Subsea Bolt Failure Analysis Using Advanced Forensics
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Resistance to environmentally assisted cracking is a key consideration in the selection of materials for subsea drilling safety critical equipment bolting applications. This paper describes several unique forensic tools used in combination to examine a safety critical bolt that failed during subsea oil and gas exploration in the Gulf of Mexico, one of several failures in a single flange. The method of examination presented here represents a new and unique toolset for examining failures in subsea bolts. The two-inch-diameter coated bolt, specified as AISI 4340 steel alloy, sheared near one of the threaded ends. The sheared bolt end was removed and cut approximately in half to examine microscopic cracks. Scanning electron microscopy techniques were utilized to examine the flat, cut face of the bolt interior. The sample and individual small sections were examined at the Advanced Photon Source at Argonne National Laboratory using high-energy synchrotron X-rays with energy levels up to 100 keV. The X-ray examinations produced a three-dimensional picture of the sample. Based on the results and discussions, design recommendations were made for increased corrosion resistance in subsea environments.
KeywordsAlloy steel Catastrophic failure Chemistry Energy-dispersive spectroscopy
This material is based upon work supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the US Department of Energy under Contract No. DE-AC02-06CH11357 and royalty funds under the same contract. This research used resources of the Center for Nanoscale Materials, which is a Department of Energy (DOE) Office of Science User Facility under DOE Contract No. DE-AC02-06CH11357. Use of the Advanced Photon Source (APS), Argonne National Laboratory (ANL), is supported by the US Department of Energy (DOE), Office of Science under Contract DE-AC02-06CH11357. This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.
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