This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17238, "Failure of Chains by Bending on Deepwater Mooring Systems," by P. Jean, Single Buoy Moorings Inc.; K. Goessens, Total E&P Angola; and D. L'Hostis, DV Offshore, prepared for the 2005 Offshore Technology Conference, Houston, 2–5 May. The premature rupture of mooring chains of the Girassol buoy after only a half-year of service was caused by bending fatigue of the first free chain link inside the chain hawse (fairlead). Although the mooring system had been designed according to offshore industry standards, it failed because of this bending-fatigue mode. A study of this bending phenomenon led to a redesign of both the top chain segment size and the hawse connection, which now includes a new chain-connecting arm (CCA). A new method was developed to estimate the fatigue damage in the chain subjected to bending, which was used to design a new CCA for the Girassol buoy. Introduction The Girassol loading buoy was installed in September 2001 at the Girassol oil field off-shore Angola in 1350-m water depth. The buoy allows export, by use of two midwater 16-in. export lines, of the stabilized crude oil processed onboard the floating production, storage, and offloading vessel, moored 1 naut mile away. The buoy is anchored to the seabed by means of three groups of three anchor legs. Before the incident, the anchor legs comprised collinear segments of 81-mm studded chains and 130-mm-diameter polyester ropes. Within each group, the legs are spread 5° apart, and the group centers are spread 120° apart. The chain segments are at the upper and lower ends of the anchor legs. In May 2002, 235 days after buoy installation, one group of anchor legs (B4, B5, and B6) broke almost simultaneously, followed 1 month later by the rupture of another anchor leg (B1). The ruptures in Anchor Legs B4, B6, and B1 occurred at exactly the same location—at the fifth link of the upper chain segment connected to the buoy inside a standard-type curved chain hawse—while Leg B5 broke in the upper rope segment. This rope-segment rupture was caused primarily by an earlier accidental cut of the rope through two-thirds of its section. The total rupture of Leg B5 followed the rupture of Legs B4 and B6 as a result of load transfer. However, the fifth link of Leg B5 was found severely cracked, thus confirming the same failure mechanism for all four legs. Studies identified the root cause as the out-of-plane bending (OPB) stress (fatigue stress), combined with tension variations, occurring mainly in the fifth link inside the chain hawses. As Fig. 1 shows, Link 5 is the first link to oscillate with respect to the Link 4, which is fixed onto the internal curved shape of the chain hawse.