tailieunhanh - Handbook Corrosion (1992) WW Part 9

Tham khảo tài liệu 'handbook corrosion (1992) ww part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | However corrosion engineers have determined that the best measure of the potential corrosivity of a given soil is its electrical resistance measured in ohms per cubic centimeter. The electrical resistivity of the soils is determined by the nature and concentration of the ions formed by the chemical salts dissolved in the soil moisture. These ions may also determine the progress of corrosion. If the primary product of corrosion is relatively insoluble and deposits as a film on the metal surface further corrosion may be reduced or completely stifled. Numerous inspections of existing structures have established that in sandy and loamy soils with resistivity of 4500 cm and higher the engineer need not be concerned with the corrosion on the soil side of galvanized steel pipe Table 13 . Table 13 Relationship of soil corrosion to electrical resistivity Soil Class Corrosion resistance Electrical resistivity í ỉvm Sandy Excellent 6000-10 000 Loams Good 4500-6000 Clays Fair 2000-4500 Peat muck Bad 0-2000 When the engineer wishes to confirm his judgment of service life requirements or when the corrosion and abrasion aspects of the proposed site may be in question reference to the California Division of Highways method for determining service life is recommended. This comprehensive method uses measurable environmental corrosion criteria and is applicable to all parts of the country. The California method correlates pH with the electrical resistivity of soils to determine the number of years necessary to perforate a galvanized steel sheet. For example an engineer considering a typical site environment with a resistivity of 10 000 cm and pH of 7 can refer to Fig. 4 and determine that it would take 40 years to perforate 16-gage or . galvanized steel pipe. Minimum resistivity 11 cm Fig. 4 Method of estimating service life as developed by the California Division of Highways. This correlates pH with the electrical resistivity of soils to determine years to perforate a