Standards and Practices - Structural Integrity of Offshore Wind Turbines - page 38

In 2000, TC 88 began to develop an offshore wind turbine standard,
Design Requirements for Offshore Wind Turbines, IEC 61400-3 (IEC 2010a).
It was intended to address requirements for offshore wind turbines that
were not previously covered. The standard defers to IEC 61400-1 for the
wind turbine aspects of the design requirements and relies on existing
mature standards for setting general support structure requirements. The
IEC offshore committee surveyed structural standards and guidelines
for offshore oil and gas structures, including those developed by the
American Petroleum Institute (API), the International Organization for
Standardization (ISO), Det Norske Veritas (DNV), and Germanischer
Lloyd (GL), and attempted to use them as the basis for the new IEC
61400-3 requirements. A European-funded project, “Requirements for
Offshore Wind Turbines” (RECOFF), included formal comparisons of
these various standards and assessed their suitability for wind turbine
design. The RECOFF study concluded that, for the vast majority of sup-
port structure requirements, standards such as those of API and ISO
could be used. However, the crucial deficiency was the manner in which
dynamic loads were estimated. Offshore wind turbines are subject to wind
and wave stochastic loadings that are nearly equal in importance with
respect to dynamic excitation of the wind turbine. IEC 61400-3 is the
only international standard that specifically addresses these issues. It is
less mature (less fully developed) than other international standards
and guidelines for land-based wind turbines, but it is based on earlier
standards and therefore represents an integrated version of all the work
that has preceded it. Because it is part of a series of international stan-
dards that address the broader wind industry's needs, such as verifica-
tion testing for performance, structural design compliance, power
quality, gearbox design requirements, and small turbines, it is the best
available standard for addressing the issues of structural design for off-
shore wind turbines.
The IEC certification standard for type and project certification is IEC
61400-22, Wind Turbines—Part 22: Conformity Testing and Certification
(IEC 2010b). This standard defines requirements for both type certification
and project certification. The IEC 61400-22 certification standard is a fur-
ther development of the previous certification standard, IEC WT 01 (IEC
2001), in particular with regard to requirements for project certification.