REMAINING LIFE PREDICTION BY THE ISO-STRESS METHOD OF BOILER TUBES AFTER PROLONGED SERVICE
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概要
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The prediction of remaining creep life by the Iso-stress method was investigated for 153500 h service-exposed boiler stubes of 1.25Cr-0.5Mo-Si, 2.25Cr-1Mo and 9Cr-1Mo steels. At first, the internal pressure creep rupture strength of the service-exposed tube specimens of the steels was shown to be the same as the tensile creep rupture strength of the sheet specimens taken from the tubes. Then the temperature-accelerated creep rupture tests under iso-stress were carried out by the tensile creep rupture tests, because of simplicity of the tests. The Iso-stress method was verified for the virgin specimens of the steels by comparing the predicted long-term rupture times as long as 10^5 h with the data in the NRIM Creep Data Sheets. The predicted rupture times agreed with the observed data within a factor of 2 or 3. The temperature-accelerated tests of the sheet specimens taken from the service-exposed tubes showed that the linear extrapolation of the rupture times to the service temperature gave the remaining creep rupture life of about 8 x 10^5 h for the 1.25Cr-0.5Mo-Si steel and about 1.6 x 10^6 h for the 2.25Cr-1Mo steel. However, the Iso-stress method could not be applied for the 9Cr-1Mo steel, because the log t_r versus T curve was not linear, where t_r is the creep rupture time and T is the testing temperature. It is concluded that the Iso-stress method is useful when the significant microstructural change does not take place during accelerated creep rupture tests at high temperatures.
- 1997-03-15
著者
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Yagi Koichi
Environmental Performance Division National Research Institute For Metals
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Abe F
Steel Research Center National Institute For Materials Seienee
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Abe Fujio
National Institute Of Materials Science
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Abe Fujio
Structural Metals Center National Institute For Materials Science
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OHBA Taiji
Materials Science and Engineering Department, Shibaura Institute of Technology
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OHBA Toshio
Environmental Performance Division National Research Institute for Metals
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KANEMARU Osamu
Environmental Performance Division National Research Institute for Metals
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Ohba Taiji
Materials Science And Engineering Department Shibaura Institute Of Technology
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SHIMIZU Masaru
Environmental Performance Division, National Research Institute for Metals
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MIYAZAKI Hideko
Environmental Performance Division, National Research Institute for Metals
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ABE Fujio
Environmental Performance Division, National Research Institute for Metals
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Miyazaki Hideko
Environmental Performance Division National Research Institute For Metals
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Shimizu Masaru
Environmental Performance Division National Research Institute For Metals
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