EN ISO 19901-7:2005

SLOVENSKI STANDARD
01-september-2006
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Petroleum and natural gas industries - Specific requirements for offshore structures -
Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
(ISO 19901-7:2005)
Erdöl- und Erdgasindustrie - Spezielle Anforderungen an Offshore-Bauwerke - Teil 7:
Betriebssysteme für die Stationsunterhalte schwimmender Anlagen und mobiler Offshore
-Einheiten (ISO 19901-7:2005)
Industries du pétrole et du gaz naturel - Exigences spécifiques relatives aux structures
en mer - Partie 7: Systemes de maintien en position des structures en mer flottantes et
des unités mobiles en mer (ISO 19901-7:2005)
Ta slovenski standard je istoveten z: EN ISO 19901-7:2005
ICS:
75.180.10 Oprema za raziskovanje in Exploratory and extraction
odkopavanje equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 19901-7
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2005
ICS 75.180.10
English Version
Petroleum and natural gas industries - Specific requirements for
offshore structures - Part 7: Stationkeeping systems for floating
offshore structures and mobile offshore units (ISO 19901-
7:2005)
Industries du pétrole et du gaz naturel - Exigences Erdöl- und Erdgasindustrie - Spezielle Anforderungen an
spécifiques relatives aux structures en mer - Partie 7: Offshore-Bauwerke - Teil 7: Betriebssysteme für die
Systèmes de maintien en position des structures en mer Stationsunterhalte schwimmender Anlagen und mobiler
flottantes et des unités mobiles en mer (ISO 19901-7:2005) Offshore-Einheiten (ISO 19901-7:2005)
This European Standard was approved by CEN on 14 November 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
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Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19901-7:2005: E
worldwide for CEN national Members.

Foreword
This document (EN ISO 19901-7:2005) has been prepared by Technical Committee ISO/TC 67
"Materials, equipment and offshore structures for petroleum and natural gas industries" in
collaboration with Technical Committee CEN/TC 12 "Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries", the secretariat of which is
held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by June 2006, and conflicting national
standards shall be withdrawn at the latest by June 2006.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 19901-7:2005 has been approved by CEN as EN ISO 19901-7:2005 without any
modifications.
INTERNATIONAL ISO
STANDARD 19901-7
First edition
2005-12-01
Petroleum and natural gas industries —
Specific requirements for offshore
structures —
Part 7:
Stationkeeping systems for floating
offshore structures and mobile offshore
units
Industries du pétrole et du gaz naturel — Exigences spécifiques
relatives aux structures en mer —
Partie 7: Systèmes de maintien en position des structures en mer
flottantes et des unités mobiles en mer

Reference number
ISO 19901-7:2005(E)
©
ISO 2005
ISO 19901-7:2005(E)
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ii © ISO 2005 – All rights reserved

