Allowable Stress and Allowable Flaw Sizes Estimated by Converted Tensile Properties from Hardness for Austenitic Stainless Steel Pipe

オーステナイト系ステンレス鋼配管の硬さから換算した引張特性による許容応力評価

河 侑成  ; 山口 義仁 ; 長谷川 邦夫; Negyesi, M.*

Ha, Yoosung; Yamaguchi, Yoshihito; Hasegawa, Kunio; Negyesi, M.*

If a flaw in a high-toughness ductile pipe of a power plant is detected during periodic in-service inspection, stress applied at the flaw location of the pipe is compared with an allowable stress. When the applied stress is less than the allowable stress, the plant can operate continuously for a certain evaluation period in accordance with ASME Code Section XI. The flow stress given by the average of yield strength and ultimate tensile strength is an important material parameter for allowable stress. Recently, many fitness-for-service codes and technical reports have adopted conversions from hardness measurement values to yield strength and ultimate tensile strength. In this paper, we introduced the flow stress obtained from converted tensile properties from Vickers hardness using the presented equations for austenitic stainless steel. The allowable stress estimated by the Vickers hardness was compared with the allowable stress determined by actual tensile properties. As a result, the flow stress converted from hardness was about 1.48 times larger than that obtained by actual flow stress. The allowable flaw sizes calculated by the flow stress converted from hardness gave an appropriate indication when the allowable or applied stress was very low. However, the flow stress converted from hardness gave unconservative allowable stress, when the applied stress was large.