New NDT gear side-steps awkward inspection
TWI has been actively involved in the application of the T-Scan ultrasonic inspection system to the detection of corrosion in ships' hulls. When the conditions creating corrosion cannot be changed, it is important to monitor corrosion progress so that corroded parts can be replaced before they fail.Work at Abington has involved computerised ultrasonic systems. The T-Scan system adopted is able to image the corroded surface and thus detect corrosion pits that could easily be missed when taking individual thickness measurements with a digital ultrasonic thickness gauge.
TWI's inspection of corrosion in ships' hulls has revealed pitting on the inside surface near the keel caused by the action of micro-organisms in sediments accumulating beneath the engines. Access to view the corroded surfaces from inside the ship is limited and inspection has to be carried out from the outside while the ship is in dry dock.
The T-Scan provides an image of the corroded surface that can be compared directly with what is observed visually. The spatial distribution of corrosion pits can be related to features such as bulkheads which helps in diagnosis of the corrosion problem. Moreover, scans can be repeated at intervals and the images compared to monitor the progress of corrosion.
The results of inspections enable the owners and operators of vessels to quantify the extent of corrosion in susceptible regions of the hulls; provides the operators with confidence in the ability of the vessels to continue in service without major problems and allows for repair scheduling to be more accurate.
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