ISO/FDIS 19900

• Abstract:

  This document specifies general provisions for the design and assessment of fixed (bottom-founded) and floating (buoyant) offshore structures. This document contains general provisions for the design of new structures and site assessment of existing structures. This document is applicable for all phases of the life of the structure, including: ¾ pre-service (e.g., fabrication, transportation, installation), ¾ service in-place, both during originally specified design service life and during any life extensions, ¾ functional upgrade, repurpose and reuse, and ¾ decommissioning, and removal. This document focusses on primary and secondary load bearing structure but also provides some provisions for tertiary and ancillary structure. NOTE ISO 24201[22] covers the design of stairs, gratings and handrails. This document was initially created for offshore oil & gas structures but is now also applicable to renewable energy offshore structures. This document does not apply to pipelines, risers or subsea systems.

• Status: Not Published
• ICS: 75.180.10 - Exploratory, drilling and extraction equipment
• Technical Committee: ISO/TC 67/SC 7 - Offshore structures
• Drafting Committee: ISO/TC 67/SC 7/WG 1 - General requirements
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 15-Sep-2026
• Completion Date: 15-Sep-2026

• Consolidates: FprEN ISO 19900 - General requirements for offshore structures (ISO/FDIS 19900:2026)
• Effective Date: 12-Feb-2026
• Revises: ISO 19900:2019 - Petroleum and natural gas industries — General requirements for offshore structures
• Effective Date: 27-Jan-2024

Overview

ISO/FDIS 19900: General requirements for offshore structures is the principal international standard published by ISO for the design and assessment of offshore structures. Developed by ISO Technical Committee 67/SC 7, this standard applies to both fixed (bottom-founded) and floating (buoyant) offshore structures and covers the full lifecycle of these structures. ISO/FDIS 19900 is relevant to the oil and gas industry as well as modern energy sectors, including offshore wind and other renewable energy applications.

This document outlines general requirements not only for new offshore facility designs but also for site assessment, repurpose, reuse, upgrades, and decommissioning and removal of existing structures. It emphasizes safety, integrity, and durability, thereby supporting the long-term performance and operational reliability of offshore infrastructure.

Keywords: offshore structures, ISO 19900, fixed offshore structure, floating offshore structure, design requirements, integrity management, renewable energy structures, oil and gas infrastructure, structural safety

Key Topics

• Lifecycle Phases: Addresses all structural life stages, from pre-service (fabrication, transportation, and installation) and in-service operation, to upgrades, repurposing, and eventual decommissioning and removal.
• Scope of Application: Covers primary and secondary load-bearing elements and provides some provisions for tertiary and ancillary structures critical for overall facility resilience.
• Design Approaches: Supports semi-probabilistic, reliability-based, and risk-informed design approaches, offering flexible pathways to demonstrate compliance.
• Integrity Management: Specifies requirements for structural and marine system integrity throughout operational life, including proper inspection, maintenance, and condition assessment.
• Environmental and Accidental Actions: Defines how structures should be designed and assessed to withstand extreme environmental events (e.g., storms, waves) and accidental events (e.g., collisions, fire, explosions).
• Performance and Limit States: Introduces ultimate, serviceability, and fatigue limit states with criteria for structural assessment to ensure ongoing fit-for-service status.
• Sustainability and Durability: Emphasizes the importance of durable designs, robustness, and sustainability considerations to maximize lifetime value and environmental stewardship.

Applications

ISO/FDIS 19900 is intended for various stakeholders, including operators, structural designers, engineers, asset managers, and regulators involved in offshore projects. Its practical applications include:

• Offshore Oil & Gas Platforms: Providing a robust framework for designing safe and resilient hydrocarbon extraction platforms in diverse offshore environments.
• Offshore Renewable Energy: Enabling consistent and safe design for offshore wind turbines, substations, and related infrastructure as the renewable energy sector expands.
• Marine Systems: Assisting in the assessment and management of floating production systems, ships, and other marine energy facilities.
• Lifecycle Management: Guiding upgrades, repurposing, and re-qualification of existing offshore structures for new uses or extended operational life.
• Decommissioning: Informing planning and safe execution of decommissioning and removal activities to comply with international best practices.
• Regulatory Compliance: Supporting adherence to national and international regulatory requirements relevant to offshore structural safety and integrity.

Related Standards

ISO/FDIS 19900 is the foundational document in a series of standards for offshore structures. Related standards include:

• ISO 19901 Series: Provides specific supplementary requirements for offshore structures, such as actions, fatigue, and seismic design.
• ISO 19902: Focuses on fixed steel offshore structures design.
• ISO 19903: Addresses concrete offshore structures.
• ISO 19904: Covers floating offshore structures including hulls and platforms.
• ISO 19905 (all parts): Deals with site-specific assessment of mobile offshore units.
• ISO 19906: Concentrates on arctic offshore structures.
• ISO 24201: Specifically covers the design of stairs, gratings, and handrails.
• ISO 2394 and ISO 22111: Set the general principles for reliability and risk-based approaches in structural engineering and inform the overall approach of ISO/FDIS 19900.

By adhering to ISO/FDIS 19900 and its related standards, organizations can ensure their offshore structures meet the highest levels of safety, reliability, and sustainability in both fossil and renewable energy sectors.

FINAL DRAFT
International
Standard
ISO/TC 67/SC 7
General requirements for offshore
Secretariat: BSI
structures
Voting begins on:
2026-09-15
Voting terminates on:
2026-11-10
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TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
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MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 67/SC 7
General requirements for offshore
Secretariat: BSI
structures
Voting begins on:
Voting terminates on:
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 SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.10
4.1 Symbols .10
4.2 Abbreviated terms .11
5 Design considerations .12
5.1 Functional and operational requirements . 12
5.2 Consequence levels . 12
5.3 Robustness .14
5.4 Durability .14
5.5 Sustainability .14
5.6 Quality management .14
6 Basis of structural and geotechnical design .15
6.1 Facility location and orientation . 15
6.2 Weights . 15
6.3 Geotechnical and geophysical conditions . 15
6.4 Environmental conditions .16
6.5 Accidental conditions .16
6.6 Topsides structures, air gap and splash zone .16
6.7 Appurtenances and ancillary systems .17
6.8 Inspectability .17
6.9 Jack-ups .17
6.10 Lower carbon energy facilities .17
6.10.1 Offshore wind turbine structures.17
6.10.2 Offshore wind substations and other lower carbon energy structures .18
7 Development of design situations .18
7.1 Hazardous events .18
7.2 Design situations .19
8 Limit states and structure performance . .20
8.1 General . 20
8.2 Ultimate limit states . 20
8.3 Serviceability limit states . 20
8.4 Fatigue limit states .21
8.5 Alternative methods for demonstrating structure performance .21
9 Characterization of actions and resistance.21
9.1 Basic variables .21
9.2 Classification of actions .21
9.3 Permanent actions . 22
9.4 Variable actions . 22
9.5 Environmental actions . 22
9.6 Accidental actions . 22
9.7 Repetitive actions . 22
9.8 Actions acting in combination . 23
9.8.1 General . 23
9.8.2 Principal actions . 23
9.8.3 Combined actions .24
9.8.4 Accompanying actions .24
9.9 Resistance .24

