Chapter IV: Biofouling And Corrosion Study
(continued)

Results: Summary and Recommendations

1. Biofouling has created a uniform layer of stable hard fouling that covers most of the hull and superstructure remnants of USS ARIZONA. That layer maintains anoxic conditions near the exterior steel surfaces and encourages formation of stable black and grey iron oxides. Corrosion products on hull showed a moderate trend toward decreasing thickness as water depth increased.

2. Most rapid corrosion has occurred on superstructure surfaces located about 6 feet above and below sea level. In this high-oxygen and high-water motion zone, corrosion has caused extensive deterioration and exfoliation of steel surfaces.

3. Application of protective coatings (such as epoxy paints) to surfaces in the high-corrosion zone would probably not be practical because of their advanced state of deterioration. Proper prepainting preparation of such surfaces would entail removal of oxide products to a degree that would likely cause further structural weakening.

4. Corrosion damage did not appear significant in the few interior spaces examined. Water-quality environment and presence of hydrocarbons should maintain reduced rates of corrosion in interior volumes as long as water flushing in those spaces remains low.

5. Potential exists for a decline in abundance of live biofouling on the ship due to a projected long-term decline of nutrients (food) available for filter-feeders. It is recommended that biofouling be monitored at the permanent photostations (established in this survey) on an annual basis so that such an event could be detected.

6. The few areas on submerged superstructure and hull that are presently devoid of fouling should be mapped and monitored on at least an annual basis. How such areas form, and how (or if) biofouling recolonizes such surfaces, is not known at present.

7. Deck surfaces receive substantial protection from corrosion and wood-burrowing mollusks by a layer of sediment that varies considerably in thickness and composition. That layer would be expected to be less stable in the long term in shallow water, where higher water motion from waves can move sediments. Colonial feather-duster worms and sponges provide cohesiveness and stability to a large percentage of shallow sediments.

8. Sediment thicknesses on deck surfaces should be monitored on about an annual basis to determine if those layers are increasing or eroding. The status of organisms binding sediments in shallow water should also be examined periodically.

9. Fish-egg nest depressions should be monitored to determine their year-round abundance and effect on teak decomposition. If nesting activity is found to be a chronic problem, it may be possible to discourage Maomao fish (pomacentrids) from schooling and nesting in specific areas by closing off access to hatches and portholes that the fish use for protective cover. Those openings could be closed by plastic mesh glued in place with epoxy. Openings in one selected area could be closed first as a pilot experiment.

10. It was the general consensus of personnel involved in the present survey that areas where fouling growth had been removed in the course of sampling procedures should be covered to prevent rapid corrosion of those areas. Initially, areas where biomass scrapings were made were also to be used as areas where PVC flange/studs were to be attached. However, it was found that the epoxy did not bond to clean steel underwater, and use of those areas as attachment surfaces was abandoned. It is recommended that those scraped areas be covered with thin sheets of rigid plastic bonded to dead fouling surrounding the areas.

11. Information on the amount of steel thickness remaining at nearly all accessible locations on the ship would be very useful in determining more precisely the deterioration state of the USS ARIZONA. High priority should be given to efforts to locate and test nondestructive means of determining steel thickness. Ultrasonic techniques seem to have the best potential at present. Experts on the monitoring and prevention of long-term corrosion should be located and consulted for assistance in planning future studies and preventive measures.

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