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4 A Risk-Informed Approach to Performance Assurance Task I of the committeeâs charge, âStandards and Practicesâ (see Box 1-2), calls for the committee to review the applicability and adequacy of exist- ing standards and practices for the design, fabrication, and installation of offshore wind turbines. Chapter 3 reviewed some of the most important standards that are in use and described some of those that are under devel- opment. It also identiï¬ed some of the deï¬ciencies that would have to be remedied and the analyses that would have to be done before these stan- dards and practices could be used in the United States. As discussed in Chapter 1, the committee believed that, to respond fully to this task, it had to do more than simply review existing stan- dards and guidance and point to where the deficiencies lie. Other studies have identified at least some of these deficiencies, and the com- mittee has drawn on these studies in developing Chapter 3 of this report. But the committeeâs view was that, to provide the Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEMRE) with useful feedback, the committee should offer its perspectives on how BOEMRE might remedy the deficiencies. 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. The committee also reviewed how the safety of engineered structures is overseen in other U.S. industriesâoil and gas production, waterborne shipping, and buildingsâand especially how regulation and other forms of oversight in these industries have evolved. 62
A Risk-Informed Approach to Performance Assurance 63 This chapter begins with a brief review of the risks to human safety and the environment posed by structural failures in offshore wind turbines. It compares these risks with those associated with other offshore industries and with land-based energy industry infrastructure. It then considers how regulation in these areas has evolved away from a detailed, prescriptive model and toward a more performance-based model, and what this sug- gests about approaches to overseeing wind energy development on the U.S. outer continental shelf (OCS). RISKS TO HUMAN LIFE AND THE ENVIRONMENT POSED BY STRUCTURAL FAILURE OF OFFSHORE FACILITIES Government regulation of offshore facilities, such as oil and gas structures and marine vessels, and of land-based infrastructure, such as buildings and bridges, focuses on mitigating risk to human life and the environment. Other risks, such as those of direct economic losses from structural dam- age and of indirect losses due to interruption of function, forgone oppor- tunities, and loss of amenity, are generally not addressed in government regulations, although they may be of concern to individuals, project oper- ators, insurers, and other stakeholder groups. Risk to Human Life and Safety Risk to human life from the structural failure of offshore wind installa- tions is limited compared with risks from other offshore facilities, such as oil and gas platforms and marine vessels. Offshore wind towers are nor- mally unmanned, so they pose limited risk to human life. The most dan- gerous element in the operation of an offshore wind farm is the transfer of personnel to the turbines for installation, inspection, and maintenance. Because the turbines can only be accessed by boat or helicopter, the abil- ity to reach the turbines is highly dependent on the sea state. Personnel may ï¬nd themselves stranded on a turbine structure if waves increase in magnitude while maintenance is being conducted. With the exception of wind turbine installations in regions of high seismic activity, how- ever, it is not anticipated that humans would be on any turbine struc- ture throughout the duration of an extreme external condition such as a powerful storm.
64 Structural Integrity of Offshore Wind Turbines The transmission platform, however, might house personnel for indefinite periods of time, and this fact must be taken into account in designing for human safety in extreme conditions. The need for person- nel to be stationed on a centralized transmission platform will increase as farms move farther offshore and the logistics of personnel transfer to shore become more difficult. Designs must also address the potential need for stationing personnel on transmission platforms during inclement weather. Risk to the Environment As stated in Chapter 1, the scope of this report is limited to oversight of structural integrity as it is affected by turbine design, fabrication, and installation. As shown in Figure 1-1, the environmental hazards associated with the establishment and operation of offshore wind energy facilities are covered through the National Environmental Policy Act (NEPA) process. These hazards include effects on birds, other wildlife, and the seabed. An environmental assessment or environmental impact state- ment, as required by NEPA, will be performed for each proposed offshore project (as was done for the Cape Wind project). 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 ser- vice vessels that would be navigating through an offshore wind park. Proper design and construction of the turbine and transmission plat- form should preclude all but minor damage due to collision with a service vessel that is moving slowly. However, if the vessel suffered sufï¬cient damage, it could leak its fuel into the ocean. In the event of a catastrophic failure of a structure or vessel, the worst-case scenario would involve discharge into the ocean of the following amounts of hydrocarbon-based ï¬uids: â¢ Wind turbine (5 MW), approximately 150 gallons (Cape Wind n.d.); â¢ Transmission platform, approximately 40,000 gallons (Cape Wind n.d.); and â¢ Installation and service vessels, up to 500,000 gallons (see Box 4-1).
A Risk-Informed Approach to Performance Assurance 65 BOX 4-1 Offshore Wind Installation and Service Vessels Installation of the foundations (driving monopiles or setting jackets) will likely be carried out with barges and tugs. A recently delivered derrick barge has a fuel capacity of 300,000 gallons pro- tected by inner bottom and wing tanks. Each tug typically has an aggregate fuel and lubricating oil capacity of 5,000 gallons. Transportation and installation of turbine components may be accomplished by using (a) a specially designed self-propelled vessel or (b) a combination of barges and barge cranes. As an example of the ï¬rst case, a turbine component installer design offered by Keppel Amfels carries 500,000 gallons of diesel fuel. In the second case, the barge and crane barge described for founda- tion installation could be used, with the fuel capacities given above. If a lift vessel is used, fuel capacity would likely not exceed 50,000 gallons. For reference, the amount of oil estimated to have been released into the ocean during the Exxon Valdez oil spill was 10.8 million gallons (Exxon Valdez Oil Spill Trustee Council n.d.). Comparison with Offshore and Land-Based Fossil Fuel Facilities Table 4-1 presents the committeeâs 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 lique- ï¬ed natural gas terminals. The table indicates the level of risk to human life and the environment under normal operating conditions. It also shows the risk levels under âdesign conditions,â which are the conditions that the facility is designed to resist or withstand. As shown, the risks to human safety and the environment associated with structural failure of offshore
66 Structural Integrity of Offshore Wind Turbines TABLE 4-1 Comparison of Risks with Traditional Offshore and Land-Based Energy Industries: Safety and the Environment Level of Risk Liquid Life Safety: Life Safety: Hydrocarbon Normal Design Energy Industry Release Operations Conditions Oil and gasâshelf M L M Oil and gasââfrontierâ H M H Land fossil (coal and natural gas), Texas VL L M Land fossil (coal and natural gas), VL L M Cook County, Illinois Land wind facility VL VL L Offshore windaââtowerâ L VL L Offshore windbâcentral platform L, Mc L M Offshore liqueï¬ed natural gas terminal VL H H Land liqueï¬ed natural gas terminal VL H H NOTE: VL = very low, L = low, M = moderate, H = high. Coding criteria include life safety, protection of the environment, and economic thresholds. a Turbines and turbine support. b Central facilities. 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. REGULATORY OPTIONS AND POLICY CONSIDERATIONS Because the environmental and life safety risks of offshore wind facilities are relatively low, the form and extent of government regulation comes into question. If there are smaller safety and environmental risks associ- ated with structural failure of an offshore wind farm, then a natural ques- tion to ask is whether the ï¬nancial and insurance risk assumed by the developer is sufï¬cient for regulating the industry. Or, to put it another way, are there reasons for overseeing the performance of offshore wind structures beyond mitigating these low risks? Policy Considerations In 2010 the United States made signiï¬cant strides in the offshore wind rulemaking process, and several projects proposed off the East Coast are