iii
9.9.1 Material properties .24
9.9.2 Geometrical properties .24
9.9.3 Resistance to repetitive actions . 25
10 Design approaches .25
10.1 Design approaches for offshore structures . 25
10.2 Semi-probabilistic design approach . 25
10.3 Alternative design approaches. 26
10.3.1 Reliability-based design approach . 26
10.3.2 Risk-informed design approach .27
11 Partial factor design method .28
11.1 Basis for partial factor design method . 28
11.2 Hazardous events . 28
11.3 Representative values . 28
11.4 Actions . 29
11.4.1 Representative values of permanent actions . 29
11.4.2 Representative values of variable actions . 29
11.4.3 Representative values of environmental actions . 29
11.4.4 Representative values of accidental actions . 29
11.4.5 Partial factors for actions . 29
11.4.6 Actions acting in combination . 30
11.4.7 Design values of actions and action effects .31
11.5 Resistance .31
11.5.1 Representative values of material variables .31
11.5.2 Representative values of geometrical variables .31
11.5.3 Design value of material variables .32
11.5.4 Design value of geometric variables .32
11.5.5 Design resistance .32
11.5.6 Partial factors for materials and resistance .32
11.5.7 Resistance for repetitive actions . 33
11.6 Verification by the partial factor design method . 33
11.6.1 Verification of ULS . 33
11.6.2 Verification of SLS . 33
11.6.3 Verification of FLS . 34
12 Structural modelling and analysis .34
12.1 Structural modelling . 34
12.1.1 General principles of structural and geotechnical modelling . 34
12.1.2 Static actions . 34
12.1.3 Dynamic actions . 35
12.1.4 Actions inducing fatigue . 35
12.1.5 Fire and explosion design . 35
12.2 Structural analysis . 36
12.2.1 General . 36
12.2.2 Linear analysis . 36
12.2.3 Non-linear analysis . 36
12.3 Design assisted by testing . 36
13 Integrity management and assessment of existing structures and marine systems.37
13.1 General .37
13.2 Integrity management of structures and marine systems .37
13.3 Assessment of existing structures and marine systems. 39
Annex A (informative) Additional information and guidance . 41
Bibliography . 76

iv
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 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, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 12, Oil and gas industries including lower carbon energy,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 19900:2019), which has been technically
revised.
The main changes are as follows:
— provisions are now applicable for all structure types and marine systems, including support structures
for wind turbines and associated facilities;
— consequence levels replace exposure levels and are summarised in Table 1;
— design situations are unchanged but are now summarized in Table 2;
— a new Clause 10 permits the use of reliability-based and risk-informed design approaches in addition to
the semi-probabilistic approach, with associated constraints;
— all provisions relating to the partial factor design method, the main method for the semi-probabilistic
design approach, have been collected in Clause 11;
— a new Clause 12 includes more detailed provisions for structural modelling and analysis;
— the normative text has been revised to conform with IOGP Report 604 Guidelines.
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.

v
Introduction
The International Standards for offshore structures developed by ISO TC 67/SC 7 comprise:
— ISO 19900, the unifying International Standard for offshore structures;
— the ISO 19901 series, providing specific requirements for offshore structures.
— ISO 19902, ISO 19903,ISO 19904,ISO 19905 series  and ISO 19906, structure-type standards.
Figure 1 illustrates the relationships between the International Standards for offshore structures developed
by ISO/TC 67/SC 7.
Figure 1 — Relationship of International Standards for offshore structures developed by
ISO/TC 67/SC 7
The International Standards for offshore structures developed by ISO/TC 67/SC 7 follow the principles of
ISO 2394 and ISO 22111 and constitutes a common basis for addressing design and assessment of offshore
structures used by the energy industries worldwide. Additional information and guidance are given in
Annex A, where the clause numbering mirrors the clauses in the body of this document to facilitate cross-
referencing.
Statements containing requirements (“shall” and “shall not”), recommendations (“should” and “should not”)
or permissions (“may”) are collectively referred to as provisions.

vi
FINAL DRAFT International Standard ISO/FDIS 19900:2026(en)
General requirements for offshore structures
1 Scope
This document contains general requirements for design of structures and marine systems and for structural
integrity management. It covers both fixed (bottom-founded) and floating (buoyant) offshore structures.
This document is applicable for all phases of the life of the structure, including:
— pre-service (e.g. fabrication, transportation, installation);
— service in-place, both during originally specified design service life and during any life extensions;
— functional upgrade, repurpose and reuse;
— decommissioning and removal.
This document focuses on primary and secondary load bearing structure but also includes some provisions
for tertiary and ancillary structure.
This document is applicable to offshore oil and gas structures, as well as lower carbon energy offshore
structures.
This document does not apply to pipelines, risers, cables or subsea systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
abnormal environmental event
environmental hazardous event (3.32) having a low probability of occurrence during the design service life
(3.18)
Note 1 to entry: The probability of occurrence selected for highest consequence level (3.12) is typically within the
−3 −4
range 10 per annum (1 in 1 000 years) to 10 per annum (1 in 10 000 years).
Note 2 to entry: Abnormal environmental events are associated with abnormal design situations (3.19), see 7.2.
3.2
accidental event
non-environmental hazardous event (3.32) having a low probability of occurrence during the design service
life (3.18)
Note 1 to entry: The probability of occurrence selected for highest consequence level (3.12) is typically within the
−3 −4
range 10 per annum (1 in 1 000 years) to 10 per annum (1 in 10 000 years).

