13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 8. Schematic illustration of corrosion fatigue mechanism in sour crude oil environment[Ebara et al.[37]]. Note: *1) SCO:Sour Crude Oil *2) HEZ; Hydrogen Embrittlement Zone *3) PZ; Plastic Zone lower stress level drastic reduction of corrosion fatigue strength may be anticipated. The long term corrosion fatigue test is expected to conduct in lower stress level. 4. Concluding remark This paper has briefly summarized hydrogen effect on fatigue crack initiation behavior of structural materials. In aggressive gas such as H2S, CO2 and SO2 in steam, humid air and aqueous solution corrosion fatigue crack initiation from corrosion pit reduce corrosion fatigue strength of structural materials. Under these environments it is stressed that corrosion pit initiated at fatigue crack initiation area drastically reduced fatigue strength of structural steels. On the contrary, in sour crude oil environment hydrogen from reaction of steel with H2S accelerated corrosion fatigue crack propagation rate of steels. It can be concluded that hydrogen effect on corrosion fatigue crack initiation in sour crude oil is still veiled. For safety use of structural materials in hydrogen environment prevention of fatigue crack initiation is indispensable. Definite fatigue crack initiation mechanism in hydrogen environment is expected to propose. In order to evaluate the hydrogen related fatigue life of the structural components more precisely the following studies are recommended to investigate. 1) Microscopic crack initiation mechanism with dislocation motion 2) Quantitative evaluation of the relation between the plastic zone and hydrogen embrittlement zone size at the fatigue crack tip 3) Hydrogen effect onΔKth and near ΔKth region in da/dN 4) Hydrogen resistant materials to prevent fatigue crack initiation References [1] R.Ebara,Hydrogen effect on fatigue strength of structural steels, Key Engineering Materials,261-263(2004)1251-1256.
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