404 



9 

 seawater, and its pH was reported in the results section to be between 13 and 

 13-5. This is consistent with other measurements reported for the pH of 

 seawater in concrete . The corrosion rate of the steel on the inner surface 

 of the container should, therefore, have been negligible and corrosion should 

 have proceeded from the outside only. The difference that this can make is 

 illustrated by the fact that the steel container was in the worst condition 

 around the rim at the concrete end where the steel extending beyond the 

 concrete by about two centimeters was exposed to ambient pH seawater on both 

 sides. The perforated condition of the steel in that area was shown in 

 Figure 6. 



The corrosion rate of steel in seawater is not usually influenced 

 significantly by the presence (or absence) of microorganisms. The one 

 noticeable exception to this is in anaerobic bottom sediments where the 

 corrosion rate of steel normally is negligible. If sulfate reducing bacteria 

 are present, however, they allow the formation of a loosely adherent FeS scale 

 on the steel which is cathodic to the bare metal surface '. This produces 

 a galvanic couple which accelerates the corrosion of the steel and is 

 accompanied by hydrogen evolution. The excellent condition of the portions of 

 the recovered drum that were buried in the sediments testifies that sulfate 

 reducing bacteria were probably not active in sediments in the recovery area. 

 This view is also supported by the negative result of the microscopic 

 investigations reported in the results section. If sulfate reducing bacteria 

 had been active, we should have been able to detect them in the corrosion 

 products. 