A Risk-Informed Approach to Performance Assurance 67 progressing through their development phases. Currently, renewable energy development is largely driven by individual state policies and renewable portfolio standards. However, several examples, highlighted below, indicate that federal policy will promote renewable energy on a national level and that offshore wind is an essential component of this policy. National security, energy independence, and economic beneï¬t are cited by government ofï¬cials as justiï¬cation for promoting offshore wind development. Creating an Offshore Wind Industry in the United States: A Strategic Work Plan for the United States Department of Energy was prepared by the U.S. Department of Energy (USDOE) Ofï¬ce of Energy Efï¬ciency and Renew- able Energyâs 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 ampliï¬es and draws conclusions from a companion report, Large-Scale Offshore Wind Power in the United States (Musial and Ram 2010). A joint initiative between USDOE and the U.S. Department of the Inte- rior (USDOI) titled âSmart from the Startâ was announced in November 2010, with a goal of speeding appropriate commercial-scale wind energy development (USDOI 2010). A fact sheet issued on this effort by USDOI states: A top priority of this Administration is developing renewable domestic energy resources to strengthen the nationâs security, generate new jobs for American workers and reduce carbon emissions. A major component of that strategy is to fully harness the economic and energy beneï¬ts of our nationâs vast wind potential, including Outer Continental Shelf Atlantic winds, by implementing a smarter permitting process that is efï¬cient, thorough, and unburdened by unnecessary red tape. (USDOI n.d.) In February 2011, USDOE and USDOI unveiled the âjoint National Off- shore Wind Strategy: Creating an Offshore Wind Industry in the United States, the ï¬rst-ever interagency plan on offshore wind energyâ (USDOE 2011). As a part of this initiative, several high-priority offshore wind regions were identiï¬ed to âspur rapid, responsible development of wind energy.â In addition, USDOE announced a research and development program at this time to âdevelop breakthrough offshore wind energy
68 Structural Integrity of Offshore Wind Turbines technology and to reduce speciï¬c market barriers to its deploymentâ (USDOE 2011). SEEKING THE RIGHT REGULATORY BALANCE The federal government has embraced offshore wind energy as an integral component of its overarching policy of developing clean, renewable energy sources. Thus, the government has a fundamental interest not only in the safety and environmental performance of offshore wind farms but also in their reliability and cost-effectiveness. At the same time, the risks of struc- tural failure to human safety and the environment are low. The committeeâs view thus is that minimal regulation will allow market forces to guide offshore wind energy to an efï¬cient solution. Such an approach has policy risk, since lack of a regulatory framework could lead to early project failures that negatively affect public perception and jeopardize future offshore wind development. Other countries have had this experience, with serial component failures leading to repercussions across the global offshore wind industry. For example, in Europe the Horns Rev 1 (see Box 4-2) failures and similar problems encountered by other offshore wind farm projects led to the introduction of site-speciï¬c project certiï¬cation and an expanded scope for veriï¬cation that extended beyond the generic type certiï¬cation scheme. As discussed later in this report, it is important that a feedback mechanism be established to ensure that lessons learned are incorporated into the regulatory requirements, standards, and recommended practices. The committee recommends that U.S. regulation be sufï¬cient to ensure a consistent minimum standard for the design and construction of off- shore wind turbines to mitigate the risk of catastrophic failure, such as the failure of a single turbine or of multiple turbines that renders repair and recovery extremely difï¬cult or impossible. 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.
A Risk-Informed Approach to Performance Assurance 69 BOX 4-2 Horns Rev 1 One of the ï¬rst large offshore wind farms, the 80âwind turbine, 160-MW Horns Rev 1 facility located off the coast of Denmark, was built in 2002. Early in the facilityâs operating life the turbines experienced numerous failures, including each of the 80 wind tur- bine transformers, generators, torque arms on gearboxes, light- ning receptors on blades, and foundation coatings. All 80 nacelles were taken ashore for modiï¬cation. The failures likely set back development of the offshore wind industry throughout Europe as industry and regulators evaluated technical risk and reliability issues. Subsequently, widespread failures in the grouting connec- tion between the foundation and the intermediate support struc- tures have occurred at Gunï¬eet Sands wind farms and at the Danish Horns Rev 2 facility (Wan 2010). If such systemwide fail- ures are not avoided, they will negatively affect the development of offshore wind resources as they erode the conï¬dence of both potential investors and the public. Regulatory oversight in other U.S. industries began with such a pre- scriptive approach but, in some areas, has been evolving toward a more âperformance-basedâ approach (see Box 4-3). The following discussion illustrates this evolution by reviewing regulatory developments in the oil and gas industry, the marine shipping industry, and the civil infrastruc- ture industry. It then turns to options for addressing the deï¬ciencies of existing standards and regulations when applied to oversight of the U.S. offshore wind industry. Oil and Gas Industry As discussed in History of the Oil and Gas Industry in Southern Louisiana (MMS 2004), the ï¬rst oil and gas structure, built in 1937, was a massive wooden platform constructed in about 15 feet of water in the Creole ï¬eld
70 Structural Integrity of Offshore Wind Turbines BOX 4-3 Performance-Based Standards and Innovation As generally understood, a performance-based standard speciï¬es the outcome required but allows each regulated entity to decide how to meet it. Performance standards give ï¬rms ï¬exibility and make it possible for them to seek the lowest-cost means to achieve the stated level of performance (Coglianese et al. 2003). By focusing on outcomes, performance-based standards accom- modate technological change and innovation, which can be key to lowering costs. 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 Organizationâs goal- based standards for an example. in the Gulf of Mexico (GOM). This was at a time when there were no data on the response of frame structures to hurricane forces. Land-based steel design codes, principally the American Institute of Steel Construc- tion (AISC) Manual of Steel Construction, were the standards most closely aligned with offshore design and construction materials. Offshore developments progressed over roughly 20 years in the GOM under a variety of operator-speciï¬c design approaches and criteria. Design con- ditions (conditions that the structure must be designed to withstand) were speciï¬ed probabilistically, where the probability of an event occur- ring is expressed in terms of the percentage chance that it will occur in any given year. The most common design condition was a 25-year return period, though other operators used return periods of up to 100 years according to their appetite for risk (MMS 2004). Data to develop the design criteria were collected on an ad hoc basis with limited cooperation between oper- ators (MMS 2004).
