Creep–fatigue damage dissimilar metal welds of modified 9Cr–1Mo steel and 316L stainless steel.pdf

I/locate/ijfatigue International Journal of Fatigue 29 (2007) 1868–1879 Journalof FatigueCreep–fatigue damage for a structure with dissimilar metal welds of modified 9Cr–1Mo steel and 316L stainless steel Hyeong-Yeon Lee *, Se-Hwan Lee, Jong-Bum Kim, Jae-Han Lee Division of Mechanical Engineering, Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yusong-gu, Daejeon 305-353, Republic of Korea Received 15 September 2006; received in revised form 1 February 2007; accepted 5 February 2007 Available online 20 February 2007Abstract A creep–fatigue test with a structural specimen made of Mod. 9Cr–1Mo steel and 316L stainless steel has been carried out and the test results were compared with those of the evaluations by the high temperature design codes of ASME subsection NH and RCC-MR to quantify the conservatism. A specimen with a diameter of 500 mm, height of 440 mm and thickness of 6.3 mm was subjected to creep– fatigue loads with two hours of a hold time at 600 C and a primary nominal stress of 30 MPa. The creep–fatigue behaviours of the dissimilar metal welds as well as the similar metal welds were investigated and the results of the test were compared with the evaluation results. Bimetallic (direct) transition metal joint and trimetallic transition metal joint for a dissimilar metal weld were employed for a specimen, and their behaviours under a creep–fatigue load were compared. The conservatism of the design codes on the creep–fatigue evaluation at the welded joints as well as at the base metal with an emphasis on Mod.9Cr–1Mo steel are highlighted through comparisons with the results from the observation and the evaluation.  2007 Elsevier Ltd. All rights reserved. Keywords: Creep–fatigue; Damage; Dissimilar metal weld; Mod.9Cr–1Mo steel; 316L stainless steel1. Introduction Modified 9Cr–1Mo steel (ASME Grade 91) has been widely used for a high temperature structure such as a steam generator, intermediate heat exchanger and second- ary piping of a liquid metal