EN ISO 19900:2002

SLOVENSKI STANDARD
01-maj-2004
Petroleum and natural gas industries - General requirements for offshore
structures (ISO 19900:2002)
Petroleum and natural gas industries - General requirements for offshore structures (ISO
19900:2002)
Erdöl- und Erdgasindustrie - Allgemeine Anforderungen an Offshore-Bauwerke (ISO
19900:2002)
Industries du pétrole et du gaz naturel - Exigences générales pour les structures en mer
(ISO 19900:2002)
Ta slovenski standard je istoveten z: EN ISO 19900:2002
ICS:
75.180.10 Oprema za raziskovanje in Exploratory and extraction
odkopavanje equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 19900
First edition
2002-12-01
Petroleum and natural gas industries —
General requirements for offshore
structures
Industries du pétrole et du gaz naturel — Exigences générales pour les
structures en mer
Reference number
ISO 19900:2002(E)
©
ISO 2002
ISO 19900:2002(E)
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ii © ISO 2002 — All rights reserved

ISO 19900:2002(E)
Contents Page
Foreword. v
Introduction . vii
1 Scope. 1
2 Terms and definitions. 1
3 Symbols and abbreviated terms. 5
3.1 Symbols . 5
3.2 Abbreviated terms. 6
4 General requirements and conditions . 6
4.1 Fundamental requirements. 6
4.2 Durability, maintenance and inspection. 6
4.3 Hazards . 7
4.4 Design basis . 7
4.5 Service requirements. 8
4.6 Operating requirements . 8
4.7 Special requirements. 8
4.8 Location and orientation . 8
4.9 Structural configuration . 9
4.10 Environmental conditions. 10
4.11 Construction. 14
4.12 Decommissioning and removal. 14
5 Principles of limit states design . 14
5.1 Limit states . 14
5.2 Design . 16
6 Basic variables . 16
6.1 General. 16
6.2 Actions . 16
6.3 Properties of materials and soils . 19
6.4 Geometrical parameters. 19
7 Analyses — calculations and testing. 19
7.1 General. 19
7.2 Calculation. 20
7.3 Model testing . 20
7.4 Prototype testing. 20
7.5 Existing reference. 20
8 Design format of partial factors. 20
8.1 Principles . 20
8.2 Actions and their combinations . 21
8.3 Properties of materials and soils . 23
8.4 Geometrical parameters. 24
8.5 Uncertainties of calculation models . 24
8.6 Determination of values for partial factors. 24
9 Quality control. 24
9.1 General. 24
9.2 Responsibilities. 25
9.3 Inspection and testing. 25
9.4 In-service inspection, maintenance and repair. 25
9.5 Records and documentation. 25
ISO 19900:2002(E)
10 Assessment of existing structures.26
10.1 General .26
10.2 Condition assessment .26
10.3 Action assessment.27
10.4 Resistance assessment.27
10.5 Component and system failure consequences and mitigation.27
10.6 Fatigue.27
Bibliography.28

iv © ISO 2002 — All rights reserved

ISO 19900:2002(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
ISO 19900 was prepared by Technical Committee ISO/TC 67, Petroleum and natural gas industries,
Subcommittee SC 7, Offshore structures.
This first edition of ISO 19900 cancels and replaces ISO 13819-1:1995, which has been editorially revised.
ISO 19900 is one of a series of standards for offshore structures. The full series consists of the following
International Standards:
ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
ISO 19901-4, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 4:
Geotechnical and foundation design considerations
ISO 19901-5, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 5:
Weight control during engineering and construction
The following International Standards are under preparation:
ISO 19901-1, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 1:
Meteocean design and operating considerations
ISO 19901-2, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 2:
Seismic design procedures and criteria
ISO 19901-3, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 3:
Topsides structure
ISO 19901-6, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 6:
Marine operations
ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
ISO/TS 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
ISO 19904, Petroleum and natural gas industries — Floating offshore structures including stationkeeping
ISO 19905-1, Petroleum and natural gas industries — Site-specific assessment of mobile offshore units —
Part 1: Jack-ups
ISO 19900:2002(E)
ISO/TR 19905-2, Petroleum and natural gas industries — Site-specific assessment of mobile offshore units —
Part 2: Jack-ups commentary
ISO 19906, Petroleum and natural gas industries — Arctic offshore structures
vi © ISO 2002 — All rights reserved

ISO 19900:2002(E)
Introduction
The offshore structures International Standards ISO 19900 to ISO 19906 constitute a common basis covering
those aspects that address design requirements and assessments of all structures used by the petroleum and
natural gas industries worldwide. Through their application the intention is to achieve reliability levels
appropriate for manned and unmanned offshore structures, whatever the nature or combination of the
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 offshore structures International Standards are intended to provide a 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.