A Risk-Informed Approach to Performance Assurance 71 By the early 1960s, there were several hundred platforms in the GOM. No major storms affected areas with large numbers of offshore structures until the mid-1960s. The ï¬rst signiï¬cant platform failures under storm conditions came in 1964, when Hurricane Hilda destroyed 13 platforms and damaged ï¬ve others beyond repair (MMS 2004). The following year, Hurricane Betsy destroyed eight platforms (MMS 2004). The storms emphasized the need for developing more consistent design approaches and for gathering better data on wind speeds, wave heights, and soil char- acteristics for use in the design process. Hurricane Camille in 1969 was another damaging storm, with measured waves far higher than those pre- dicted by the use of existing data (MMS 2004; Berek 2010). In 1966, the American Petroleum Institute (API) created the Commit- tee on Standardization of Offshore Structures (Berman et al. 1990), and the Ocean Data Gathering Program was set up in 1968 (Ward 1974). These steps were among the ï¬rst by the industry as a whole to standardize the design of offshore platform structures in the GOM, and they led to the ï¬rst API design standard for ï¬xed jacket structures, Recommended Practice 2A (RP 2A), in 1969 (Berek 2010). This standard did not specify a design return period for storm conditions. A design wave with a 100-year return period was ï¬rst speciï¬ed in the 7th edition of API RP 2A in 1976 (Berek 2010). The 9th edition of RP 2A (which included, among other improvements, more robust joint design guidance) was issued in 1978, and platforms designed to this or later editions are considered by the industry to be âmodern.â The superiority of such platforms was demon- strated 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). Though storms and their damage were not the only drivers for changes to design guides and industry practice, they have had a signiï¬cant effect. Figure 4-1 shows a timeline of GOM oil and gas development from its beginnings to the present along with signiï¬cant storms and subsequent standards developments and changes, as well as changes in industry prac- tice and regulations (Puskar et al. 2006). The storms of the late 1960s led directly to the establishment of the RP 2A standard and its subsequent improvement through the 1970s. Hurricane Andrew led directly to the
72 Structural Integrity of Offshore Wind Turbines FIGURE 4-1 Timeline of GOM development, industry standards, and practices. (SOURCE: Puskar et al. 2006.) development of revised load calculations represented in the 20th edition of RP 2A as well as the development of guidance on reassessment of exist- ing structures (Berek 2010; Puskar et al. 2006). The magnitude of destruc- tion brought about by Hurricanes Ivan, Katrina, Rita, and Ike in the mid- and late 2000s has led to a reassessment of the deï¬nition of the design waves for GOM structures. The GOM has been divided into four regions, each with its own design criteria, and the use of older storm data (i.e., pre- 1950 data) has been revised in formulating the statistics for calculating design waves (Berek 2010; Puskar et al. 2006). Just as industry cooperation and standardization were limited in the early years of GOM development, the regulatory environment was limited and uncoordinated. As discussed in Chapter 1, leasing was handled by both state and federal authorities (via USDOI through the Outer Conti- nental Shelf Lands Act of 1953); the U.S. Army Corps of Engineers had some authority, especially as related to installations in navigable waters; and the U.S. Coast Guard (USCG) was responsible for safety (MMS 2004). Setting forth and enforcing design standards were not a focus of any of these groups. The Bureau of Land Management and the Conservation
A Risk-Informed Approach to Performance Assurance 73 Division of the U.S. Geological Survey (USGS) shared leasing and regula- tory functions for USDOI until the formation of the Minerals Management Service (MMS) in 1982. MMS became BOEMRE in 2010. Its regulatory role includes the handling of permits and applications for wells, platforms, pro- duction facilities, and pipelines; environmental and safety controls; and inspections (BOEMRE n.d.). By the late 1970s, platforms were being installed in waters nearing 1,000 ft in depth in areas subject to seaï¬oor instability, earthquakes, and ice and in areas for which little information on the local offshore environ- ment was available. Because of the increasing complexity and perceived risk in these areas, in 1977 USDOI requested the National Research Coun- cil to study the need for third-party oversight. The study resulted in the development and implementation of the certiï¬ed veriï¬cation agent (CVA) program still in use for the design, fabrication, and installation of offshore oil and gas facilities. The CVA requirements are included in Appendix B of this report. CVA oversight is required for the more complex offshore structures located in deeper water. Assessment of compliance with the rules of a clas- siï¬cation society is not mandatory. Some companies elect to obtain class certiï¬cation; others do not. Some insurers offer reduced rates if the vessel or structure is certiï¬ed by class. API design standards are primarily experience-based and prescriptive. The design levels are well described, usually a 100-year return period load- ing level with associated factors of safety stated and inherent design parame- ters speciï¬ed, such as effective length coefï¬cients, inherent assumption of space frame load redistribution, and normal minimum steel yield to actual yield ratios. The prescriptive methodologies developed over the past six decades have proved to be robust and ï¬exible in that they have been adjusted as experience has been gained and the knowledge base has evolved. Maritime Industry The maritime industry covers ocean-based shipping, including interna- tional shipping. High-level regulation of international shipping is carried out by the International Maritime Organization (IMO), an agency of the United Nations speciï¬cally dedicated to maritime affairs. The two princi- pal IMO conventions, Safety of Life at Sea and MARPOL and MARPOL
74 Structural Integrity of Offshore Wind Turbines 73/78 (Prevention of Pollution from Ships), contain the safety and pollu- tion prevention regulations. The nation of registry of a vessel, generally referred to as the ï¬ag state, can supplement the IMO regulations with addi- tional requirements. USCG has regulatory authority for vessels registered in the United States. Regulations applicable to U.S.-ï¬ag vessels include those of IMO as well as additional safety requirements incorporated into the Code of Federal Regulations (CFR). Nations at which a vessel is calling (referred to as port states) may also implement inspection programs to ensure compliance with international regulations. The USCGâs Alternative Compliance Program (ACP) allows pre- approved classiï¬cation societies, which are nongovernmental and private rule development organizations, to inspect and certify vessels for compli- ance1 on behalf of USCG. These classiï¬cation society rules go beyond the safety and environmental regulations of IMO and cover many aspects of the design, construction, and maintenance of the vessel. Under the ACP, the international conventions, the rules of the classiï¬- cation society acting on behalf of USCG, and a supplement to the rules are applied as an alternative to the USCG regulations set forth in the CFR. The supplement, which covers the gaps between the speciï¬c set of classiï¬cation society rules and the CFR, is audited (reviewed) for equivalency before a classiï¬cation society is authorized by USCG to administer the ACP. To date, the American Bureau of Shipping (ABS), Lloydâs Register, Det Norske Veritas (DNV), and Germanischer Lloyd (GL) have received such approval from USCG. USCG itself maintains a sufï¬cient level of expertise to audit (review) classiï¬cation society rules for compliance with interna- tional 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 âclassedâ by a recog- nized classiï¬cation society. A classed ship is one that has been determined to conform with the classiï¬cation societyâs rules. Classiï¬cation is an expec- 1 Certain vessel types, such as towed barges, are not covered by the ACP. In such cases, vessels must comply directly with the USCG regulations. USCG Navigation and Inspection Circular 10-82 authorizes USCG to delegate to the classiï¬cation societies authority to verify compliance with USCG regulations. Offshore ï¬xed and ï¬oating structures are also not covered by the ACP.
