Learning From A Past Single Point Moorings Accident

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[Posted on April 9th 2014 by Bill Stewart]

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There are many considerations in the marine industry that can pose possible threats to industry property and employee well-being. Understanding those considerations and possible risks is crucial to running a safe and profitable operation. One of the key elements to keeping your own company and your  employees safe is to understand risk factors, and to keep yourself well informed of current and past catastrophic marine events as they pertain to equipment similar to your own. Single point moorings are one tenant of marine industry which can pose a threat to your business and employees when all safety measures are not adhered to. Although every operation would like to boast a zero accident rate, this is rarely the case. When catastrophic failures do occur, fellow marine industrialist would do well to pay attention and learn a lesson.

One recent accident involving the single point moorings of a deep water GOM operation makes an appropriate object lesson. In 2011 this operation experienced a failure at the tether chain of a free standing hybrid riser. This catastrophic failure caused the buoyancy can and free standing flow line riser to separate. The air can, weighing 440 tons rose suddenly to the surface while the riser suffered complete collapse. The event was investigated thoroughly in order to establish just what might have caused such a large scale failure.

The investigation of the single point moorings quickly located a compromised link in the tether chain which was connecting the buoyancy air can to the hybrid riser. It was later determined that the link failed because of a past welding repair which had been performed on it. The investigation determined that the defect in the link had been grinded down. The  void was then filled with weld material. Once heat treated welding repairs are not permitted in accordance with DNV’s chain standard. It was also found during the investigation that three other links in the tether chain had also been repaired in a similar way, compromising the structural integrity of these links as well.  Weld repairs of this nature create a weakness making the links more susceptible to cracking.

Although in this incident there were no employee injuries or fatalities to report, the risk factor was great. Avoiding such risk should be a critical part of your business plan.

Stewart Technology has been helping marine industries understand and assess risks like these for years. Our expert consultation services can help educate you and your employee base on the best and safest marine practices concerning your single point mooring system and steel catenary risers.