TAILIEUCHUNG - Handbook Corrosion (1992) WW Part 11

Tham khảo tài liệu 'handbook corrosion (1992) ww part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Table 5 Plants affected by primary-side cracking Type of primary-side attack a Number of plants affected as of 1985 U-bend tangent cracks 16 Roll transition cracks 16 Roll expansion cracks 10 Explosive expansion transition cracks 1 Total number of plants affected 29 a Excluding those caused by denting Cracking in the U-bend has occurred mainly on the inner row at the apex and at the tangent points Fig. 32 . Cracks have also occurred in the tubesheet at transition expansion and roll expansion regions Fig. 33 . Apex cracking zone-assisted by denting or excess tube ovality in. Dented support plate cracking zone .750 in. Fig. 32 Location of cracking in steam generator inner row U-bends. 1 in. mm _ Cracking zone no denting irregular transition a I bỉ Fig. 33 Details of tubesheet expansion transition region. a Partial tubesheet expansion transition region. b Full tubesheet explosive hydraulic or roller expansion transition region Primary-side cracking is a form of intergranular SCC. This type of intergranular SCC in common with other forms of SCC occurs when certain environmental tensile stress and material susceptibility factors are sufficiently severe. Environmental factors influence the initiation of primary-side SCC of these temperature must be considered a major factor. The first roll transitions experiencing SCC were located on the hot leg side. Because the hot leg at 320 C 610 F is 30 to 40 C 55 to 70 F hotter than the cold leg at 280 C 535 F it would appear that temperature has a significant influence on SCC initiation indicating a thermally activated process. The reaction rate can be characterized by an Arrhenius factor exp -Q kT where Q is an apparent activation energy k is the Boltzmann constant and T is absolute temperature. Thus the influence of temperature can be graphically represented by an Arrhenius plot of .

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