Prediction of Long-Term Creep Rupture Life of Grade 122 Steel by Multiregion Analysis

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
K. Maruyama ◽  
J. Nakamura ◽  
K. Yoshimi
Keyword(s):  
Rupture Life ◽  
Creep Rupture ◽  
Data Sets ◽  
Data Set ◽  
Life Estimation ◽  
Rupture Data ◽  
Temperature Dependences ◽  
Temperature Parameter ◽  
Term Creep

Conventional time-temperature-parameter (TTP) methods often overestimate long-term rupture life of creep strength enhanced ferritic steels. Decrease in activation energy Q for rupture life in long-term creep is the cause of the overestimation, since the TTP methods cannot deal with the change in Q. Creep rupture data of a heat of Gr.122 steel (up to 26,200 h) were divided into several data sets so that Q was unique in each divided data set. Then a TTP method was applied to each divided data set for rupture life prediction. This is the procedure of multiregion analysis of creep rupture data. The predicted rupture lives have been reported in literature. Long-term rupture lives (up to 51,400 h) of the same heat of the steel have been published in 2013. The multiregion analysis of creep rupture life can predict properly the long-term lives reported. Stress and temperature dependences of rupture life show similar behavior among different heats. Therefore, database on results of the multiregion analyses of various heats of the steel is helpful for rupture life estimation of another heat.

Prediction of Long-Term Creep Rupture Life of Grade 122 Steel by Multi-Region Analysis

2014 ◽  
Author(s):  
K. Maruyama ◽  
J. Nakamura ◽  
K. Yoshimi
Keyword(s):  
Rupture Life ◽  
Creep Rupture ◽  
Data Sets ◽  
Data Set ◽  
Region Analysis ◽  
Rupture Data ◽  
Temperature Dependences ◽  
Temperature Parameter ◽  
Term Creep

Conventional time-temperature-parameter (TTP) methods often overestimate long-term rupture life of creep strength enhanced ferritic steels. Decrease in activation energy Q for rupture life in long-term creep is the cause of the overestimation, since the TTP methods cannot deal with the change in Q. Creep rupture data of a heat of Gr.122 steel (up to 26200h) were divided into several data sets so that Q was unique in each divided data set. Then a TTP method was applied to each divided data set for rupture life prediction. This is the procedure of multi-region analysis of creep rupture data. The predicted rupture lives have been reported in literature. Long-term rupture lives (up to 51400h) of the same heat of the steel have been published in 2013. The multi-region analysis of creep rupture life can predict properly the long-term lives reported. Stress and temperature dependences of rupture life show similar behavior among different heats. Therefore, database on results of the multi-region analyses of various heats of the steel is helpful for rupture life estimation of another heat. Paper published with permission.

Methodology of Creep Data Analysis for Advanced High Cr Ferritic Steel

2007 ◽  
Author(s):  
Kouichi Maruyama ◽  
Kyosuke Yoshimi
Keyword(s):  
Data Analysis ◽  
Rupture Life ◽  
Creep Rupture ◽  
Creep Data ◽  
Short Term ◽  
Data Set ◽  
Region Analysis ◽  
Rupture Data ◽  
Term Creep

Long term creep rupture life is usually evaluated from short term data by a time-temperature parameter (TTP) method. The apparent activation energy Q for rupture life of steels sometimes changes from a high value of short term creep to a low value of long term creep. However, the conventional TTP analyses ignore the decrease in Q, resulting in the overestimation of rupture life recognized recently in advanced high Cr ferritic steels. A multi region analysis of creep rupture data is applied to a creep data set of Gr.122 steel; in the analysis a creep rupture data is divided into several data sets so that Q value is unique in each divided data set. The multi region analysis provides the best fit to the data and the lowest value of 105 h creep rupture strength among the three ways of data analysis examined. The conventional single region analysis cannot correctly represent the data points and predicts the highest strength. A half of 0.2% proof stress could not be an appropriate boundary for dividing data to be used in the multi region analysis. In the 2001 Edition of ASME Code an F average concept has been proposed as a substitution for the safety factor of 2/3 for average rupture stress. The allowable stress of Gr.122 steel may decrease significantly when the F average concept and the multi region analysis are adopted.

