High-Performance Bolting Technology for Offshore Oil and Natural Gas Operations (2018) / Chapter Skim
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Extracting these offshore petroleum resources involves the possibility, however remote, of oil spills, with resulting damage to the ocean and the coastline ecosystems and risks to life and limb of those performing the extraction. The environmental consequences of an oil spill can be more severe underwater than on land because sea currents can quickly disperse the oil over a large area and, thus, 1 merican A Oil and Gas Historical Society, "Offshore Petroleum History," http://aoghs.org/offshore-history/offshore-oil-history/, accessed March 13, 2017.
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Other agencies are charged with OCS oil and gas lease sales, marine safety, and revenue generation.5 At the request of BSEE, the National Academies of Sciences, Engineering, and Medicine studied subsea threaded fastener failures. The result is this report of the Committee on Connector Reliability for Offshore Oil and Natural Gas Opera tions, which is based on the somewhat limited data provided to the committee.
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To date, a few dozen mechanical failures among thousands of bolts in critical pressure boundary applications have been reported in the field, with the overall bolting failure rate estimated to be in the range of 10−4 to 10−5 based on the total reported failures divided by the number of fasteners employed in-service.6 However, this small number provides little comfort, or basis for analysis, given the "censored data" problem produced by lack of an industry wide program to inspect for bolts that are progressing to failure, or have failed completely and are merely being held in position by gravity. Sobering accounts, such as the failed studs on the Seadrill's West Capricorn (WC)
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Because bolts are subject to multiple time-dependent failure modes in addition to mechanical overloads, all potential failure modes must be identified and the risks must be mitigated during the design process. Further, there are important environmental factors that directly influence the rate of degradation of fastener materials, such as ocean water salinity and chemis try, the presence of hydrogen from cathodic protection systems or the presence of hydrogen, hydrogen sulfide (H2S)
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Damage-induced modifications to fasteners include corrosion, fatigue crack nucleation and growth, and crack nucleation and growth by environmentally assisted cracking mechanisms, including hydrogen embrittlement8,9 and stress corrosion cracking.10 Fastener failures have an service environment, mechanical, human, and material component. The predominant failure mode depends on the application environment and processing history.
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The sequence of cracking leading to failure involves hydrogen pro duction, adsorption, subsequent diffusion of adsorbed hydrogen, and hydrogen accumulation in a fracture process zone often associated with the microstructure. Little non-proprietary work has been reported regarding fully characterized subsea bolting material failure modes using state-of-the-art sophisticated failure analysis methods.
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The committee believes that the root cause of these cluster failures, possessing very different hardness, heat treating, and ingot creation is better explained by consideration of the various factors (e.g., coatings, impressed current systems, sacrificial anodes, etc.) which potentially contribute to the electrochemical nature of environmentally assisted cracking.
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Therefore, there is a need for leadership in harmonizing standards, using a balanced group of subject matter experts from industry, government, and trade organizations to provide uniformity and improved clarity for the supply chain. Standards, as prepared today, will not totally solve the fastener reliability issues as they are reactive to known issues, usually do not address potential issues, and the enforcement process is not always clear-cut.
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The FAA's Aviation Safety organization is responsible for the certification, production approval, and continued airworthiness of aircraft; and certification of pilots, mechanics, and others in safety-related positions.16 This organization promotes safe flight through standards for design, material construction, quality work and performance of aircraft and aircraft engines. FAA Aviation Safety establishes 14 ne O example was presented during the committee visit to Schlumberger on March 23, 2017.
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The JETQC has established detailed specifications for reporting inclusions at all stages of the processes used for manufacturing premium quality titanium alloys. As a result of this initiative the number of identified melt inclusions in premium quality titanium material, which was already low, has been reduced by a factor of one to two orders of magnitude.
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Communication across multidisciplinary teams and between scientists and field workers can be challenging throughout the bolt life cycle. Sharing information about bolt performance, failures, and near misses across different disciplines and organizations is critical to promote the safety culture required by oil and gas operations.
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Prudent risk management necessitates the continuous reduction of the potential for fastener failures. A meaningful comprehensive government-industry initiative could be constructed, aimed primarily at improving fastener reliability for the most critical subsea applications.
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Industry should have a large role in determining the priority for addressing potential improvements. The roadmap could be divided into several sections: • Investigate bolting cluster failures using a large-scale fully instrumented flange test rig that simulates subsea conditions on fasteners in bolted joints including structural loads, environmental conditions and cathodic protection.
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From page 14... ...
[Recommendation 2.8] • Establish a standard accepted laboratory standard test method to assess the susceptibility to environmentally assisted cracking/hydrogen embrittlement of bolting materials and their coatings used in offshore applications [Recommendation 2.10]
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