ISO 19900 applies to offshore structures and is in accordance with the principles of ISO 2394 (see Reference
[1] in the Bibliography). It includes, where appropriate, additional provisions that are specific to offshore
structures.
INTERNATIONAL STANDARD ISO 19900:2002(E)

Petroleum and natural gas industries — General requirements
for offshore structures
1 Scope
This International Standard specifies general principles for the design and assessment of structures subjected
to known or foreseeable types of actions. These general principles are applicable worldwide to all types of
offshore structures including bottom-founded structures as well as floating structures and to all types of
materials used including steel, concrete and aluminium.
This International Standard specifies design principles that are applicable to the successive stages in
construction (namely fabrication, transportation and installation), to the use of the structure during its intended
life and to its decommissioning. Generally, the principles are also applicable to the assessment or modification
of existing structures. Aspects related to quality control are also addressed.
This International Standard is applicable to the design of complete structures including substructures, topsides
structures, vessel hulls, foundations and mooring systems.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
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.
2.2
action effect
effect of actions on structural components
EXAMPLE Internal force, moment, stress or strain.
2.3
air gap
clearance between the highest water surface that occurs during the extreme environmental conditions and the
lowest exposed part not designed to withstand wave impingement
2.4
appurtenance
part of the structure that is installed to assist installation, to provide access or protection, or for transfer of
fluids
ISO 19900:2002(E)
2.5
basic variable
one of a specified set of variables representing physical quantities which characterize actions, environmental
influences, geometrical quantities, or material properties including soil properties
2.6
catenary mooring
mooring system where the restoring action is provided by the distributed weight of mooring lines
2.7
characteristic value
value assigned to a basic variable associated with a prescribed probability of not being violated by
unfavourable values during some reference period
NOTE The characteristic value is the main representative value. In some design situations a variable can have two
characteristic values, an upper and a lower value.
2.8
compliant structure
structure that is sufficiently flexible that applied lateral dynamic actions are substantially balanced by inertial
reactions
2.9
conductor
tubular pipe extending upward from the sea floor or below containing pipes that extend into the petroleum
reservoir
2.10
decommissioning
process of shutting down a platform and removing hazardous materials at the end of its production life
2.11
design criteria
quantitative formulations that describe the conditions to be fulfilled for each limit state
2.12
design service life
assumed period for which a structure is to be used for its intended purpose with anticipated maintenance, but
without substantial repair being necessary
2.13
design situation
set of physical conditions representing real conditions during a certain time interval for which the design will
demonstrate that relevant limit states are not exceeded
2.14
design value
value derived from the representative value for use in the design verification procedure
2.15
exposure level
classification system used to define the requirements for a structure based on consideration of life safety and
of environmental and economic consequences of failure
[2]
NOTE The method for determining exposure levels are described in ISO 19902 . An exposure level 1 platform is the
most critical and exposure level 3 the least. A normally manned platform which cannot be reliably evacuated before a
design event will be an exposure level 1 platform.
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ISO 19900:2002(E)
2.16
fit-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
2.17
fixed structure
structure that is bottom founded and transfers all actions on it to the seabed
2.18
floating structure
structure where the full weight is supported by buoyancy
2.19
jack-up
mobile offshore unit that can be relocated and is bottom founded in its operating mode
NOTE A jack-up reaches its operational mode by lowering legs to the sea floor and then jacking the hull to the
required elevation.
