The Welded joint strength reduction factors of modified 9Cr-1Mo Steel for the advanced loop-type sodium cooled fast reactor

次世代高速炉における改良9Cr-1Mo鋼の溶接継手低減係数

山下 拓哉  ; 若井 隆純 ; 鬼澤 高志  ; 佐藤 健一郎*; 山本 賢二*

Yamashita, Takuya; Wakai, Takashi; Onizawa, Takashi; Sato, Kenichiro*; Yamamoto, Kenji*

Modified 9Cr-1Mo steel (ASME Gr.91) is widely used in fossil power plants. In the advanced loop type sodium cooled fast reactor, modified 9Cr-1Mo steel is going to be adopted as a structural material. In welded joints of enhanced creep-strength ferritic steels including modified 9Cr-1Mo steel, creep strength may markedly degrade, especially in the long-term region. This phenomenon is known as Type-IV damage. Therefore, considering strength degradation due to Type-IV damage is necessary. In this study, we propose a creep strength curve and a welded joint strength-reduction factor (WJSRF). The creep strength curve of welded joints was proposed by employing a second-order polynomial equation with LMP using the stress range partitioning method. WJSRF was proposed on the basis of design creep rupture stress intensities. The resulting allowable stress was conservative compared with that prescribed in the ASME code. In addition, the design of the hot-leg pipe in the advanced loop type sodium cooled fast reactor was reviewed considering WJSRF.