Corrosion monitoring of ships and in offshore technology

摘要

Above waterline of ships' hulls and in offshore technology coating and duplex systems are used for corrosion protection. For underwater surfaces and for structures and components in the sea bed without exception cathodic protection is to beinstalled, at times in combination with appropriate coating systems.Above the waterline conventional methods are applied to monitor corrosion, while under water visual inspection by means of underwater TV cameras requires operations by divers. Remote control is also a standard feature of equipment today and permits therecording of data and, as a result thereof documentation.For internal inspections of pipelines intelligent pigs are primarily employed. From outside the effectiveness of cathodic protection has to be checked, for instance by potential measurements.For non-destructive testing under water ultrasonic testing devices have been developed to measure the wall thickness and for crack detection. So far this measurements have been employed with assistance by divers or in stationary condition. Wall thicknessmeasurement does not present any problems and is monitored by the surveyor on board the diving support vessel, using a TV camera. Ultrasonic crack detection requires qualified Level 2 divers. Magnetic particle tests can also be performed under water andbe monitored from the ship.Acoustic emission analysis which has been recommended over and over again has proved appropriate, but is hardly justified on account of the expense involved in the apparatus required. Recent investigations are aimed at applying fatigue analysis andassessment in comparison with the calculations performed.