Note 2 to entry: Accidental events are associated with a substantial release of energy, such as vessel collisions, fires
and explosions.
Note 3 to entry: Accidental events are associated with accidental design situations (3.19), see 7.2. Lesser accidents
that can be expected during the life of the structure (3.71), such as dropped objects and low-energy vessel impact, are
termed incidents (3.34) and are addressed under operational design situations (3.19).
3.3
action
external load applied to the structure (3.71) (direct load) or imposed deformation or acceleration (indirect
load)
EXAMPLE An imposed deformation can be caused by enforcing fabrication tolerances, differential settlement,
temperature change or moisture variation. An imposed acceleration can be caused by an earthquake.
Note 1 to entry: Individual action types are categorised in Clause 9.
3.4
action effect
result of actions (3.3) on a structural component (3.68), e.g. internal force, moment, stress, strain, or on the
structure (3.71), e.g. deflection, rotation
3.5
air gap
distance between the highest water surface elevation and the lowest exposed part of the deck primary
structure (3.51) not designed to withstand associated environmental action effects (3.4) for a specified
return period (3.58)
Note 1 to entry: This definition can be refined for different facility (3.27) types in their respective standards.
3.6
appurtenance
accessory or attachment to the structure (3.71) which typically assists installation, provides access or
protection, or carries fluids or gas
EXAMPLE Caisson, anodes, boat landing, fender and protection frames.
Note 1 to entry: Appurtenances do not normally contribute to the stiffness of the structure (3.71) but can attract
significant environmental loading.
3.7
ancillary system
system not under responsibility of the structural discipline or a group of appurtenances (3.6), attached to or
within the structure (3.71)
EXAMPLE Risers (3.59), subsea systems, cables, umbilicals.
3.8
basic variable
variable representing physical quantities which characterize actions (3.3) and environmental influences,
geometric quantities, and material properties including soil properties
Note 1 to entry: Basic variables are typically random variables or random processes used in the calculation or
assessment of representative values (3.56) of actions (3.3) or resistance (3.57).
3.9
calibration
process used to specify acceptance criteria for different design approaches (3.15)
Note 1 to entry: Code calibration for the partial factor method (3.49), partial factor and annual probabilities associated
with representative values (3.56) are based on experience, known cases or reliability targets. For other methods in the
semi-probabilistic design approach (3.66), this can involve the selection of safety factors.

Note 2 to entry: For methods in the reliability-based design approach (3.54), a reliability target can be calibrated to
proven safe cases or to risk indices.
3.10
characteristic value
value assigned to a basic variable (3.8) with a prescribed probability of exceedance
Note 1 to entry: A basic variable (3.8) can have two or more characteristic values, e.g. an upper value and a lower value.
3.11
conductor
tubular pipe set into the ground to provide the initial stable structural foundation for setting the surface
casing and protecting the internal well string from metocean actions (3.3)
Note 1 to entry: The conductor provides lateral and, in some cases, axial support, enables circulation of drilling fluid,
and guides the drill string to facilitate setting of the surface casing.
3.12
consequence level
classification system used to establish relevant criteria for a structure (3.71) based on consequences of
failure
3.13
damage state
discrete state that describes the level of impairment
Note 1 to entry: Damage states can be categorized between no damage and complete loss of a structure (3.71) or a
marine system (3.40).
3.14
decommissioning
process of shutting down a facility (3.27) enabling preparations for cleaning, dismantling and removal from
location at, or after, the end of its design service life (3.18)
3.15
design approach
framework used to ensure acceptable structure (3.71) performance
Note 1 to entry: Design approaches are categorized as semi-probabilistic (3.66), reliability-based (3.54) and risk-
informed (3.60).
Note 2 to entry: Different design approaches can be applied for different design situations (3.19).
Note 3 to entry: Acceptable structure (3.71) performance is achieved by satisfying limit state (3.38) criteria.
Note 4 to entry: Different design methods (3.17) can be applied within a design approach.
3.16
design criteria
quantitative formulations using design values (3.20) describing the conditions to be fulfilled for each design
situation (3.19)
3.17
design method
proven procedure, categorized within a design approach (3.15), used to demonstrate the safety of a structure
(3.71)
Note 1 to entry: Safety can involve limit state (3.38) verification, or account for relevant consequences and
uncertainties.
3.18
design service life
design life
life
planned period for which a structure (3.71) is used for its intended purpose with anticipated maintenance
(3.39), but without substantial repair (3.55) being necessary
Note 1 to entry: The originally specified design service life can be updated during the operating phase to include any
life extension periods until removal of the facility (3.27).
3.19
design situation
set of physical conditions for which the structure (3.71) or its components are subject to limit state (3.38)
verification
Note 1 to entry: Six design situations are categorised in Table 2: operational, extreme, abnormal, accidental, short
duration and serviceability.
3.20
design value
value derived from the representative value (3.56) for use in the semi-probabilistic design approach (3.66)
Note 1 to entry: Design values can be different according to the different design situations (3.19) and associated safety
partial factors.
Note 2 to entry: Design value for resistance is calculated by dividing its representative value (3.56) by a partial factor
for resistance (3.57), while design value (3.20)action effect (3.4) is calculated by multiplying its representative value
(3.56) by a partial factor for action (3.3) or action effect (3.4).
3.21
deterioration
process that adversely affects structural integrity (3.69) over time
Note 1 to entry: Deterioration can be caused by naturally occurring chemical, physical, or biological processes
including corrosion, by environmental actions (3.3), by incidents (3.34) and accidental actions (3.3), by fatigue, wear,
abrasion, and by improper operation and maintenance (3.39) of the structure (3.71).
3.22
ductility
ability of a material to deform and absorb energy beyond its elastic limit
3.23
ductility
ability of a structural component (3.68) to sustain action effects (3.4) beyond yield
3.24
ductility
ability of a structural system to deform and dissipate energy, and to redistribute action
effects (3.4)
3.25
durability
ability of a structure (3.71) or structural component (3.68) to maintain its function throughout its design
service life (3.18)
3.26
extreme environmental event
−2
environmental hazardous event (3.32) typically having probability of occurrence of 10 per annum (1 in
100 years) for highest consequence level (3.12)
Note 1 to entry: Extreme environmental events are associated with extreme design situations (3.19), see 7.2.

