROV operations, maintenance records and dive logs for each ROV should bepresented. Sufficient spares should be available.

2.9.3.2 For complex and critical stages of the installation that are dependent on ROV operations, Client/Contractor shall demonstrate ROV capability of executing the planned intervention. This may be demonstratedby used of 3D models, mock-up tests, previous experience, etc.




2.9.3.3 Function testing of ROV, ROV equipment and survey spread should be part of the test programdescribed in [2.10.4.1].

2.9.4 ROV Tools

2.9.4.1 All tools shall be adequate for the intended work task.

2.9.4.2 Tools shall be adequately tested and calibrated. Cutting tools shall be tested on deck (using similar wiretype) prior to operation.

2.9.4.3 Tools can influence the ROV operability and power consumption. This should be duly considered inthe ROV/tool selection process.

2.9.5 Operation

2.9.5.1 If complex operations reliant on the skill of the ROV operator alone cannot be avoided, ROV operatorexperience shall be evaluated - training sessions specially adapted for the proposed operation can beappropriate.

Guidance note:

See also [2.9.1.2]c, [2.9.3.2] and [2.10.5.2].


2.9.5.2 ROV thruster capacity for time critical operations should be at least 30% higher than the maximumexpected current force acting on the ROV and its umbilical.

Guidance note:

The horizontal current force on the ROV and the submerged cable may be taken as:

Fcur = 0.615(dcab lcab + AROV) vcur 2[kN]

where

dcab: diameter of submerged cable [m]lcab: projected length of submerged cable [m]AROV: projected cross sectional area of ROV [m

2]vcur: maximum current velocity [m/s]


2.9.5.3 For operations using both ROV(s) and diver(s), any restrictions on simultaneous working should beclarified and considered in advance.

Guidance note:

For guidance on safety considerations that should be taken into account when divers are working with or in the vicinityof ROVs, see AODC 032 Remotely Operated Vehicle Intervention during Diving Operations. These considerationsinclude entanglement of umbilicals, physical contact and electrical hazards.


2.9.5.4 Wire cutting by use of ROVs should only be performed on slack wire ropes or on ropes with very lowtension, e.g. carrying own weight only.

2.9.6 Navigation

2.9.6.1 Means for locating and tracking of the ROV from the surface are required for navigational purposesand emergency recovery.

Guidance note:

There is a potential risk of acoustic interference, such as shadowing or noise under several conditions, for example ifseveral vessels are operating in the same area. Frequencies for acoustic beacons should be selected to avoidinterference.


2.9.7 Launching restrictions

2.9.7.1 ROV launching and recovery restrictions shall be defined based on the capacity of the launch andrecovery system, including capacity of the umbilical. In addition any restrictions related to operational aspectsneed to be considered.

2.9.7.2 The over-boarding system shall be safely operated within its intended design limit and dueconsideration of ROV recovery needs to accounted for in the definition of the weather criteria.




Guidance note:

The launch and recovery system should incorporate a guide/cursor system to ensure controlled clearance withvessel side during lowering through the splash zone.

Overboard launching and retrieval of large ROV's should not take place in sea states exceeding 2.5-3.0 m (Hs) ifnot the ability to operate in a safe manner under more severe conditions has been documented.

Moon-pool ROV operations may be extended to Hs < 5-6 m, depending on the motion characteristics of the vessel.


2.9.7.3 Launch and recovery shall as much as practically possible take place at safe distance from sensitivesubsea infrastructure.

2.9.8 Monitoring

2.9.8.1 Video monitoring of all Subsea operations should in general be provided, e.g. ROV, diver-operated,etc. Any critical part of the operation should be performed with such monitoring.

2.9.8.2 All diving and complex Work-ROV operations should be monitored by independent ROV withmonitoring as its only task.

2.9.8.3 The ROV used for monitoring subsea operations should, as far as practically possible, be operated fromthe installation vessel.

2.9.8.4 If the ROV operation has to be performed by a vessel other than the installation vessel, the stability andreliability of the video-link system between the vessels shall be proven under the given conditions.

Guidance note:

Some operations can require a large horizontal distance between the installation vessel and the observation ROV, thusnecessitating a separate ROV vessel. The video-link should be tested prior to start of operation.


2.9.9 Deep water ROV operations

2.9.9.1 ROV equipment capacities shall be chosen to suit the relevant depth.

Guidance note:

Both the ROV and any ROV tooling should be depth rated, and their stated depth limitation should not be exceeded.General wear on the complete ROV spread during deep water operations is more extensive than during moderatedepth operations, it is important therefore that all required maintenance is done prior to operation. During deep wateroperations special attention shall be given to lubrication systems which can be affected by the external water pressure.


2.9.9.2 Current forces acting on the umbilical and ROV shall be defined, see [2.9.5.2].

2.9.9.3 Potential effects due to resonance in wires, cables, umbilicals, etc. shall be investigated and accountedfor in the design.

2.10 Operational requirements

2.10.1 Application

2.10.1.1 Requirements in DNV-OS-H101 Sec.4 will generally apply. This section should be consideredsupplementary to the requirements for subsea operations.

2.10.1.2 For lifting operations in air the requirements to operational aspects given in DNV-OS-H205 [2.3] areapplicable.

2.10.2 Operation criteria

2.10.2.1 Operational limiting criteria and required weather windows shall be clearly defined for all parts ofsubsea operations.

Guidance note:

DNV OSH Rule

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