The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community
Issue link: http://sea-technology.epubxp.com/i/653412
36 st / March 2016 www.sea-technology.com to outriggers on the buoy, with each tether connected to the outrigger via a 300-Te SWL D shackle. The buoy has a large sub- merged cylindrical body with a narrower periscope-like cylinder projecting upward out of the water. Boat access to the buoy is via a bow-catcher boat landing on the side of the peri-scope cylinder that projects above the water. The buoy is continually exposed to the weather, in particular extreme wave-in- duced loadings caused by the swells pass- ing over this climatic region in the South- ern Atlantic. Such waves are some of the most severe weather systems experienced by offshore structures, and are most severe in the winter months. A survey identifed that one of the 300-Te SWL D shackle pin heads had been sheared off due to the con- tinuous fatigue loading, and the tether was in danger of parting with potentially disas- trous consequences to the buoy. In order to carry out remedial work, a chartered vessel was used as a diving support vessel for air and saturation diving operations. The repairs required a series of heavy construction aids, including a subsea davit that could be installed on the outrigger and a retractable temporary tether system incorporating a 4-m stroke 200-Te hydraulic puller to take the load off the damaged tether to carry out repairs, as well as various steel deployment buoys. All of this equipment was deployed over the stern roller of the dive support vessel with appropriate steel fotation devices. Once deployed, the equipment had to be col- lected and towed into position at the buoy using a suitable offshore workboat that would be sturdy enough to operate in extreme conditions with plenty of impact loading. A 6-m HDPE Rhino Craft workboat (Rhino 600) was deployed. These heavy-duty offshore workboats, originally developed for use with bow-catcher boat landings in Nigeria, can be exposed to extreme abuse and impact loading. Fabrication Material, Results HDPE is a robust, strong and extremely abrasion-resistant material that is also extremely ductile. This allows the boats to be subjected to large impact loading because the duc- Repair scenarios such as pipeline rupture, pin-hole leak, dents and buckles, internal and external pipeline pitting and problems due to corrosion are all considered pipeline emergencies. EPRS will be driven by the nature of the pipe- line failure or damage, the pipeline size and specifcation, as well as the site location, and offers a complete range of specialized equipment required to work in intertidal zones, including multipurpose amphibious units, amphibious ex- cavators, modular trench shoring systems and all-terrain/ amphibious personnel carriers. Case Study: Buoy Repairs During Winter South Atlantic Storms Rhino Craft was deployed off the coast of South Africa one recent winter to assist with the installation of a large unmanned semi-submerged control buoy. The buoy facili- tated radio communications between the foating platform in order to open and shut valves to allow gas to fow from the feld to the platform. The semi-submerged buoy, situated in approximately 90 m water depth in the South Atlantic 100 km south of the Af- rican continent, is anchored to a large gravity base. The base lies on the seabed with three vertical tethers that connect Maneuvering the steel buoy with hanging replacement tether pendant.