TAILIEUCHUNG - Handbook Corrosion (1992) WW Part 2

Tham khảo tài liệu 'handbook corrosion (1992) ww part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | mean resistivities of less than 2000 cm and a mean redox potential more negative than 400 mV on the normal hydrogen scale corrected to pH 7. Soils that were borderline based on these two tests tended to be aggressive if their water content was over 20 . With regard to redox potential alone soil corrosivity varied as follows Ref 48 Soil E. Corrosivity 100 mV Severe 100-200 mV Moderate 200-400 mV Slight 400 mV Noncorrosive Other attempts to assess the risk of corrosion by SRB have been sporadic. One investigation attempted to assess the severity of the SRB hazard on the inside of submarine pipelines carrying North Sea crude oil by measuring both the numbers of SRB present in the oil and the activity or vigor of growth of the organisms Ref 49 . The risk was assessed as extreme if both the numbers of organisms and their activity were rated high and the risk was considered to be minimal if both were rated low. Efforts to solve the anaerobic iron and steel corrosion problem as outlined in Ref 48 include Replacing the iron or steel with noncorrodible materials such as fiberglass PVC polyethylene and concrete Creating a nonaggressive environment around the steel by backfilling with gravel or clay-free sand to encourage good drainage that is oxygenating to suppress SRB making the environment alkaline or using biocides in closed industrial systems Using cathodic protection although potentials of V versus Cu CuSO4 or even more negative are often required at these potentials the risk of hydrogen cracking or blistering should be assessed Using various barrier coatings some with corrosion inhibitors and or biocides Aerobic Corrosion. Corrosion of iron and steel under oxygenated conditions generally involves the formation of acidic metabolites. The aerobic sulfur-oxidizing bacteria Thiobacillus can create an environment of up to about 10 H2SO4 thus encouraging rapid corrosion. Other organisms produce organic acids with similar results. This corrosion can be localized or .