tailieunhanh - INSPECTION, EVALUATION AND REPAIR OF HYDRAULIC STEEL STRUCTURES Episode 2

Tham khảo tài liệu 'inspection, evaluation and repair of hydraulic steel structures episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-6054 1 Dec 01 failure of the paint system adjacent to the contact area of the two steels and decreases as the distance from the metal junction increases. d Stray current corrosion may occur when sources of direct current . welding generators are attached to the gate structures or unintended fields from cathodic protection systems are generated. e Filiform corrosion occurs under thin paint films and has the appearance of fine filaments emanating from one or more sources in random directions. 3 Three types of mechanically assisted corrosion are also possible in hydraulic steel structures. a Erosion corrosion is caused by removal of surface material by action of numerous individual impacts of solid or liquid particles and usually has a direction associated with the metal removal. The precursor of erosion corrosion is directional removal of the paint film by the impacting particles. b Cavitation corrosion is caused by cavitation associated with turbulent flow. It can remove surface films such as oxides or paint and expose bare metal producing rounded microcraters. c Fretting corrosion is a combination of wear and corrosion in which material is removed between contacting surfaces when very small amplitude motions occur between the surfaces. Red rust is formed and appears to come from between the contacting surfaces. c. Factors influencing corrosion. The type and amount of corrosion that may occur on a hydraulic steel structure are dependent on many factors that include design details material properties maintenance and operation environment and coating system. In general the primary factors are the local environment and the protective coating system. 1 The pH and ion concentration of the river water and rain are significant environmental factors. Corrosion usually occurs at low pH highly acidic conditions or at high pH highly alkaline conditions . At intermediate pH a protective oxide or hydroxide often forms. Deposits of film-forming materials such as oil

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