ISO 19901-7:2005(E)
Contents Page
Foreword. vi
Introduction . viii
1 Scope. 1
2 Normative references. 2
3 Terms and definitions. 2
4 Symbols and abbreviated terms . 7
4.1 Symbols. 7
4.2 Abbreviated terms. 8
5 Overall considerations. 9
5.1 Functional requirements. 9
5.2 Safety requirements. 9
5.3 Planning requirements. 10
5.4 Inspection and maintenance requirements .10
5.5 Analytical tools. 10
6 Design requirements . 10
6.1 Exposure levels. 10
6.2 Limit states . 11
6.3 Defining design situations. 11
6.4 Design situations. 12
7 Actions. 14
7.1 General. 14
7.2 Site-specific data requirements . 14
7.3 Environmental actions on mooring lines . 15
7.4 Indirect actions . 16
7.4.1 General. 16
8 Mooring analysis. 18
8.1 Basic considerations. 18
8.2 Floating structure offset. 19
8.3 Floating structure response . 20
8.4 Mooring line response. 22
8.5 Line tension. 23
8.6 Line length and geometry constraints. 24
8.7 Anchor forces. 24
8.8 Typical mooring configuration analysis and assessment. 24
8.9 Thruster-assisted moorings. 25
8.10 Transient analysis of floating structure motions . 26
9 Fatigue analysis. 27
9.1 Basic considerations. 27
9.2 Fatigue resistance. 28
9.3 Fatigue analysis procedure . 30
10 Design criteria. 35
10.1 Floating structure offset. 35
10.2 Line tension limit . 35
10.3 Grounded line length. 35
10.4 Anchoring systems. 36
10.5 Fatigue safety factor. 38
10.6 Corrosion and wear . 38
ISO 19901-7:2005(E)
10.7 Clearances. 39
10.8 Supporting structures . 39
11 Mooring hardware. 39
11.1 Mooring line components . 39
11.2 Winching equipment. 40
11.3 Monitoring equipment . 40
12 In-service inspection, monitoring and maintenance. 41
12.1 General. 41
12.2 Mobile moorings . 41
12.3 Permanent moorings. 41
13 Dynamic positioning system . 43
13.1 Basic considerations . 43
13.2 Design and analysis. 44
13.3 Design, test and maintenance . 45
13.4 Operating personnel . 45
13.5 Determination of stationkeeping capability . 45
14 Synthetic fibre rope mooring. 45
14.1 Basic considerations . 45
14.2 Fibre rope mooring analysis. 46
14.3 Fatigue analysis. 46
14.4 Creep analysis. 46
14.5 Design criteria. 47
14.6 Model testing. 48
Annex A (informative) Additional information and guidance. 49
A.1 Scope. 49
A.1.1 General. 49
A.1.2 Spread moorings (catenary, taut-line and semi-taut-line) . 49
A.1.3 Single point moorings . 50
A.1.4 Dynamic positioning (DP) systems. 51
A.1.5 Thruster-assisted moorings. 51
A.1.6 Permanent and mobile stationkeeping systems. 51
A.1.7 Mooring line components . 51
A.2 Normative references. 58
A.3 Terms and definitions. 59
A.4 Symbols and abbreviated terms. 59
A.5 Overall considerations. 59
A.5.1 Functional requirements . 59
A.5.2 Safety requirements. 59
A.5.3 Planning requirements . 61
A.5.4 Inspection and maintenance requirements. 61
A.5.5 Analytical tools. 61
A.6 Design requirements . 62
A.6.1 Exposure levels. 62
A.6.2 Limit states . 62
A.6.3 Defining design situations . 62
A.6.4 Design situations . 62
A.7 Actions. 64
A.7.1 General. 64
A.7.2 Site-specific data requirements. 64
A.7.3 Environmental actions on mooring lines . 65
A.7.4 Indirect actions. 66
A.8 Mooring analysis. 67
A.8.1 Basic considerations . 67
A.8.2 Floating structure offset. 67
A.8.3 Floating structure response. 68
A.8.4 Mooring line response. 69
A.8.5 Line tension . 71
iv © ISO 2005 – All rights reserved

ISO 19901-7:2005(E)
A.8.6 Line length and geometry constraints. 71
A.8.7 Anchor forces. 71
A.8.8 Typical mooring configuration analysis and assessment. 71
A.8.9 Thruster-assisted moorings. 73
A.8.10 Transient analysis of floating structure motions . 80
A.9 Fatigue analysis. 80
A.9.1 Basic considerations. 80
A.9.2 Fatigue resistance. 82
A.9.3 Fatigue analysis procedure . 84
A.10 Design criteria. 86
A.10.1 Floating structure offset. 86
A.10.2 Line tension limit . 87
A.10.3 Grounded line length. 87
A.10.4 Anchoring systems. 87
A.10.5 Fatigue safety factor. 95
A.10.6 Corrosion and wear . 95
A.10.7 Clearances. 95
A.10.8 Supporting structures . 95
A.11 Mooring hardware. 95
A.11.1 Mooring line components . 95
A.11.2 Winching equipment. 98
A.11.3 Monitoring equipment . 100
A.12 In-service inspection, monitoring and maintenance. 100
A.12.1 General. 100
A.12.2 Mobile moorings . 100
A.12.3 Permanent moorings. 100
A.13 Dynamic positioning system . 102
A.13.1 Basic considerations. 102
A.13.2 Design and analysis . 102
A.13.3 Design, test and maintenance . 103
A.13.4 Operating personnel. 104
A.13.5 Determination of stationkeeping capability . 104
A.14 Synthetic fibre rope mooring. 104
A.14.1 Basic considerations. 104
A.14.2 Fibre rope mooring analysis. 105
A.14.3 Fatigue analysis. 106
A.14.4 Creep analysis. 106
A.14.5 Design criteria. 108
A.14.6 Model testing. 108
Annex B (informative) Regional information . 109
B.1 Introduction . 109
B.1.1 General comments to the regional information. 109
B.1.2 Specific comments to the regional information . 109
B.2 Offshore Norway. 109
B.2.1 Description of region. 109
B.2.2 Regulatory framework. 109
B.2.3 Technical information. 110
B.2.4 Technical commentary. 112
B.2.5 Additional national requirements. 112
Bibliography . 113

