報告書番号

Q11025

タイトル（和文）

単相流および二相流条件での水化学が配管減肉挙動へ及ぼす影響

タイトル（英文）

Effects of water chemistry on wall thinning behavior in single - phase and two - phase flow

概要 （図表や脚注は「報告書全文」に掲載しております）

FACに及ぼすDOの影響をFAC試験により評価した。この結果、FAC停止に必要なDO濃度は、140℃中性条件（pH25℃7）では、40～60 ppb以上、アルカリ性条件（pH25℃ 9.2）では10 ppb以上であり、pH25℃ 7においてFAC停止後に、再びFACが発生するDO濃度は10ppb以下であることを明らかとした。また、単相流のH2Oが、質量保存の状態で二相流（均質流）となった際の液膜のNH3濃度を算出した。これにより、二相流の液膜pHが求まり、これまでに開発したFAC速度予測評価式を二相流条件に適用することを可能とした。

概要 （英文）

It is very important for the wall thickness management and the prevention of FAC of the feed water piping in the commercial power plants to clarify the flow accelerated corrosion (FAC) phenomenon. In the previous study, we proposed a FAC model taken into consideration the diffusion of dissolved species. Effect of dissolved oxygen (DO) on the FAC should be clarified to verify the model. In the steam and steam extraction line, the distribution behaviors of volatile agents are not exactly clear. The NH3 concentration in the liquid film under the gas–liquid two phase flow condition has been required.
In this study, the effects of DO on FAC rates were evaluated. FAC were suspended by DO more than 40 to 60 ppb and more than 10 ppb under neutral (pH25 ºC 7) and alkaline condition (pH25 ºC 9.2) at 140 ºC, respectively. FAC of the specimen in neutral solution were redeveloped when DO were decrease to less than 10 ppb after FAC was suspended by DO injection.
NH3 concentration in the liquid phase of the gas–liquid two phase flow was calculated. The homogeneous flow model, the mass balance of H2O and NH3 was taken into consideration in the calculation. This calculation brings pH value of the liquid film at two phase flow. The FAC model became applicable to the two phase flow condition.

報告者

キーワード