2.20
mobile offshore unit
MOU
structure intended to be frequently relocated to perform a particular function
2.21
limit state
state beyond which the structure no longer fulfils the relevant design criteria
2.22
nominal value
value assigned to a basic variable determined on a non-statistical basis, typically from acquired experience or
physical conditions
2.23
platform
complete assembly including structure, topsides and, where applicable, foundations
2.24
reference period
period of time used as basis for determining values of basic variables
2.25
reliability
ability of a structure or a structural component to fulfil the specified requirements
2.26
representative value
value assigned to a basic variable for verification of a limit state
2.27
resistance
capacity of a component, or a cross-section of a component, to withstand action effects without failure
2.28
return period
reciprocal of the probability of exceeding an event during a particular period of time
NOTE The return period is the average time (usually in years) between occurrences of an event exceeding a
specified magnitude.
ISO 19900:2002(E)
2.29
riser
tubular used for the transport of fluids between the sea floor and a termination point on the platform
NOTE For a fixed structure the termination point is usually the topsides. For floating structures the riser may
terminate at other locations of the platform.
2.30
scour
removal of seabed soils caused by currents and waves
NOTE Such erosion can be due to natural processes or can be due to interruption of the natural flow regime near the
sea floor by structural elements.
2.31
splash zone
area of a structure that is frequently wetted due to waves and tidal variations
2.32
structural system
load-bearing components of a structure and the way in which these components function together
2.33
structural component
physically distinguishable part of a structure
EXAMPLE Column, beam, stiffened plate, tubular joint, or foundation pile.
2.34
structural model
idealization of the structural system used for design or assessment
2.35
structure
organized combination of connected parts designed to withstand actions and provide adequate rigidity
2.36
structure orientation
position of a structure in plan referenced to a fixed direction such as true north
2.37
taut-line mooring
mooring system where the restoring action is provided by elastic deformation of mooring lines
2.38
topsides
structures and equipment placed on a supporting structure (fixed or floating) to provide some or all of a
platform’s functions
NOTE 1 For a ship-shaped floating structure, the deck is not part of the topsides.
NOTE 2 For a jack-up, the hull is not part of the topsides.
NOTE 3 A separate fabricated deck or module support frame is part of the topsides.
4 © ISO 2002 — All rights reserved

ISO 19900:2002(E)
3 Symbols and abbreviated terms
3.1 Symbols
A accidental action
a design value of geometrical parameter
d
a characteristic value of geometrical parameter
k
C constraint (see 5.1.4 and 8.1)
E environmental action
F design value of action
d
F representative value of action
r
f design value of material property, for example strength
d
f characteristic value of material property, for example strength
k
G permanent action
G characteristic value of permanent action
k
Q variable action
Q characteristic value of variable action
k
R design value of component resistance
d
R characteristic value of component resistance, based on characteristic values of material properties
k
γ factor related to model uncertainty or other circumstances that are not taken into account by the other
d
γ values
γ partial action factor of which the value reflects the uncertainty or randomness of the action (see 8.2.2)
f
γ partial material factor of which the value reflects the uncertainty or variability of the material property (see
m
8.3.2)
γ factor by which the importance of the structure and the consequences of failure, including the significance
n
of the type of failure, may be taken into account and of which the value of γ depends on the design
n
situation under consideration
γ partial resistance factor of which the value reflects the uncertainty or variability of the component
R
resistance including those of material properties (see 8.5)
∆ additive partial geometrical quantity of which the value reflects the uncertainties of the geometrical
a
parameter (see 8.4.2)
Ψ reduction factor to account for reduced probability of simultaneous independent actions (see 8.2.3)
Ψ , Ψ factors relating characteristic values to representative values for variable actions (see 8.2.1)
1 2
ISO 19900:2002(E)
3.2 Abbreviated terms
ALS accidental limit state
FLS fatigue limit state
SLS serviceability limit state
ULS ultimate limit state
4 General requirements and conditions
4.1 Fundamental requirements
A structure and its structural components shall be designed, constructed and maintained so that it is suited to
its intended use. In particular, it shall, with appropriate degrees of reliability, fulfil the following performance
requirements:
a) it shall withstand actions liable to occur during its construction and anticipated use (ULS requirement);
b) it shall perform adequately under all expected actions (SLS requirement);
c) it shall not fail under repeated actions (FLS);
d) in the case of hazards (accidental or abnormal events), it shall not be subsequently damaged
disproportionately to the original cause (ALS);
e) appropriate degrees of reliability depend upon:
 the cause and mode of failure;
 the possible consequences of failure in terms of risk to life, environment and property;
 the expense and effort required to reduce the risk of failure;
 different requirements at national, regional or local level.