−2
Note 2 to entry: For offshore wind structures (3.45) and jack-ups (3.37) a probability of occurrence of 2 x 10 per
annum (1 in 50 years) is typically applied.
3.27
facility
constructions, pieces of equipment, and services that are provided for the offshore (3.43) energy sector
Note 1 to entry: The facility includes the structure (3.71) and non-structural systems such as topsides (3.73) equipment,
marine systems (3.40), piping and accommodation.
Note 2 to entry: A hydrocarbon facility (platform) includes structural appurtenances (3.6) and ancillary systems (3.7)
but does not include the non-structural components (3.68) of the hydrocarbon wells.
Note 3 to entry: The facility does not include the geological strata supporting the foundation. However, site-specific
geotechnical parameters provide the boundary conditions necessary to model the facility’s foundation or anchoring.
3.28
fit-for-service
in compliance with the applicable structural requirements
Note 1 to entry: Compliance with this standard indicates that the structure (3.71) provides the required level of
structural safety, functionality, and integrity for the defined design and operating conditions and assessment period.
Note 2 to entry: Risk-informed design approach (3.60) or reliability-based design approach (3.54) can be used to
demonstrate compliance, where permitted, see 10.3.
3.29
fixed structure
structure (3.71) that is bottom-founded and transfers most of the actions (3.3) on it to the seabed (3.64)
3.30
floating structure
structure (3.71) where the full weight is supported by buoyancy
3.31
hazard
potential source of harm
Note 1 to entry: Harm is typically differentiated between harm to people, harm to the environment, harm in terms of
costs to organizations, or harm to society in general.
3.32
hazardous event
event which occurs when a hazard (3.31) interacts with a structure (3.71)
EXAMPLE Wave impacting the structure (3.71), iceberg impacting the structure (3.71), excessive topsides (3.73)
weight added to the structure (3.71), vessel collision, fire, explosion, and landslip in the vicinity of structural anchors
(piles).
Note 1 to entry: A hazardous event can be a storm involving waves, currents and winds acting from different directions.
Note 2 to entry: A hazardous event can be a combination of basic variables (3.8) such as wave height and period, or ice
floe size and drift speed.
Note 3 to entry: A hazardous event can be an action (3.3) associated with a hazard (3.31) that involves various
combinations of basic variables (3.8).
3.33
ice gouge
ice scour
incision in the seabed (3.64) or removal of seabed (3.64) material by an ice feature

3.34
incident
non-environmental hazardous event (3.32) considered in an operational design situation (3.19)
Note 1 to entry: An incident is a lesser accidental event (3.2), associated with possible local damage or damage to
structural components (3.68), occurring with low probability, most typically associated with probabilities not less
−2
than 10 per annum (1 in 100 years).
3.35
inspection
on-site examination within the scope of quality control and condition assessment aiming to assess the
present condition of a structure (3.71)
3.36
integrity management
systematic process intended to assure integrity of a structure (3.71) or a marine system (3.40)
3.37
jack-up
mobile offshore (3.43) unit with a buoyant hull and one or more legs that can be moved up and down relative
to the hull
Note 1 to entry: A jack-up reaches its operational mode by lowering the leg(s) to the seabed (3.64) and then raising
the hull to the required elevation. The majority of jack-ups have three or more legs, each of which can be moved
independently and which are supported in the seabed (3.64) by spudcans.
3.38
limit state
state beyond which the structure (3.71) or structural component (3.68) no longer satisfies the design criteria
(3.16)
Note 1 to entry: Three limit states are categorised in Clause 8: ultimate, serviceability and fatigue.
3.39
maintenance
routine work undertaken to ensure the continuing performance of a facility (3.27)
3.40
marine system
system contributing to the structural safety, stability and position keeping ability of a floating facility (3.27)
3.41
marine system integrity
ability of a marine system (3.40) to maintain performance (3.50) throughout the design service life (3.18),
with respect to structural safety, robustness (3.61), serviceability and durability (3.25)
3.42
nominal value
value assigned to a basic variable (3.8) on a non-statistical basis, either determined from acquired experience
or physical conditions, or as specified in a published code or standard
3.43
offshore
situated in water some distance from the shore
Note 1 to entry: Alternatively, "near-shore" or “coastal” can be used to specify locations next to the coast or in mouths
of rivers.
3.44
offshore wind farm
group of offshore wind turbine structures (3.47) and offshore wind substations (3.46) in the same location

3.45
offshore wind structure
part of an offshore wind turbine facility (3.27) which extends upwards from the seabed (3.64) and connects
the foundation to the wind turbine tower, or part of an offshore wind substation (3.46) that supports the
topsides (3.73)
Note 1 to entry: The offshore wind structure can include a transition piece.
3.46
offshore wind substation
an electrical facility that collects and manages the power generated by wind turbines before transmitting it
to shore.
3.47
offshore wind turbine structure
support structure for a wind turbine assembly that is used to convert kinetic energy from the wind into
electricity
3.48
operator
owner
duty holder
principal company or company representative leasing the offshore (3.43) site from a government
3.49
partial factor method
method within the semi-probabilistic design approach (3.66) where a safety coefficient (partial factor) is
applied to basic variables (3.8) to ensure structural reliability (3.53)
Note 1 to entry: Partial factors can be applied to actions (3.3), resistances (3.57) and materials, see 11.4 and 11.5.
3.50
performance
ability of a structure (3.71) or a structural component (3.68) to fulfil specified requirements
Note 1 to entry: Specified requirements include requirements for structural functionality, structural integrity (3.69)
and functionality of marine systems (3.40).
Note 2 to entry: Performance levels are established as a means of mitigating consequences associated with life-safety,
environmental pollution, reliability (3.53) of energy supply and business disruption.
3.51
primary structure
all main structural components (3.68) that provide the structure's (3.71) main strength and stiffness
3.52
recognized classification society
RCS
member of the international association of classification societies (IACS), with recognized and relevant
competence and experience in offshore (3.43)structures (3.71) and with established rules and procedures for
classification and certification of offshore (3.43)structures (3.71) located at a specific site
3.53
re
...

Date: 2026-07-03
ISO/DISFDIS 19900:2026(en)
ISO/TC 67/SC 7/WG 1
Secretariat: BSI
Date: 2026-09-01
General requirements for offshore structures
Industries du pétrole et du gaz, y compris les énergies à faible teneur en carbone — Exigences générales
relatives aux structures en mer
This draft is submitted to a parallel vote in ISO, CEN.

FDIS stage
2 © ISO 2019 – All rights reserved

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
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Tel.Phone: + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
iii
Contents
Foreword . vi
Introduction . viii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 11
4.1 Symbols . 11
4.2 Abbreviated terms . 12
5 Design considerations . 13
5.1 Functional and operational requirements . 13
5.2 Consequence levels . 13
5.3 Robustness . 14
5.4 Durability . 15
5.5 Sustainability . 15
5.6 Quality management . 15
6 Basis of structural and geotechnical design . 16
6.1 Facility location and orientation . 16
6.2 Weights . 16
6.3 Geotechnical and geophysical conditions . 16
6.4 Environmental conditions . 16
6.5 Accidental conditions . 17
6.6 Topsides structures, air gap and splash zone . 17
6.7 Appurtenances and ancillary systems . 17
6.8 Inspectability . 18
6.9 Jack-ups . 18
6.10 Lower carbon energy facilities . 18
7 Development of design situations . 19
7.1 Hazardous events . 19
7.2 Design situations . 19
8 Limit states and structure performance. 20
8.1 General. 20
8.2 Ultimate limit states . 21
8.3 Serviceability limit states . 21
8.4 Fatigue limit states . 21
8.5 Alternative methods for demonstrating structure performance . 22
9 Characterization of actions and resistance . 22
9.1 Basic variables . 22
9.2 Classification of actions . 22
9.3 Permanent actions . 23
9.4 Variable actions . 23
9.5 Environmental actions . 23
9.6 Accidental actions . 23
9.7 Repetitive actions . 23
9.8 Actions acting in combination . 24
9.9 Resistance . 25
10 Design approaches . 26
10.1 Design approaches for offshore structures . 26
iv
10.2 Semi-probabilistic design approach . 26
10.3 Alternative design approaches . 27
11 Partial factor design method . 29
11.1 Basis for partial factor design method . 29
11.2 Hazardous events . 29
11.3 Representative values . 29
11.4 Actions . 30
11.5 Resistance . 32
11.6 Verification by the partial factor design method . 34
12 Structural modelling and analysis . 35
12.1 Structural modelling . 35
12.2 Structural analysis . 36
12.3 Design assisted by testing . 37
13 Integrity management and assessment of existing structures and marine systems . 38
13.1 General. 38
13.2 Integrity management of structures and marine systems . 38
13.3 Assessment of existing structures and marine systems . 40
Annex A (informative) Additional information and guidance . 41
Bibliography . 81

