FUTURE INTERNATIONAL ARCTIC OFFSHORE STRUCTURES
ICE LOAD CODE ISO 19906
Mauri Määttänen, Prof.
Helsinki University of Technology
P.O.Box 4300
FIN-02015 TKK
Tel: +358-9-451 3440
Fax: +358-9-451 3449
mauri.maattanen@tkk.fi
http://www.tkk.fi/Units/Materialmechanics/
ABSTRACT
European objectives for wind energy production cannot be achieved without installing a great number of OWECs into
ice infested waters, mainly in the Baltic. Design requirements against ice loads are presently not well defined which
makes unbiased international design and contracting competition difficult. Starting from Petroleum and Natural Gas
Industries initiative an international Arctic Offshore Structures Standard ISO 19906 has been under development since
year 2002. The planned schedule to complete and ratify the code is by the end of year 2009. Even though the word
Arctic is adopted into the name, the European contribution has been to include also sub-arctic climate with more benign
ice load scenarios to the code. This includes especially ice load and their dynamic effects design requirements for
OWEC foundations. The paper describes the international cooperation, schedule to accomplish the code, ice climate,
load scenarios, and design principles. The code will pave way to open vast ice infested waters in the Baltic for wind
energy park exploitation.
Keywords: OWEC, ice action, international cooperation, design code
Purpose: To inform on the status and schedule of preparation work for the future international ice load design code that
will be applicable for OWEC design.
Method of approach: To describe the state of existing ice load design codes, efforts to prepare an international code,
progress and schedule, and expected relevance for OWEC design in ice infested waters.
Results: International offshore structures ice load design code that is applicable for OWEC design is due to be published
as an international standard by 2009.
Acknowledgements: The financial support by the EU 6 th Framework program: Sustainable Energy Systems, Specific
Support Action project: STANDICE (Standardization of Ice Forces on Offshore Structures Design), Contract n:o
503721, has on its behalf helped to complete this conference paper.
1. INTRODUCTION
European Union has objectives to have 1200 GW installed wind power by the year 2020. Most of the wind energy
power plant locations on land have already been utilized. Expansion is limited both by the available land and the
opposition of neighbouring people. Some increase to wind energy production on land capacity can be expected by
replacing existing small and outdated units with more efficient modern large wind energy converters.
Major potential in future is mostly in offshore locations. This far only few offshore wind energy production parks
have been constructed. The main obstacle is more expensive foundation construction cost. More difficult access for
service and maintenance, and longer distance for power transmission to consumers is another factor. On the other
hand the advantages of offshore wind parks are immense: vast areas with smooth wind conditions can be found well
beyond the annoyance range of eyes and ears. In large scale cost efficient serial production and installation methods
can bring down installation cost. E.g. 800 GW of new offshore power production would need one thousand 8 MW
wind energy converters!
The foundation cost of bottom founded wind energy converters (OWECs) increases with water depth. The Baltic
offers extensive shallow offshore areas as well as good wind conditions. Additional problem in the Baltic is annually
occurring ice. Depending on the location, most of the first year ice load scenarios can be met. These include both
static and dynamic ice loads due to moving ice fields, vertical uplift actions, loads due to pressure ridges, and
thermal ice cover expansion. Ice loads can be a severe threat to realise an offshore wind energy park but may also be
a less significant cost effect than that of wave loads.
Design against ice loads on offshore structures is not yet a mature engineering discipline. Northern European
countries have their own national design practices and recommendation for ice loads. The experience has bee gained
from bridge pier or aids to navigations structures design. However international ice load codes, or even design
recommendations, are missing. This pitfall is an obstruction to allow true international bidding for most cost
efficient wind park constructions in ice infested waters.
European Union has been funding ice load research projects since 1997. These have had also an objective to pave
way for an European Ice Load Design Code. In 2002 the ISO Offshore Oil and Gas Industries subcommittee
founded a working group to prepare an Arctic Ice Load Code. In order to have really international code the EUcountries joined in this working group. European objective is to have also sub-arctic ice load design scenarios
included, especially for OWEC ice load design. The planned schedule is to have International ISO-CEN ice load
design code completed by 2009.