This International Standard provides criteria so that the above requirements are fulfilled during the intended
life of the structure.
A structure designed and constructed in accordance with this International Standard may be assumed to
comply with the above requirements.
4.2 Durability, maintenance and inspection
The durability of the structure in its environment shall be such that the general state of the structure is kept at
an acceptable level during its life.
Maintenance shall include the performance of regular inspections, inspections on special occasions (e.g. after
an earthquake or other severe environmental event), the upgrading of protection systems and repair of
structural components.
Durability of the structure shall be achieved by either
a) a maintenance program, or
b) by designing the structure so as to allow for deterioration in those areas which cannot be, or are not
expected to be, maintained during the planned life of the structure.
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ISO 19900:2002(E)
In the case of a), the structure shall be designed and constructed so that no significant degradation is likely to
occur within the time intervals between the inspections. The necessity of relevant parts of the structure being
available for inspection, without unreasonably complicated dismantling, shall be considered during design.
Degradation may be reduced or prevented by providing a suitable protection system.
The rate of deterioration may be estimated on the basis of calculations, experimental investigations,
experience from other structures or a combination of these.
NOTE Structural integrity, serviceability throughout the intended service life and durability are not simply functions of
the design calculations but are also dependent on the quality control exercised in construction, the supervision on site and
the manner in which the structure is used and maintained.
4.3 Hazards
4.3.1 General
Hazardous circumstances, that alone or in combination with normal conditions could cause the SLS or ULS to
be exceeded, shall be taken into account.
Possible hazards to the structure and its components include
a) an error caused by lack of information, omission, misunderstanding, etc.,
b) effects of abnormal actions, or
c) operation malfunction that could lead to fire, explosion, capsizing, etc.
The measures taken to counter such hazards basically consist of
 careful planning at all phases of development and operation,
 avoiding the structural effects of the hazards by either eliminating the source or by bypassing and
overcoming them,
 minimizing the consequences, or
 designing for the hazards.
In considering a specific hazard, a design situation shall be defined (see 5.2.2). This design situation will
normally be dominated by one hazardous occurrence with expected concurrent normal operating conditions.
4.3.2 Accidental events
The possibility of accidental events shall be considered, and suitable criteria shall be established, when
appropriate. Possible accidental events include, for example, vessel collision, dropped objects, explosion, fire
and unintentional flooding. Design requirements shall be established taking account of the operational
conditions and the type, function and location of the structure.
4.4 Design basis
The influences arising from the intended use of the structure and the environmental conditions shall be
described as the design situations associated with normal use of the structure. The influences arising during
construction of the structure and the associated environmental conditions shall also be covered by suitable
design situations (see 5.2.2).
All relevant influences and conditions shall be considered in order to establish the design basis for the
structure. The principal influences and conditions that should be considered to establish the design basis for
offshore structures are described in 4.5 to 4.12.
ISO 19900:2002(E)
4.5 Service requirements
The service requirements and the expected service life shall be specified. The structure may be used for
drilling, producing, storage, personnel accommodation, or other function or combination of functions.
4.6 Operating requirements
4.6.1 Manning
The manning level for each phase of the structure’s life shall be specified.
4.6.2 Conductors and risers
The number, location, size, spacing and operating conditions of all conductors and risers shall be specified
and taken into account in the structural design. The design and/or layout shall provide protection to
conductors and risers from accidental damage.
The design should have provisions to mitigate the consequences of accidental damage to conductors and
risers.
4.6.3 Equipment and material layouts
Equipment and material layouts and their associated weights, centres of gravity and exposure to
environmental actions shall be specified. Consideration should be given to planned future operations.
4.6.4 Personnel and material transfer
Plans for transferring personnel and materials shall be specified, for example
a) the types, sizes and weights of helicopters,
b) the types, sizes and displacements of supply and other service vessels,
c) the number, types, sizes and locations of the deck cranes and other materials handling systems, and
d) planned emergency personnel evacuation.
