Hydrex Cofferdam

Hydrex Case Study - Underwater insert repair in Rotterdam

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Measuring and marking the exact area that needed to be removed.

A 130-meter chemical tanker suffered erosion damage in the grey water tank. Hydrex was contacted by the owner to provide an underwater solution that would allow the vessel to keep her schedule. A team of Hydrex diver/technicians therefore mobilized to Rotterdam to perform on-site repairs.

This type of smaller damage is created over time as the result of the recurring impact of for instance water on the exact same spot over and over again. On vessels this occurs regularly in the ballast tanks under bell mouths or sounding pipes as was the case with the chemical tanker.

If the damage is caught before the hull plates are perforated, clad welding can be used to fill up the area. This is also a permanent repair that will avoid a condition of class. During the operation in Rotterdam this was no longer an option as a hole had formed in the hull plating.

A fast, permanent solution

The divers started the operation by installing a cofferdam on the waterside of the affected plating. Next they removed the sounding pipe covering the area on the inside. They could then safely remove a plug which had been installed as a temporary solution. The damaged plating was then cleaned and prepared for the operation.

As agreed with the classification society, the team then cut away an area measuring 300 x 300 mm. Next they prepared the edges of the hole for the insert and positioned the new plate. The insert was then welded following the Hydrex class-approved procedure for insert plates, using a full penetration weld.

An independent inspector carried out ultrasonic testing and the repair was approved by the classification surveyor who was present during the operation. The team then reinstalled the sounding pipe and removed the cofferdam.

A small round doubler plate was installed under the pipe to prevent the new insert from eroding again.

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New plate insert seen from the waterside.
Photo Credits Hydrex

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