ISO 19901-7:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 19901-7 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 7, Offshore structures.
This first edition of ISO 19901-7 cancels and replaces ISO/TR 13637:1997, of which it constitutes a technical
revision.
ISO 19901 consists of the following parts, under the general title Petroleum and natural gas industries —
Specific requirements for offshore structures:
⎯ Part 1: Metocean design and operating considerations
⎯ Part 2: Seismic design procedures and criteria
⎯ Part 4: Geotechnical and foundation design considerations
⎯ Part 5: Weight control during engineering and construction
⎯ Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
The following parts are under preparation:
⎯ Part 3: Topsides structure
⎯ Part 6: Marine operations
ISO 19901 is one of a series of standards for offshore structures. The full series consists of the following
International Standards.
⎯ ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
⎯ ISO 19901 (all parts), Petroleum and natural gas industries — Specific requirements for offshore
structures
vi © ISO 2005 – All rights reserved

ISO 19901-7:2005(E)
1)
⎯ ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
1)
⎯ ISO 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
⎯ ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls,
2)
semi-submersibles and spars
⎯ ISO 19904-2, Petroleum and natural gas industries — Floating offshore structures — Part 2: Tension leg
3)
platforms
⎯ ISO 19905-1, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
3)
units — Part 1: Jack-ups
⎯ ISO/TR 19905-2, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
3)
units — Part 2: Jack-ups commentary
3)
⎯ ISO 19906, Petroleum and natural gas industries — Arctic offshore structures

1) To be published.
2) To be published.
3) Under preparation.
ISO 19901-7:2005(E)
Introduction
The series of International Standards applicable to types of offshore structure, ISO 19900 to ISO 19906,
constitutes a common basis covering those aspects that address design requirements and assessments of all
offshore structures used by the petroleum, petrochemical and natural gas industries worldwide. Through their
application the intention is to achieve reliability levels appropriate for manned and unmanned offshore
structures, whatever type of structure and nature or combination of materials used.
It is important to recognize that structural integrity is an overall concept comprising models for describing
actions, structural analyses, design rules, safety elements, workmanship, quality control procedures and
national requirements, all of which are mutually dependent. The modification of one aspect of design in
isolation can disturb the balance of reliability inherent in the overall concept or structural system. The
implications involved in modifications, therefore, need to be considered in relation to the overall reliability of all
offshore structural systems.
The series of International Standards applicable to types of offshore structure is intended to provide wide
latitude in the choice of structural configurations, materials and techniques without hindering innovation.
Sound engineering judgement is therefore necessary in the use of these International Standards.
This part of ISO 19901 was developed in response to the worldwide offshore industry’s demand for a coherent
and consistent definition of methodologies to analyse, design and evaluate stationkeeping systems used for
floating production and/or storage platforms of various types (e.g. semi-submersibles, spar platforms, ship-
shaped structures) and to assess site-specific applications of mobile offshore units (such as mobile offshore
drilling units, pipelay units, construction units).
Stationkeeping is a generic term covering systems for keeping a floating structure, which is under the constant
influence of external actions, on a pre-defined location and/or heading with limited excursions. Stationkeeping
systems resist external actions by means of any combination of the following:
⎯ mooring systems (e.g. spread moorings or single point moorings);
⎯ dynamic positioning systems (generally consisting of thrusters).
The external actions generally consist of wind, wave, current and ice actions on the floating structure, mooring
and/or risers.
Some background to, and guidance on, the use of this part of ISO 19901 is provided in informative Annex A.
The clause numbering in Annex A is the same as in the normative text to facilitate cross referencing.
Regional information, where available, is provided in informative Annex B.

viii © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 19901-7:2005(E)