Guidelines to the Assessment of Creep Rupture Reliability for 316SS Using the Larson-Miller Time-Temperature Parameter Model

2017 ◽  
Author(s):  
Christopher Ramirez ◽  
Mohammad Shafinul Haque ◽  
Calvin Maurice Stewart
Keyword(s):  
Thermomechanical Processing ◽  
Rupture Life ◽  
Creep Rupture ◽  
Statistical Uncertainty ◽  
Rupture Data ◽  
Temperature Parameter ◽  
Long Life ◽  
Lower Temperature ◽  
Term Creep

It is common practice to perform accelerated creep testing (ACT) using time-temperature parameter (TTP) models. The TTP models are calibrated to creep-rupture data at high temperature and/or stress and extrapolate to lower temperature and/or stress where data is not available. The long-term creep rupture behavior (at low temperature and stress) is often not available due to the quantity, duration, and cost of testing. A limited scope of creep-rupture data is often analyzed using the TTP models. When conducting long-term extrapolation, statistical uncertainty becomes an issue. The ability of the TTP models to accurately predict creep-rupture at long life is often limited and the inherent material properties can dramatically influence creep-rupture life. Unfortunately, there is no consensus on the statistic for assessing the quality of TTP extrapolation. This study demonstrates methodology to assessing the uncertainty in creep rupture predictions for 316SS using the Larson Miller parameter. Over 2,000 creep-rupture data points are collected and digitized from the NIMS, ASM, MAPTIS, and ORNL databases; metadata such as the material’s form, thermomechanical processing, and chemical composition are recorded. Statistical uncertainty is measured using the “Z parameter”, which describes the deviation of creep-rupture data to a TTP model. The ability of the TTP models to extrapolate to long life is analyzed via exclusion of data. This is accomplished by: excluding 50% of the data, and by excluding the longest 10% of the data. It is shown that culling data in any way produces more conservative creep rupture predictions. The spread of the dataset will also affect the width of the reliability bands.

Influence of Data Analysis Method and Allowable Stress Criterion on Allowable Stress of Gr.122 Heat Resistant Steel

2006 ◽  
Vol 129 (3) ◽  
pp. 449-453 ◽  
Author(s):  
Kouichi Maruyama ◽  
Kyosuke Yoshimi
Keyword(s):  
Data Analysis ◽  
Rupture Strength ◽  
Rupture Life ◽  
Creep Rupture ◽  
Allowable Stress ◽  
Short Term ◽  
Rupture Data ◽  
Asme Code ◽  
Term Creep

Long-term creep rupture life is usually evaluated from short-term data by a time-temperature parameter (TTP) method. The allowable stress of Gr.122 steel listed in the ASME code has been evaluated by this method and is recognized to be overestimated. The objective of the present study is to understand the causes of the overestimation and propose appropriate methodology for avoiding the overestimation. The apparent activation energy Q for rupture life of the steel changes from a high value of short-term creep to a low value of long-term creep. However, the decrease in Q is ignored in the conventional TTP analyses, resulting in the overestimation of rupture life. A multiregion analysis of creep rupture data is employed to avoid the overestimation; in the analysis creep rupture data are divided into a couple of regions so that the Q value is unique in each divided region. The multiregion analysis provides a good fit to the data and the lowest value of 105h creep rupture strength among the three ways of data analysis examined. A half of 0.2% proof stress cannot provide an appropriate boundary for dividing data to be used in the multiregion analysis. In the 2001 edition of the ASME code an F average concept has been proposed as a substitution for the safety factor of 2∕3 for average rupture stress. The allowable stress of Gr.122 steel changes significantly depending on the allowable stress criteria as well as the methods of rupture data analysis: i.e., from 74MPato48MPa.

Creep–rupture model of aluminum alloys: Cohesive zone approach

2014 ◽  
Vol 229 (8) ◽  
pp. 1343-1347 ◽  
Author(s):  
Kyungmok Kim
Keyword(s):  
Aluminum Alloys ◽  
Cohesive Zone ◽  
Rupture Life ◽  
Stress Rupture ◽  
Creep Rupture ◽  
Time Dependent ◽  
Element Analysis ◽  
Rupture Model ◽  
Term Creep

In this article, a creep–rupture model of aluminum alloys is developed using a time-dependent cohesive zone law. For long-term creep rupture, a time jump strategy is used in a cohesive zone law. Stress–rupture scatter of aluminum alloy 4032-T6 is fitted with a power law form. Then, change in the slope of a stress-rupture line is identified on a log–log scale. Implicit finite element analysis is employed with a model containing a cohesive zone. Stress–rupture curves at various given temperatures are calculated and compared with experimental ones. Results show that a proposed method allows predicting creep–rupture life of aluminum alloys.

