Structural Integrity of Offshore Wind Turbines Oversight of Design, Fabrication, and Installation - Special Report 305 (2011) / Chapter Skim
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4 A Risk-Informed Approach to Performance Assurance
4 A Risk-Informed Approach to Performance Assurance
Pages 62-95
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From page 62... ...
The best way to do this, it believed, was to step back and review the underlying philosophies that could guide the development of additional standards, regulations, or other guidance documents for offshore wind turbines in the United States. In applying this broader perspective, the committee reviewed the approaches to oversight of offshore wind turbines taken by European countries.
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From page 63... ...
Other risks, such as those of direct economic losses from structural damage and of indirect losses due to interruption of function, forgone opportunities, and loss of amenity, are generally not addressed in government regulations, although they may be of concern to individuals, project operators, insurers, and other stakeholder groups. Risk to Human Life and Safety Risk to human life from the structural failure of offshore wind installations is limited compared with risks from other offshore facilities, such as oil and gas platforms and marine vessels.
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From page 64... ...
. The most significant risk to the environment emanating from structural failure of an offshore wind turbine or transmission platform involves the release of transmission fluid or other hydrocarbon-based liquids from the wind farm structures or from the installation and service vessels that would be navigating through an offshore wind park.
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From page 65... ...
. Comparison with Offshore and Land-Based Fossil Fuel Facilities Table 4-1 presents the committee's judgment, based on its experience across industries, of the relative risks of offshore wind facilities, offshore oil and gas facilities, land-based fossil fuel extraction facilities, and liquefied natural gas terminals.
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From page 66... ...
c L if evacuated prior to design condition; M if manned. wind turbines are generally lower than for structural failure in the fossil energy industries.
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From page 67... ...
Office of Energy Efficiency and Renewable Energy's Wind and Water Power Program to outline the actions that it will pursue in supporting the development of a world-class offshore wind industry in the United States. The Strategic Work Plan is an action document that amplifies and draws conclusions from a companion report, Large-Scale Offshore Wind Power in the United States (Musial and Ram 2010)
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From page 68... ...
REGULATORY EVOLUTION IN THE OIL AND GAS, MARINE, AND CIVIL INFRASTRUCTURE INDUSTRIES As noted in Chapter 3, standards, guidelines, and regulation of offshore wind turbines in Europe are primarily prescriptive in nature.
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From page 69... ...
. The following discussion illustrates this evolution by reviewing regulatory developments in the oil and gas industry, the marine shipping industry, and the civil infrastructure industry.
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From page 70... ...
To the extent that they reduce the costs of power generated by using offshore wind, they increase the abil ity of this source to compete with other sources of electricity. See Box 4-4 on the International Maritime Organization's goal based standards for an example.
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From page 71... ...
was issued in 1978, and platforms designed to this or later editions are considered by the industry to be "modern." The superiority of such platforms was demonstrated in the aftermath of Hurricane Andrew in 1992, when 75 structures were destroyed, the majority of which were older platforms designed with 25-year return periods and lower decks (Berek 2010; Energo Engineering 2010)
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From page 72... ...
. Setting forth and enforcing design standards were not a focus of any of these groups.
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From page 73... ...
API design standards are primarily experience-based and prescriptive. The design levels are well described, usually a 100-year return period loading level with associated factors of safety stated and inherent design parameters specified, such as effective length coefficients, inherent assumption of space frame load redistribution, and normal minimum steel yield to actual yield ratios.
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From page 74... ...
classification society rules for compliance with international standards and the USGS regulations, to participate effectively in the rulemaking processes at IMO, and to develop additional standards when necessary. Nearly all ships involved in international trade are "classed" by a recognized classification society.
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From page 75... ...
The reliance on prescriptive regulations meant that regulatory development in the maritime industry, as in the oil and gas industry, was primarily reactive, usually relying on a catastrophic event to trigger the next round of changes. This began changing in the 1970s with the introduction of probability-based methodologies for evaluating the survivability of ships.
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From page 76... ...
systems, is governed by codes, standards, and regulatory guidelines that represent judgments by the professional engineering community based on experience. These documents are key tools for structural engineers in managing civil infrastructure risk in the public interest, and the traditional structural design criteria they contain address the risks in structural performance as engineers have historically understood them.
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From page 77... ...
Experience-based codes and standards were not an option for the oil and gas industry, and therefore risk assessment has always played a fundamental role in the design of offshore structures. In the United States, the performance concept (as it was called at the time)
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From page 78... ...
