Miscellaneous Alloys 



Columbium, tantalum and tantalum-tungsten alloy Ta60 were uncor- 

 roded. However, magnesium alloy FS-1 was practically disintegrated 

 after one year of exposure in seawater. 



The corrosion of lead (antimonial chemical and tellurium) , tin, 

 zinc, lead-tin solder, molybdenum and tungsten were not depth dependent. 



The corrosion rates of lead, tin, lead-tin solder, molybdenum and 

 tungsten decreased with the concentration of oxygen in seawater while 

 that of zinc was not dependent on the oxygen concentration. 



The corrosion rate of molybdenum decreased with increasing time of 

 exposure in seawater at the surface while that of tungsten increased. 



CONCLUSIONS 



Seawater at depth in the Pacific Ocean at the NCEL test sites was 

 more aggressive to aluminum alloys than was seawater at the surface 

 after one year of exposure, except for 5086-H34 alloy whose corrosion 

 rate was slightly lower at depth. 



In general, the corrosion rates and maximum pit depths of the 

 aluminum alloys increased with decreasing oxygen concentration of sea- 

 water. 



Aluminum alloys, because their modes of corrosion are the localized 

 pitting and crevice types, must be protected for seawater applications 

 if reasonable service life is desired. In general, aluminum alloys 

 could not be recommended for deep sea applications for periods longer 

 than three years if protective maintenance cannot be performed. 



In most cases the copper base alloys corroded either at the same ' 

 rates or slightly slower rates at depth than at the surface in seawater. 

 Copper base alloys which are susceptible to dezincification and dealumi- 

 nification are not recommended for seawater service. The other copper 

 alloys corroded uniformly and can be recommended for seawater service 

 where their low corrosion rates can be tolerated. 



The nickel base alloys which were not corroded in seawater can be 

 recommended for seawater applications. 



Nickel base alloys susceptible to crevice corrosion are not recom- 

 mended for seawater applications unless satisfactory precautions can be 

 taken to prevent this type of attack. 



The use of welded nickel alloys for seawater applications can be 

 recommended only for those alloys which are not preferentially attacked 

 in either the weld beads or the adjacent heat affected zones or both. 



Steels and cast irons, because they corrode uniformly, can be rec- 

 ommended for seawater applications and their reliability can be increased 

 by the use of adequate protective measures. 



The stainless steels, because of their susceptibility to crevice, 

 pitting and tunnel corrosion, are not recommended for seawater applica- 

 tions. Alloys 309, 316L, 317, 329, 633, 20Cb-3 and Ni-Cr-Mo-Si could 

 be used for limited applications of not more than one year if adequate 

 protective measures are used. 



15 



