Influence of Data Scattering on Estimation of 100,000 hrs Creep Rupture Strength of Alloy 617 at 700 °C by Larson–Miller Method

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Fujio Abe ◽  
M. Tabuchi ◽  
M. Hayakawa
Keyword(s):  
Regression Analysis ◽  
Rupture Strength ◽  
Large Data ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Alloy 617 ◽  
Time To Rupture ◽  
Reciprocal Temperature ◽  
Rupture Data ◽  
C Value

The 100,000 hrs creep rupture strength of Alloy 617 at 700 °C is estimated by Larson–Miller method using the rupture data of longer duration than 500 hrs in the temperature range between 593 and 816 °C, corresponding to 700 ± 100 °C. The maximum time to rupture was 40,126.7 hrs. The rupture data exhibit large scattering, especially at 760 °C. After eliminating the shorter time to rupture data at 760 °C, the regression analysis gives us the Larson–Miller constant C = 12.70 and the 100,000 hrs creep rupture strength of 100 MPa at 700 °C, by Swindeman program. The present regression analysis underestimates the constant C and 100,000 hrs creep rupture strength. The linear extrapolation of log tr versus reciprocal temperature 1/T plots to 1/T = 0 gives us an average C value of Cav = 18.5, which is much larger than the constant C of 12.70 obtained by the Swindeman program. It is concluded that the origin of underestimation of the constant C and corresponding 100,000 hrs creep rupture strength is large data scattering. Using an appropriate constant C of 18.45, the 100,000 hrs creep rupture strength at 700 °C is estimated to be 123 MPa. Using the rupture data including the shorter time to rupture data at 760 °C and using C = 18.45, the 100,000 hrs creep rupture strength at 700 °C is estimated to be 116 MPa.

Statistical Modeling of Creep Rupture Data

1999 ◽  
Vol 121 (3) ◽  
pp. 264-271 ◽  
Author(s):  
R. B. Davies ◽  
R. Hales ◽  
J. C. Harman ◽  
S. R. Holdsworth
Keyword(s):  
Statistical Modeling ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Confidence Limits ◽  
Creep Rupture Strength ◽  
Statistical Research ◽  
Modeling Framework ◽  
Failure Times ◽  
Rupture Data ◽  
Model Improvement

A flexible statistical modeling framework for the analysis of creep rupture data is proposed, which offers an improvement on traditional methods of deriving creep rupture strength values and confidence limits. The paper reviews a family of models that can be used to represent the trend relationship between failure times about the trend line, and examines the reliability of extrapolations. Areas of statistical research which would lead to model improvement are discussed, such as variance heterogeneity, left censoring and allowance for the cluster (cast) structure of the data.

Evaluation of Long-Term Creep Strength of Welded Joints of ASME Grades 91, 92 and 122 Type Steels

2012 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Takuaki Matsumura ◽  
Katsuaki Hoshino
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Strength Reduction Factor ◽  
Rupture Data ◽  
Term Creep

Creep rupture data of welded joints of ASME Grades 91, 92 and 122 type steels have been collected and long-term creep rupture strength of the materials has been evaluated. Similar study was conducted by the SHC Committee in 2004 and 2005, therefore, the evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained after the previous study, in addition to discussion of the effects of product form, welding procedure and test temperature etc. on the creep strength. Almost the same results were obtained on the welded joint of Grade 92 as the previous study, however, the master creep life equations for the welded joints of Grades 91 and 122 were lower than the previous results, especially in the case of Grade 122. Furthermore, the creep strength reduction factor obtained from 100,000 hours creep strength of welded joints and base metal was given as a function of temperature.

Long-Term Creep Rupture Strength of Individual Heats and Restriction of Al Concentration in 304HTB and 316HTB Stainless Steels for Gen IV Application

2014 ◽  
Author(s):  
Fujio Abe
Keyword(s):  
Rupture Strength ◽  
Nitrogen Concentration ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Available Nitrogen ◽  
Time To Rupture ◽  
Using Data ◽  
Gen Iv ◽  
Term Creep

The long-term creep rupture strength has been investigated for 9 heats of JIS SUS 304HTB (18Cr-8Ni) and for 9 heats of JIS SUS 316HTB (18Cr-12Ni-Mo) steels at 600 to 750 °C, using data in NIMS Creep Data Sheets. The heats with high Al exhibit the significant degradation in creep strength at long times. The formation of AlN and TiN during creep reduces the beneficial effect due to nitrogen. The heat-to-heat variation in time to rupture is analyzed using available nitrogen concentration Nav, which is defined as the concentration of nitrogen free from AlN and TiN, and also using nitrogen to soluble Al ratio (N/sol Al). The Nav clearly explains the observed heat-to-heat variation in time to rupture of 304HTB and 316HTB at long times. The precipitation hardening due to fine NbC carbides and the effect of small amount of Cu cause additional heat-to-heat variation in time to rupture for 304HTB at short times and for 316HTB at long times, respectively. The restriction of soluble Al concentration is proposed to be below 0.038 and 0.033 mass % for 304HTB and 316HTB, respectively, so that the creep rupture strength of 304HTB and 316HTB is larger than the ASME Sec.III-NH values for up to 300,000 h at 650 to 700 °C. At long times above 300,000 h, such as 500,000 h, the concentration of soluble Al should be further lowered.