v
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 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., in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 12, Oil and gas industries including lower carbon energy,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 19900:2019), which has been technically
revised.
The main changes are as follows:
— provisions are now applicable for all structure types and marine systems, including support structures for
wind turbines and associated facilities;
— consequence levels replace exposure levels and are summarised in Table 1Table 1;;
— design situations are unchanged but are now summarized in Table 2Table 2;;
— a new Clause 10Clause 10 permits the use of reliability-based and risk-informed design approaches in
addition to the semi-probabilistic approach, with associated constraints;
— all provisions relating to the partial factor design method, the main method for the semi-probabilistic
design approach, have been collected in Clause 11Clause 11;;
— a new Clause 12Clause 12 includes more detailed provisions for structural modelling and analysis;
— the normative text has been revised to complyconform with IOGP Report 604 Guidelines on good
requirement writing and current ISO directives.
vi
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.
vii
Introduction
The International Standards for offshore structures developed by ISO TC 67/SC 7 comprise:
— — ISO 19900, the unifying International Standard for offshore structures;
[6] – [15]
— — the ISO 19901 series ,, providing specific requirements for offshore structures.
[16] [17] [18] [19]–[22] [23]
— — ISO 19902 , , ISO 19903 , ,ISO 19904 , ,ISO 19905 series  and ISO 19906 ,, structure-
type standards.
Figure 1Figure 1 illustrates the relationships between the International Standards for offshore structures
developed by ISO/TC 67/SC 7.
viii
Figure 1 — Relationship of International Standards for offshore structures developed by
ISO/TC 67/SC 7
The International Standards for offshore structures developed by ISO/TC 67/SC 7 follow the principles of ISO
[1] [24]
2394 and ISO 22111 and constitutes a common basis for addressing design and assessment of offshore
structures used by the energy industries worldwide. Additional information and guidance are given in
Annex AAnnex A,, where the clause numbering mirrors the clauses in the body of this document to facilitate
cross-referencing.
Statements containing requirements (“shall” and “shall not”), recommendations (“should” and “should not”)
or permissions (“may”) are collectively referred to as provisions.
ix
General requirements for offshore structures
1 Scope
This document contains general requirements for design of structures and marine systems and for structural
integrity management. It covers both fixed (bottom-founded) and floating (buoyant) offshore structures.
This document is applicable for all phases of the life of the structure, including:
— — pre-service (e.g. fabrication, transportation, installation);
— — service in-place, both during originally specified design service life and during any life extensions;
— — functional upgrade, repurpose and reuse;
— — decommissioning and removal.
This document focuses on primary and secondary load bearing structure but also includes some provisions
for tertiary and ancillary structure.
This document is applicable to offshore oil and gas structures, as well as lower carbon energy offshore
structures.
This document does not apply to pipelines, risers, cables or subsea systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
abnormal environmental event
environmental hazardous event (3.32(3.32)) having a low probability of occurrence during the design service
life (3.18(3.18))
Note 1 to entry: The probability of occurrence selected for highest consequence level (3.12(3.12)) is typically within the
−3 −4
range 10 per annum (1 in 1 000 years) to 10 per annum (1 in 10 000 years).
Note 2 to entry: Abnormal environmental events are associated with abnormal design situations (3.19(3.19),), see 7.27.2.
3.2 3.2
accidental event
non-environmental hazardous event (3.32(3.32)) having a low probability of occurrence during the design
service life (3.18(3.18))
Note 1 to entry: The probability of occurrence selected for highest consequence level (3.12(3.12) ) is typically within the
−3 −4
range 10 per annum (1 in 1 000 years) to 10 per annum (1 in 10 000 years).
Note 2 to entry: Accidental events are associated with a substantial release of energy, such as vessel collisions, fires and
explosions.
Note 3 to entry: Accidental events are associated with accidental design situations (3.19(3.19),), see 7.27.2. Lesser
accidents that can be expected during the life of the structure (3.71(3.71),), such as dropped objects and low-energy
vessel impact, are termed incidents (3.34(3.34)) and are addressed under operational design situations (3.19(3.19).).
3.3 3.3
action
external load applied to the structure (3.71(3.71)) (direct load) or imposed deformation or acceleration
(indirect load)
EXAMPLE An imposed deformation can be caused by enforcing fabrication tolerances, differential settlement,
temperature change or moisture variation. An imposed acceleration can be caused by an earthquake.
Note 1 to entry: Individual action types are categorised in Clause 9Clause 9.
3.4 3.4
action effect
result of actions (3.3(3.3)) on a structural component (3.68(3.68),), e.g. internal force, moment, stress, strain,
or on the structure (3.71(3.71),), e.g. deflection, rotation
3.5 3.5
air gap
distance between the highest water surface elevation and the lowest exposed part of the deck primary
structure (3.51(3.51)) not designed to withstand associated environmental action effects (3.4(3.4)) for a
specified return period (3.58(3.58))
Note 1 to entry: This definition can be refined for different facility (3.27(3.27)) types in their respective standards.
3.6 3.6
appurtenance
accessory or attachment to the structure (3.71(3.71)) which typically assists installation, provides access or
protection, or carries fluids or gas
EXAMPLESEXAMPLE Caisson, anodes, boat landing, fender and protection frames.
Note 1 to entry: Appurtenances do not normally contribute to the stiffness of the structure (3.71(3.71)) but can attract
significant environmental loading.
3.7 3.7
ancillary system
system not under responsibility of the structural discipline or a group of appurtenances (3.6(3.6),), attached
to or within the structure (3.71(3.71))
EXAMPLESEXAMPLE Risers (3.59(3.59),), subsea systems, cables, umbilicals.
3.8 3.8
basic variable
variable representing physical quantities which characterize actions (3.3(3.3)) and environmental influences,
geometric quantities, and material properties including soil properties
Note 1 to entry: Basic variables are typically random variables or random processes used in the calculation or assessment
of representative values (3.56(3.56)) of actions (3.3(3.3)) or resistance (3.57(3.57).).
