Feature: Corrosion repair to stern seal shaft areas

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Mark Specialist Applications was called out by Cammell Laird shipyard to repair corroded surfaces on both stern shaft seal areas of a ship after a problem was found during drydocking.

The repair work was not expected nor planned until the moment the rope guards were removed and the extent of erosion/corrosion became apparent.
The dry docking period wasn’t a particularly long one on this occasion, and the project time available to complete a high-quality repair was minimal.  Considerations needed to be given to the time needed for the final cure of the products used as the vessel needed to undock on schedule.
Upon inspection of the stern seal areas, it was evident that there were a number of contributing factors which had led to the erosion of the surfaces. The erosion was due to high sand content waters and galvanic corrosion following the use of dissimilar metals, which was compounded by highly corrosive salt water. This had caused pitting and surface loss of up to 12mm depth in certain areas. 
Alternative repair methods, such as puddle welding were considered. However, it was decided this was not an option because the risk of heat near to the rubber seals made this unviable and the undocking schedule time made it impractical.
Repair process 
Mark Specialist Applications provided a specification which included abrasive blast cleaning of the stern seal areas and application of Resimac 201 Ceramic Repair Paste. The repair paste was applied by brush and applicator to rebuild the eroded surface profiles. The use of heat via three phases sped up the curing process, which allowed the build-up of ceramic paste layers.
 Upon post curing for around four hours, two coats of Resimac 202 Ceramic Repair Fluid were applied to further protect the repair by brush and applicator, and heaters were reinstalled to further post cure the materials.
The rope guards were reinstalled, and the vessel undocked on schedule some 24 hours later, to the delight of the shipyard and the ship owners.
The key benefits of using a specialist contractor and the Resimac 200 series products is years of experience in the marine industry, in depth knowledge, 24/7 availability, longevity in service and most of all, cost and time saving.
The same vessel recently drydocked in July 2019, and upon inspection the repairs were found to be in near perfect condition following almost 30 months’ service – the ship owner was extremely pleased with this outcome.
Whilst it was drydocked, Mark Specialist Applications was asked by the ship owner to carry out a sweep blast to the existing coating. Minimal repairs were then carried using the Resimac 201 product, and a new topcoat of Resimac 202 was applied to offer further protection for the coming years. It was agreed with the vessel’s technical team that the next inspection wouldn’t be until July 2021, when the next drydock is due.
The 200 series products, manufactured in the UK by Resimac, are two-component solvent-free epoxy repair materials that are ideal for rebuilding and resurfacing metallic surfaces subjected to sea water erosion and corrosion. The products have been approved by Bureau Veritas for cold repairs to surface vessels, and have been used in the global marine market for over 10 years.

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