prEN ISO 19901-7

SLOVENSKI STANDARD
01-december-2024
Naftna in plinska industrija, vključno z nizkoogljično energijo - Posebne zahteve za
naftne ploščadi - 7. del: Sistemi za vzdrževanje postaj na plavajočih strukturah in
premičnih enotah (ISO/DIS 19901-7:2024)
Oil and gas industries including lower carbon energy - Specific requirements for offshore
structures - Part 7: Station-keeping systems for floating offshore structures and mobile
offshore units (ISO/DIS 19901-7:2024)
Erdöl- und Erdgasindustrie - Spezielle Anforderungen an Offshore-Bauwerke - Teil 7:
Positions-Erhaltungssysteme für schwimmende Offshore-Bauwerke und mobile
Offshore-Einheiten (ISO/DIS 19901-7:2024)
Industries du pétrole et du gaz, y compris les énergies à faible teneur en carbone -
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 (ISO/DIS
19901-7:2024)
Ta slovenski standard je istoveten z: prEN ISO 19901-7
ICS:
75.180.10 Oprema za raziskovanje, Exploratory, drilling and
vrtanje in odkopavanje extraction equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 19901-7
ISO/TC 67/SC 7
Oil and gas industries including
Secretariat: BSI
lower carbon energy — Specific
Voting begins on:
requirements for offshore
2024-10-16
structures —
Voting terminates on:
2025-01-08
Part 7:
Station-keeping systems for floating
offshore structures and mobile
offshore units
ICS: 75.180.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
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Reference number
ISO/DIS 19901-7:2024(en)
DRAFT
ISO/DIS 19901-7:2024(en)
International
Standard
ISO/DIS 19901-7
ISO/TC 67/SC 7
Oil and gas industries including
Secretariat: BSI
lower carbon energy — Specific
Voting begins on:
requirements for offshore
structures —
Voting terminates on:
Part 7:
Station-keeping systems for floating
offshore structures and mobile
offshore units
ICS: 75.180.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2024
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
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Published in Switzerland Reference number
ISO/DIS 19901-7:2024(en)
ii
ISO/DIS 19901-7:2024(en)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 2
3 Terms, Definitions, Symbols, and Abbreviations . 3
3.1 Terms and Definitions .3
3.2 Symbols .11
3.3 Abbreviations . 12
4 Mooring hardware .13
4.1 General . 13
4.2 Off-vessel mooring line components .14
4.2.1 Anchors .14
4.2.2 Chain .14
4.2.3 Fibre rope.14
4.2.4 Steel wire rope . 15
4.2.5 Connecting hardware . 15
4.2.6 Buoys . . 15
4.2.7 Clump weights . 15
4.2.8 Mooring Connectors .16
4.2.9 Quick release connectors .16
4.2.10 Disconnectable turret buoy .16
4.3 On-vessel mooring line components .16
4.3.1 Fairleads .16
4.3.2 Bending shoes .16
4.3.3 Chain stoppers .16
4.3.4 Uni-joints .17
4.3.5 Turret .17
4.4 On-vessel tensioning equipment .17
4.5 Monitoring equipment .17
4.5.1 General .17
4.5.2 Line tension / Line Payout .18
4.5.3 Floating structure position and heading .18
5 Metocean and other site data .18
5.1 General .18
5.2 Metocean data .18
5.2.1 Wave data .18
5.2.2 Wind data .19
5.2.3 Current data.19
5.3 Bathymetry .19
5.4 Geotechnical and Geophysical data .19
5.5 Marine growth . 20
5.6 Physicochemical parameters . 20
5.7 Ice-related . 20
6 Design and site assessment of station-keeping systems .20
6.1 Fundamental Requirements . 20
6.2 Functional requirements . 20
6.3 Safety requirements .21
6.4 Planning requirements . 22
6.4.1 General . 22
6.4.2 Design basis . 22
6.4.3 Design Practices . . 22
6.4.4 Installation Considerations at Design Stage . 23
6.4.5 Integrity Management strategy . 23