3.9 3.9
calibration
process used to specify acceptance criteria for different design approaches (3.15(3.15))
Note 1 to entry: Code calibration for the partial factor method (3.49(3.49),), partial factor and annual probabilities
associated with representative values (3.56(3.56)) are based on experience, known cases or reliability targets. For other
methods in the semi-probabilistic design approach (3.66(3.66),), this can involve the selection of safety factors.
Note 2 to entry: For methods in the reliability-based design approach (3.54(3.54),), a reliability target can be calibrated
to proven safe cases or to risk indices.
3.10 3.10
characteristic value
value assigned to a basic variable (3.8(3.8)) with a prescribed probability of exceedance
Note 1 to entry: A basic variable (3.8(3.8)) can have two or more characteristic values, e.g. an upper value and a lower
value.
3.11 3.11
conductor
tubular pipe set into the ground to provide the initial stable structural foundation for setting the surface casing
and protecting the internal well string from metocean actions (3.3(3.3))
Note 1 to entry: The conductor provides lateral and, in some cases, axial support, enables circulation of drilling fluid, and
guides the drill string to facilitate setting of the surface casing.
3.12 3.12
consequence level
classification system used to establish relevant criteria for a structure (3.71(3.71)) based on consequences of
failure
3.13 3.13
damage state
discrete state that describes the level of impairment
Note 1 to entry: Damage states can be categorized between no damage and complete loss of a structure (3.71(3.71)) or a
marine system (3.40(3.40).).
3.14 3.14
decommissioning
process of shutting down a facility (3.27(3.27)) enabling preparations for cleaning, dismantling and removal
from location at, or after, the end of its design service life (3.18(3.18))
3.15 3.15
design approach
framework used to ensure acceptable structure (3.71(3.71)) performance
Note 1 to entry: Design approaches are categorized as semi-probabilistic (3.66(3.66),), reliability-based (3.54(3.54)) and
risk-informed (3.60(3.60).).
Note 2 to entry: Different design approaches can be applied for different design situations (3.19(3.19).).
Note 3 to entry: Acceptable structure (3.71(3.71)) performance is achieved by satisfying limit state (3.38(3.38)) criteria.
Note 4 to entry: Different design methods (3.17(3.17)) can be applied within a design approach.
3.16 3.16
design criteria
quantitative formulations using design values (3.20(3.20)) describing the conditions to be fulfilled for each
design situation (3.19(3.19))
3.17 3.17
design method
proven procedure, categorized within a design approach (3.15(3.15),), used to demonstrate the safety of a
structure (3.71(3.71))
Note 1 to entry: Safety can involve limit state (3.38(3.38)) verification, or account for relevant consequences and
uncertainties.
3.18 3.18
design service life
design life
life
planned period for which a structure (3.71(3.71)) is used for its intended purpose with anticipated
maintenance (3.39(3.39),), but without substantial repair (3.55(3.55)) being necessary
Note 1 to entry: The originally specified design service life can be updated during the operating phase to include any life
extension periods until removal of the facility (3.27(3.27).).
3.19 3.19
design situation
set of physical conditions for which the structure (3.71(3.71)) or its components are subject to limit state
(3.38(3.38)) verification
Note 1 to entry: Six design situations are categorised in Table 2Table 2:: operational, extreme, abnormal, accidental, short
duration and serviceability.
3.20 3.20
design value
value derived from the representative value (3.56(3.56)) for use in the semi-probabilistic design approach
(3.66(3.66))
Note 1 to entry: Design values can be different according to the different design situations (3.19(3.19)) and associated
safety partial factors.
Note 2 to entry: Design value for resistance is calculated by dividing its representative value (3.56(3.56)) by a partial
factor for resistance (3.57(3.57),), while design value (3.20(3.20) )action effect (3.4(3.4)) is calculated by multiplying its
representative value (3.56(3.56)) by a partial factor for action (3.3(3.3)) or action effect (3.4(3.4).).
3.21 3.21
deterioration
process that adversely affects structural integrity (3.69(3.69)) over time
Note 1 to entry: Deterioration can be caused by naturally occurring chemical, physical, or biological processes including
corrosion, by environmental actions (3.3(3.3),), by incidents (3.34(3.34)) and accidental actions (3.3(3.3),), by fatigue,
wear, abrasion, and by improper operation and maintenance (3.39(3.39)) of the structure (3.71(3.71).).
3.22 3.22
ductility
ability of a material to deform and absorb energy beyond its elastic limit
3.23 3.23
ductility
ability of a structural component (3.68(3.68)) to sustain action effects (3.4(3.4))
beyond yield
3.24 3.24
ductility
ability of a structural system to deform and dissipate energy, and to redistribute action
effects (3.4(3.4))
3.25 3.25
durability
ability of a structure (3.71(3.71)) or structural component (3.68(3.68)) to maintain its function throughout its
design service life (3.18(3.18))
3.26 3.26
extreme environmental event
−2
environmental hazardous event (3.32(3.32)) typically having probability of occurrence of 10 per annum (1
in 100 years) for highest consequence level (3.12(3.12))
Note 1 to entry: Extreme environmental events are associated with extreme design situations (3.19(3.19),), see 7.27.2.
−2
Note 2 to entry: For offshore wind structures (3.45(3.45)) and jack-ups (3.37(3.37)) a probability of occurrence of 2 x 10
per annum (1 in 50 years) is typically applied.
3.27 3.27
facility
constructions, pieces of equipment, and services that are provided for the offshore (3.43(3.43)) energy sector
Note 1 to entry: The facility includes the structure (3.71(3.71)) and non-structural systems such as topsides (3.73(3.73))
equipment, marine systems (3.40(3.40),), piping and accommodation.
Note 2 to entry: A hydrocarbon facility (platform) includes structural appurtenances (3.6(3.6)) and ancillary systems
(3.7(3.7)) but does not include the non-structural components (3.68(3.68)) of the hydrocarbon wells.
Note 3 to entry: The facility does not include the geological strata supporting the foundation. However, site-specific
geotechnical parameters provide the boundary conditions necessary to model the facility’s foundation or anchoring.
3.28 3.28
fit-for-service
in compliance with the applicable structural requirements
Note 1 to entry: Compliance with this standard indicates that the structure (3.71(3.71)) provides the required level of
structural safety, functionality, and integrity for the defined design and operating conditions and assessment period.
Note 2 to entry: Risk-informed design approach (3.60(3.60)) or reliability-based design approach (3.54(3.54)) can be used