This paper describes the status of existing European ice load design recommendations, and background on ice load
design research with an objective on own code preparation, ISO ice load design code development for Petroleum
and Gas Industries Arctic Offshore Structures Standard, European needs, commitment and cooperation, joint effort
and progress, and brief description on what will be applicable for OWEC foundation design.
2. PRESENT ICE LOAD DESIGN RECOMMENDATIONS
National ice load design recommendations in Europe are scarce regardless of ice infested waters in the Northern
Europe. Danish, as a leading wind energy converter manufacturer nation, have proposed ice load design
requirements for OWEC foundations in their Design Code DS472 (2001). However this has not yet been realised.
Finnish RIL-144, (2001), Finnish civil engineers association, Guideline for the loads of structures, includes since
1981 most of such ice load cases that would be relevant for OWEC design as well. However, many of these ice load
cases are outdated, being at over 20 years old state-of-the art level. Sweden has ice load recommendations only for
bridge piers. Norwegian DNV, Det Norske Veritas, and NORSOK refer only to recognized theoretical models and to
API, American Petroleum Institute. In Germany Germanisches Lloyd (GL) has in 2003 proposed many of the ice
load design cases applicable for OWECs in Guideline for the Construction of Fixed Offshore Installations in Ice
Infested Waters.
Russian is part of Europe and has two national standards: SNiP 2.06.04.82 (1995), and VSN 41.88 (1988). Both of
these are originating from river ice actions on bridge piers and later on extended to offshore applications. The SNiP
is more comprehensive and covers better the load cases needed for OWEC foundations. However, dynamic ice loads
are missing and guidance for design is minimal.
In offshore applications the de facto standard is American Petroleum Institute API RP 2N (1995), Recommended
practice for planning, designing, and constructing structures and pipelines for arctic conditions. However, for
OWEC foundation ice load design it has two major pitfalls: the API recommendations are intended for arctic
conditions, and design guidelines for dynamic ice loads are missing.
International Electrotechnical Commission IEC TC88 WG3 is preparing a new design code for OWECs: IEC614003 (WD2, 2006), WIND TURBINES - Part 3: Design requirements for offshore wind turbines. This is yet a not public
second working draft. The design requirements will include all of the essential ice load cases relevant to OWEC
design. ISO and IEC work together similarly as ISO and CEN. IEC is already referring to other ISO 19900 series
offshore standards. The redundancy before both IEC 61400-3 and ISO 19906 have been published will perhaps be
solved by a revision: IEC standardizes OWEC electrotechnical issues and refers to ISO 19906 in structural ice load
design.
International Association for Lighthouse Authorities (IALA, 1984) prepared: Design Recommendations for Ice
Effects on Aids-to-Navigation. For OWEC design missing ice load cases are due to pressure ridges and thermal ice
expansion. Partly IALA recommendations are outdated, and give only minimal guidance for designers.
3. EU FUNDED ICE LOADS RESEARCH
First EU funded ice load research project LOLEIF (Low LEvel Ice Forces) started in September 1997 and ended in
February 2000. Participating countries were Germany, Finland, France, Norway, Sweden, and UK. The objectives
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were to reduce design ice loads by reducing uncertainties in previous ice load prediction methods. This involved
carrying through own ice load measurements, compiling existing measurement data, comparing and refining
theoretical models.
The second EU project STRICE (STRuctures in Ice) started in January 2001, and ended in December 2003. The
same countries as in LOLEIF participated. The objectives were to conduct more full-scale measurements, conduct
thorough data processing and comparison to theoretical models. The objectives included to prepare
recommendations for European Ice Load Code. The structure of code was planned and its list of contents was
prepared when it was learnt that ISO is preparing an Arctic Offshore Structures Ice Load Code. In January 2002 it
was decided that a better result will be achieved by merging STRICE contribution into ISO code work and by
observing the European need for sub-arctic ice conditions to be included in the future ISO-CEN code.
EU contributed the third time into ice load design improvement by a Specific Support Action project STANDICE
(STANDardization for ICE forces on offshore structures design). Four partners, two from both Germany and
Finland are participating. The main objectives were set to cooperate with ISO standard preparation work, and to
have European sub-arctic perspective included into the originally Arctic structures code. The project started in June
2004 and will continue to the end of May 2007. This period is the most work intensive in the ISO code development.
The normative part was already compiled by the end of 2004 while the more extensive informative part is due by
June 30 2006. However, editing and revision phase will continue until the code is published by 2009.
