A witness to progress

I was in a position to see the origin of ultrasonic thickness testing on ships and the progressive development of access to the critical locations for measurements. It all started for me in 1961 in the USA.

Access was by scaffolding, which was slow and expensive. Measurements were taken by drilling a hole and using a feeler gauge to make a physical measurement. The next forward step was to obtain the measurement by resonance ultrasonic thickness measurement, which needed a ground and polished surface and required scaffolding.

When pulse-echo ultrasonic thickness measurements became sufficiently developed to provide an acceptable accuracy, measurements could then be obtained by chipping scale to bare metal and having the technician climb the existing support structure within the tank. This also freed the inspection function from the shipyard and permitted gauging surveys ‘at sea’ on ballast voyages, with repair estimates possible prior to dry-docking.

This process continued from 1962 through the turn of the century, with the addition of safety requirements and alternative processes. The idea of filling the tanks slowly with water and floating in an inflatable raft as the level rose was popular both alongside and at sea. The ‘at sea’ segment was eliminated when there was a fatal accident due to wave motion acceleration within the tank. There was also the danger of gases becoming more concentrated as the water filled more space and compressed the remaining gas.

Another process was temporarily popular. The tanks were completely filled and a diver equipped with a video camera and an ultrasonic transducer, with coaxial cable taped to the air hose, was able to obtain thickness readings at the desired locations. The UT operator topside could verify the location of the reading from the video. This also provided a recording of the visual condition of all inspection areas and satisfied classification societies’ requirements for ‘close-up’ inspection. This method, although effective, fell victim to excessive cost.

So, it was inevitable that the advent of the drone provided a safe process for conducting the ‘close-up’survey and at least two surveys have been conducted to show the viability of the process.

On 2 September 2015, it was reported that Poland’s Remontowa shipyard had recently used a drone to inspect the internal spaces in a 51,747 dwt chemical product tanker.

The ship, the UK-flagged LR-classed CPO Japan is owned by Claus-Peter Offen Reederei, headquartered in Hamburg, Germany, and was delivered in 2009 by a South Korean shipbuilder. It arrived at Remontowa on 15 June for its first five-year class renewal overhaul.

The tests with the drone were carried out inside one of the ship’s cargo tanks. The drone, which is equipped with a high-definition camera (with its own lighting), capable of recording HD video and still pictures, was able to access all parts of the tank. It was even able to rest against the bulkhead, while hovering. The contact with the tank wall is possible as the drone’s propellers are protected by special shrouding.

“The drone demonstrated excellent stability in a confined space, allowing for good quality visual inspection material recording,” said a spokesperson for Remontowa. The drone is intended to provide a surveyor with an overall impression of the state of the hull and bulkheads of a vessel under inspection. The technology may also be applied to the inspection of external structures, such as masts of deck crane jibs. The drone serves as a means of visual inspection, mainly for surface (protective coating) condition assessment, for example corrosion and crack detection. In many cases, visual inspection results may rule out the necessity of conducting more detailed ‘hands-on’ inspection, such as ultrasound thickness measurements, etc, thus allowing to refrain from time-consuming setting up of the scaffoldings, which in turn saves time.

All that is needed now is to add a UT thickness capability and a recording ability, but it would not surprise me if that has not already happened! And ships’ structures are only one of the large numbers of applications where drones can replace scaffolding or more dangerous access techniques on offshore platforms, refinery structures and in numerous other applications!

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