Standards and Practices - Structural Integrity of Offshore Wind Turbines - page 42

(Oceanographic and Meteorological) and 2GEO (Geotechnical) have
been developed to address conditions applicable to both fixed and float-
ing structures.
API has been engaged with ISO in developing an ISO series of offshore
standards using many of the API standards as their base documents. More
than 80 percent of the ISO 19900 series has been published. API has
restructured about 50 percent of its offshore series to match the ISO struc-
ture and incorporate the ISO standards. This integration provides for
a single international set of offshore standards with U.S.-specific criteria
attached to the universal core technical requirements.
Description of Relevant Standards
The API Series 2 standards are comprehensive and cover all aspects of off-
shore design: planning requirements, installation requirements, fixed and
floating platform structural requirements, operations throughout the life
of the system, and decommissioning requirements. For structural design,
API RP 2A-WSD, the commonly applied standard for fixed offshore plat-
forms, uses an elastic component design methodology prescribing load
development procedures, structural design methods, extreme load condi-
tions, material and component safety factors, and the character and return
periods for design-level extreme events for both sea states and wind
conditions. The standard focuses mainly on sea states rather than wind
because that is the primary source of platform loads (usually about 70 per-
cent of the total load on a fixed platform). Detailed wind conditions are
frequently characterized on the basis of a quasi-static load definition,
which is generally sufficient for a statically responding facility. For dynam-
ically sensitive facilities, wind loading is usually developed by using an
offshore-specific wind spectrum model.
IEC AND API DIFFERENCES
Standards such as IEC 61400-3 and API RP 2A have some overlapping
design requirements for wave and current loading conditions. However,
a direct comparison of the IEC and API standards indicates differences
that should be assessed in any effort to use these standards together for