Table E.1 is a summary of selected subsea bolt failures but does not include data from proprietary failure databases.
TABLE E.1 Selected Subsea Bolt Failures
|≈2002||Specific application not identified||First Major riser bolt/insert environmentally assisted failure since drilling vessels began using impressed current systems (ICS) in 1998-2000. As a consequence, bolt hardness was reduced to HRC34; an ICS safety alert was issued related to removal of metallic coating from bolt holes. The number of incidents was not reported. Adamek noted that “riser bolt/insert cracking observed on several vessels with ICS; no failures observed on rigs with fixed anode systems.” The number of incidents was not reported.||Adamek, 2017|
|May 21, 2003||Flanged riser bolt/bolt insert failure
Transocean (TO) Discover Enterprise (DE)
|“The bolts’ inserts (nuts) that secure the drilling riser failed between joints 39 and 40. The inserts and the bolts’ material was AISI 4340 with a material hardness of 34-38 HRC and yield strength of 145 ksi. The 2003 Combined RCA Report . . . identified that the bolt inserts and bolts fractured due to severe, accelerated, environmentally assisted corrosion. The high material hardness, yield strength, bolt design, impressed current and thermal spray aluminum coating were identified as contributing factors for the failure.” (Product Advisory issued by Vetco Gray on April 8, 2005)||BSEE, 2014|
|2012-2013||Flanged riser bolt/bolt insert failure
|Per QC-FIT Report, Appendix G, “Riser bolt inserts (nuts) & bolt fractures due to environmentally assisted cracking, hydrogen embrittlement. Corrosion brittle fracture. High material hardness, coating/material compatibility issues, strength loading.” The number of bolts and bolt inserts or details for each were not identified.
Per QC-FIT Report, Appendix H, “In 2003, four other TO rigs: TO-Millennium, TO-Horizon, TO-Deepseas, and TO-Pathfinder bolt inserts failed in the same brittle corrosion fracture manner as the 2003 TO-DE and the 2012-2013 H4 connector bolt failures of TO-DI, TO-DAS, TO-Deepwater Champion and P-10K. The same third laboratory performed the RCA for both of the 2003 and recent 2012-2013 bolt failures.”
|Before 2010; specific date not identified||Shaffer Division of National Oilwell Varco (NOV) for Diamond Offshore Drilling, Inc.||Studs used in the construction of a blow out preventer (BOP) stack; three fractured, 3-in.-diameter Inconel 718 studs were evaluated out of 20 (11 had fractured, and 9 exhibited stripped threads).||Jones and Buehler, 2010|
|November 1, 2012||Blind shear ram bolt failures
Transocean (TO) Discoverer India (DID)
|“Blind shear ram (BSR)/shear ram (SR) bolts fracture during a 15,000 psi pressure test (stump test). . . . A similar failure also occurred on an ENSCO 8506 drilling riser. The bolts failed due to tensile overload and bolt hardness due to incorrect heat treatment. The initial identified contributing factor for the failure was QC issues with GE’s subcontracted vendor regarding communication and improper heat treatment procedures for the raw bolt material.”||BSEE, 2014|
|December 18, 2012||Transocean (TO) Discoverer India (DID)||Lower marine riser package (LMRP) separated from blow-out preventer (BOP); Thirty-six H4 connector bolts, AISI 4340, fractured; bolts identified as 2-in. diameter, approximately 9 in. long; Stress Engineering Services indicated “failures of the incident bolts initiated due to hydrogen stress cracking” and “it is likely that atomic hydrogen present in the bolts due to the plating process (and not removed via a subsequent bake-out) played a major role in the failures” (GE issued GE Safety Notice SN 13-001, REV. NC H4 Connector Bolt Inspection).||BSEE, 2014|
|January 5, 2013||Transocean (TO) Discoverer Americas (DAS)||Four fractured bolts were received for analysis by SES. The total number and bolt details for the application were not indicated. The SES report did note that the application appeared to “use the same series of connectors and part-numbered bolts” and “exhibit similar fracture features as those removed from the DID” (see December 18, 2012 above).||BSEE, 2014; SES, 2013|