to demonstrate compliance, where permitted, see 10.310.3.
3.29 3.29
fixed structure
structure (3.71(3.71)) that is bottom-founded and transfers most of the actions (3.3(3.3)) on it to the seabed
(3.64(3.64))
3.30 3.30
floating structure
structure (3.71(3.71)) where the full weight is supported by buoyancy
3.31 3.31
hazard
potential source of harm
Note 1 to entry: Harm is typically differentiated between harm to people, harm to the environment, harm in terms of
costs to organizations, or harm to society in general.
3.32 3.32
hazardous event
event which occurs when a hazard (3.31(3.31)) interacts with a structure (3.71(3.71))
EXAMPLESEXAMPLE Wave impacting the structure (3.71(3.71),), iceberg impacting the structure
(3.71(3.71),), excessive topsides (3.73(3.73)) weight added to the structure (3.71(3.71),), vessel collision, fire, explosion,
and landslip in the vicinity of structural anchors (piles).
Note 1 to entry: A hazardous event can be a storm involving waves, currents and winds acting from different directions.
Note 2 to entry: A hazardous event can be a combination of basic variables (3.8(3.8)) such as wave height and period, or
ice floe size and drift speed.
Note 3 to entry: A hazardous event can be an action (3.3(3.3)) associated with a hazard (3.31(3.31)) that involves various
combinations of basic variables (3.8(3.8).).
3.33 3.33
ice gouge
ice scour
incision in the seabed (3.64(3.64)) or removal of seabed (3.64(3.64)) material by an ice feature
3.34 3.34
incident
non-environmental hazardous event (3.32(3.32)) considered in an operational design situation (3.19(3.19))
Note 1 to entry: An incident is a lesser accidental event (3.2(3.2),), associated with possible local damage or damage to
structural components (3.68(3.68),), occurring with low probability, most typically associated with probabilities not less
−2
than 10 per annum (1 in 100 years).
3.35 3.35
inspection
on-site examination within the scope of quality control and condition assessment aiming to assess the present
condition of a structure (3.71(3.71))
3.36 3.36
integrity management
systematic process intended to assure integrity of a structure (3.71(3.71)) or a marine system (3.40(3.40))
3.37 3.37
jack-up
mobile offshore (3.43(3.43)) unit with a buoyant hull and one or more legs that can be moved up and down
relative to the hull
Note 1 to entry: A jack-up reaches its operational mode by lowering the leg(s) to the seabed (3.64(3.64)) and then raising
the hull to the required elevation. The majority of jack-ups have three or more legs, each of which can be moved
independently and which are supported in the seabed (3.64(3.64)) by spudcans.
3.38 3.38
limit state
state beyond which the structure (3.71(3.71)) or structural component (3.68(3.68)) no longer satisfies the
design criteria (3.16(3.16))
Note 1 to entry: Three limit states are categorised in Clause 8Clause 8:: ultimate, serviceability and fatigue.
3.39 3.39
maintenance
routine work undertaken to ensure the continuing performance of a facility (3.27(3.27))
3.40 3.40
marine system
system contributing to the structural safety, stability and position keeping ability of a floating facility
(3.27(3.27))
3.41 3.41
marine system integrity
ability of a marine system (3.40(3.40)) to maintain performance (3.50(3.50)) throughout the design service life
(3.18(3.18),), with respect to structural safety, robustness (3.61(3.61),), serviceability and durability
(3.25(3.25))
3.42 3.42
nominal value
value assigned to a basic variable (3.8(3.8)) on a non-statistical basis, either determined from acquired
experience or physical conditions, or as specified in a published code or standard
3.43 3.43
offshore
situated in water some distance from the shore
Note 1 to entry: Alternatively, "near-shore" or “coastal” can be used to specify locations next to the coast or in mouths of
rivers.
3.44 3.44
offshore wind farm
group of offshore wind turbine structures (3.47(3.47)) and offshore wind substations (3.46(3.46)) in the same
location
3.45 3.45
offshore wind structure
part of an offshore wind turbine facility (3.27(3.27)) which extends upwards from the seabed (3.64(3.64)) and
connects the foundation to the wind turbine tower, or part of an offshore wind substation (3.46(3.46)) that
supports the topsides (3.73(3.73))
Note 1 to entry: The offshore wind structure can include a transition piece.
3.46 3.46
offshore wind substation
an electrical facility that collects and manages the power generated by wind turbines before transmitting it to
shore.
3.47 3.47
offshore wind turbine structure
support structure for a wind turbine assembly that is used to convert kinetic energy from the wind into
electricity
3.48 3.48
operator
owner
duty holder
principal company or company representative leasing the offshore (3.43(3.43)) site from a government
3.49 3.49
partial factor method
method within the semi-probabilistic design approach (3.66(3.66)) where a safety coefficient (partial factor)
is applied to basic variables (3.8(3.8)) to ensure structural reliability (3.53(3.53))
Note 1 to entry: Partial factors can be applied to actions (3.3(3.3),), resistances (3.57(3.57)) and materials, see 11.411.4
and 11.511.5.
3.50 3.50
performance
ability of a structure (3.71(3.71)) or a structural component (3.68(3.68)) to fulfil specified requirements
Note 1 to entry: Specified requirements include requirements for structural functionality, structural integrity
(3.69(3.69)) and functionality of marine systems (3.40(3.40).).
Note 2 to entry: Performance levels are established as a means of mitigating consequences associated with life-safety,
environmental pollution, reliability (3.53(3.53)) of energy supply and business disruption.
3.51 3.51
primary structure
all main structural components (3.68(3.68)) that provide the structure's (3.71(3.71)) main strength and
stiffness
3.52 3.52
recognized classification society
RCS
member of the international association of classification societies (IACS), with recognized and relevant
competence and experience in offshore (3.43(3.43) )structures (3.71(3.71)) and with established rules and
procedures for classification and certification of offshore (3.43(3.43) )structures (3.71(3.71)) located at a
specific site
3.53 3.53
reliability
performance (3.50(3.50)) over a specified time period
Note 1 to entry: When reliability is used in the context of limit states (3.38(3.38),), it can be expressed as the probability
that the limit is not exceeded.
Note 2 to entry: The specified time period is typically one year.
3.54 3.54
reliability-based design approach
design approach (3.15(3.15)) where uncertainty and variability in the basic variables (3.8(3.8)) are
represented by means of probabilistic methods and models
Note 1 to entry: This approach is based on probabilistic models of action effects and resistances, e.g. FORM, SORM, Monte-
Carlo simulations, or hazard and fragility curves.
3.55 3.55
repair
restoring the condition of a structure (3.71(3.71)) that has been damaged or deteriorated