4.6.5 Motions and vibrations
Structures and parts of structures shall be designed so that accelerations, velocities and displacements do not
impair safety and serviceability within defined limits.
4.7 Special requirements
All special operational, construction and maintenance requirements not covered under 4.6.1 to 4.6.5 that can
affect the safety of the structure shall be specified, together with their expected concurrent environmental
conditions.
The limiting environmental conditions specific to certain operations should be specified.
NOTE This will normally apply to floating units (e.g. limiting environmental conditions for certain drafts) or MOUs
(e.g. limiting environmental conditions for a jack-up when the cantilever is fully extended).
4.8 Location and orientation
The site location and structure orientation shall be specified. For structures designed to be relocatable, the
range of limiting environmental conditions, water depths and soil conditions should be provided.
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ISO 19900:2002(E)
The site for the structure in latitude and longitude should be identified early in order that the appropriate
environmental conditions and soil conditions can be identified.
4.9 Structural configuration
4.9.1 General
The choice of the structural system shall be made such that the primary structure is able to maintain adequate
structural integrity during normal service and after specified situations that apply actions on the structure. The
choice of materials, detailing and method of construction as well as quality control can influence structural
integrity.
4.9.2 Deck elevation
The topsides structure shall normally have adequate clearance above the design wave crest. Any topsides
structure or piping not having adequate clearance (air gap) shall be designed for actions caused by waves
and currents. Minor structure or components may be excluded from this requirement.
The deck elevation and air gap shall be determined taking into account the values of and uncertainties in the
following parameters as applicable:
a) water depth;
b) tides and surges;
c) crest elevation of extreme waves;
d) wave-structure interaction;
e) structure motion and draft;
f) initial and long-term settlements and inclination;
g) subsidence.
4.9.3 Splash zone
The splash zone extent shall be established taking into account the values of the platform elevation, motions
of floating vessels, tidal ranges, wave crests and wave troughs.
For floating structures with possibilities for draft adjustment, the splash zone shall be defined relative to the
extreme draft levels expected.
NOTE The splash zone is that part of a structure that is intermittently exposed to air and immersed in the sea. The
splash zone is important in relation to inspection and maintenance considerations and can have an impact on the design
to resist corrosion and fatigue.
4.9.4 Stationkeeping systems
Floating structures shall be provided with a stationkeeping system, which may be either passive or active or a
combination of both passive and active.
The stationkeeping system shall be designed to maintain adequate position reference as well as directional
control when orientation is important for safety or operational considerations.
Passive stationkeeping systems include catenary mooring, taut-line mooring, spring buoy, articulated leg and
tension leg systems. Active systems include dynamic positioning based on thrusters or catenary systems
based on changing mooring line tensions.
ISO 19900:2002(E)
A mooring system for floating structures may be designed to be disconnectable to mitigate the effects of
severe storms, if the disconnection can be accomplished in a controlled manner without
a) impairing the safety of personnel on board the unit or a neighbouring infrastructure, or
b) creating undue risk to the environment.
4.9.5 Compartmentation of structures
Floating structures or structures for which buoyancy is important shall normally be subdivided into
compartments to limit the consequences of unintended flooding (see 5.1.6).
The amount of compartmentation should be determined after considering special conditions and protection
measures that can be used to prevent flooding. Fewer compartments may be justified, if buoyancy is only
needed in temporary phases or if the consequences of flooding have only minor effects on the overall
reliability.
4.10 Environmental conditions
4.10.1 Meteorological and oceanographical information
4.10.1.1 General
The phenomena listed in 4.10.1.2 through 4.10.1.9 shall, where appropriate to the region, be taken into
account in the design.
These phenomena shall be described by physical characteristics and, where available, statistics. The joint
occurrence of different values of parameters should also be defined when suitable data are available. From
this information, appropriate environmental design conditions shall be established that will consider the
following:
a) the type of structure being designed;
b) the phase of development (e.g. construction, transportation, installation, drilling, production, etc.);
c) the limit-state considered.
Usually two sets of conditions have to be established that take into consideration the following:
 Consideration for normal meteorological and oceanographical conditions that are expected to occur
frequently during the life of the structure. These conditions are needed to plan field operations such as
installation and to develop the actions caused by the environment associated with particular operations or
serviceability checks.
 Consideration for extreme meteorological and oceanographical conditions that recur with a given return
period or probability of occurrence.
Extreme, normal and other meteorological and oceanographical parameters shall be determined from actual
measurements at the site or by suitable validated model data such as from hindcast models.
NOTE 1 Environmental actions are generally derived from design environmental conditions. The extreme
environmental conditions normally have a specified return period for the in-service condition (see 8.2.1). Alternatively, the
action associated with extreme environmental conditions can be defined to have a specified return period, if adequate data
exist to reliably determine the specified return period, allowing for the joint occurrence of extreme meteorological and
oceanographical conditions occurring at the site and further provided that the partial factors are selected accordingly.
NOTE 2 Normally the structure’s response to actions caused by the environment are investigated for a range of
potential combinations of environmental parameters and consideration is given to the relationship considering the
closeness of the wave period compared to the natural response period of motion or vibration. For example, for two
10 © ISO 2002 — All rights reserved

ISO 19900:2002(E)
different sea-state conditions, each having the same composite return period, it is possible that the sea-state having lower
wave heights but a longer or shorter associated period will develop more severe action effects on some components.
NOTE 3 Compliant or floating structures are generally sensitive to more environmental parameters than fixed or
bottom-founded structures, since dynamic effects are more significant for such structures.
NOTE 4 Normally consideration is given to specific problems such as the tuning of a characteristic dimension of the
structure with respect to wavelengths, for example
a) the distance between the main legs of gravity-based structures or semi-submersible units, or
b) the length of the hull of a ship-shaped barge.
4.10.1.2 Wind
Actions caused by wind acting on a structure shall be considered for both the global and local design.
Site-specific information on wind speed, direction and duration shall be determined.
Wind is usually characterized by the mean value of its velocity over a given time interval at a given elevation
above the mean water level. In specific cases (for example, design of flexible structures such as flare-towers
and compliant structures with periods of motion that are large), the frequency content is of importance and
should be taken into account.
The variability with elevation and the spatial coherence should be considered.
NOTE Generally, the sustained wind speed at the time of peak actions caused by waves is used for global design in
conjunction with wave actions. Maximum gust conditions during the design storm are used to design topsides and
individual members.
4.10.1.3 Waves
Actions caused by waves acting on a structure shall be considered for both the global and the local design.
Site-specific information shall be established to consider the following:
a) sea state characteristics in terms of wave height, period, duration, directions and spectra, and
b) the long-term statistics of these characteristics.
4.10.1.4 Water depth and sea level variations
The water depth shall be determined. The magnitude of the low and high tides and positive and negative
storm surges shall be determined.
The possibility of ground subsidence shall be considered when determining the water depth.
4.10.1.5 Currents
Phenomena such as tidal, wind driven, global circulation, loop and eddy currents shall be considered when
relevant.
Currents shall be described by their velocity (magnitude and direction), variability with water depth and
persistence.
The occurrence of fluid motion caused by internal waves should be considered.
NOTE Global circulation currents are driven by large-scale global effects. Loop currents are associated with major
ocean current circulation patterns as they conform to the landmasses, e.g. Gulf of Mexico loop current. Eddy currents are
meso-scale circulatory features shed from loop or other major circulation currents. Eddy currents can persist for several
months or more. Internal waves are propagating waves that can occur at the interface between layers of fluids having
different densities.
ISO 19900:2002(E)
4.10.1.6 Marine growth
Marine growth shall be considered and defined by its thickness, roughness, density and variation with depth.
The design may rely on periodic marine growth cleaning or anti-fouling systems during the platform life. Any
such reliance shall be documented and the cleaning program defined over the life of the platform. The
consequences of not maintaining this program should be determined and reported.
NOTE In most offshore areas, marine growth will occur on submerged platform members. Marine growth increases
surface roughness, member diameter and mass, which in turn affects actions caused by waves and earthquakes and
structural motions.
4.10.1.7 Ice and snow
Ice and snow accumulations shall be considered when relevant to the region. The accumulation of snow on
horizonta
...