BP wished to confirm the integrity of a mooring chain in the chain stopper location which had been in service a number of years, and required an inspection technique that would give quantitative information. It was agreed that in order to be conservative the detectable flaw size with 90% probability of detection should be 20mm through wall and 100mm long. The restrictions for the inspection were that it had to be carried out in 15m depth of water inside the turret structure, with no demanding tasks on the diver such as probe scanning because of the difficult water conditions. The total distance from the inspection site to the location of the NDE equipment and inspector was around 100 metres. The cables pass through a hazardous area so all inspection cabling and equipment needed to be doubly insulated and protected against sparking of any type.
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