A Risk-Informed Approach to Performance Assurance 75 tation of insurance companies and is an explicit requirement of many ï¬ag states. Historically, rules and regulations in the maritime industry have been experience-based and prescriptive, as has been the case for those developed by API. 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 intro- duction of probability-based methodologies for evaluating the survivabil- ity of ships. IMO has now adopted guidelines for formal risk assessment that are used in assessing new and updating existing regulations (IMO 2002). IMO has recently adopted goal-based standards applicable to ship structures. This approach is discussed later in this chapter in the section âRisk Mitigation Through Performance-Based Engineering.â Buildings, Bridges, and Civil Infrastructure The ï¬rst probability-based standards and speciï¬cations in the United States were introduced in the early to mid-1980s [American National Standards Institute Standard A58, now American Society of Civil Engi- neers Standard 7, and the AISC load and resistance factor design (LRFD) speciï¬cation for steel buildings]. They have been followed by other spec- iï¬cations as the rationale of the approach has taken hold in the structural engineering community. In these standards and speciï¬cation documents, the load and resistance criteria were predicated on a set of reliability tar- gets for member and component limit states, expressed as a reliability index that was determined from an extensive assessment of reliabilities associ- ated with members designed by traditional methods. Over the years, most building construction materials that have moved toward probability- based limit states design have adopted similar benchmarks, indicating a degree of professional consensus in the structural engineering standard- writing community in the United States. More recent speciï¬cations in the bridge and transportation area, typified by the American Associa- tion of State Highway and Transportation Ofï¬cials LRFD Bridge Design Speciï¬cations (AASHTO 2007), have adopted essentially the same prob- abilistic methodology as that used in building structures. These ï¬rst- generation probability-based limit states design standards continue to be
76 Structural Integrity of Offshore Wind Turbines member-based; any treatment of system effects is hidden in the member safety-checking equations in the form of effective length factors, strength or ductility factors, and similar simpliï¬cations of complex structural sys- tem behavior. TRANSITION FROM PRESCRIPTIVE TO PERFORMANCE-BASED REGULATIONS The performance of civil infrastructure systems, unlike that of many other common mass-produced engineered (for example, automotive and avia- tion) 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 engi- neers in managing civil infrastructure risk in the public interest, and the traditional structural design criteria they contain address the risks in struc- tural performance as engineers have historically understood them. For the most part, these criteria have been based on judgment. This approach to performance assurance generally has served society reasonably well because construction technology has evolved slowly. As in the case of civil infrastructure, the design and construction of marine vessels date back thousands of years, and the development of design codes, standards, and practices has been gradual and deliberate. Historically, these regulations have been prescriptive, consisting of detailed, experience-based require- ments and formulations that must be satisï¬ed to prove compliance. In recent years, however, innovation in technology has occurred rapidly, leaving less opportunity for learning through trial and error. New tech- nologies have taken form not only in new concepts, materials, and manu- facturing techniques but also through more sophisticated analysis and optimization tools that enable the design of more efï¬cient structures. The public furor caused by recent disasters has made it clear that approaches to risk management based on judgment may not be acceptable and are dif- ï¬cult to justify after the fact. Standards for public health, safety, and envi- ronmental protection now are often debated in the public arena, and societal expectations of facility performance have increased. Over the past several decades, regulations pertinent to the civil and marine industries have begun shifting from empirical or prescrip- tive formula-based (experienced-based) to performance-based (goal-
A Risk-Informed Approach to Performance Assurance 77 oriented) standards necessitating application of ï¬rst principlesâbased analytical techniques. Risk-based decision making provides a foundation for assessing compliance with goals and objectives and evaluating alter- native solutions, and it is now applied extensively both in the development of regulations and in the evaluation of engineering solutions. The ï¬rst sig- niï¬cant offshore oil platforms were designed and constructed in the 1970s; this industry does not have the long history of the civil infrastructure and maritime industries. 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) in building construction dates back to the late 1960s, when the U.S. Department of Housing and Urban Development sponsored a large pro- gram at the National Bureau of Standards (NBS) to develop criteria for designing and evaluating innovative housing systems. Subsequent work at NBS led to a performance criteria resource document for innovative con- struction (Ellingwood and Harris 1977). A set of building elements and desirable performance attributes were identiï¬ed, which served as a check- list for ensuring that design professionals considered and addressed all items signiï¬cant to building performance. Each provision consisted of the following: 1. A requirement expressing a fundamental human need qualitatively (e.g., âbuildings shall be designed and constructed so as to maintain stability under extreme environmental loadsâ), 2. A set of criteria used to check that the requirement is satisï¬ed, 3. An evaluation giving approved methods of supporting analysis or test procedures that demonstrate compliance, and 4. Commentary that explains the technical bases for each criterion and its evaluation. RISK MITIGATION THROUGH PERFORMANCE-BASED ENGINEERING The new paradigm of performance-based engineering (PBE) is evolving to enable new construction technologies and structural design to meet heightened public expectations, to allow more reliable prediction and
78 Structural Integrity of Offshore Wind Turbines control of facility performance, and to provide engineers with more flexibility in designing with nontraditional systems and materials and in achieving innovative design solutions. One common feature of most recent proposals for PBE is their distinction among levels of performance for different facility categories where life safety or economic consequences of damage or failure differ. Current codes generally make such distinc- tions by simply stipulating a higher design load, a step that may not lead to better performance and indeed may be irrelevant for dealing with cer- tain low-probability events where effective design requires other consid- erations 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) and the second identiï¬es frequency of occurrence. The severity of the incident (consequence) can also be thought of in terms of performance objectives (continued function, life safety, collapse prevention). PBE might require that a critical facility remain functional under an extremely rare event (sus- taining minor damage) and provide continued service without inter- ruption under a rare event. Current prescriptive design codes for offshore Severity of Incident (or Consequences) Frequency Occurrence Likelihood Serious Major Catastrophic Incidental Minor (1) (2) (3) (4) (5) Frequent (5) High Risk Occasional (4) Seldom (3) Remote Low Risk (2) Unlikely (1) FIGURE 4-2 Example risk matrix driven by safety or environmental consequences. (SOURCE: TRB 2008, Figure 2-5).
