Corrosion Measurement of Hull Plates with Ultrasonic Testing (UT):
Hull Inspections are often overlooked by boat owners. Just about anything that is made of common structural metals is subject to corrosion – more so in the marine environment than elsewhere and hull plates of boats are no exception.
Usually, boats are lifted ashore regularly, thus ensuring a superficial inspection of hull plates from the exterior. The particularly important problem on boats is the measurement of remaining wall thickness of hull plates which may be corroded on the inside surface. Such corrosion is often not detectable by visual inspection as the access to bilges is limited due to various components and structures such as tanks and machinery.
If undetected over a period of time, corrosion will weaken hull plates and possibly lead to dangerous structural failures. Both safety and economic considerations require that hull plates that are subject to corrosion be inspected on a regular basis.
To make things more complex, boat hull exteriors are coated with fillers often applied thickly for fairing, antifouling paints and various other types of coatings. Measurement with simple thickness gauges can be less effective at detecting pitting and measuring the true minimum thickness. An Ultrasonic Flaw Detector is by far superior to thickness gauges as it displays ultrasonic waveforms. From waveform, attenuation and phase shifts, an experienced NDT surveyor can infer remarkable information about the structure under inspection. The surveyor can also directly distinguish between true and false echoes. Furthermore, we are able to determine the exact wall thickness of hull plates without removing the fillers, paints or any coatings and without any harm to them.
We use Olympus Epoch 650 Ultrasonic Flaw Detector, a state of the art digital flaw detector and Olympus Panametrics transducers for inspections. The instrument configuration is accepted and used in aerospace industry. We keep the instrument calibration up to date.