Re-Evaluation of Long-Term Creep Strength of Base Metal of ASME Grade 91 Type Steel

2016 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Masatsugu Yaguchi
Keyword(s):  
Rupture Strength ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Creep Data ◽  
High Chromium ◽  
Rupture Data ◽  
Assessment Committee ◽  
Grade 91 ◽  
Term Creep

Creep rupture strength of ASME Grades 91, 92, 122 and 23 type steels were evaluated by the SHC committee in 2004 and 2005, and the Assessment Committee on Creep Data of High Chromium Steels in 2010. According to the evaluation of creep rupture strength, allowable stress of the steels was revised and weld strength reduction factor (WSRF) was established. In 2015, the creep rupture data of those steels was collected from materials producers, power plant manufacturers and institutes in Japan and a review of long-term creep rupture strength of the steels was conducted by the Assessment Committee on Creep Data of High Chromium Steels in reference to the previous evaluation. It has been confirmed with the latest dataset that re-evaluation of long-term creep rupture strength is not required for Grades 92, 122 and 23 type steels. On the other hand, lower creep rupture strength compared with the previous evaluation was recognized on the new creep rupture data of Grade 91 steels, therefore, re-evaluation of creep rupture strength was conducted on Grade 91 steels. Creep rupture strength was assessed by means of region splitting analysis method in consideration of 50% of 0.2% offset yield strength, in the same way as the previous study. According to the evaluation of long-term creep strength of the steels, allowable tensile stress was reviewed and proposed revision was concluded.

Region Splitting Analysis on Creep Strength Enhanced Ferritic Steels

2007 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Hideaki Kushima ◽  
Kota Sawada ◽  
Yoshiaki Toda
Keyword(s):  
Creep Strength ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Ferritic Steels ◽  
Creep Rupture Strength ◽  
Delta Ferrite ◽  
Time To Rupture ◽  
Term Creep ◽  
Region Splitting

Overestimation of long-term creep strength of creep strength enhanced ferritic steels is caused by inflection of a relation between stress and time to rupture. Creep rupture strength of those steels has been re-evaluated by a region splitting analysis and allowable tensile stress of some steels regulated in METI (Ministry of Economy, Trade and Industry) Thermal Power Standard Code in Japan has been reduced. A region splitting analysis method evaluates creep rupture strength in the short- and the long-term individually, which is separated by 50% of 0.2% offset yield stress. Inflection of stress vs. time to rupture curve is attributable to longer creep rupture life with a stabilized microstructure of creep strength enhanced ferritic steels, since tensile strength property, which determines short-term creep rupture strength, remains the same level. Accuracy of creep rupture strength evaluation is improved by region splitting analysis. Delta ferrite produces concentration gap due to difference in equilibrium composition of austenite and ferrite at the normalizing temperature. It increases driving force for diffusion and promotes recovery of tempered martensite adjacent to delta-ferrite. Concentration gap may be produced also in heat affected zone (HAZ), especially in fine grain HAZ similar to that in dual phase steel, and it has possibilities to promote recovery and, therefore, to decrease creep strength.

Evaluation of Long-Term Creep Strength of ASME Grades 91, 92, and 122 Type Steels

2012 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Yukio Takahashi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Rupture Strength ◽  
Nickel Content ◽  
Creep Rupture ◽  
Tube Steel ◽  
Creep Rupture Strength ◽  
Rupture Data ◽  
Term Creep

Creep rupture data of ASME Grades 91, 92 and 122 type steels have been collected and long-term creep rupture strength of the steels has been evaluated. Similar study was conducted by the SHC committee in 2004 and 2005, therefore, the evaluation of long-term creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained after the previous study. Creep rupture strength was analyzed by means of region splitting analysis method in consideration of 50% of 0.2% offset yield strength, in the same way as the previous study. Almost the same results were obtained on base metal of Grade 92 as the previous study, however, evaluated 100,000 hours creep rupture strength of base metal of Grades 91 and 122 were lower than the previous results. For Grades 91 and 122 type steels, moreover, creep rupture strength of the plate steel were lower than those of pipe and forging steels. Tendency to decrease with increase in nickel content was observed on long-term creep rupture strength of tube steel of Grade 91 at 600°C. According to the evaluation of long-term creep strength of the steels, allowable tensile stress was reviewed and proposed revision was concluded.