A Risk-Informed Approach to Performance Assurance 79 oil and gas facilities, marine vessels, and civil infrastructure essentially limit their focus to life safety under rare events. The approach represented by Figure 4-2 is a more mature method for managing risk, but one that requires careful communication and mutual understanding among mem- bers of the design team rather than a simple reliance on prescriptive code provisions. Whereas the consequence of an event is often quantiï¬ed in terms of loss of life and environmental damage, the implications for the success or failure of government policy are also a concern. Figure 4-3 illus- trates potential policy consequences of various failure types and how regulations can be used to mitigate this risk. Policy Consequence: Low High Scale of Impact: Small Large Common Fleetwide Routine Inspection, Component Failure Maintenance and Repair Consequence: 1â2 year delay No Policy Consequence â¢ Monopileâtransition piece grout â¢ Lightning strike damaging (serial design defect) rotor blade tip â¢ Gearbox bearings â¢ Small vessel collision damaging (serial manufacturing defect) boat access landing Fleetwide Isolated Turbine Failure Turbine Failure Consequence: 5â10 year delay Low Policy Consequence (few months delay) Very Rare â¢ Structural collapse in single first-of-a-kind project (Cape Wind) â¢ Blade strike collapsing turbine â¢ Structural collapse across multiple (waterspout during grid outage) nth-of-a-kind projects â¢ 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. Policy consequences represent the implications for success or failure of gov- ernment policyâin this case, a policy of supporting the development of the offshore wind resource. Not shown is the consequence of normal but subpar performanceâlow plant availability or higher costs than projected. These could also delay the development of the industry by making ï¬nancing and public approval more difï¬cult to obtain. (SOURCE: Generated by the committee.)
80 Structural Integrity of Offshore Wind Turbines ALTERNATIVE APPROACHES TO REGULATING THE U.S. OFFSHORE WIND INDUSTRY U.S. offshore wind regulations could take one of the following forms: a. A comprehensive set of prescriptive regulations that explicitly describe design characteristics, design methodologies, materials, manufacturing standards, and installation procedures; b. A set of regulations relying on existing national and international stan- dards that are generally prescriptive in nature, with gaps in these regu- lations ï¬lled by a supplementary set of prescriptive regulations; c. 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 speciï¬city on environmental conditions to be consid- ered, design performance metrics, service life expectations, and so forth. There are advantages and disadvantages associated with each of these options. The following are some of the advantages of a comprehensive pre- scriptive set of regulations (Option a): â¢ Prescriptive regulations are simpler and easier to implement and typ- ically lead to lower engineering, testing, and design development costs. â¢ Compliance oversight is more straightforward, placing less reliance on the level of expertise and competence of the regulatory authorities and third-party reviewers. â¢ Prescriptive regulations are distillations of experience and are gener- ally effective in reducing the risk of the types of accidents that have occurred in the past. Disadvantages of prescriptive regulations include the following: â¢ By their nature, prescriptive regulations make suppositions about the design approach and analytical techniques to be applied and can limit the application of innovative approaches that do not suit the assump- tions implicit in the regulations.
A Risk-Informed Approach to Performance Assurance 81 â¢ Deficiencies in prescriptive regulations can lead to failures on mul- tiple projects, as was the case for the grouting failures described in Box 4-2. â¢ Prescriptive regulations require a vigilant program of reassessment and updating by a team with a wide range of technical expertise and experience. 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. This disadvantage is mitigated when the governmental body actively participates in the stan- dards development and review process. Advantages of performance-based regulations include the following: â¢ Performance-based regulations more readily allow for innovative solutions. â¢ Performance-based regulations provide the designer with greater ï¬ex- ibility and ability to optimize, enabling more efï¬cient solutions. â¢ Performance-based regulations maintain their relevance. In contrast, prescriptive regulations tend to encompass best practices at the time they are written and eventually become outdated and can conï¬ict with evolving technologies. â¢ Performance-based regulations are more readily maintained. Adjust- ing them to reï¬ect evolving public and regulatory expectations is straightforward. â¢ Performance and safety-based regulations have greater transparency, backed up by deï¬ned goals and objectives. â¢ Performance-based regulations require greater involvement and buy- in by industry, leading to a better understanding of responsibility. The following are some of the disadvantages of performance-based regulations: â¢ Performance standards place a greater reliance on the technical com- petency of the design engineer, fabricator, and third-party reviewer. â¢ It is more difï¬cult to verify conformity with performance standards than prescriptive standards.
82 Structural Integrity of Offshore Wind Turbines If Option c is implemented with only overarching performance standards, there is risk that important design concerns will be overlooked. Therefore, where goal-based standards are specified, requirements are generally further deï¬ned by functional requirements, Option d. Although goal-based standards are often qualitative, to maintain consistency and provide metrics for monitoring compliance, the functional requirements may be performance-based quantitative standards. When goal-based standards and functional requirements are man- dated by the governmental body, prescriptive standards are frequently developed by standards bodies or industry organizations to comple- ment the goal-based and functional requirements. The prescriptive standards are developed such that, at least for conventional structures, compliance with the standard will ensure compliance with the goal- based and functional requirements. This facilitates design and veriï¬ca- tion when the facilities and environmental conditions are consistent with the assumptions implicit in the prescriptive standards. 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). Such regulations will allow for the development of new technologies that are necessary if offshore wind farms are to develop into a cost-effective energy source. Moreover, the regulations should be risk-informed. Further background on the evolution of risk-informed approaches for regulating the safety of engineered structures is provided in Appendix A. The goal-based standards can be supplemented by pre- scriptive international and national standards and industry-developed guidelines where appropriate. The committee recommends that the federal government, presumably under the auspices of BOEMRE, develop a set of goal-based standards for offshore wind turbines by using an approach similar to that applied by IMO for the maritime industry (refer to Box 4-4 for a description of IMO
A Risk-Informed Approach to Performance Assurance 83 BOX 4-4 Goal-Based Standards Applicable to the Maritime Industry As described earlier, the rules for design and construction of ships are developed by classification societies in conformance with national and international regulations. The regulatory authorities concentrated on issues of safety and environmental performance and left standards for hull structural design, mate- rials, coatings, and construction largely in the hands of the clas- siï¬cation societies. Comparison of the various classiï¬cation rules revealed signiï¬cant differences in structural requirements and expected performance. With encouragement from both national authorities who sought a more consistent level of structural reli- ability and safety and industry representatives who sought a more level playing ï¬eld where reduced robustness in the shipâs structure and acceptance of higher safety risks were not used for competitive advantage, IMO developed a set of goal-based stan- dards (IMO 2010). These standards establish minimum objec- tives with which all classiï¬cation rules must comply. The standards consist of three tiers. Tier 1: Goals Tier 1 deï¬nes the high-level objective. An example of a Tier 1 goal is that ships shall be designed and constructed to be safe and envi- ronmentally friendly throughout their design lifetimes (when properly operated and maintained under the appropriate condi- tions). Further deï¬nition of terms can be given (e.g., that âsafe and environmentally friendly means the ship shall have adequate strength, integrity, and stability to minimize the risk of loss of the ship or pollution to the marine environment due to structural (continued on next page)
84 Structural Integrity of Offshore Wind Turbines BOX 4-4 (continued) Goal-Based Standards Applicable to the Maritime Industry failure, including collapse, resulting in ï¬ooding or loss of water- tight integrityâ). Tier 2: Functional Requirements Tier 2 defines the criteria to be satisfied to conform with the goals. 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: Veriï¬cation of Conformity Tier 3 speciï¬es the procedures for verifying that class societiesâ rules and regulations for ship design and construction conform or are consistent with the goals and functional requirements. IMO recognized that it did not have the technical expertise to develop rules with the speciï¬city necessary to satisfy industry and regulatory needs or the resources to maintain the currency of such rules. Thus, the decision was made to keep the goal-based standards at a high level and rely on the classiï¬cation societies to develop and maintain comprehensive rule sets. The Tier 3 veri- ï¬cation process calls for parties seeking veriï¬cation of rules to provide documentation demonstrating conformity with the goal-based standards. Again recognizing its technical limitations, IMO intends to use consultants with a range of expertise per- forming under the direction of IMO staff to audit rules submit- ted for veriï¬cation.
