報告書番号

T94033

タイトル（和文）

アルカリ水溶液中におけるインコネル６００合金のＩＧＡ／ＳＣＣ発生予測の検討

タイトル（英文）

EVALUATION OF IGA/SCC INITIATION FOR INCONELALLOY 600 IN ALKALINE SOLUTION

概要 （図表や脚注は「報告書全文」に掲載しております）

熱交換器用の初期の伝熱管材料に用いられているインコネル６００ＭＡ合金および熱処理を改善した中期の伝熱管材料６００ＴＴ合金の耐粒界腐食／応力腐食割れ（ＩＧＡ／ＳＣＣ）発生試験を行い、以下の知見を得た。１．６００ＭＡ合金および６００ＴＴ合金を用いアルカリ環境中においてＩＧＡ／ＳＣＣ発生評価試験を実施し、試験時間とＩＧＡ／ＳＣＣ発生の累積確率の関係を求めた。統計解析の結果、６００ＴＴ合金それ自身の耐ＩＧＡ／ＳＣＣ発生時間は、６００ＭＡ合金の数倍程度と評価された。２．熱処理および支持構造の改善に伴う６００ＴＴ合金の耐ＩＧＡ／ＳＣＣ発生は、両改善効果の重畳により古い支持構造の６００ＭＡ合金の９倍以上と評価された。

概要 （英文）

PLANT OPERATING HISTORIES AND TUBE DEGRADATION DATA ON INTERGRANULAR ATTACK/STRESS CORROSION CRACKING (IGA/SCC) IN PWR STEAM GENERATORS (SG) WERE COLLECTED. STATISTICAL ANALYSES WERE PERFORMED TO PROVIDE A METHOD FOR EVALUATING SCC TUBE DEGRADATION RATES. THE RESULTS SHOW THAT IGA/SCC DEGRADATION OF MILL-ANNEALED ALLOY 600 (600MA) TUBES IS DESCRIBED BY THE WEIBULL DISTRIBUTION FUNCTION. ON THE OTHER HAND, LABORATORY TESTS WERE PERFORMED TO DEVELOP A PREDICTION METHOD FOR IGA/SCC OF ALTERNATIVE SG TUBES BY COMBINING TUBE DEGRADATION RATE DATE OF PLANTS AND LABORATORY TEST DATA. IGA/SCC TESTS ON 600 MA AND THERMALLY-TREATED ALLOY 600 (600TT) WERE CONDUCTED IN ALKALINE SOLUTIONAT 320 DEGREE USING THE C-RING TEST METHOD. THE DATE FOR TEST TIME ANDCUMULATIVE FRACTION FAILED WERE PLOTTED ON WEIBULL PAPER. THE ADJUSTABLE PARAMETERS OF WEIBULL DISTRIBUTION (SLOPE, SCALE PARAMETER) WERE DETERMINED. STATISTICAL ANALYSIS SHOWED THAT THE TUBE DEGRADATION RATE OF 600 TT WAS 1.77 TIMES SLOWER THAN THAT OF 600 MA. IN ADDITION, TAKING INTO ACCOUNT THE LOWERING OF IMPURITY CONCENTRATIONS BY IMPROVING SUPPORT PLATE STRUCTURE (FROM DRILLED TYPE TO BROACH-QUATREFOIL TYPE) THE DEGRADATION RATE OF 600 TT ALLOY WAS ABOUT 9 TIMES SLOWER THAN THAT OF 600MA ALLOY.

報告者

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