Corrosion Resistance of Several Conductive Caulks and Sealants from Marine Field Tests and Laboratory Studies with Marine, Mixed Communities Containing Sulfate-Reducing Bacteria (SRB)

Abstract

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.