A Risk-Informed Approach to Performance Assurance 85 goal-based standards). There are parallels between the situations faced by BOEMRE in rule development for offshore wind turbines and by IMO for oceangoing ships: 1. IMO did not have the expertise or resources to develop rules with suf- ï¬cient speciï¬city. Although the committee strongly recommends that the size and capability of BOEMRE staff be enhanced, it is not envi- sioned that BOEMRE will have the means to develop detailed rules. 2. The classiï¬cation societies had well-developed and validated rules before IMOâs involvement in regulating hull structures. Similarly, inter- national standards for offshore wind turbines (e.g., IEC 61400-3) and class rules and guides (GL, DNV, and ABS) are already in place. 3. Deï¬ciencies and inconsistencies among the various classiï¬cation soci- ety rules for shipbuilding were identiï¬ed as an area of concern. Simi- larly, there are deï¬ciencies and inconsistencies in the rules for offshore wind turbines, as discussed in Chapter 3. 4. In the case of both offshore wind turbines and shipbuilding, the clas- siï¬cation societies and international standards groups are prepared to maintain the currency of their rules and regulations through continu- ous validation and revision. The committee envisions the federally mandated goal-based standards for offshore wind energy installations to be a relatively short documentâ perhaps four or ï¬ve pages. The goal-based standards should be high-level objectives expressed in terms of performance expectations. The standards will apply to the design, fabrication, and installation of offshore wind farms within U.S. waters and are intended to ensure a level of consistency meet- ing safety, environmental performance, and policy expectations, while being sufï¬ciently ï¬exible to enable introduction of new technologies and concepts. While the committee does not have the time, the resources, or the expertise to establish a complete set of speciï¬c criteria, an example of the scope and type of evaluation criteria that should be incorporated is given below. Tier 1âtype high-level general requirements are given ï¬rst, followed by Tier 2âtype functional requirements. In the latter, the numerical values shown as examples for various items are provided for illustrative purposes only. Actual criteria would be subject to development by BOEMRE and its consultants.
86 Structural Integrity of Offshore Wind Turbines Examples of General Requirements Structures, foundations, and nonstructural components shall be designed by analysis or by a combination of analysis and testing to provide a per- formance not less than as stated below when they are subjected to the inï¬uence of operating, environmental, and accidental loads. Consider- ation shall be given to uncertainties in loading and in resistance. Analysis shall employ rational methods based on accepted principles of engineering mechanics and shall consider all signiï¬cant sources of deformation and resistance. Assumptions of stiffness, strength, damp- ing, and other properties of components and connections shall be based on approved test data or referenced standards. Testing used to substantiate the performance capability of structural and nonstructural components shall accurately represent the materials, conï¬guration, construction, load intensity, and boundary conditions expected. Where an approved industry standard or practice that governs the testing of similar components or materials exists, the test program and determination of design values shall be in accordance with that industry standard or practice. Examples of Functional Requirements The examples below are provided for illustrative purposes only. 1. Offshore wind turbines and electric service platforms shall have a service life of at least _____ years (e.g., at least 20 years). 2. Site-speciï¬c environmental conditions shall be used for design. 3. The primary structures (foundations, superstructure, platforms, blades, nacelle supports, etc.) shall be designed and constructed so that the probabilities of falling short (during their service life) of limit states associated with deï¬ections, ultimate strength, loss of sta- bility (buckling), and fatigue are sufï¬ciently small for each individ- ual structure as well as for the ï¬eet of structures (typically installed near one another) that make up an offshore wind farm. 4. The probability, given the design-basis event, of collapse of primary structures (towers, platforms, blades, nacelle supports, etc.) within a wind energyâgenerating facility shall not exceed ___ (e.g., shall not exceed 10 percent).
A Risk-Informed Approach to Performance Assurance 87 5. Wind turbine towers and electric service platforms shall be designed with sufï¬cient robustness that localized damage does not lead to progressive, catastrophic failure. 6. The design fatigue life shall be not less than _____ times the speci- ï¬ed service life. For uninspectable areas, the design service life shall be not less than _____ times the speciï¬ed service life (e.g., 1Ã, 5Ã). 7. The primary structures shall have protection against corrosion ade- quate to ensure that sufï¬cient strength is maintained over the spec- iï¬ed service life. 8. Wind energy generation facilities shall be designed to minimize emission of pollutants as far as practical. 9. Wherever practical, structures and equipment shall be constructed of materials that can be recycled in an environmentally acceptable manner without compromising safety. 10. The towers and other structures shall be designed to provide ade- quate means of access to all internal structures to facilitate close-up inspections of structures and equipment. 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. Industry Compliance with BOEMRE Goal-Based Standards Industry will be responsible for proposing a collection of national and international standards, rules, industry-developed guidelines, and rec- ommended practices (referred to here as a âpackage of Guidelinesâ) that conform to the goal-based standards established by BOEMRE. As noted later in this section, the standards, rules, industry guidelines, and recom- mended practices making up the packages of Guidelines could be drawn from classiï¬cation societies, the International Electrotechnical Commis- sion (IEC), or elsewhere. The packages of Guidelines will likely have prescriptive elements, which are often easier to implement than perfor- mance-based requirements. This is acceptable provided that they comply with the goals and objectives established by BOEMRE. It is anticipated that these packages of Guidelines will have as their basis the IEC stan- dards, with additional rules, industry guidelines, and recommended
88 Structural Integrity of Offshore Wind Turbines practices to cover all necessary aspects of wind turbine design covered by the BOEMRE goal-based standards and to rectify any areas of noncon- formance with the BOEMRE requirements. To streamline the regulatory compliance process and provide a level of regulatory certainty to the developer, the committee recommends that BOEMRE be prepared to review the packages of Guidelines proposed by a rulemaking or standards development body in the light of BOEMREâs goal-based standards before their application to any particular project. The review process would proceed as follows: 1. The rulemaking body develops a package of Guidelines conforming to the BOEMRE goal-based standards along with the underlying docu- mentation and analysis. 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. 2. When it submits its package of Guidelines for approval, the rulemaking body shall provide documentation and analysis demonstrating that the standards, rules, industry guidelines, and recommended practices con- tained in the package fulï¬ll all the requirements of the BOEMRE goal- based standards, or it shall clearly identify which requirements are not covered by its package of Guidelines. 3. BOEMRE reviews the package of Guidelines and the underlined docu- mentation and analysis for conformance with the goal-based standards. Once compliance is ascertained, BOEMRE publishes notiï¬cation of its approval of the package of Guidelines. If the package Guidelines does not fully cover BOEMRE requirements, any deï¬ciencies that must be covered by other standards, rules, industry guidelines, and recom- mended practices should be identiï¬ed in the notiï¬cation. Alternatively, a developer should be permitted to identify a package of Guidelines that will be apply to a speciï¬c project, along with the underly- ing documentation and analysis, and BOEMRE should be prepared to review and approve such packages on a case-by-case basis. This process is anticipated to take longer than would use of preapproved packages of Guidelines, but it will allow for the introduction of novel concepts that
A Risk-Informed Approach to Performance Assurance 89 may not be covered in existing, preapproved packages of Guidelines. This approach would proceed as follows: 1. The developer assembles the package of Guidelines (see above) that it proposes to use for a particular project, and it prepares documentation and analysis demonstrating that all requirements of the goal-based stan- dards are satisï¬ed. 2. A third-party CVA reviews the developerâs package of Guidelines and the underlying documentation and analysis and provides a statement indicating that the package is in full compliance with the goal-based standards. If the CVA identiï¬es deï¬ciencies or has concerns that are not fully reconciled by the developer, they should be explained in the CVAâs report. 3. The developer submits its package of Guidelines, including the CVAâs report, to BOEMRE, seeking approval for the package of Guidelines to be applied to the project. 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) that will be followed to ensure compliance with the goal-based standards does not imply that site-speciï¬c assessment and analysis are not required. Project certiï¬cation (see Chap- ter 3) with on-site assessment is expected to be a standard part of the design and review process. OVERVIEW OF PROJECTED BOEMRE ROLE It is important that a single government agency, presumably BOEMRE, have overall responsibility for regulatory development, monitoring and maintenance of the regulations, and implementation of the veriï¬cation and oversight regime. Below is a summary of the role that BOEMRE would play under the approach recommended by the committee. The role is a large one, and BOEMRE may wish to consider creating an expert panel to assist with the initial development of the goal-based standards and then with continuous monitoring and evaluation of the standards and regulations.