iii
ISO/DIS 19901-7:2024(en)
6.5 Rules and regulations . 23
6.6 Independent verification for permanent systems .24
6.7 Numerical tools .24
6.8 Design conditions .24
6.8.1 Limit States.24
6.8.2 Analysis Cases for Ultimate Limit State. 25
6.8.3 Analysis Cases for Serviceability Limit State .27
6.8.4 Analysis Cases for Fatigue Limit State . 28
6.8.5 Analysis Cases for Accidental Limit State . 29
6.8.6 Analysis Cases for Temporary Phases . 29
7 Design and site assessment criteria . .30
7.1 Safety factors for mooring component strength . 30
7.1.1 Line tensions . 30
7.1.2 Anchor factors of safety .31
7.1.3 Factors of safety for buoyancy elements . . 33
7.2 Vessel offsets and heading . 34
7.3 Requirements for clearances . 34
7.3.1 Mooring line with seabed (thrash zone) . 34
7.3.2 Mooring line with sea surface . 35
7.3.3 Mooring line with hull . 35
7.3.4 Mooring line with riser, umbilical, mooring line, pipeline, seabed assets, and
exclusion zones . 35
7.3.5 Submerged turret buoy . 35
7.3.6 Anchor with mooring line, pipeline, seabed assets, and exclusion zones . 35
7.4 Safety factors for mooring component fatigue resistance . 36
8 Analysis . .38
8.1 General . 38
8.2 Analysis methods . 39
8.3 Coupling effects . 39
8.4 Environmental loads on the floating structure . 40
8.4.1 Wave forces . 40
8.4.2 Wind forces . 40
8.4.3 Current forces and VIM .41
8.5 Environmental loads on mooring lines and risers .41
8.5.1 Wave forces .41
8.5.2 Current forces .41
8.6 Mooring analysis for strength, offsets, and clearances.41
8.6.1 Basic considerations .41
8.6.2 Extreme value statistics .41
8.6.3 Design values for responses to transient wind squalls .42
8.6.4 Mitigating mooring line trenching effects .42
8.7 Mooring analysis for fatigue.42
8.7.1 Basic considerations .42
8.7.2 Analysis Approach .42
8.7.3 Fatigue damage calculation methods .43
8.8 Response based analysis .45
9 Dynamic positioning and thruster-assisted mooring.45
9.1 General .45
9.1.1 Dynamic positioning (DP) . 46
9.1.2 Thruster assisted mooring (TAM) . 46
9.2 Equipment . 46
9.2.1 DP and TAM equipment . 46
9.2.2 DP equipment classes .47
9.3 Available effective thrust .47
9.4 Determination of allowable thrust .47
9.5 Load sharing of TAM System . 48
9.5.1 General . 48

iv
ISO/DIS 19901-7:2024(en)
9.5.2 Mean load reduction method . 48
9.5.3 Weathervaning Units . . 48
9.5.4 System dynamic analysis . 49
9.6 Failure mode and effects analysis . 49
9.7 Design, test and maintenance . 49
9.8 Operating personnel . 49
9.9 Determination of station-keeping capability . 50
10 Installation, test load and as-installed survey .50
10.1 General . 50
10.2 Installation considerations and storm-safe criteria . 50
10.3 Mooring line handling and installation procedure . 50
10.4 Test loading requirements .51
10.4.1 Anchor test load for permanent mooring .51
10.4.2 Anchor test load for mobile mooring .51
10.5 Installation Tolerances .52
10.6 Traceability Records .52
10.7 As-installed survey and establishment of as-installed capacity .52
11 Integrity Management, Survey & Inspection, and Monitoring .53
11.1 Integrity management . 53
11.2 Surveys & Inspections . 54
11.3 Mobile moorings. 55
11.4 Permanent moorings . 55
11.4.1 Annual surveys . 55
11.4.2 Complete surveys. 55
11.5 Evaluation & acceptance/discard criteria. 56
11.6 Monitoring . 56
Annex A (informative) Mooring systems .58
Annex B (informative) Regional information .146
Bibliography .192

v
ISO/DIS 19901-7:2024(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO [had/had not] received notice of
(a) patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 67, Oil and gas industries including lower carbon
energy, Subcommittee SC 7, Offshore structures.
This third edition cancels and replaces the second edition (ISO 19901-7:2013), which has been technically
revised.
The main changes are as follows:
— Reorganisation of the table of contents for a more logical flow of requirements from material and
equipment selection, site survey, design considerations, criteria and associated analysis methods to
integrity management during station-keeping system installation and along the system service life.
— Addition of requirements for a formal mooring integrity management system;
— Emphasis on Operator performance standard expectations definition;
— Inclusion of fibre ropes as a standard material such as chain and steel wire ropes;
— Extensive transfer of information material into the informative Annex A;
— Deletion of informative sections related to geotechnical design of anchors to incorporate the same in
19901-4;
— Inclusion of OPB fatigue guidance and Squall design cases guidance;
— Some minor corrections.
A list of all parts in the ISO series 19901 can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

