sediment after 403 days of exposure were much lower than those after 

 other times of exposure at the 6,000 foot depth, Table 7 and Figures 

 5, 6, 7, 8, 9, 12, 15 and 16, These low corrosion rates are attributed 

 to a rather passive sediment at this location; i.e., very little if 

 any sulfate reducing bacteria. This assumption is substantiated by 

 the large population of wood borers and the presence of many deep-sea 

 sponges found at the water-sediment interface which require oxygen to 

 live and reproduce. 



The performance of the copper-zinc alloys in sea water at the 

 2,500 and 6,000 foot depths is summarized in Figure 17 and in the 

 bottom sediments at these depths in Figure 18. 



Except for Muntz metal and manganese bronze the corrosion rates 

 for the copper-zinc alloys at the 6,000 foot depth decreased with 

 increasing time of exposure and could be encompassed within a rather 

 narrow band as shown in Figure 17. The width of the band decreased 

 from 1,2 MPY after 123 days of exposure to 0,6 MPY after 1064 days of 

 exposure. The dotted curve within this band is for copper for compari- 

 son purposes; showing that after 1064 days of exposure the copper-zinc 

 alloys corrode at rates which are within + 0.3 MPY of that of copper. 

 The curves above this band are for Muntz metal and manganese bronze 

 both of which were dezincified to considerable degrees. Two other 

 points, both for nickel-manganese bronze, were outside this band and 

 are attributed to dezincif ication. The band encompassing the corrosion 

 rates for the copper-zinc alloys at the 2,500 foot depth indicate that, 

 in general, they were constant with time and were lower than the cor- 

 rosion rate for copper. These bands also show that the corrosion rates 

 of the copper-zinc alloys in sea water at depths of 2,500 feet and 6,000 

 feet were comparable, except for Muntz metal and manganese bronze. 



Most of the corrosion rates for the copper-zinc alloys in the 

 bottom sediments at the 6,000 foot depth can be conveniently encompass- 

 ed within a band whose width is about 1.2 MPY after 123 days of expos- 

 ure which narrows to 0.5 MPY after 1064 days of exposure as shown in 

 Figure 18. The average corrosion rates decrease from 1.0 MPY after 123 

 days of exposure to 0.6 MPY after 1064 days of exposure. The dotted 

 corrosion rate curve for copper bisects this band with the copper-zinc 

 alloy corrosion rates being slightly higher than that for copper after 

 1064 days of exposure. The curve above the band is for manganese bronze 

 which suffered considerable dezincif ication. The other points outside 

 this band are for manganese bronze and nickel-manganese bronze which 

 also were dezincified. The small band for the alloys in the bottom 

 sediments at the 2,500 foot depth shows quite clearly that in addition 

 to the corrosion rates being low, they were essentially constant with 

 time . 



A comparison of the bands for the copper-zinc alloys at the 6,000 

 foot depth shows that after 1064 days of exposure they were corroding 

 at essentially the same rates in sea water and in the bottom sediments. 

 However, at the 2,500 foot depth the corrosion rates in sea water were 

 higher than those in the bottom sediments. 