90 Structural Integrity of Offshore Wind Turbines a. If so decided, establish an expert panel to assist in initial development of the goal-based standards and then continuous monitoring and evaluation of the regulations (see Chapter 6). b. Determine the scope of the regulatory standards. To ensure a level of reliability consistent with public policy expectations, the committee believes that the standards must consider design, fabrication, instal- lation, and commissioning from the export cable through to the tow- ers and incorporated systems. c. By the end of calendar year 2011, develop the goal-based standards and functional requirements, including a rigorous public review process. d. Review proposed âpackages of Guidelinesâ (compilations of interna- tional and national standards, rules, industry-developed guidelines, and recommended practices) for compliance with the U.S. goal- based standards. (As submitted) e. Review proposed packages of Guidelines during project assessment, where preapproved packages are not applied or where gaps in the preapproved packages are identiï¬ed. (As requested) f. By the end of calendar year 2011, establish the intent and scope of the third-party review process (see Chapter 5). g. By the end of calendar year 2011, establish qualiï¬cations for CVAsâ third-party reviewers (see Chapter 6). h. Exercise ï¬nal approval authority for design and construction in com- pliance with the regulations (see Chapter 5). i. Review qualiï¬cations and approve CVAs on a project-speciï¬c basis (see Chapter 6). j. Monitor performance of projects versus regulatory expectations and provide periodic feedback to the industry (see Chapter 6). k. Monitor the effectiveness of the goal-based standards and periodi- cally revise them as appropriate. l. Monitor the effectiveness of the preapproved packages of Guidelines (national and international standards, rules, industry guidelines, and recommended practices) to ensure compliance with the latest goal- based standards. m. Monitor the effectiveness of the third-party review process. n. Periodically review and update the goal-based standards.
A Risk-Informed Approach to Performance Assurance 91 o. Serve as the U.S. representative on offshore wind standards develop- ment committees, both nationally and internationally. IMPLEMENTATION: CAPACITY AND EXPERTISE USDOIâs Offshore Energy and Minerals Management program includes both offshore oil and gas and offshore renewable energy regulatory pro- grams. It is staffed by roughly 900 professionals in three regional ofï¬ces (GOM, Alaska, and Paciï¬c); associated district ofï¬ces; and headquarters ofï¬ces in Washington, D.C., and Herndon, Virginia. The headquarters staff has one engineer with a background in civil and marine engineer- ing and naval architecture, and the GOM regional office is supplying an engineer to support the Office of Alternative Energy Projects on an as-needed basis. The Ofï¬ce of Structural and Technical Support (OSTS) is responsible for ensuring that the platforms operating on the OCS are designed, fab- ricated, installed, and maintained in accordance with regulations. This group is based in the GOM regional ofï¬ce in New Orleans, Louisiana, and serves as structural support for the Paciï¬c region as well. On the oil and gas side, roughly 3,500 facilities are installed in the U.S. OCS (primarily GOM), and OSTS has fewer than 10 engineers to address permit applica- tions, inspection data, repair information, and all other structural data and requests. Since Hurricane Katrina in 2005, many of the more experi- enced staff in OSTS, including its director, have left the organization. Remaining staff have less experience in addressing offshore structural issues and no experience in addressing issues related speciï¬cally to off- shore wind structures. To enhance its ability to oversee the offshore wind industry effectively, BOEMRE may wish to focus on obtaining staff or contractors with experi- ence 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 com- missioning, with a preference for offshore experience; and offshore struc- tures operation and maintenance, with a preference for offshore wind facilities experience. Experience with the standards development process would also be beneï¬cial.