Evaluation of Stress Rupture Factors for Grade 91 Weldments

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Kazuhiro Kimura ◽  
Masatsugu Yaguchi
Keyword(s):  
Base Metal ◽  
Rupture Strength ◽  
Stress Rupture ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Premature Failure ◽  
Rupture Data ◽  
Grade 91 ◽  
Grade 91 Steel

Abstract Stress rupture factors and weld strength reduction factors for Grade 91 steel weldments in the codes and literatures have been reviewed. Stress rupture factors for weld metals proposed for code case N-47 in the mid 1980's was defined as a ratio of average rupture strength of the deposited filler metal to the average rupture strength of the base metal. Remarkable drop in creep rupture strength of weldments is significant issue of Grade 91, especially in the low-stress and long-term regime. A premature failure of Grade 91 steel weldments in the long-term, however, is caused by type IV failure which takes place in the fine grain heat affected zone (FG-HAZ), rather than fracture in the deposited weld metal. The stress rupture factor of the Grade 91 steel, therefore, was based on the creep rupture strength of cross weld test specimens. Creep rupture data of Grade 91 steel weldments reported in the publication of ASME STP-PT-077 were integrated with the creep rupture data collected in Japan and used for this study. Time- and temperature-dependent stress rupture factors for Grade 91 steel have been evaluated based on the consolidated database as a ratio of average creep rupture strength of cross weld test specimen to the average creep rupture strength of base metal.

Creep Deformation Property and Creep Life Evaluation of Super304H

2020 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Rupture Strength ◽  
Rupture Life ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Rupture Ductility ◽  
Time To Rupture ◽  
Life Evaluation ◽  
Creep Exposure

Abstract Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increases in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C (1292°F) and above. In the short-term, at 600°C (1112°F), creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing this maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C (1112°F). Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into account the change in slope of stress vs. time to rupture curves was demonstrated.

Assessment of Long-Term Creep Rupture Strength of T91 Steel by Multiregion Rupture Data Analysis

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
K. Maruyama ◽  
J. Nakamura ◽  
K. Yoshimi
Keyword(s):  
Rupture Strength ◽  
Creep Rupture ◽  
Data Selection ◽  
Creep Rupture Strength ◽  
Rupture Data ◽  
Data Points ◽  
Service Conditions ◽  
Term Creep ◽  
Term Data

Creep rupture strength of creep strength enhanced ferritic steels is often overestimated, and its evaluated value has been reduced repeatedly. In this paper, the cause of the overestimation is discussed, and the creep rupture strength of T91 steel is assessed with its updated creep rupture data. Effects of residual Ni concentration on the creep rupture strength and necessity of F factor in T91 steel are also discussed. Decrease in activation energy Q for rupture life in long-term creep is the cause of the overestimation, since conventional time–temperature parameter (TTP) methods cannot deal with the change in Q. Due to the decrease in Q, long-term creep rupture strength evaluated decreases as longer-term data points are added or shorter-term data points are discarded in the conventional TTP analysis. The long-term region with small values of activation energy and stress exponent is named region L2 in this paper. Region L2 appears in all the heats of T91 steel and plate products of Gr.91 steel. Since service conditions of the T91 steel are usually in region L2, the creep rupture strength under the service conditions should be evaluated from the rupture data in region L2 only. The 5 × 105 hrs rupture strength at 550 °C decreases from 129 MPa (evaluated from the whole data of T91 steel) to 79 MPa (evaluated from the data in region L2 only) with increasing cut-off time for data selection. The 105 hrs rupture strength at 600 °C also decreases from 87 MPa (whole data) to 70 MPa (region L2 only) despite sufficient number of long-term data points at 600 °C. Careful consideration on the data selection is necessary in evaluation of creep rupture strength of the T91 steel. A multiregion rupture data analysis (MRA) is helpful to select data points belonging to region L2.

Reliability Design for Allowable Stress of Creep Rupture Strength of 4Cr25Ni35 Steel

2012 ◽  
Vol 476-478 ◽  
pp. 2552-2555
Author(s):  
Ji Bin Pei ◽  
Yun Feng Zhao ◽  
Shao Ping Yu ◽  
Jie Zhao
Keyword(s):  
Experimental Data ◽  
Statistical Analysis ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Parameter Method ◽  
Allowable Stress ◽  
Creep Rupture Strength ◽  
Reliability Design ◽  
Z Parameter ◽  
Rupture Data

Creep rupture data plays vital role in life prediction and safety assessment of high temperature components. In order to describe the scattering of the data, a statistical analysis of creep rupture data for 4Cr25Ni35 steel was performed by Z-parameter method. With the application of Z-parameter, reliability design for allowable stress of creep rupture strength was carried out according to design life. It is found that Manson-Haferd method appears better correlation results with experimental data. Statistical analysis shows that the scattering of Z-parameter for 4Cr25Ni35 steel is supported by normal distribution. Compared with safety factor method, the method based on Z-parameter can perform reliability design for allowable stress of creep rupture strength by considering the dispersibility of the rupture data. Reliability design based on Z-parameter is more agree with experimental data.

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