manner conducive to crevice attack, i.e., proximity of adjacent wires 

 and inner sides form crevices, this places a severe limitation on the 

 long-term use of stainless steel outer strength members in electro- 

 mechanical cables. Those stainless steel wires in or under the jacket 

 may be acceptable. Some stainless steel alloys are, however, superior 

 to others in corrosion resistance. The following table shows the extent 

 of tunnel corrosion (crevice-type attack which forms a tunnel-like 

 failure along the surface starting at the edge or crevice) which occurred 

 after one year of exposure at a water depth of 2,340 feet. 



MSI Type Extent of Tunnel Attack 



302 6 inches long 



304 2 inches long 



316 .5 inch long 



It must be remembered that the corrosion of stainless steels is highly 

 unpredictable and non-uniform. Some exposed areas will exhibit no cor- 

 rosion while similarly exposed adjacent areas will exhibit severe attack. 

 The corrosion on stainless steels in seawater is usually not evident for 

 the first few months of exposure, but then proceeds at an increasing 

 rate. Constant abrading action on stainless steels can actually improve 

 their corrosion resistance; however, due to the construction of strength 

 members, complete exposure like complete protection is impossible to 

 achieve. 



Due to the nature of the corrosive attack on stainless steel by sea- 

 water, its use in electro-mechanical cable is not recommended. Jacketing, 

 unless 100 percent protection is assured, is ineffective in the mitigation 

 of such attack. 



For E-M cable strength members with required lifetimes in excess of 

 ten years, alloys which do not corrode to any measurable extent in sea- 

 water are available. These alloys are: nearly all titanium alloys, 

 nickel alloy Inconel 625*, and nickel alloy Hastelloy "C"*. These 

 materials have been fabricated into wire ropes and their high cost may 

 be justified for many operations. 



Table II-3 is an outline of the relative strengths, corrosion 

 resistances and costs of the wires described in this section. 



^Trademarks of IN CO and Cabot Corporation. 



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