92 Structural Integrity of Offshore Wind Turbines FINDINGS FOR TASK I: CHAPTER 4 As noted above, the federal government has embraced offshore wind energy as an integral component of its overarching policy of developing clean, renewable energy sources. Thus, the government has a fundamen- tal interest not only in the safety and environmental performance of off- shore wind farms but also in their reliability and cost-effectiveness. 1. Improvements in the efï¬ciency of offshore wind turbine installations and reductions in capital and operating costs are needed if offshore wind energy is to become a highly competitive renewable energy source. Performance-based (goal-based) standards, which are grad- ually replacing prescriptive standards in other industries including the civil infrastructure, offshore oil and gas, and shipping industries, pro- vide the ï¬exibility needed to accommodate new technologies. They can be administered and modiï¬ed by the regulatory bodies in a straightfor- ward way, they clarify the responsibility of industry in meeting project goals, and they result in the transparency that comes with the delin- eation of goals and objectives. 2. As a result of the signiï¬cant uncertainties affecting facility performance under operating and extreme conditions, recent PBE standards have a risk-informed basis. 3. Unless its stafï¬ng levels and experience are substantially enhanced, BOEMRE will be unable to provide the leadership and decision- making capability necessary for development of U.S. offshore wind standards. RECOMMENDATIONS FOR TASK I: CHAPTERS 3 AND 4 These recommendations ï¬ow from the ï¬ndings in Chapters 3 and 4. To enable timely development of U.S. offshore wind energy within a robust regulatory framework, the following approach is recommended: 1. 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) and should cover design, fabrication, and installation. Offshore wind energy is an emerging technology; therefore, the stan-
A Risk-Informed Approach to Performance Assurance 93 dards should be crafted to allow and encourage introduction of inno- vative solutions that improve the safety, environmental performance, reliability, and efï¬ciency of offshore wind facilities. BOEMRE should either develop these regulations within the agency in a timely manner or facilitate development through, or with the advice of, an outside group of experts. In any case, it is imperative that BOEMRE take responsibility for the process and the ï¬nal product. 2. Because offshore wind projects are already under way, it is essential that BOEMRE provide industry with a well-deï¬ned regulatory frame- work as soon as practical. The U.S. offshore wind turbine regulations should be promulgated no later than the end of calendar year 2011, and a speciï¬c plan for meeting that target should be established as soon as possible. 3. On request of a rule development body, BOEMRE should review the rules and guidelines proposed by that body for compliance2 with BOEMREâs goal-based standards and identify any deï¬ciencies. Once BOEMRE deems a set of rules to be in full compliance with the goal- based standards, it should approve such rules for application to U.S. off- shore wind turbines. Examples of rules and guidelines that could be considered are those developed by GL, DNV, and ABS. Preapproved rules should have the beneï¬t of expediting the regulatory review process. However, BOEMRE should be prepared to review standards and guide- lines proposed by a developer and accepted by a CVA for compliance with its goal-based regulations on a case-by-case basis. 4. It is critical that BOEMRE establish a substantial core competency within the agency with the capacity and expertise to lead the development of the goal-based standards and review the packages of standards, rules, industry guidelines, and recommended practices submitted by project developers and rules-development bodies. The section âGoal-Based Standards for Offshore Wind Turbinesâ in this chapter contains more details with regard to the experience and capabilities that are needed. 5. BOEMRE should take a leading role in promoting awareness of lessons learned in the offshore wind and offshore oil and gas industries among 2 A set of rules is deemed compliant if meeting those rules will be taken as sufï¬cient evidence that the performance-based goals have been met.
94 Structural Integrity of Offshore Wind Turbines project developers, industry professionals, and standards development bodies. The goal is to help industry avoid mistakes that have been encountered elsewhere and to promote practices that have proved to be successful. 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. REFERENCES Abbreviations AASHTO American Association of State Highway and Transportation Ofï¬cials BOEMRE Bureau of Ocean Energy Management, Regulation, and Enforcement IMO International Maritime Organization MMS Minerals Management Service TRB Transportation Research Board USDOE U.S. Department of Energy USDOI U.S. Department of the Interior AASHTO. 2007. AASHTO LRFD Bridge Design Speciï¬cations. Washington, D.C. Berek, G. 2010. Changing Practice in Gulf of Mexico Design and Operating Criteria. http://www.iooc.us/wp-content/uploads/2010/09/Changing-Practice-in-Gulf-of- Mexico-Design-and-Operating-Criteria.ppt. Berman, M. Y., N. D. Birrell, J. T. Irick, G. C. Lee, M. Rubin, and M. E. Utt. 1990. The Role of the API Committee on Standardization of Offshore Structures. Paper 6206. Proc., Offshore Technology Conference. BOEMRE. n.d. Overview of OCS Regulations. http://www.gomr.boemre.gov/homepg/ regulate/regs/reg_sum.html. Cape Wind. n.d. Frequently Asked Questions. http://www.capewind.org/FAQ-Category8- Cape+Wind+and+the+Environment-Parent0-myfaq-yes.htm#44. Accessed Dec. 13, 2010. Coglianese, C., J. Nash, and T. Olmstead. 2003. Performance-Based Regulation: Prospects and Limitations in Health, Safety, and Environmental Protection. Administrative Law Review, vol. 55, issue 4, pp. 705â730. Ellingwood, B., and J. R. Harris. 1977. Reliability-Based Performance Criteria for Structures. Proc., 2nd Engineering Mechanics Division Specialty Conference, ASCE, pp. 124â127.
A Risk-Informed Approach to Performance Assurance 95 Energo Engineering. 2010. Assessment of Damage and Failure Mechanisms for Offshore Structures and Pipelines in Hurricanes Gustav and Ike. MMS TA&R No. 642, Feb. http://www.boemre.gov/tarprojects/642/642AA_FinalReport.pdf. Exxon Valdez Oil Spill Trustee Council. n.d. Details About the Accident. http://www. evostc.state.ak.us/facts/details.cfm. Accessed Oct. 30, 2010. IMO. 2002. Guideline for Formal Safety Assessment (FSA). MSC/Circ. 1023, MEPC/ Circ. 392. IMO. 2010. Resolution MSC.287(87), Annex 1. Adoption of the International Goal-Based Ship Construction Standards for Bulk Carriers and Oil Tankers. Adopted May 20. MMS. 2004. History of the Oil and Gas Industry in Southern Louisiana. Interim Report, Vol. 1. MMS 2004-049. http://www.gomr.mms.gov/homepg/regulate/environ/studies/ 2004/2004-049.pdf. Musial, W., and B. Ram. 2010. Large-Scale Offshore Wind Power in the United States: Assessment of Opportunities and Barriers. Report TP-500-40745. National Renewable Energy Laboratory, Golden, Colo. Puskar, F. J., H. S. Westlake, P. E. OâConnor, and J. Bucknell. 2006. The Development of a Recommended Practice for Structural Integrity Management (SIM) of Fixed Offshore Platforms. Paper 18332. Proc., Offshore Technology Conference, May. TRB. 2008. Special Report 293: Risk of Vessel Accidents and Spills in the Aleutian Islands: Designing a Comprehensive Risk Assessment. National Academies, Washington, D.C. USDOE. 2011. Salazar, Chu Announce Major Offshore Wind Initiatives. Press release. Feb. 7. http://www.energy.gov/news/10053.htm. Accessed Feb. 7, 2011. USDOI. 2010. Salazar Launches âSmart from the Startâ Initiative to Speed Offshore Wind Energy Development off the Atlantic Coast. Press release. Nov. 23. http://www.doi. gov/news/pressreleases/Salazar-Launches-Smart-from-the-Start-Initiative-to-Speed- Offshore-Wind-Energy-Development-off-the-Atlantic-Coast.cfm. Accessed Feb. 13, 2011. USDOI. n.d. Smart from the Start Fact Sheet. http://www.doi.gov/news/pressreleases/ loader.cfm?csModule=security/getï¬le&PageID=73317. Accessed Feb. 13, 2011. Wan, K. W. 2010. Flaw Hits Hundreds of EU Offshore Wind Turbines. Reuters, April 23, 2010. http://uk.reuters.com/article/2010/04/23/uk-offshore-wind-ï¬aw-idUKTRE63M 3H720100423. [Accessed February 13, 2011] Ward, E. G. 1974. Ocean Data Gathering ProgramâAn Overview. Paper 2108. Proc., Offshore Technology Conference.