Petroleum and natural gas industries — Specific requirements
for offshore structures —
Part 7:
Stationkeeping systems for floating offshore structures and
mobile offshore units
1 Scope
This part of ISO 19901 specifies methodologies for
a) the design, analysis and evaluation of stationkeeping systems for floating structures used by the oil and
gas industries to support
⎯ production,
⎯ storage,
⎯ drilling, well intervention and production,
⎯ production and storage,
⎯ drilling, well intervention, production and storage, and
b) the assessment of stationkeeping systems for site-specific applications of mobile offshore units (e.g.
mobile offshore drilling units, construction units, and pipelay units).
Most stationkeeping systems used with the class of floating structures covered by a) are termed “permanent
mooring systems”, for which this part of ISO 19901 is applicable to all aspects of the life cycle and includes
requirements relating to the manufacture of mooring components, as well as considerations for in-service
inspections. Most stationkeeping systems used with mobile offshore units, the class covered by b), are termed
“mobile mooring systems”. Throughout this document, the term “floating structure”, sometimes shortened to
“structure”, is used as a generic term to indicate any member of the two classes, a) and b).
This part of ISO 19901 is applicable to the following types of stationkeeping systems, which are either covered
directly in this document or through reference to other guidelines:
⎯ spread moorings (catenary, taut-line and semi-taut-line moorings);
⎯ single point moorings, anchored by spread mooring arrangements;
⎯ dynamic positioning systems;
⎯ thruster-assisted moorings.
Descriptions of the characteristics and of typical components of these systems are given in Annex A.
The requirements of this part of ISO 19901 mainly address spread mooring systems and single point mooring
systems with mooring lines composed of steel chain and wire rope. This document also provides guidance on
the application of the methodology to synthetic fibre rope mooring systems, and includes additional
requirements related to the unique properties of synthetic fibre ropes.
ISO 19901-7:2005(E)
The document applies to single anchor leg moorings (SALMs) and other single point mooring systems (e.g.
tower soft yoke systems) only to the extent to which the requirements are relevant.
The requirements of this document do not apply to the vertical moorings of tension leg platforms (TLPs).
The methodology described in this part of ISO 19901 identifies a set of coherent analysis tools that, combined
with an understanding of the site-specific metocean conditions, the characteristics of the floating structure
under consideration, and other factors, can be used to determine the adequacy of the stationkeeping system
to meet the document’s functional requirements.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 19900, Petroleum and natural gas industries – General requirements for offshore structures
ISO 19901-1, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 1:
Metocean design and operating considerations
ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls, semi-
submersibles and spars
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
action
external load applied to the structure (direct action) or an imposed deformation or acceleration (indirect action)
EXAMPLE An imposed deformation can be caused by fabrication tolerances, settlement, temperature change or
moisture variation.
NOTE An earthquake typically generates imposed accelerations.
[ISO 19900:2002]
3.2
action effect
effect of actions on structural components
[ISO 19900:2002]
EXAMPLE Internal forces, moments, stresses, strains, rigid body motions or elastic deformations.
3.3
catenary mooring
mooring system where the restoring action is provided by the distributed weight of mooring lines
[ISO 19900:2002]
3.4
characteristic value
value assigned to a basic variable, an action or a resistance from which the design value can be found by the
application of a partial factor
2 © ISO 2005 – All rights reserved

ISO 19901-7:2005(E)
NOTE 1 The value usually has a prescribed probability of not being violated which, in the case of an action, will
normally relate to a reference period.
NOTE 2 Adapted from ISO 19900:2002, definition 2.7.
3.5
design criteria
quantitative formulations that describe the conditions to be fulfilled for each limit state
[ISO 19900:2002]
3.6
design service life
assumed period for which a structure or a structural component is to be used for its intended purpose with
anticipated maintenance, but without substantial repair being necessary
NOTE Adapted from ISO 19900:2002, definition 2.12.
3.7
design situation
set of physical conditions during a certain reference period for which the design will demonstrate that relevant
limit states are not exceeded
NOTE Adapted from ISO 19900:2002, definition 2.13.
3.8
dynamic action
action that induces acceleration of a structure or a structural component of a magnitude sufficient to require
specific consideration
3.9
dynamic positioning
DP
stationkeeping technique consisting primarily of a system of automatically controlled on-board thrusters, which
generate appropriate thrust vectors to counter the mean and slowly varying induced actions
3.10
expected value
first-order statistical moment of the probability density function for the considered variable that, in the case of a
time-dependent parameter, can be associated with a specific reference period
3.11
fit-for-purpose
fitness-for-purpose
meeting the intent of an International Standard although not meeting specific provisions of that International
Standard in local areas, such that failures in these areas will not cause unacceptable risk to life safety or the
environment
[ISO 19900:2002]
3.12
floating structure
structure where the full weight is supported by buoyancy
[ISO 19900:2002]
NOTE The full weight includes lightship weight, mooring system pre-tension, riser pre-tension, operating weight, etc.
ISO 19901-7:2005(E)
3.13
limit state
state beyond which the structure no longer fulfils the relevant design criteria
[ISO 19900:2002]
3.14
maintenance
set of activities performed during the operating life of a structure to ensure it is fit-for-purpose
3.15
minimum breaking strength
MBS
RCS certified strength of a chain, wire rope, fibre rope or accessories
3.16
mobile mooring system
mooring system, generally retrievable, intended for deployment at a specific location for a short-term operation,
such as those for mobile offshore units (MOUs)
3.17
mobile offshore drilling unit
MODU
structure capable of engaging in drilling and well intervention operations for exploration or exploitation of
subsea petroleum resources
3.18
mobile
...