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.

A Proposal for Post-Assessment Test of Long-Term Creep Rupture Strength of Grade 91 Steel

2018 ◽  
Author(s):  
Kouichi Maruyama ◽  
Nobuaki Sekido ◽  
Kyosuke Yoshimi
Keyword(s):  
Rupture Strength ◽  
Creep Rupture ◽  
Rupture Data ◽  
Data Points ◽  
Grade 91 ◽  
Term Creep ◽  
Off Time ◽  
Term Data ◽  
Grade 91 Steel

Predictions as to 105 hrs creep rupture strength of grade 91 steel have been made recently. The predictions should be verified by some means, since they are based on certain assumptions. A formula for predicting long-term creep rupture lives should correctly describe long-term data points used in its formulation. Otherwise the formula cannot properly predict further longer-term creep rupture lives. On the basis of this consideration, the predictions are examined with long-term creep rupture data of the steel. In the predictions three creep rupture databases were used: data of tube products of grade 91 steel reported in NIMS Creep Data Sheet (NIMS T91 database), data of T91 steel collected in Japan, and data of grade 91 steel collected by an ASME code committee. Short-term creep rupture data points were discarded by the following criteria for minimizing overestimation of the strength: selecting long-term data points with low activation energy (multi-region analysis), selecting data points crept at stresses lower than a half of proof stress (σ0.2/2 criterion), and selecting data points longer than 1000 hrs (cut-off time of 1000 hrs). In the case of NIMS T91 database, a time-temperature parameter (TTP) analysis of a dataset selected by the multi-region analysis can properly describe the long-term data points. However, the TTP analyses of datasets selected by the σ0.2/2 criterion and by the cut-off time of 1000 hrs from the same database overestimate the long-term data points. The different criteria for data selection have more substantial effects on predicted values of the strength of the steel than difference of the databases.

Re-Evaluation of Long-Term Creep Strength of Welded Joint of ASME Grade 91 Type Steel

2016 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Kaoru Nakamura ◽  
Sosuke Nakahashi
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Base Metals ◽  
Rupture Data ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

Creep rupture data of welded joints of ASME Grade 91 type steel have been collected from Japanese plants, milling companies and institutes, and the long-term creep rupture strength of the material has been evaluated. This evaluation of welded joints of Grade 91 steel is the third one in Japan as similar studies were conducted in 2004 and 2010. The re-evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained since the previous study, with durations of the new data of up to about 60000h. The new long-term data exhibited lower creep strength than that obtained from the master creep life equation for welded joints of Grade 91 steel determined in 2010, then the master creep life equation was again reviewed on the basis of the new data using the same regression method as that used in 2010. Furthermore, the weld strength reduction factors obtained from 100000h creep strength of welded joints and the base metals are given as a function of temperature, where the master creep equations of the base metals are also redetermined in this study.

Influence of Oxidation on Long-Term Creep Strength of ASME Grade 23 Steel

2009 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Masakazu Fujitsuka ◽  
Hideaki Kushima
Keyword(s):  
Creep Strength ◽  
Rupture Strength ◽  
Rupture Life ◽  
Microstructural Change ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Gas Atmosphere ◽  
Helium Gas ◽  
Term Creep

Creep test of ASME Grade 23 steel has been conducted at 625 and 650°C in helium gas atmosphere. Long-term creep strength of the steel in helium gas was compared with that in air and the influence of oxidation on long-term creep strength was investigated. Creep rupture strength drop was observed in the long-term at 625 and 650°C in air, and the same creep rupture strength drop was observed also in helium gas at 625°C. On the other hand, although creep rupture strength drop was observed in the long-term at 650°C in helium gas, creep rupture life in the long-term in helium gas was slightly longer than that in air at 650°C. Creep rupture life in the long-term at 650°C in air is reduced by not only degradation due to microstructural change, but also marked oxidation, however, that at 625°C is considered to be shortened mainly by a degradation caused by microstructural change. Long-term creep strength of ASME Grade 23 steel at 600°C and above should be reevaluated in consideration of strength drop due to microstructural change.

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