小型パンチ(SP)試験法ならびに電気化学的再活性化法(EPR)によるオーステナイト系ステンレス鋼の材質経年劣化診断技術

概要

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The fracture toughness of austenitic stainless steels decreases so drastically after 5〜10 years long time service operation at the temperature of 550〜850 ℃ due to grain boundary embrittlement. In this study, therefore, an appropriate NDE procedure of the material characterization of SUS 316H and SUS 321H used as boiler superheater tubes was developed by means of Small Punch test and EPR method. A significant transition behavior from ductile to brittle intergranular fracture was observed in SP energy for the degraded materials, whereas no DBTT for the nondegraded ones. Moreover EPR method was applied to detect the grain boundary embrittlement due to sensitization or σ phase formation in austenite stainless steel. The relation between the material degradation and EPR results was also obtained. Based upon these experimental calibrations of material degradation and NDE parameters, a realistic periodic NDE procedure for austenitic stainless boiler tubes has been proposed.
1987-03-15