• Class approved underwater hull repairs in Europe and Africa

    Class approved underwater hull repairs in Europe and Africa

    09/03/2012

    Flying all across the world Hydrex diver/technician teams have carried out numerous underwater insert and doubler plate repairs over the last couple of months. Besides the larger repairs discussed in our previous magazines (and found on our website) a lot of smaller underwater hull repairs were also carried out. Despite the relative size of these operations they are nonetheless vital for shipowners if they want to avoid unscheduled drydock visits for their vessels.

    Insert repair in Cameroon
    In Douala, Cameroon, Hydrex diver/technicians performed an insert repair on the stern area of a 70-meter accommodation ship. Together with the repair they also carried out a full underwater survey of the vessel and installed new sacrificial anodes on the stern area. Combining several jobs without causing any unnecessary delay is part of the service Hydrex offers. Our divers are trained to perform a wide range of procedures; they stay in close communication with each other and with the technical department in the office, throughout the operation. This allows them to finish the entire job within the shortest possible timeframe and this without any compromise of the high quality standards Hydrex is known for.

    Multiple doubler plates installed on two roro vessels in Belgium
    Close to the Hydrex headquarters a total of six damaged areas on the hull plating of the ballast tank of a 160-meter roro vessel were covered with the same number of doubler plates during the ship’s stay in Antwerp, Belgium. The doubler plates ranged in size from 200 x 350 mm to 900 x 370 mm and were installed by Hydrex certified welders according to the Hydrex class approved procedures. This temporary repair allowed the shipowner to keep his vessel in service and on schedule until the next scheduled drydocking.

    Also in Antwerp a Hydrex diver/technician team performed a full underwater inspection and carried out a rudder crack repair as well as the installation of a doubler plate on the shell plating of a 216-meter roro vessel. The team first performed the underwater inspection and ground away the crack on the corner of the rudder blade. Next they made arrests on both sides of the 300-mm crack in the shell plating on the starboard side of the vessel and welded up the crack. This was done to prevent it from spreading any further. A doubler plate was then installed over the crack with the approval of the Rina class surveyor who was present during the entire operation.

    Underwater hull repair on tanker in France
    The Hydrex cofferdam technique was used to reinforce the weld seams of a leaking doubler plate that had been installed in drydock on a 183-meter tanker. The operation took place in Marseille. An inspection carried out by the Hydrex diver/technician team revealed that there was a hole in the weld seam and cavitation damage was present in another area. Grinding out the damaged weld and replacing it was therefore the best solution. The team installed a cofferdam over the waterside of the affected area and then removed the weld seam over a length of 500 mm. Next they re-welded the seam to the approval of the present ABS surveyor, finishing the repair.

    Insert repair in Setubal, Portugal
    A Hydrex diver/technician team installed a 640 x 300 mm insert in the bottom shell plating of a 266-meter bulk carrier during the vessel’s stay in Setubal after a 350-mm crack was found in the ship’s hull plating. After the team installed a cofferdam over the underwater side of the crack they cut away the affected area. Next they prepared the edges of the hole and installed the new insert with a full penetration weld. This was done under the supervision of the LR surveyor present during the operation. The insert repair was then successfully tested by an ultrasonic testing operator.

    Two hull repairs for the same owner
    In the same port five doubler plates were installed to cover the same number of cracks found in the flat bottom area of a 130-meter bulk carrier. To prevent the cracks from spreading further, the Hydrex diver/technician team first drilled crack arrests. Next they fitted the doubler plates and welded them with a full penetration weld. The meet the DNV class requirements, extra brackets were installed on the largest doubler plate (measuring 1400 x 800 mm). The vessel could then sail safely until the next scheduled drydocking where permanent repairs would be carried out.

    The same owner asked Hydrex to perform a permanent insert repair on another of his vessels, a 113-meter bulk carrier which was also under DNV classification. This operation was carried out in Tarragona, Spain. A 720-mm crack was found on the vertical side of the port side ballast tank as well as a 2400-mm crack on the longitudinal frame in the same location. Heavy corrosion damage was also discovered around both cracks. Because the damage was located in a high stress region, a specially designed cofferdam was installed over the affected area. A 2400 x 400 mm plate was then cut away and replaced with a new insert. After the insert had been secured, ultrasonic testing showed the repair to be successful.

    The owner of these vessels was very satisfied with the operations as they allowed him to keep the schedule of both ships.

    Underwater insert repair on bulk carrier in Ghent
    A 330 x 480 mm insert was installed in the flat bottom plate of a 225-meter bulk carrier during the ship’s stay in Ghent, Belgium. Once the area was declared gas free, the diver/technician team positioned and secured a cofferdam over the outboard side of the damage. Next they cut away the frames covering the damage and removed a plate the exact size as the new insert. After the insert had been secured with full penetration welding and approved by the present Lloyd’s Register surveyor, the team reinstalled the frames. This concluded the operation.

    Summary
    Repairs of this kind can only be done rapidly and successfully by trained divers/technicians who are familiar with them and who have the relevant know-how to resolve all of the technical difficulties encountered during underwater operations. This is why all Hydrex technical staff from all offices undergo stringent training after which they are able to perform a wide range of operations. They can achieve the same high quality without loss of time.

    To offer the fastest possible service to customers, Hydrex offices have fast response centers where an extensive range of state-of-the-art tools and diving support equipment is available at all times for the repair teams. These fast response centers enable Hydrex to mobilize diver/technician teams immediately to any location around the world.

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