Corrosion resistance of certain strength wires used in small fiber-optic cables exposed to seawater

Abstract

Theoretical analyses and the results of corrosion tests on fiber-optic cables with different strength wires and designs are used to evaluate the suitability of the cables as candidates for use on the sea bottom. The strength wires in the cables were made of certain Inconel, stainless steel, and steel alloys and had diameters ranging from 0.008 to 0.015 in. The materials, coatings, and distribution of the wires are reviewed to evaluate their effects on cable failure modes and survivability in seawater applications on the ocean bottom. The initial, final, and average corrosion rates of the candidate cable wires and losses in cable tensile breaking strength over test periods of several months are compared. Wire corrodability, seawater corrosivity, and corrosion mechanisms are discussed, along with the relative importance and contributions of dissolved oxygen, dissolved-oxygen distribution, and crevices. Corrosion of as-received cable samples, of single cable wires, and of cable samples with jackets damaged as might be expected during installation and service life are compared and discussed. Analytical predictions of the cable loss in tensile breaking strength and experimentally measured tensile breaking strengths, including range and amount of loss, are presented. Finally, a basis is discussed for recommending wires made of Inconel 625 over wires made of 316L stainless steel. Nitronic 50 stainless steel, galvanized steel, or ungalvanized steel.