4. ISO ICE LOAD CODE 19906 DEVELOPMENT
International Organization for Standardization (ISO) Technical Committee 67 (TC67) Subcommittee 7 (SC7) has
been preparing since 1993 a Code for “Offshore Structures for Petroleum and Natural Gas Industries”. The first of
these offshore structures codes, ISO 19900-19904, are already at final stages of revisions before publishing, or being
processed as an Draft International Standard (DIS). These include definitions of MetOcean, foundations, and steel
and concrete structures. In the Milan meeting January 2002 SC7 made a decision to form Working Group 8 (WG8)
to prepare international ARCTIC OFFSHORE STRUCTURES STANDARD. As the offshore structures per se were
already covered in SC7 standard development work, the main contribution of WG8 is to define the additional
requirements for the subzero climate, and especially for ice load design.
According to Vienna Agreement all new EU CEN codes will be harmonized to ISO codes, resulting in common
name ISO-CEN codes. Hence there was no more sense to prepare a distinct EU Code for ice loads. As EU main
interests are for offshore applications in sub-arctic regions - other than ISO TC67 SC7 objectives for petroleum and
gas industry in arctic climate – it was agreed after negotiations to include all ice action scenarios into the future ISO
19906 standard. Its Working Draft (WD) name is: “Petroleum and natural gas industries – Arctic offshore
structures”. Considering the already accepted scope and application field, a more appropriate name for the code
would be simply “Arctic offshore structures”, or better “Offshore structures in ice infested waters”.
The practical standard development work is carried out in Technical Panels (TP) that are nominated by WG8 and
report to WG8 - Arctic offshore structures. WG8 has 17 members from 12 ISO countries, both from the original
Offshore Structures for Petroleum and Gas Industries group and two new members from Europe. After Technical
Panels have produced Working Draft (WD) of the standard, WG8 makes review, editing into ISO format,
acceptance, and provide the Committee Draft (CD) for the ISO TC67 SC7. After committee review and acceptance
the Draft International Standard (DIS) is prepared and sent to ISO member countries for review and acceptance.
Thereafter the International Standard is published - according to the schedule by 2009 - and sent to member
countries for ratification. The ISO 19906 code preparation work has by now proceeded into the phase for submitting
the Committee Draft (CD) by October 15 2006. The normative requirements have already been accepted by the
WG8. Most parts of the informative section are completed and under editing into ISO Code format.
5. ISO WG8 WORK CONTENTS
Arctic Offshore Structures WG8 has 10 Technical Panels with a nominated TP leader and from five to over 20
members. Ten European countries have members actively participating in writing the code: D, DK, F, FI, GR, I, N,
NL, RU, and UK. Each of the Technical Panels is allocated to write a part of the future standard. That includes
definitions, scope, normative section and informative section. WG8 secretariat is thereafter making editorial changes
and unifying the text into ISO format. Also references to other ISO 19900 series Offshore Structures Codes are
crosschecked. A lot of existing and new full-scale ice load measurement data is reanalysed in reference to recent
understanding of ice-structure interaction to reduce large uncertainty that has earlier hampered reliable ice load
design.
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The titles of WG8 Technical Panels describe the scope of the future standard:
TP0 Editorial
TP1 Environmental
TP2 Actions/ Loading
2a) Reliability
2b) Ice
2c) MetOcean
2d) Seismic
TP3 Foundations
TP4 Artificial Structures
TP5 Fixed Steel Structures
TP6 Fixed Concrete Structures
TP7 Floating Structures
TP8 8a) Topsides
8b) EER
TP9 Ice Engineering
The scope of code development activity in all WG8 TPs is limited to applications in arctic and sub-arctic ice
infested waters. TP1 gives environmental information and requirements for structures and operations. That includes
Annexe C that tabulates typical ice conditions for conceptual design at different water bodies in the world, e.g. at the
Baltic. TP2 is concentrated in ice loads and structural design requirements. TPs 3 - 7 refer to and supplement ISO
standards 19902-19905. TP8 deals with operational aspects in the cold, both for personnel and equipment. TP9
considers e.g. ice management as a means to reduce ice effects, possibilities to utilize ice cover in transportation, etc.
