ISO 19901-1:2005
(Main)Petroleum and natural gas industries — Specific requirements for offshore structures — Part 1: Metocean design and operating considerations
Petroleum and natural gas industries — Specific requirements for offshore structures — Part 1: Metocean design and operating considerations
ISO 19901-1:2005 gives general requirements for the determination and use of meteorological and oceanographic (metocean) conditions for the design, construction and operation of offshore structures of all types used in the petroleum and natural gas industries.
Industries du pétrole et du gaz naturel — Exigences spécifiques relatives aux structures en mer — Partie 1: Dispositions océano-météorologiques pour la conception et l'exploitation
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 19901-1
First edition
2005-11-15
Petroleum and natural gas industries —
Specific requirements for offshore
structures —
Part 1:
Metocean design and operating
considerations
Industries du pétrole et du gaz naturel — Exigences spécifiques
relatives aux structures en mer —
Partie 1: Dispositions océano-météorologiques pour la conception et
l'exploitation
Reference number
ISO 19901-1:2005(E)
©
ISO 2005
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ISO 19901-1:2005(E)
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ii © ISO 2005 – All rights reserved
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ISO 19901-1:2005(E)
Contents Page
Foreword. v
Introduction . vii
1 Scope . 1
2 Normative references . 2
3 Terms and definitions. 2
4 Symbols and abbreviated terms . 9
4.1 Main symbols . 9
4.2 Abbreviated terms . 11
5 Determining the relevant metocean parameters . 11
5.1 General. 11
5.2 Expert interpretation of the metocean database . 12
5.3 Selecting appropriate parameters for determining design actions or action effects. 12
5.4 The metocean database . 13
5.5 Storm types in a region. 13
5.6 Directionality . 14
5.7 Extrapolation to rare conditions . 14
5.8 Metocean parameters for fatigue assessments . 14
5.9 Metocean parameters for short-term activities . 14
6 Water depth, tides and storm surges . 16
6.1 General. 16
6.2 Tides. 16
6.3 Storm surge. 16
7 Wind . 17
7.1 General. 17
7.2 Wind actions and action effects. 18
7.3 Wind profile and time-averaged wind speed . 19
7.4 Wind spectra . 19
8 Waves. 19
8.1 General. 19
8.2 Wave actions and action effects . 20
8.3 Intrinsic, apparent and encounter wave periods. 20
8.4 Two-dimensional wave kinematics . 21
8.5 Maximum height of an individual wave for long return periods . 21
8.6 Wave spectra. 21
8.7 Wave directional spreading function and spreading factor. 21
8.8 Wave crest elevation . 22
9 Currents . 22
9.1 General. 22
9.2 Current velocities. 22
9.3 Current profile . 23
9.4 Current profile stretching . 23
9.5 Current blockage . 23
10 Other environmental factors. 24
10.1 Marine growth . 24
10.2 Tsunamis . 24
10.3 Seiches . 25
10.4 Sea ice and icebergs . 25
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ISO 19901-1:2005(E)
10.5 Snow and ice accretion . 25
10.6 Miscellaneous. 25
Annex A (informative) Additional information and guidance. 26
A.1 Scope. 26
A.2 Normative references . 26
A.3 Terms and definitions. 26
A.4 Symbols and abbreviations . 26
A.5 Determining the relevant metocean parameters. 26
A.6 Water depth, tides and storm surges. 35
A.7 Wind. 36
A.8 Waves. 41
A.9 Currents . 57
A.10 Other environmental factors. 61
Annex B (informative) Discussion of wave frequency spectra. 64
B.1 The Pierson-Moskowitz spectrum. 64
B.2 The JONSWAP spectrum . 67
B.3 Comparison of Pierson-Moskowitz and JONSWAP spectra . 68
B.4 Ochi-Hubble spectra . 70
Annex C (informative) Regional information . 74
C.1 General . 74
C.2 North-west Europe . 74
C.3 West coast of Africa. 84
C.4 US Gulf of Mexico . 94
C.5 US Coast of California . 112
C.6 East coast of Canada. 118
Bibliography . 130
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ISO 19901-1:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 19901-1 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 7, Offshore structures.
ISO 19901 consists of the following parts, under the general title Petroleum and natural gas industries —
Specific requirements for offshore structures:
⎯ Part 1: Metocean design and operating considerations
⎯ Part 2: Seismic design procedures and criteria
⎯ Part 4: Geotechnical and foundation design considerations
⎯ Part 5: Weight control during engineering and construction
⎯ Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units
The following parts are under preparation:
⎯ Part 3: Topsides structure
⎯ Part 6: Marine operations
ISO 19901 is one of a series of standards for offshore structures. The full series consists of the following
International Standards.
⎯ ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
⎯ ISO 19901 (all parts), Petroleum and natural gas industries — Specific requirements for offshore
structures
1)
⎯ ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
1)
⎯ ISO 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
1) To be published.
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ISO 19901-1:2005(E)
⎯ ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls,
2)
semi-submersibles and spars
⎯ ISO 19904-2, Petroleum and natural gas industries — Floating offshore structures — Part 2: Tension leg
3)
platforms
⎯ ISO 19905-1, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
3)
units — Part 1: Jack-ups
⎯ ISO/TR 19905-2, Petroleum and natural gas industries — Site-specific assessment of mobile offshore
3)
units — Part 2: Jack-ups commentary
3)
⎯ ISO 19906, Petroleum and natural gas industries — Arctic offshore structures
2) To be published.
3) Under preparation.
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ISO 19901-1:2005(E)
Introduction
The series of International Standards applicable to types of offshore structure, ISO 19900 to ISO 19906,
constitutes a common basis covering those aspects that address design requirements and assessments of all
offshore structures used by the petroleum and natural gas industries worldwide. Through their application the
intention is to achieve reliability levels appropriate for manned and unmanned offshore structures, whatever
the type of structure and 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 series of International Standards applicable to types of offshore structure is 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.
The overall concept of structural integrity is described above. Some additional considerations apply for
metocean design and operating conditions. The term “metocean” is short for “meteorological and
oceanographic” and refers to the discipline concerned with the establishment of relevant environmental
conditions for the design and operation of offshore structures. A major consideration in the design and
operation of such a structure is the determination of actions on, and the behaviour of, the structure as a result
of winds, waves and currents.
Environmental conditions vary widely around the world. For the majority of offshore locations there are little
numerical data from historic conditions; comprehensive data often only start being collected when there is a
specific need, for example, when exploration for hydrocarbons is being considered. Despite the usually short
duration for which data are available, designers of offshore structures need estimates of extreme and
−2
abnormal environmental conditions (with an individual or joint probability of the order of 1 × 10 / year and
−3 −4
1 × 10 to 1 × 10 / year, respectively).
Even for areas like the Gulf of Mexico, offshore Indonesia and the North Sea, where there are up to 30 years
of fairly reliable measurements available, the data are insufficient for rigorous statistical determination of
appropriate extreme and abnormal environmental conditions. The determination of relevant design
parameters has therefore to rely on the interpretation of the available data by specialists, together with an
assessment of any other information, such as prevailing weather systems, ocean wave creation and regional
and local bathymetry, coupled with consideration of data from comparable locations. It is hence important to
employ specialists from both the metocean and structural communities in the determination of design
parameters for offshore structures, particularly since setting of appropriate environmental conditions depends
on the chosen option for the offshore structure.
This part of ISO 19901 provides procedures and guidance for the determination of environmental conditions
and their relevant parameters. Requirements for the determination of the actions on, and the behaviour of, a
structure in these environmental conditions are given in ISO 19901-3, ISO 19901-6, ISO 19901-7, ISO 19902,
ISO 19903, ISO 19904, ISO 19905 and ISO 19906.
Some background to, and guidance on, the use of this part of ISO 19901 is provided in informative Annex A.
The clause numbering in Annex A is the same as in the normative text to facilitate cross-referencing.
A discussion on wave spectra is provided in informative Annex B.
Regional information, where available, is provided in informative Annex C.
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INTERNATIONAL STANDARD ISO 19901-1:2005(E)
Petroleum and natural gas industries — Specific requirements
for offshore structures —
Part 1:
Metocean design and operating considerations
1 Scope
This part of ISO 19901 gives general requirements for the determination and use of meteorological and
oceanographic (metocean) conditions for the design, construction and operation of offshore structures of all
types used in the petroleum and natural gas industries.
The requirements are divided into two broad types:
a) those that relate to the determination of environmental conditions in general, together with the metocean
parameters that are required to adequately describe them;
b) those that relate to the characterization and use of metocean parameters for the design, the construction
activities or the operation of offshore structures.
The environmental conditions and metocean parameters discussed comprise
⎯ extreme and abnormal values of metocean parameters that recur with given return periods that are
considerably longer than the design service life of the structure,
⎯ long-term distributions of metocean parameters, in the form of cumulative, conditional, marginal or joint
statistics of metocean parameters, and
⎯ normal environmental conditions that are expected to occur frequently during the design service life of the
structure.
Metocean parameters are applicable to
⎯ the determination of actions and action effects for the design of new structures,
⎯ the determination of actions and action effects for the assessment of existing structures,
⎯ the site-specific assessment of mobile offshore units,
⎯ the determination of limiting environmental conditions, weather windows, actions and action effects for
pre-service and post-service situations (i.e. fabrication, transportation and installation or decommissioning
and removal of a structure), and
⎯ the operation of the platform, where appropriate.
[1]
NOTE Specific metocean requirements for tension leg platforms are to be contained in ISO 19904-2 , for site-
[2] [3]
specific assessment of jack-ups in ISO 19905-1 , for arctic structures in ISO 19906 and for topsides structures in
[4]
ISO 19901-3 .
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ISO 19901-1:2005(E)
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
4)
ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
ISO 19903, Petroleum and natural gas industries — Fixed concrete offshore structures
ISO 19904-1, Petroleum and natural gas industries — Floating offshore structures — Part 1: Monohulls, semi-
submersibles and spars
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 19900 and the following apply.
3.1
abnormal value
design value of a parameter of abnormal severity used in accidental limit state checks in which a structure is
intended not to suffer complete loss of integrity
−3 −4
NOTE Abnormal events have probabilities of the order of 10 to 10 per annum. In the limit state checks, some or
all of the partial factors are set to 1,0.
3.2
chart datum
local datum used to fix water depths on a chart or tidal heights over an area
NOTE Chart datum is usually an approximation to the level of the lowest astronomical tide.
3.3
conditional distribution
conditional probability
statistical distribution (probability) of the occurrence of a variable A, given that other variables B, C, … have
certain assigned values
NOTE The conditional probability of A given that B, C, … occur is written as P(A|B,C,…). The concept is applicable to
metocean parameters, as well as to actions and action effects.
EXAMPLE When considering wave parameters, A can be the individual crest elevation, B the water depth and C the
significant wave height, and so on.
3.4
design crest elevation
extreme crest elevation measured relative to still water level
NOTE The design crest elevation is used in combination with information on astronomical tide, storm surge, platform
settlement, reservoir subsidence and water depth uncertainty and is derived from an extreme value analysis. Because of
the simplified nature of the models used to estimate the kinematics of the design wave, the design crest elevation can be
different from, usually somewhat greater than, the crest elevation of the design wave used to calculate actions on the
structure.
4) To be published.
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ISO 19901-1:2005(E)
3.5
design wave
deterministic wave used for the design of an offshore structure
NOTE 1 The design wave is an engineering abstract. Most often it is a periodic wave with suitable characteristics (e.g.
height H, period T, steepness, crest elevation). The choice of a design wave depends on
⎯ the design purpose(s) considered,
⎯ the wave environment,
⎯ the geometry of the structure,
⎯ the type of action(s) or action effect(s) pursued.
NOTE 2 Normally, a design wave is only compatible with design situations in which the action effect(s) are quasi-
statically related to the associated wave actions on the structure.
3.6
extreme value
design value of a parameter used in ultimate limit state checks, in which a structure's global behaviour is
intended to stay in the elastic range
−2
NOTE Extreme events have probabilities of the order of 10 per annum.
3.7
gust
brief rise and fall in wind speed lasting less than 1 min
NOTE In some countries, gusts are reported in meteorological observations if the maximum wind speed exceeds
approximately 8 m/s.
3.8
gust wind speed
maximum value of the wind speed of a gust averaged over a short (3 s to 60 s) specified duration within a
longer (1 min to 1 h) specified duration
NOTE 1 For design purposes, the specified duration depends on the dimensions and natural period of the (part of the)
structure being designed such that the structure is designed for the most onerous conditions; thus, a small part of a
structure is designed for a shorter gust wind speed duration (and hence a higher gust wind speed) than a larger (part of a)
structure.
NOTE 2 In practice, for design purposes, the gust wind speeds for different durations (e.g. 3 s, 5 s, 15 s, 60 s) are
derived from the wind spectrum.
3.9
highest astronomical tide
HAT
level of high tide when all harmonic components causing the tides are in phase
NOTE The harmonic components are in phase approximately once every 19 years, but these conditions are
approached several times each year.
3.10
hindcasting
method of simulating historical (metocean) data for a region through numerical modelling
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ISO 19901-1:2005(E)
3.11
long-term distribution
probability distribution of a variable over a long time scale
NOTE The time scale exceeds the duration of a sea state, in which the statistics are assumed constant (see short-
term distribution in 3.29). The time scale is hence comparable to a season or to the design service life of a structure.
EXAMPLE Long-term distributions of
⎯ significant wave height,
⎯ significant wave height in the months May to September,
⎯ individual wave heights,
⎯ current speeds (such as for the vortex induced vibrations of drilling risers),
⎯ scatter diagrams with the joint distribution of significant wave height and wave period (such as for a fatigue analysis),
or
⎯ a particular action effect.
3.12
lowest astronomical tide
LAT
level of low tide when all harmonic components causing the tides are in phase
NOTE The harmonic components are in phase approximately once every 19 years, but these conditions are
approached several times each year.
3.13
marginal distribution
marginal probability
statistical distribution (probability) of the occurrence of a variable A that is obtained by integrating over all
values of the other variables B, C, …
NOTE The marginal probability of A for all values of B, C, … is written as P(A). The concept is applicable to metocean
parameters, as well as to actions and action effects.
EXAMPLE When considering wave conditions, A can be the individual crest elevation for all mean zero-crossing
periods B and all significant wave heights C, occurring at a particular site.
3.14
marine growth
living organisms attached to an offshore structure
3.15
mean sea level
MSL
arithmetic mean of all sea
...
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