vi
ISO/DIS 19901-7:2024(en)
Introduction
The series of International Standards applicable to offshore structures, ISO 19900 to ISO 19906, constitutes
a common basis covering those aspects that address design requirements and assessments of offshore
structures used by the petroleum, petrochemical and natural gas industries worldwide. The intention in
their application is to achieve reliability levels appropriate for manned and unmanned offshore structures,
irrespective type of structure and the nature or combination of materials used.
It is important to recognize that structural integrity is a concept comprised of models that describe 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 design 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 structures are intended to provide a
wide breadth of choice for structural configurations, materials and techniques without hindering innovation.
Informed 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 station-keeping 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 and flotels) and construction units (such as heavy lift vessels and pipelay units).
For permanent production systems operating procedures for station-keeping systems assume as a minimum
the ability to shut-in wells and the facility in case of emergency (e.g., emergency shut-down valves on the
seabed), otherwise the consequence of mooring failure could be significantly different.
Station-keeping is a generic term covering systems for keeping a floating structure, which is under the
constant influence of external actions, at a pre-defined location and/or heading with limited excursions.
Station-keeping systems resist external actions by means of any of the following:
— mooring systems (e.g., spread moorings or single point moorings),
— dynamic positioning systems (generally consisting of thrusters), and
— a combination of mooring system and thrusters (thruster assisted moorings).
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.

vii
DRAFT International Standard ISO/DIS 19901-7:2024(en)
Oil and gas industries including lower carbon energy —
Specific requirements for offshore structures —
Part 7:
Station-keeping 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 station-keeping systems for floating structures used by the oil
and gas industries to support any combination of:
1) production,
2) storage,
3) offloading,
4) drilling and well intervention.
b) the assessment of station-keeping systems for site-specific applications of mobile offshore units and
construction units.
Most station-keeping 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 station-keeping systems used with mobile offshore units, the class covered by b), are termed
“mobile mooring systems”. Throughout this part of ISO 19901, 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 station-keeping systems, which are either
covered directly in this part of ISO 19901 or through reference to other guidelines:
i) spread moorings,
ii) single point moorings
iii) dynamic positioning systems,
iv) thruster-assisted moorings.
This part of ISO 19901 is not applicable to:
— station keeping systems which do not have redundancy against failure of any single component (e.g.,
single anchor leg moorings (SALMs)),
— station keeping systems which use any means other than mooring lines or thrusters such as tower soft
yoke systems, or tension leg platforms (TLPs) that are using tendons.
The requirements for this part of ISO 19901 address spread mooring systems and single point mooring
systems with mooring lines composed of steel chain, steel wire or synthetic fibre rope.

ISO/DIS 19901-7:2024(en)
Descriptions of characteristics and typical components found in these systems are given in Annex A.
This document includes requirements relating to the selection of mooring components, mooring system
configuration and performance, components design, installation, post-installation survey, and as-installed
assessments as needed for mooring integrity management.
The procedures for the design of permanent or site assessment of mobile mooring systems specified in this
document are based on a deterministic approach where mooring system responses (such as line tensions,
vessel offsets, and anchor loads) are evaluated for a design environment defined by an annual probability
of exceedance or return period. Mooring system responses are then checked against acceptance criteria for
mooring strength, offsets and orientation, clearances, anchor capacity, fatigue resistance, etc. The minimum
acceptance criteria are either defined in this document or are to be specified by the Operator.
NOTE 1 Station-keeping systems designed based on this deterministic approach might have differing levels of
reliability.
For moored structures (vessels), system responses are calculated and compared to minimum acceptance
criteria for:
— Ultimate limit states (ULS): Mooring component strength. Vessel offset, orientation, and clearance
constraints. Herein the ULS includes both intact and single failure condition for station-keeping systems.
— Serviceability limit states (SLS): Vessel offset, orientation, and clearance constraints. For mooring
components this includes clearances with the vessel, risers, umbilicals, seabed, water surface, field
infrastructure, exclusion zones, etc.
— Fatigue limit states (FLS) : Cumulative mooring component fatigue damage.
— Accidental limit state (ALS): no criteria are given for accidental or abnormal limit state which are left
to owner decision or local Authorities requirements.
The methodology described in this part of ISO 19901 identifies a set of coherent analysis techniques 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 station-
keeping system to meet the functional requirements of this document.
NOTE 2 For moorings deployed in ice-prone environments, additional requirements are given in ISO 19906
subclause 13.7.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 9089, Marine structures — Mobile offshore units — Mooring positioning windlasses and winches
ISO 18692-1:2018, Fibre ropes for offshore stationkeeping — Part 1: General specification
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 19901-3, Oil and gas industries including lower carbon energy — Specific requirements for offshore
structures — Part 3: Topsides structure
ISO 19901-4, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 4:
Geotechnical and foundation design considerations
ISO 19901-6, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 6:
Marine operations
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