-
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
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DET NORSKE VERITAS AS
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.
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
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.
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction Page 9
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction Page 10
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
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
Sec.1 Introduction Page 11
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.
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DET NORSKE VERITAS AS
Offshore Standard DNV-OS-H206, September 2014
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.
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
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.
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
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)
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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.
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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]
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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).
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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].
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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].
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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%.
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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.
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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.
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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.
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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.
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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.
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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]).
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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
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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).
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Guidance note 3:
If the rigging includes multiple PHC systems the stability of
the system should be demonstrated.
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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.
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Guidance note:
To use an efficiency factor of 80%, system performance of 90% of
theoretical values should be documented.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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].
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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.
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2.8.1.3 DP capability should be continuously monitored
throughout the operation, and the operation should be
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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.
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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.
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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.
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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.
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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.
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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].
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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.
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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.
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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].
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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]
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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.
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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.
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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.
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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.
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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.
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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.
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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: