prEN ISO 19901-7

SLOVENSKI STANDARD
01-januar-2018
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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/DIS 19901-7:2017)
Erdöl- und Erdgasindustrie - Spezielle Anforderungen an Offshore-Anlagen - Teil 7:
Betriebssysteme für das Positionshalten schwimmender Anlagen und mobiler Offshore-
Einheiten (ISO/DIS 19901-7:2017)
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 (ISO/DIS 19901-7:2017)
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 Secretariat: BSI
Voting begins on: Voting terminates on:
2017-11-06 2018-01-29
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
ICS: 75.180.10
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 19901-7:2017(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2017

ISO/DIS 19901-7:2017(E) ISO/DIS 19901-7:2017(E)

Contents Page
1 Scope.8
2 Normative references.9
3 Terms and definitions .9
4 Symbols and abbreviated terms .15
4.1 Symbols.15
4.2 Abbreviated terms .16
5 Overall considerations.18
5.1 General requirements .18
5.2 Functional requirements.18
5.3 Safety requirements .18
5.4 Planning requirements.19
5.5 Rules and regulations.20
5.6 Independent verification.20
5.7 Analytical tools .20
6 Design requirements.20
6.1 Exposure levels .20
6.2 Limit states.21
6.3 Defining design situations.21
6.4 Design situations.21
7 Actions.25
7.1 General .25
7.2 Site-specific data requirements .25
7.3 Environmental actions on mooring lines.27
7.4 Indirect actions .27
8 Mooring analysis .30
8.1 Basic considerations .30
8.2 Actions considerations.31
8.3 Floating structure response.32
8.4 Floating structure offset .37
8.5 Mooring line response .38
8.6 Line tension .38
8.7 Line length and geometry constraints .39
8.8 Anchor forces .40
8.9 Typical mooring configuration analysis and assessment .40
8.10 Thruster-assisted moorings.41
8.11 Transient analysis of floating structure motions.43
9 Fatigue analysis.44
9.1 Basic considerations .44
9.2 Tension-tension (T-T) fatigue.45
9.3 Bending-Tension (B-T) fatigue.53
9.4 Other types of fatigue loading .55
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
10 Design criteria.56
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
10.1 Floating structure offset .56
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
10.2 Line tension limit .56
the requester.
10.3 Grounded line length .56
ISO copyright office
10.4 Anchoring systems .57
Ch. de Blandonnet 8 • CP 401
10.5 Mooring line fatigue safety factor.59
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
10.6 Corrosion and wear.59
Fax +41 22 749 09 47
10.7 Clearances .60
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
ISO/DIS 19901-7:2017(E)
Contents Page
1 Scope . 8
2 Normative references . 9
3 Terms and definitions . 9
4 Symbols and abbreviated terms . 15
4.1 Symbols . 15
4.2 Abbreviated terms . 16
5 Overall considerations . 18
5.1 General requirements . 18
5.2 Functional requirements . 18
5.3 Safety requirements . 18
5.4 Planning requirements . 19
5.5 Rules and regulations . 20
5.6 Independent verification . 20
5.7 Analytical tools . 20
6 Design requirements . 20
6.1 Exposure levels . 20
6.2 Limit states . 21
6.3 Defining design situations . 21
6.4 Design situations . 21
7 Actions. 25
7.1 General . 25
7.2 Site-specific data requirements . 25
7.3 Environmental actions on mooring lines . 27
7.4 Indirect actions . 27
8 Mooring analysis . 30
8.1 Basic considerations . 30
8.2 Actions considerations . 31
8.3 Floating structure response . 32
8.4 Floating structure offset . 37
8.5 Mooring line response . 38
8.6 Line tension . 38
8.7 Line length and geometry constraints . 39
8.8 Anchor forces . 40
8.9 Typical mooring configuration analysis and assessment . 40
8.10 Thruster-assisted moorings . 41
8.11 Transient analysis of floating structure motions . 43
9 Fatigue analysis . 44
9.1 Basic considerations . 44
9.2 Tension-tension (T-T) fatigue . 45
9.3 Bending-Tension (B-T) fatigue . 53
9.4 Other types of fatigue loading . 55
10 Design criteria . 56
10.1 Floating structure offset . 56
10.2 Line tension limit . 56
10.3 Grounded line length . 56
10.4 Anchoring systems . 57
10.5 Mooring line fatigue safety factor . 59
10.6 Corrosion and wear . 59
10.7 Clearances . 60
ISO/DIS 19901-7:2017(E)
10.8 Supporting structures . 60
10.9 Installation considerations . 61
11 Mooring hardware . 61
11.1 Mooring line components . 61
11.2 Winching equipment. 63
11.3 Winches should meet the provisions specified in internationally recognized design
standards, see A.11.2 and the requirements of a RCS.Monitoring equipment . 63
12 In-service inspection, monitoring and maintenance . 64
12.1 General . 64
12.2 Mobile moorings . 64
12.3 Permanent moorings . 65
13 Dynamic positioning system . 67
13.1 Basic considerations . 67
13.2 Design and analysis . 68
13.3 Design, test and maintenance . 68
13.4 Operating personnel . 69
13.5 Determination of stationkeeping capability . 69
14 Synthetic fibre rope mooring . 69
14.1 Basic considerations . 69
14.2 Fibre rope mooring analysis . 70
14.3 Fatigue analysis . 70
14.4 Creep analysis . 71
14.5 Design criteria . 71
14.6 Model testing . 72
Annex A (informative) Additional information and guidance . 73
A.1 Scope . 73
A.2 Normative references . 82
A.3 Terms and definitions . 82
A.4 Symbols and abbreviated terms . 83
A.5 Overall considerations . 83
A.6 Design requirements . 87
A.7 Actions . 90
A.8 Mooring analysis. 100
A.9 Fatigue analysis . 125
A.10 Design criteria . 132
A.11 Mooring hardware . 161
A.12 In-service inspection, monitoring and maintenance . 172
A.13 Dynamic positioning system . 174
A.14 Synthetic fibre rope mooring . 177
Annex B (informative) Regional information . 182
B.1 Introduction . 182
B.2 Offshore Norway . 182
B.3 Canada . 186
B.4 Russia . 187

iv © ISO 2017 – All rights reserved

ISO/DIS 19901-7:2017(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.
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).
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. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/XXX
This second/third/. edition cancels and replaces the first/second/. edition (), [clause(s) / subclause(s) /
table(s) / figure(s) / annex(es)] of which [has / have] been technically revised.
ISO XXXX consists of the following parts. [Add information as necessary.]

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 third edition cancels and replaces the second edition (ISO 19901-7:2013), which has been technically
revised.
ISO/DIS 19901-7:2017(E)
This third edition of ISO 19901-7 includes several changes. The largest changes are the deletion of
informative sections related to geotechnical design of anchors to incorporate the same in 19901-4 and the
inclusion of OPB fatigue guidance.
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 3: Topsides structure
 Part 4: Geotechnical and foundation design considerations
 Part 5: Weight control during engineering and construction
 Part 6: Marine operations
 Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
 Part 8: Marine soil investigations
Part 9: Structural integrity management (under preparation).
ISO 19901 is one of a series of International 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
 ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
 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,
semi-submersibles and spars
 ISO 19905 (all parts), Petroleum and natural gas industries — Site-specific assessment of mobile
offshore units
 ISO 19906, Petroleum and natural gas industries — Arctic offshore structures
vi © ISO 2017 – All rights reserved

ISO/DIS 19901-7:2017(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 and flotels) and construction units (such as heavy lift vessels and pipelay units).
Stationkeeping 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. Stationkeeping
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);
 a combination of mooring system and thrusters (thruster assisted)
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.