|January 25, 2013||Petrobras 10,000 (PB10K)||Per QC-FIT report, PB10K was in service about 2.5 years when bolt failures discovered in response to GE safety notice. Five fractured bolts were received for analysis by SES. The total number and bolt details for the application were not indicated. The SES report did note that the application appeared to “use the same series of connectors and part-numbered bolts” and “exhibit similar fracture features as those removed from the DID” (see December 18, 2012, above).||BSEE, 2014; SES, 2013|
|January 5, 2013||Transocean (TO) Discoverer Clear Leader||Per QC-FIT Report, Appendix G, “H4 connector bolts failed inspection were rejected.” The bolts were inspected by magnetic particle techniques and the number of bolts and bolt details were not indicated.||BSEE, 2014|
|January 5, 2013||Transocean (TO) Deepwater Champion||Per QC-FIT Report, Appendix G, “H4 Connector bolts had significant corrosion products, fractures.” The number of bolts and bolt details were not indicated.||BSEE, 2014|
|June 2014||Seadrill West Capricorn||Twenty HC Connector studs were received by SES for analysis. Of these, nine were completely fractured and four exhibited significant cracking based on magnaflux testing. The material was AISI 4340 steel with average bolt hardness values between 31 and 41 HRC. The 3-in. diameter double-ended studs were 18 3/4 in. long. The SES report indicated that the “studs exhibited multiple fracture origins at the root of the threads in what is likely the first engaged thread” and “that Environmentally Assisted Cracking (EAC) was the most probable cause of the observed fractures.” Cameron issued a product advisory on July 15, 2014||SES, 2013; BSEE, 2014|
|Not specified||Brazil—Petrobras Vessel n Gulf of Mexico Region||Per QC-FIT Report, Appendix G, “Severe corrosion fractured failed H4 connector bolts.” The number of bolts and bolt details were not indicated.||BSEE, 2014|
|Not specified||Brazil—Noble-Paul Wolf n Gulf of Mexico Region||Per QC-FIT Report, Appendix G, “Fractured bolts identified during leak during pressure test.” The number of bolts and bolt details were not indicated.||BSEE, 2014|
|Not specified||Norway Vessel (BP Operator) in Gulf of Mexico Region||Per QC-FIT Report, Appendix G, “Chloride Stress Corrosion Cracking (Cl-SCC) fracture failure of bolts for valve. Likely same alloy material as H4 connector bolt.” The number of bolts and bolt details were not indicated.||BSEE, 2014|
|Not specified||DNN-GL Failure nvestigation Database ncidents varied and not specified||Presentation summarizes results from the DNV-GL failure investigation database and notes that 9% of the failure investigations were on fasteners. Of these, 65% were brittle fractures. Of these brittle fractures 57% were attributed to hydrogen embrittlement, 29% to temper embrittlement, and 14% to other/undetermined causes.||Heiberg, 2017|
SOURCES: Adamek, F.C., Adamek Engineering and Technology Solutions LLC, “A Historical View of Subsea Bolting,” presentation to the Workshop on Bolting Reliability for Offshore Oil and Natural Gas Operations, April 10-11, 2017.
BSEE (Bureau of Safety and Environmental Enforcement), QC-FIT Evaluation of Connector and Bolt Failures: Summary of Findings, QC_FIT Rpt. #2014-01, Office of Offshore Regulatory Programs, August 2014.
Heiberg, G., 2017, “Bolted Connection: Is It a Need for Improved Requirements?,” Paper No. OMAE2017-62730, 36th International Conference on Ocean, Offshore, and Arctic Engineering, June 28, 2017.
Jones, R.L., and W.M. Buehler, Examination of Three Failed Inconel 718 Studs, Report No. 0091-10-19492R, Stork Testing and Metallurgical Consulting, Inc., March 1, 2010.
SES (Stress Engineering Services, Inc.), Site Inspection, Metallurgical Examination, and Mechanical Damage Analysis of Discover India LMRP, Report No.: PN1252494, February 27, 2013, Houston, Tex.
SES, Metallurgical Failure Analysis of HC Connector Studs from West Capricorn Facility, Report No. 1253345-FA-RP-01, October 6, 2014, Houston, Tex.