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Research Papers: Materials and Fabrication

Evaluation of Creep Strength Reduction Factors for Welded Joints of Grade 122 Steel

[+] Author and Article Information
Yukio Takahashi

 Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken 240-0196, Japanyukio@criepi.denken.or.jp

Masaaki Tabuchi

 National Institute of Materials Science, 1-2-1 Sengen, Tsukuba-shi, Ibaraki-ken 305-0047, Japantabuchi.masaaki@nims.go.jp

J. Pressure Vessel Technol 133(2), 021401 (Feb 09, 2011) (5 pages) doi:10.1115/1.4002678 History: Received March 17, 2009; Revised September 11, 2009; Published February 09, 2011; Online February 09, 2011

HCM12A (ASME Grade 122) is used for boiler components in thermal power plants because of its high creep strength. However, a type IV creep damage formed in the heat-affected zone can cause a considerable decrease in the creep strength of the weldment and a failure of large diameter piping due to this damage took place recently in a thermal power plant. In order to update the design method and develop life estimation method for this kind of piping system with axial weld, the creep rupture data of base metal and welded joints have been collected and analyzed by the Strength of High-Chromium Steel Committee in Japan. In the present paper, the creep rupture data of over 400 points for welded joint specimens of HCM12A offered from six Japanese organizations are analyzed. These data clearly indicate that the long-term creep strength of the welded joints becomes weaker than that of the base metal at above 600°C due to the type IV fracture in the fine grain heat-affected zone. After the discussions on the effects of product form, welding procedure, specimen sampling procedure, etc., on the creep strength, the master creep life equation for the welded joints is developed. The so-called region decomposition technique was adopted to fit the data in both high and low stress regimes with a reasonable accuracy. The creep strength reduction factor obtained from 100,000 h creep strength of the welded joints and the base metal is given as a function of temperature.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison of creep rupture data of HCM12A base metal and welded joint

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Figure 2

Comparison of creep strength of welded joints made by different welding procedures (650°C)

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Figure 3

Stress versus rupture time relationship, including rupture location (600°C)

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Figure 4

Relationship between rupture time and reduction of area (600°C)

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Figure 5

Result of regression for all data by one equation

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Figure 6

Result of regression for selected data by one equation

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Figure 7

Result of independent regressions for two regions

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Figure 8

Comparison of WSRFs

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Figure 9

Comparison of inner pressure creep strength with master curves

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