3.56 3.56
representative value
value used in the semi-probabilistic design approach (3.66(3.66)) based on the characteristic value (3.10(3.10))
or the nominal value (3.42(3.42)) or a combination of characteristic values (3.10(3.10)) and nominal values
(3.42(3.42))
Note 1 to entry: For strength models, a representative value can be either a characteristic value (3.10(3.10)) or a nominal
value (3.42(3.42)) while for action models, a representative value can usually be calculated from a combination of
characteristic values (3.10(3.10)) and nominal values (3.42(3.42).).
3.57 3.57
resistance
ability of a structure (3.71(3.71),), or a structural component (3.68(3.68),), to withstand action effects
(3.4(3.4))
3.58 3.58
return period
average time between occurrences of an event
Note 1 to entry: The offshore (3.43(3.43)) industry commonly uses a return period measured in years for environmental
events. The return period in years is equal to the reciprocal of the annual probability of occurrence of the event.
Note 2 to entry: Events include both discrete hazardous events (3.32(3.32)) and exceedances of a threshold of a relevant
variable.
3.59 3.59
riser
pipe designed to carry fluids (typically hydrocarbons) between the sea floor (3.63(3.63)) and a termination
point on a facility (3.27(3.27))
Note 1 to entry: For fixed structures (3.29(3.29),), the termination point is usually the topsides (3.73(3.73).).
Note 2 to entry: For floating structures (3.30(3.30),), the riser can terminate at other locations on the facility (3.27(3.27).).
3.60 3.60
risk-informed design approach
design approach (3.15(3.15)) where uncertainty and variability in both the basic variables (3.8(3.8)) and the
consequences are represented by proven risk assessment methods
Note 1 to entry: Depending on the design situation (3.19(3.19),), consequences can include life-safety, environmental
pollution, reliability of energy supply and business disruption.
Note 2 to entry: Uncertainty and variability in basic variables (3.8(3.8)) and hazardous events (3.32(3.32)) are typically
represented by probabilistic methods and models.
Note 3 to entry: Uncertainty and variability in consequences are often modelled by their expected value but can also be
represented by probabilistic methods and models.
3.61 3.61
robustness
ability of a structure (3.71(3.71)) to withstand hazardous events (3.32(3.32)) without being damaged to an
extent disproportionate to the cause
3.62 3.62
scour
removal of seabed (3.64(3.64)) material caused by currents and waves
3.63 3.63
sea floor
interface between sea and seabed (3.64(3.64))
3.64 3.64
seabed
materials below the sea floor (3.63(3.63))
3.65 3.65
secondary structure
structural components (3.68(3.68)) that, when removed, do not significantly alter the overall strength and
stiffness of the structure (3.71(3.71))
3.66 3.66
semi-probabilistic design approach
design approach (3.15(3.15)) where uncertainty and variability in the basic variables (3.8(3.8)) are
represented by factored representative values (3.56(3.56))
Note 1 to entry: Partial factor method (3.49(3.49),), working stress method and event-based design method are
categorized within this approach.
3.67 3.67
splash zone
part of a structure (3.71(3.71)) that is intermittently exposed to air and immersed in the sea
3.68 3.68
structural component
discrete part of a structure (3.71(3.71))
EXAMPLE Examples of components include columns, beams, stiffened plates, tubulars and joints, mooring lines and
tendons, foundation anchors and piles, but not the geological strata.
Note 1 to entry: A component can include an assembly of components, e.g. a subsystem.
3.69 3.69
structural integrity
ability of a structure (3.71(3.71)) or a structural component (3.68(3.68)) to maintain performance (3.50(3.50))
throughout the design service life (3.18(3.18),), with respect to structural safety, robustness (3.61(3.61),),
serviceability and durability (3.25(3.25))
3.70 3.70
structural reliability analysis
probabilistic methodology for determining limit state (3.38(3.38)) or damage state exceedance probabilities
3.71 3.71
structure
organized combination of physically connected elements designed to withstand actions (3.3(3.3)) and provide
adequate rigidity
3.72 3.72
tertiary structure
non-loadbearing elements associated with outfitting offshore (3.43(3.43)) energy facilities (3.27(3.27))
EXAMPLESEXAMPLE Handrails, guardrails, safety gates, stairs, ladders, staircases, floor gratings, kick plates,
drip pans, cable trays, pipe supports, vents, access covers, manhole covers, attachments for corrosion protection systems.
[25]
Note 1 to entry: ISO 24201 covers the design of tertiary outfitting structures.
3.73 3.73
topsides
structure (3.71(3.71)) and equipment placed on a supporting fixed structure (3.29(3.29)) or floating structure
(3.30(3.30)) to provide some or all of a facility’s (3.27(3.27)) functions
Note 1 to entry: For a ship-shaped floating structure (3.30(3.30),), the hull deck is not part of the topsides (3.73(3.73).).
Note 2 to entry: For a jack-up (3.37(3.37),), the hull is not part of the topsides (3.73(3.73).).
Note 3 to entry: A separate fabricated deck or module support frame is part of the topsides (3.73(3.73).).
Note 4 to entry: For an offshore wind turbine facility (3.27(3.27),), the topsides (3.73(3.73)) comprise the wind turbine
tower and the rotor-nacelle assembly.
4 Symbols and abbreviated terms
4.1 Symbols
A accidental action
a design value of geometric variable
d
a representative value of geometric variable
r
C design value of the deformation or constraint
d
E environmental action
E repetitive environmental action
R
E environmental action with a specified return period
RP
F action
F design action
d
F representative value of an action
r
f design value of material variable
d
f representative value of material variable
r
G permanent action
N numbers of cycles to failure for different stress, strain or action levels
p annual probability of occurrence or probability of exceedance
Q variable (functional) action
Q repetitive variable (functional) action
R
Q variable action of long duration
Q variable action of short duration
R reliability of a structural system
R design value of resistance
d
R representative value of resistance
r
S total design action effect
d
T annual return period of an event or an action
γ partial factor for environmental action
E
γ partial factor for action
F
γ partial factor for material
M
γ partial factor for resistance
R
Δa additive deviation in the geometric variable
4.2 Abbreviated terms
ALARP as low as reasonably practicable
ALE abnormal level earthquake (from ISO 19901-2)
ALS procedure for limit state verification of abnormal and accidental design situations
COV coefficient of variation
DS damage state
DL damage limitation (type of damage state, from ISO 19901-3)
DLB ductility level blast (from ISO 19901-3)
ELE extreme level earthquake (from ISO 19901-2)
...