6. ISO 19906 COMPOSITION
The composition of ISO.CEN 19906 will follow closely the list of contents of the previous 19900 series Offshore
Structures codes. The substance of ISO-CEN 19906 can roughly be divided into three major classes. Definitions
define the scope and coverage, while Normative part set requirements for structural design and operations in ice
infested waters. Informative section in Appendices A, B and C, give background information, design equations, and
further references. As ice science and engineering is not as mature discipline as say steel structural engineering, the
informative section is relatively extensive.
The table of contents is presently:
Petroleum and natural gas industries – Arctic offshore structures
Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 Abbreviated terms
6 Physical environment of cold offshore regions of the world
7 Limit states and reliability
8 Foundations
9 Man-made islands
10 Fixed steel structures
11 Fixed concrete structures
12 Floating structures
13 Sub-sea installations
14 Topsides
15 Ice engineering
16 Ice management for marine operations
17 Escape, evacuation and rescue
Annex A (informative) Commentary, recommendations and information
Annex B (informative) Regional information
Annex C (informative) (further annexes with discrete information)
Bibliography
OWEC design can directly utilize ISO 19906 Standard. Design requirements and guidelines can be found for all
design cases in sub-arctic waters both in land-fast or pack ice zones. In the former thermal ice expansion or up- and
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down-lift loads are more important when only thin moving ice is present early in the season before the land-fast ice
stabilizes. However, dynamic ice actions will be a design consideration even with thin moving ice. At pack ice zone
both static and dynamic level ice loads have to be considered, as well as a chance of pressure ridge loads. Ice
accretion, and ice and cold climate effects to operations – especially to human operations – is also covered.
Considering the OWEC design the presence of ice brings forward the following possible design cases that are
defined in ISO 19906:
Ice climate
Limit driving force
Limit momentum
Thermal ice expansion loads
Ice uplift loads
Ice crushing loads
Cone ice loads
Pressure ridge loads
Dynamic ice loads
Ice buckling
Ice accretion
Cold climate effects
In this list “Ice climate” is only one title even though it includes the most important diversified environmental
factors that determine how severe the ice actions will be and how frequently they can be encountered. The outcome
of the rest of the titles follows more or less straightforwardly once the initial conditions - ice climate - is defined.
Depending on the application location only few of the ice load scenarios are real design considerations. Both
statistical and deterministic design approaches will be covered.
SUMMARY
International ice load design code is missing. European national ice load design codes or recommendations are
inadequate and not consistent with each other. This jeopardizes free international competitive bidding on offshore
structures design and construction in ice infested waters. In Europe a huge potential exist to construct offshore wind
power. Chances for wind power utilization in ice infested waters will improve after ice load design is better defined.
After initially two separate efforts to develop an offshore structures ice load design code for different ice climate
ISO and EU CEN code development work has in 2002 merged into a common effort for ISO-CEN 19906 Arctic
Offshore Structures Standard.
The writing of the ice load standard is now in such a phase that the first Committee Draft will be completed in the fall
2006. Thereafter there will be revisions by the committees and ISO countries before the new code is scheduled for
publication in 2009.
The ISO-CEN 19906 will include all the required ice load scenarios for a reliable OWEC design and construction. The
common international code will improve the efficiency in constructing large offshore wind energy parks.
REFERENCES
API RP 2N (1995), Recommended practice for planning, designing, and constructing structures and pipelines for arctic
conditions. American Petroleum Institute
DS472 (2001), Recommendation for technical approval of offshore wind turbines. Danish Standards
GLO-03-319, (2003), Guideline for the construction of fixed offshore installations in ice infested waters. Germanischer
Lloyd
IEC 61400-3 (WD2, 2006), WG3, Recommendations for design of wind turbine structures with respect to ice loads.
International Electrotechnical Commission
ISO 18806 (WD 2005) Arctic Offshore Structures. International Organisation for Standardization.
RIL-144, (2001), Guideline for structural loads (in Finnish only), Finnish civil engineers association.
SNiP 2.06.04.82 (1995). Russian national standards,
VSN 41.88 (1988). Russian national standards
IALA (1984): Design Recommendations for Ice Effects on Aids-to-Navigation. International Association of Lighthouse
Authorities, Technical Committee to study the Effect of Ice on Lighthouse Structures, Määttänen M., (Editor)
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