This paper proposes provisional welded joint strength reduction factors (WJSRF) of modified 9Cr-1Mo steel (ASME Gr.91) applicable to the structural designing of “Japan sodium cooled fast reactor (JSFR)”. In the welded joints of creep strength enhanced ferritic steels including modified 9Cr-1Mo steel, creep strength may obviously degrade especially in long-term region. This phenomenon is known as “Type-IV” damage. The authors had proposed provisional allowable stress for the welded joints made of the steel in PVP 2010 conference, taking creep strength degradation due to “Type-IV” damage into account. Available creep rupture data of the welded joints made of the steel provided by Japanese steel venders were collected. The temperature range was from 500 to 650°C. The database was analyzed by stress range partitioning method. The creep rupture data were divided into two regions of short-term and long-term and those were individually evaluated by regression analyses with Larson Miller Parameter (LMP). The difference in the creep failure mechanisms between short-term and long-term regions is taken into account in this method. Boundary between these regions was half of 0.2% proof stress of the base metal at corresponding temperature. First order polynomial equation of logarithm stress was applied. For conservativeness, allowable stress was proposed provisionally considering design factor for each region. JSME (Japan Society of Mechanical Engineers) published a revised version of the elevated temperature design code in last year. Modified 9Cr-1Mo steel was officially registered in the code as a new structural material for sodium cooled fast reactors. The creep rupture curve for the base metal of the steel was standardized by employing stress range partitioning method, same as for the welded joint. However, second order polynomial equation of logarithm stress was applied in the analysis for the base metal. In addition, the creep rupture data obtained at 700°C were included in the database and data ruptured in very short term, i.e. smaller than 100 hours, were excluded from the analysis. Thus, there are some differences between the procedures to determine the creep rupture curves for base metal and welded joint made of modified 9Cr-1Mo steel. This paper discusses the most feasible procedure to determine the creep rupture curve of the welded joint of the steel by performing some case studies to focus on physical adequacy and harmonization with the determination procedure of the creep rupture curve for the base metal. Then, the WJSRF are provisionally proposed based on the design creep rupture stress intensities. In addition, the design of JSFR pipes was reviewed taking WJSRF into account.
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ASME 2013 Pressure Vessels and Piping Conference
July 14–18, 2013
Paris, France
Conference Sponsors:
- Pressure Vessels and Piping Division
- Nondestructive Evaluation Engineering Division
ISBN:
978-0-7918-5567-6
PROCEEDINGS PAPER
A Study for Proposal of Welded Joint Strength Reduction Factors of Modified 9Cr-1Mo Steel for Japan Sodium Cooled Fast Reactor (JSFR)
Takashi Wakai
,
Takashi Wakai
Japan Atomic Energy Agency, Oarai, Ibaraki, Japan
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Takashi Onizawa
,
Takashi Onizawa
Japan Atomic Energy Agency, Oarai, Ibaraki, Japan
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Takehiko Kato
,
Takehiko Kato
Ascend Co. Ltd., Tokai, Ibaraki, Japan
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Shingo Date
,
Shingo Date
Mitsubishi Heavy Industries, Ltd., Nagasaki, Japan
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Koichi Kikuchi
,
Koichi Kikuchi
Mitsubishi Heavy Industries, Ltd., Kobe, Japan
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Kenichiro Satoh
Kenichiro Satoh
Mitsubishi FBR Systems, Inc., Tokyo, Japan
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Takashi Wakai
Japan Atomic Energy Agency, Oarai, Ibaraki, Japan
Takashi Onizawa
Japan Atomic Energy Agency, Oarai, Ibaraki, Japan
Takehiko Kato
Ascend Co. Ltd., Tokai, Ibaraki, Japan
Shingo Date
Mitsubishi Heavy Industries, Ltd., Nagasaki, Japan
Koichi Kikuchi
Mitsubishi Heavy Industries, Ltd., Kobe, Japan
Kenichiro Satoh
Mitsubishi FBR Systems, Inc., Tokyo, Japan
Paper No:
PVP2013-97091, V003T03A105; 8 pages
Published Online:
January 17, 2014
Citation
Wakai, T, Onizawa, T, Kato, T, Date, S, Kikuchi, K, & Satoh, K. "A Study for Proposal of Welded Joint Strength Reduction Factors of Modified 9Cr-1Mo Steel for Japan Sodium Cooled Fast Reactor (JSFR)." Proceedings of the ASME 2013 Pressure Vessels and Piping Conference. Volume 3: Design and Analysis. Paris, France. July 14–18, 2013. V003T03A105. ASME. https://doi.org/10.1115/PVP2013-97091
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