exposed to seawater. Corrosion rates of bright steel are initially in 

 the range of from .003 inch to .008 inch per year during the first year 

 of exposure. This rate decreases with time to a range of from .001 inch 

 to .005 inch per year after three years. Thus, the percentage of origi- 

 nal breaking strength remaining after exposure is primarily dependent on 

 the original wire diameter and time of exposure. The cross-sectional 

 area and, thus, the breaking strength of a large wire is less affected 

 than that of a small wire when equal losses of diameter are experienced. 

 Abrasion of the wires during exposure can greatly increase the corrosion 

 rate of carbon steel. In fact, exposure to constant abrasion like that 

 of sand in the surf zone can cause corrosion rates as high as several 

 inches per year. 



The corrosion of carbon steel wires in electro-mechanical cables 

 can be mitigated in several ways. The most obvious is to isolate the 

 wires from the seawater by some type of protective jacket. However, in 

 cables of practical length, complete protection is rarely, if ever, 

 achieved because of permeable materials, cracks and access of water at 

 terminations. Also, abrasion can expose the underlying wires and allow 

 corrosion to occur. Carbon steel wire will corrode at such exposed areas 

 at the same rate as unprotected cable if the exposed areas are large and 

 at a reduced rate if the exposed areas are very small, say, due to pin 

 hole imperfections in the jacketing. Coatings of anodic metals can also 

 effectively mitigate the corrosion of carbon steel wires. They have an 

 advantage over inert jacketing in that their protection can extend over 

 small distances even when breached by defect or damage. 



The most common type of anodic metal coating is hot dip galvanizing. 

 In this process the wires are passed through a molten zinc bath which 

 coats the wires with a complex zinc-iron alloy which is anodic to the 

 underlying steel wire. Normal coating thicknesses of .0005 inch to .002 

 inch can prevent corrosion of the wires for periods of up to two years, 

 depending on coating thickness. However, the process reduces the 

 strength of the wires by approximately 20 percent. After the coating is 

 corroded or abraded away, the underlying carbon steel wire will corrode 

 at the same rate as uncoated wire. 



Another common type of anodic coating is hot dip aluminizing. Simi- 

 lar to galvanizing, aluminizing protects the steel wire with a complex 

 aluminum-iron coating which is anodic to the underlying wire. Aluminized 

 coatings are normally thinner than galvanized coating (.0003 inch to .001 

 inch versus .0005 inch to .002 inch) but have similar lifetimes and 

 properties. They, too, reduce the strength of the wire. 



Hot dip coated carbon steel wires of usual diameter (.030 inch) can 

 be expected to last from three to five years with less than a 50 percent 

 loss in breaking strength. Jacketing of similar wires will increase their 

 lifetime to four to six years. 



Anodic coatings, either aluminum or zinc, applied by electroplating 

 methods have the advantage of not affecting the strength of the material 

 coated. However, due to their composition and porosity they are poor 

 substitutes for the hot dip applied coatings. 



All stainless steels are subject to crevice corrosion in seawater. 

 Since the strength members in an E-M cable will normally be exposed in a 



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