An innovative solution for making mooring chain lockers weather-tight is to be type-tested in August by ABS. After these tests have been passed, the system will be installed on a floating production platform in the US Gulf of Mexico.
Existing solutions are not wholly satisfactory, explains MoorLink's Morten Gundersen, especially for larger chain sizes. At times, authorities have even granted exemptions from the regulatory requirement that chain lockers should be weather-tight due to the unavailability (hitherto) of a solution to this requirement.
There are two main drivers for finding a more effective solution. First, compliance with the requirements avoids the detrimental effect on the platform's stability curve that non-compliance inevitably entails. Second, the volume of the chain lockers can be included in the rig's stability calculations, thereby opening the way to an increased deck load. The volume occupied by chain lockers can be substantial.
The function of the closure device is to seal the circular opening through which the chain exits the locker. The bottom of the device is bolted onto the flange mounted at the top of the chain locker hawse pipe opening. The upper part of the device is suspended on springs and sits on a rubber bellow, which together give it the mobility to center itself around the chain. All the parts come in halves, so that the device can be installed while the chain is in position. The device can also be retrofitted onto existing rigs.
At the top are two pivoting covers, one on either side. Fitted around the rim of each cover is an inflatable seal. The covers are closed and locked manually, and the seals are then inflated to form a weather-tight enclosure around both the chain and the outside of the covers.
Moorlink's solution for chain lockers is due to be delivered to a Gulf of Mexico platform.
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As the chain often exits the locker pipe at an angle, a guide is integrated into the lower part of the device to ensure that the chain is aligned both with the device itself and with the pocket wheel. To withstand the wear and tear caused by movement of the chain, the guide is fitted with replaceable linings made of highly abrasive-resistant composite material.
The total weight of the device is around 250 kg. In the upcoming Gulf of Mexico installation, it has to seal a pipe opening of 28-in. diameter through which passes a 150-mm chain. The design life is 30 years, although the rubber bellows may have to be replaced periodically. The device has otherwise been designed to be maintenance free.
Moorlink's delivery is scheduled for October. Negotiations are under way with other platform operators, Gundersen says. In the case of a weather-tight seal, the damage water line has to be below the device. Otherwise, the device has to provide a watertight seal. Although this is a more demanding application, Gundersen says it can be achieved with the same basic design.
For more information, contact Morten Gundersen, MoorLink. Tel +46 31 721 38 00, fax +46 31 708 79 00. [email protected], www.moorlink.com.
