報告書番号

Q10018

タイトル（和文）

還元性硫化腐食における高温腐食挙動に及ぼす雰囲気ガス組成の影響（その3）－実機材料温度範囲における腐食量評価指標の提案－

タイトル（英文）

The Influence of Gases Composition to Corrosion Behavior in Reducing Atmosphere Including H2S (vol.3) -proposal of an indicator for evaluating the amount of corrosion of STBA24 in material temperature range from 723K to 823K-

概要 （図表や脚注は「報告書全文」に掲載しております）

実機使用材の一つである低合金鋼（STBA24）の試験片に対して電気炉による静止場ガス腐食試験を実施した結果、以下のことが明らかとなった。
1. PO2とPS2の相関図内での腐食量評価指標と腐食領域区分
材料温度450℃と550℃でも、500℃と同様に、実機で想定されるPO2とPS2の範囲を、腐食量評価指標の異なる領域Ⅰ、Ⅱ、Ⅲの3領域に区分できることがわかった。また、腐食領域境界線は、材料温度の変化によりPO2とPS2の相関図内を平行に移動するが、異なる材料温度でも腐食領域と実機想定範囲の相対関係は維持されることがわかった。
2. 領域ⅠにおけるSO2濃度とH2S濃度の相関図内での腐食量評価指標と腐食領域区分
いずれの材料温度でも、領域Ⅰでは、腐食量に対するSO2濃度およびH2S濃度変化の影響が見られる。この領域Ⅰは、材料温度450℃と550℃でも、500℃と同様に、腐食量評価指標の異なる領域Ⅰ-A、Ⅰ-B、Ⅰ-Cの3領域に区分できることがわかった。一方で、材料温度が高いほど、腐食量に対してSO2濃度とH2S濃度が影響する範囲（領域Ⅰ-B、Ⅰ-C）が広くなることがわかった。
以上のことから、450℃から550℃の温度範囲における腐食量評価指標が明らかとなり、任意の温度と任意の雰囲気での腐食形態を予測できるようになった。

概要 （英文）

To obtain an indicator for evaluating the amount of corrosion of water wall tube materials in a coal-fired boiler, we investigated the influence of pseudo-partial pressures of oxygen (PO2) and sulfur (PS2), which are calculated from the equilibrium gas composition at the combustion temperature (about 1573K) and the equilibrium constant at the tube surface temperature (about 773K) on the amount of corrosion of Fe-2.25wt.%Cr-1wt.%Mo (STBA24) alloy at 723K and 823K in N2-CO-CO2-H2-H2O-H2S-SO2 mixed gases. As a result, it was clarified that there are three regions in the PO2- PS2 plane in which the corrosion behaviors are different in a coal combustion atmosphere. (Region I: in this region, Fe sulfide is mainly formed and the amount of corrosion cannot be evaluated using only PO2 and PS2 because the effect of H2S or SO2 concentration significant. Region III: in this region, the amount of corrosion can be evaluated using only PO2 and PS2, and Fe oxide is mainly formed. Region II: transition region between the above two regions). Next, we investigated the effect of H2S and SO2 concentration on the amount of corrosion of STBA24 at 723K and 823K in N2-CO-CO2-H2-H2O-H2S-SO2 mixed gases. As a result, it was clarified that the amount of corrosion and the scale structure were not affected by concentrations of H2S and SO2 when they were high concentration. In contrast, under the condition of low SO2 concentration or low H2S concentration, the amount of corrosion was affected by the concentrations of SO2 and H2S. Therefore, it appears that the concentrations of SO2 and H2S are necessary to evaluate the amount of corrosion in this range. These corrosion behaviors at the material temperature of both 723K and 823K are very similar to behavior at the material temperature of 773K. As mentioned above, in the material temperature range from 723K to 823K, the corrosion behavior in a coal combustion atmosphere of STBA24 was clarified and indicators for evaluating the amount of corrosion were able to be proposed.

報告者

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