Manuel MaligasNovember 15, 2010

Subsea Bolting Failure With ASTM A320

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

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

Microstructure of Failed Bolts

Microstructure of Failed Bolts

Segregation Failure Mechanisms

Sea Water + CP+=

+=H2S

Hard Ban

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