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Microbiologically Induced Corrosion |
10/24/2009 11:51:10 AM
We had been keeping the schooner in the water year round and hauling for each 5 year drydock inspection as required by the Coast Guard - all with no problems. The bottom had been sandblasted, a series of marine primers, finish coats of antifouling etc all applied to manufactures specs. Divers had periodically examined the bottom and reported no problems.
In August of this year, we sailed to Sodus Point (see attachment) for a haulout/inspection. To our surprise we found the bottom covered with blisters under which were pits some up to 3/16" deep in the 1/4" plate! The Coast Guard inspector had never seen or expected this. A metallurgy lab examined photos, took water samples from the Oswego dock area ( a former drydock), conducted Electron Microscope scans of the hull samples etc, etc. and confirmed that the damage was due to Microbiologically Induced Corrosion (MIC). The identified microbes (bacteria) use iron/steel as an energy source by converting the iron/steel into soluble forms, resulting in the pits. They recommended not docking in a stagnant water area (the drydock), application of specialized coatings to isolate the steel such as epoxy, and frequent haulouts and seasonal out of the water storage.
Similar problems have occurred worldwide whenever stagnant conditions exists - in pipe, tanks, docks, sheet piling etc. The Port Of Duluth reportedly has a major corrosion in their docks due to MIC.
We have removed over half of the damaged plates and are preparing the frames for new plate some of which is already on hand. On the plus side, we will install a bow thruster to aid in reducing crew tension ! and we will install separate tanks for water, fuel, waste, etc to replace the integral tanks that were a part of the lower hull but were difficult to service and inspect.
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