Current codes generally make such distinctions by simply stipulating a higher design load, a step that may not lead to better performance and indeed may be irrelevant for dealing with certain low-probability events where effective design requires other considerations in addition to strength. The design objectives in PBE are often displayed in a risk matrix such as that illustrated in Figure 4-2, in which one axis describes severity of hazard (e.g., minor, moderate, severe)
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From page 79... ...
• Blade strike collapsing turbine • Structural collapse across multiple (waterspout during grid outage) nth-of-a-kind projects • Ship collision collapsing turbine External Event Mitigate by Standards and Probability: Certified Third-Party Reviews FIGURE 4-3 Example risk matrix driven by policy consequences of failures.
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From page 80... ...
Goal-based standards that describe the overarching expectations for pro tection of life, environmental performance, and system reliability; or d. Goal-based standards combined with functional requirements that establish high-level expectations for performance while providing a greater level of specificity on environmental conditions to be consid ered, design performance metrics, service life expectations, and so forth.
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From page 81... ...
Option a requires the greatest investment by the regulatory agency with regard to the development and the maintenance of the regulations. Option b reduces the level of resources required of the government but has the disadvantage of relying on the expertise and diligence of an outside standards development body to maintain standards.
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From page 82... ...
GOAL-BASED STANDARDS FOR OFFSHORE WIND TURBINES The committee recommends that offshore wind turbine regulations promulgated at the federal level be goal-based standards and functional requirements that are performance-based rather than prescriptive in nature (Option d above)
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From page 83... ...
Comparison of the various classification rules revealed significant differences in structural requirements and expected performance. With encouragement from both national authorities who sought a more consistent level of structural reliability and safety and industry representatives who sought a more level playing field where reduced robustness in the ship's structure and acceptance of higher safety risks were not used for competitive advantage, IMO developed a set of goal-based standards (IMO 2010)
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From page 84... ...
Examples of functional requirements are that ships have a design life of not less than 25 years; that they be suitable for North Atlantic environmental conditions; and that they comply with the structural strength, ultimate hull girder strength, and fatigue criteria after accounting for corrosion expected over the design life. Tier 3: Verification of Conformity Tier 3 specifies the procedures for verifying that class societies' rules and regulations for ship design and construction conform or are consistent with the goals and functional requirements.
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From page 85... ...
4. In the case of both offshore wind turbines and shipbuilding, the clas sification societies and international standards groups are prepared to maintain the currency of their rules and regulations through continu ous validation and revision.
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From page 86... ...
1. Offshore wind turbines and electric service platforms shall have a service life of at least _____ years (e.g., at least 20 years)
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From page 87... ...
11. Designs shall take due consideration of the health and safety of personnel accessing offshore wind turbines and power platforms, including ready access and protection against falls, lightning, and other hazards.
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From page 88... ...
Examples of standards, rules, industry guide lines, and recommended practices that could be considered are those developed by GL, DNV, and ABS, or the standards and recommended practices currently being developed by the American Wind Energy Association.
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From page 89... ...
BOEMRE either approves the package or sends it back to the developer requesting revisions or further documen tation and analysis, or both. The approval of the package of Guidelines (standards, rules, industry guidelines, and recommended practices)
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From page 90... ...
l. Monitor the effectiveness of the preapproved packages of Guidelines (national and international standards, rules, industry guidelines, and recommended practices)
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From page 91... ...
Remaining staff have less experience in addressing offshore structural issues and no experience in addressing issues related specifically to offshore wind structures. To enhance its ability to oversee the offshore wind industry effectively, BOEMRE may wish to focus on obtaining staff or contractors with experience in the following areas: offshore structures design, with a preference for experience in offshore wind design; offshore installations, with a preference for experience in pile-founded structures; wind turbine hookup and commissioning, with a preference for offshore experience; and offshore structures operation and maintenance, with a preference for offshore wind facilities experience.
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From page 92... ...
BOEMRE should proceed immediately with development of a set of goal-based standards governing the structural safety of offshore wind turbines and power platforms. The regulations should be risk-informed (see Appendix A)
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From page 93... ...
The section "Goal-Based Standards for Offshore Wind Turbines" in this chapter contains more details with regard to the experience and capabilities that are needed.
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From page 94... ...
6. BOEMRE should be fully engaged in the national and international process for developing standards for offshore wind turbines and should be represented on IEC technical committees and other relevant national and international committees.
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From page 95... ...
2010. Flaw Hits Hundreds of EU Offshore Wind Turbines.
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