SECTION 3 

 COPPER ALLOYS 



The excellent corrosion resistance of copper and 

 its alloys is partially due to its being a relatively noble 

 metal. However, in rr.anv environments, its satisfac- 

 tory performance depends on the formation of 

 adherent, relatively thin films of corrosion products. 

 In seawater corrosion, resistance depends on the 

 presence of a surface oxide film through which 

 oxygen must diffuse in order for corrosion to con- 

 tinue. This oxide film adjoining the metai is cuprous 

 oxide covered with a mixture of cupric oxy-chloride, 

 cupric hydroxide, basic cupric carbonate, and calcium 

 sulfate. Since oxvgen must diffuse through this film 

 for corrosion to occur, it would be expected that 

 under normal circumstances the corrosion rates 

 would decrease with increase in time of exposure. 



Copper allovs corrode uniformly; hence, corrosion 

 rates calculated from weight losses and reported as 

 mils per year reflect the true condition of the alloys. 

 Therefore, corrosion rates for the copper alloys can 

 be used reliably for design purposes. However, this 

 does not apply to those copper base allovs which arc 

 susceptible to parting corrosion. (Parting corrosion is 

 defined as rne selective attack of one or more of the 

 components of a so! i solution allow) Examples of 

 parting corrosion arc dezincification, dealuminifica- 

 tion, denickelification, desiheonification, etc. 



The data on the copper alloys were obtained from 

 the reports given in References 3 through 19 and 23. 

 The copper alloys are separated into the different 

 classes of copper alloys (coppers, brasses, bronzes, 

 and copper-nickel alloys) for comparison and dis- 

 cussion purposes. 



The chemical compositions, corrosion rates and 

 types of corrosion, stress corrosion characteristics, 

 and changes in mechanical properties due to cor- 

 rosion of the coppers are given in Tables 10 through 

 13. The effects of duration of exposure are shown 

 graphically in Figures 8 and 15. 



The chemical compositions, corrosion rates and 

 types of corrosion, stress corrosion characteristics, 

 and changes in mechanical properties due to the cor- 

 rosion of the brasses are given in Tables 14 through 

 17. The effects of the duration of exposure are shown 

 graphically in Figures 11 and 15. 



i he chemical composr.ions, corrosion '-ate c and 

 types of corrosion, stress corrosion characteristics, 

 and changes in mechanical properties due to 

 corrosion of the bronzes are given in Tables 18 

 through 21. The effects of the duration of exposure 

 are shown graphically in Figures 12 and 15. 



The chemical compositions, corrosion rates and 

 types of corrosion, stress corrosion characteristics, 

 and changes in mechanical properties due to cor- 

 rosion of the copper-nickel alloys are given m Tables 

 22 through 25. The effects of the duration of 

 exposure are shown graphically in Figures 13 and 15. 



The effects of depth and the effect of the concen- 

 tration of oxygen in seawater on the corrosion of the 

 copper alloys are shown in Figures 9 and 14. 



The effect of the iron content on the corrosion of 

 the copper-nickel allovs is shown in Figure 14. 



3.1. COPPERS 



The chemical compositions of the coppers are 

 given : n Table 10. their corrosion rates and ^'pes of 

 corrosion in Table 11, their resistance to stress cor- 

 rosion cracking in Table 12, and the changes in their 

 mechanical properties due to corrosion in Table 13. 



3.1.1. Duration of Exposure 



The effects of the duration of exposure on the 

 corrosion of copper in seawater at depth, at the 

 surface, and in the bottom sediments are shown 

 graphically in Figure 8. At the surface and at the 

 6,000-foot depth, both in the seawater and in the 

 bottom sediment, the corrosion rates decreased with 

 increasing duration of exposure. At the 2,500-foot 

 depth the corrosion rates in the seawater and in the 

 bottom sediment were essentially constant. Also, the 

 corrosion rates were practically the same at depth as 

 at the surface. 



The beryllium-copper alloys behaved very 

 similarly to copper, and their corrosion rates were 

 comparable. Beryllium-copper chain corroded at the 



43 