ISO/DIS 19901-7:2017(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 any combination of:
1) production,
2) storage,
3) offloading,
4) drilling and well intervention.
b) the assessment of stationkeeping systems for site-specific applications of mobile offshore units and
construction 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 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 stationkeeping systems, which are either covered
directly in this part of ISO 19901 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 part of ISO 19901 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.
This part of ISO 19901 is applicable 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.
This part of ISO 19901 is not applicable to the vertical moorings of tension leg platforms (TLPs).
8 © ISO 2017 – All rights reserved

ISO/DIS 19901-7:2017(E)
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 functional requirements of this part of ISO 19901.
NOTE For moorings deployed in ice-prone environments, additional requirements are given in ISO 19906.<< Sec
13.7 of 19906>>
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 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
ISO 19901-8, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 8:
Marine soil investigations.ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures
— Part 1: Monohulls, semi-submersibles and spars
ISO 19905-3, Petroleum and natural gas industries — Site-specific assessment of mobile offshore units —
Part 3: Floating units1)
ISO 19906, Petroleum and natural gas industries – Arctic Offshore Structures
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 19900:2013]
3.2
action effect
effect of actions on structural components
[ISO 19900:2013]
1) Under preparation.
ISO/DIS 19901-7:2017(E)
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 19900:2013]
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
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 19900:2013, definition 2.7.
3.5
common mode/common cause failure:
failure of similar components on different mooring legs resulting from the same direct cause, occurring within a
relatively short time, where these failures are not consequences of another
3.6
damage event
event-driven damage to mooring components including physical damage, overload, excessive bending, etc.,
often experienced during the installation phase.
3.7
degradation mechanisms
time-based physical or chemical mechanisms or processes by which mooring components degrade.
Examples are corrosion, wear, fatigue, etc.

3.8
design criteria
quantitative formulations that describe the conditions to be fulfilled for each limit state
[ISO 19900:2013]
3.9
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 19900:2013, definition 2.12.
3.10
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 19900:2013, definition 2.13.

3.11
disconnectable floating structure
floating structure capable of discontinuing production and rapidly disconnecting from its ancillary components
such as risers, moorings, and/or well systems in response to the occurrence or to the detection of a threshold
event.
10 © ISO 2017 – All rights reserved

ISO/DIS 19901-7:2017(E)
3.12
dynamic action
action that induces acceleration of a structure or a structural component of a magnitude sufficient to require
specific consideration
3.13
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
3.14
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
3.15
failure causes
includes the initiators, defects, processes and mechanisms generating damage or degradation which are the
basic reasons for failure, and may be introduced into the mooring system across all phases of the mooring
system lifecycle from design to operation.
3.16
failure mode
the manifestation of loss of functionality of a mooring component and it is the manner by which failure is
observed
3.17
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 failure in these areas will not cause unacceptable risk to life-safety or the
environment
[ISO 19900:2013]
3.18
floating structure
structure where the full weight is supported by buoyancy
[ISO 19900:2013]
NOTE The full weight includes lightship weight, mooring system pre-tension, riser pre-tension, operating weight, etc.
3.19
limit state
state beyond which the structure no longer fulfils the relevant design criteria
[ISO 19900:2013]
3.20
maintenance
set of activities performed during the operating life of a structure to ensure it is fit-for-purpose
3.21
minimum breaking strength
MBS
RCS certified strength of a chain, wire rope, fibre rope or accessories
ISO/DIS 19901-7:2017(E)
3.22
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)
NOTE Some components of a mobile mooring system might not be retrievable and should be designed following the
requirements of permanent mooring system.
3.23
mobile offshore drilling unit
MODU
structure capable of engaging in drilling and well intervention operations for exploration or exploitation of
subsea petroleum resources
3.24
mobile offshore unit
MOU
structure intended to be frequently relocated to perform a particular function
[ISO 19900:2002]
EXAMPLE Pipelaying vessel or barge, offshore construction structure, accommodation structure (floatel), service
structure, or mobile offshore drilling units.
3.25
mooring component
general class of component used in the mooring of floating structures
EXAMPLE Chain, steel wire rope, synthetic fibre rope, clump weight, buoy, winch/windlass, fairlead or anchor.
3.26
owner
representative of the company or companies which own a development, who can be the operator on behalf of
co-licensees
3.27
permanent mooring system
mooring system normally used to moor floating structures deployed for long-term operations, such as those
for a floating production system (FPS)
3.28
proximity
closeness in distance
NOTE 1 Mooring systems are considered to be in proximity
...