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Manuel Maligas November 15, 2010

Subsea Bolting Failure With ASTM A320 . Manuel Maligas November 15, 2010. Background. Several failure occurred with major oil company operating in South American L7 Bolts were supplied by two Wellhead Manufacturing Companies Bolts were purchased from two fasteners companies

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Manuel Maligas November 15, 2010

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  1. Subsea Bolting Failure With ASTM A320 Manuel Maligas November 15, 2010

  2. Background • Several failure occurred with major oil company operating in South American • L7 Bolts were supplied by two Wellhead Manufacturing Companies • Bolts were purchased from two fasteners companies • Two raw material suppliers were used by the two fasteners companies • Raw material supplied to fastener company was manufactured using continuously cast, in lieu of ingot cast • Cause of failure was attributed to segregation • Segregation resulted in a band of excessive hardness at interior of bolts • Subsea bolts are connected to CP systems and are susceptible to stress cracking from high hardness

  3. Current Practice • ASTM A193 permits ingot or strand cast • ASTM A962 permits ingots or continuously • ASTMA320 has no requirements for melt practice but permits requirements of ASTM A320 ??962?? to prevail

  4. Microstructure of Failed Bolts

  5. Microstructure of Failed Bolts

  6. Segregation Failure Mechanisms Hard Ban Sea Water + CP = + H2S = +

  7. Discussion • Applicable to 6A: USV valves and exposed bolting • Use of the continuous cast process is increasing • Since no requirement is included in ASTM A320, suggest that ingot cast be specified • Standard macro hardness is not sufficient for detection • Standard sample size is not sufficient for detection

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