USS ARIZONA MEMORIAL
Submerged Cultural Resources Study:
USS Arizona and Pearl Harbor National Historic Landmark
Chapter IV: Biofouling And Corrosion Study
Water Quality and Biofouling in Interior Spaces
Fouling growth observed on interior surfaces through portholes and other openings was composed largely of vermetid worms and oysters occurring in patchy distribution. Although large clumps of fouling were often common within a radius of a few feet inside hull and superstructure openings, fouling coverage was generally less than 50 percent on interior walls and ceilings. Fine sediment covered most wall areas not covered by fouling, and silt/mud layers estimated at several inches to several feet in thickness covered all upward-facing horizontal surfaces. Ceiling areas contained patchy fouling. Unfouled surfaces were often black and flossy in appearance, probably being coated by hydrocarbon (fuel and oil) residues.
It was not possible to visually determine the corrosion state of interior surfaces because of coverage of fouling, sediment and hydrocarbons. However, exfoliating corrosion layers were not observed on any surfaces in the spaces deeper than about 8 feet, suggesting that high rates of corrosion were not occurring in those areas.
As expected, oxygen levels measured 15 to 16 feet inside interior spaces were substantially lower than ambient values (Table 4.6). At distances of 8 to 9 feet inside openings, oxygen levels were only moderately lower than ambient, indicating that water volumes within about 10 feet of hull openings are relatively well flushed. Oxygen concentrations were at or less than 1 mg/l at 15-foot distance from opening in 3 out of 6 stations, thus it would be reasonable to assume that most other enclosed volumes in the hull that are distant from openings would also exhibit sub-1 mg/l oxygen concentrations.
Temperature and pH values measured in interior spaces were only slightly below ambient values. Those differences were not large enough to alter the corrosion or biofouling status of interior metal surfaces.
At the three midships stations (D, E and F), viscous black hydrocarbon residue was encountered while pumping at maximum probe insertions. Water samples collected at those times had a distinct volatile hydrocarbon fuel odor. Hydrocarbons were pumped in pulses when the intake end of the probe pipe was allowed to drop down and thus sample water closer to or at the bottom level of spaces. These heavy-fraction hydrocarbons are thus trapped in low stagnant areas of the ship and will likely persist in those areas for a long time.
Low oxygen and near-normal seawater pH values documented in the spaces sampled would be expected to reduce corrosion rates substantially below those that would exist in high-oxygen harbor water (ref. 2). The presence of viscous hydrocarbon compounds as coatings on steel surfaces would further reduce availability of oxygen. Furthermore, oxygen consumption by microbes digesting hydrocarbon products would be another process that may help maintain an oxygen-depleted environment in the ship's stagnant areas. Collectively, these anticorrosion factors would probably more than compensate for the scarcity of protective biofouling cover expected on interior substrates.
Table 4.6. Oxygen, pH and temperature measurements made inside hull openings shown in Figure 4.9. Units. 02 = mg/liter (ppm), pH = pH units, temperature = degrees centigrade.
LOCATION A -- Porthole about 3 feet below starboard gunnel. About even with aft end of No. 4 gun foundation. Depth = about 10 feet.
LOCATION B -- 25-foot depth inside No. 4 gun foundation "well."
LOCATION C -- Porthole about 3 feet below starboard gunnel. About even with forward end of No. 3 gun foundation. Depth = about 10 feet.
LOCATION D -- Porthole about 3 feet above starboard gunnel. About 5 feet aft of bio/photo station No.- VS18. Depth = about 10 feet.
LOCATION E -- Open inspection hatch on main deck near starboard gunnel. Below location D. Depth = about 13 feet. Opening extends downward on vertical axis.
LOCATION F -- Fourth porthole aft of location D on starboard side.- Immediately below Arizona Memorial structure. Depth = about 10 feet.
Last Updated: 27-Apr-2001