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Sulfur isotope fractionation was demonstrated in corrosion products resulting from the activities of sulfate-reducing bacteria within biofilms on copper surfaces. 32S accumulated in corrosion products, while 34S was concentrated in the culture medium due to fractionation. The accumulation of the lighter isotope was related to surface derivatization or corrosion as measured by weight loss.

Microbial colonization of metals (zirconium, chromium, niobium, tantalum, molybdenum, tungsten, and type 4340 steel [UNS G43400]) and susceptibility of these metals to microbiologically influenced corrosion by sulfate-reducing bacteria was investigated. Environmental scanning electron microscopy characterization after 12 months and 21 months showed patchy biofilms on all metals except tungsten. Weight loss after 24 months for zirconium and niobium were either nonexistent or negligible, indicating that these metals did not experience MIC under the test conditions.

Fungi were isolated and identified in ten aircraft that had been operating in marine tropical environments. Distribution and growth of fungi depended on availability of water and nutrients. Laboratory experiments demonstrated that surface washes, including the approved military maintenance procedure, were ineffective in removing fungal hyphae embedded in polyurethane coatings. Surface cleaning removed spores and discoloration associated with fungi, but fragments of the hyphae remained and grew as soon as conditions were favorable. Aged coatings fouled more rapidly than new coatings. Fungicides incorporated into the topcoats produced mixed results. Bare aluminum suffered localized corrosion when colonized by fungi.

Due to seawater intrusion and moisture accumulation, corrosion of antenna foundations/ship's super-structure has been observed and was attributed to galvanic corrosion of the aluminum with the silver-based conductive caulk used for electromagnetic interference/ electromagnetic pulse (EMI/EMP) conductivity between the antennas and the ship's super structure. Several conductive caulks and sealants were field tested and evaluated to determine if the environment would degrade their performance, for the prevention of seawater intrusion, and to prevent potential failures due to corrosion. A nickel-based conductive caulk with a corrosion inhibitor (PRC 1764) performed well in all of the field tests over a period of 15 months. Because of the excellent corrosion resistance, adequate EMI/EMP and shielding characteristics, the nickel-loaded caulk with a corrosion inhibitor has been recommended for antenna applications. Among the sealants, GE RTV 157, GE RTV 167 and Product Research Corporation ProSeal 870 polysulfide performed well. GE RTV 157 is already in use for topside applications and its use is being continued. Three conductive caulks (PRC 1764, PI 8500, PI 8505) were applied to 4140 steel coupons. Caulked coupons were exposed to five mixed, microbial cultures in the laboratory for 15 months. At the end of the exposure period, environmental scanning electron microscopy (ESEM) analyses were used to demonstrate that bacteria including sulfate-reducing bacteria (SRB) were found under the conductive caulks. In laboratory testing, there was water and bacterial intrusion which resulted in corrosion of the steel under the conductive caulk. The laboratory caulked samples were not covered with a sealant such as RTV as described previously for the field test samples.

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