Metal Hull Inspections and Corrosion Measurement

Metal Hull Inspections

Overlooking metal hull inspections are surprisingly common. Be it plain neglect, bei it burying the head in sand – compromised hull integrity is invitation to the worst.

(Please contact us here for a free Hull Inspection Quote.)

Just about anything that is made of metals is subject to corrosion – more so in the marine environment than elsewhere and metal hull plates of boats are no exception.
Usually, boats are lifted ashore regularly, thus enabling a superficial inspection of hull plates from the exterior. However, corrosion also progresses from the interior and only after most material is wasted interior damages can be detected from outside with conventional means. To make it worse, interior corrosion progresses mainly in areas impossible or almost impossible to see by bilge inspections. Interior 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 may be subject to corrosion be inspected on a regular basis.
To make things more complex, yacht hull exteriors are coated with fillers often applied thickly for fairing, antifouling paints and various other types of coatings.

Corrosion Measurement of Hull Plates with Ultrasonic Testing (UT)

Metal hull plate thickness assessment with ultrasound and without removing  fillers, paint layers or any coatings. To left: Olympus Epoch 650 Ultrasonic Flaw Detector spectrum on a progressively pitted aluminium hull plate.
Metal hull plate thickness assessment with ultrasound and without removing  fillers, paint layers or any coatings. To left: Olympus Epoch 650 Ultrasonic Flaw Detector spectrum on a progressively pitted aluminium hull plate. The distinct double hump (with summit to left) of this severe case would dissolve at less severe pitting into a single hump with “softened up left shoulder”. The hull plate section, as seen to right, will not reveal the pitting, for once, as the surface has been faired and coated and furthermore, as the interior is masked by tanks and other internal structures.

Metal plate thickness can be assessed with ultrasonic thickness gauges without removing  fillers, paint layers or any coatings and without any harm to them. However, these devices deduct minimum plate thicknesses by preset algorithms and may be misleading at times, in particular when attempting to assess pitted plates. An Ultrasonic Flaw Detector as we utilize in house, is by far superior to thickness gauges as it displays the ultrasonic echo spectrum. From waveform, attenuation and phase shifts, an experienced NDT surveyor can infer remarkable information about the plate and further structure under inspection. The experienced surveyor can also distinguish between true echoes and the many false reflections and diffractions and more.
We use the Olympus Epoch 650 Ultrasonic Flaw Detector, a state of the art digital flaw detector and Olympus Panametrics transducers for inspections. This state of the art instrument configuration is accepted and used in many disciplines, including the pipeline and aerospace industry. Our surveyors are trained regularly and both on job and theoretical and we keep our instruments calibrated and up to date. We have invested into numerous sound and flawed samples in order to have standards at hand for most of the issues we encounter.

(Please contact us here for a free Ultrasonic Inspection Quote.)

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