Cathodic Protection of Carbon Steel Pipes Affected by Microbial Corrosion in Different Soil Texture

Abstract

Study had been done at Tikrit University/ College of Science/ Biology Department/ Environment Laboratory, from September/2014 to June/2015 . This study was done on carbon steel pipes and those pipes with diameter 1.75 inch were cut in to 38 pieces with a length of 20cm with nearly the same weight (The carbon steel pipes and the donor Aluminum had been measured with a balance that is so accurate up to 3 decimal fractions).Soil samples were taken from three different regions which are: Altun Kopry/ Kirkuk (Soil 1, Loamy sand), Tikrit University (Soil 2, Sandy Loam) and Al- Siniya/ Baiji/ Tikrit (Soil 3, Sand) and these three samples were taken from depth 0-50 cm. The results showed that the highest value of electric conductivity was (28.13 ms/cm) in dry soil 3, while the lowest value was (19.19 ms/cm) in wet soil 3 . As a mean, soil texture has a significant effect on electric conductivity, whereas the highest value of electric conductivity was (23.66 ms/cm) in soil 2, while the lowest value was (20.77 ms/cm) in soil1. The highest value of organic matter was (6.216 %) in dry soil 2, while the lowest value was (2.358 %) in wet soil 3. As a mean, soil texture has a significant effect on organic matter, whereas the highest value of organic matter was (5.706 %) in soil 2, while the lowest value was (2.720 %) in soil 3. Cathodic protection has a significant effect on decreasing corrosion rate, whereas the corrosion of protected pipe was (1.462 %) while the corrosion of the pipe buried in the same circumstances but without protection was (11.267%). The presence of Pseudomonas aeruginosa bacteria caused corrosion, microbiological analysis showed that biofilm are formed as microcolonies, which subsequently caused corrosion shows the role of Pseudomonas aeruginosa , Enterobacter sp. ,and Staphylococcus aureus bacteria these three types of bacteria oxidize the iron that means it is corrosive.