Underwater inspection of offshore structures

Abstract

SynopsisUnder the Offshore Installations (Construction and Survey) Regulations 1974 all structures established or maintained in UK waters must possess a valid certificate of fitness. To obtain this certificate annual visual inspections of parts of the structure must be carried out both above and below water. A major survey of the complete structure or platform is required every five years.Underwater inspections may be carried out down to 50 m by divers on surface demand. Below 50 m when divers are involved it is essential to use either a diving bell or lock-out submersible. To avoid saturation diving and reduce diving hazards, the unmanned submersible has been developed as an underwater inspection tool.Various navigation systems have been developed for offshore position fixing. Deepwater navigation and surveying relies on a combination of surface radio stations and seabed underwater acoustic transponders. Platform navigation for underwater inspection and maintenance is a major problem due to poor diving access and few underwater reference points.The inefficiency of the present diver operated navigation and survey systems round platforms is now being investigated by a research team from the University of Strathclyde. Preliminary tests of equipment have already been carried out in a diving tank and at sea.