Experience in Applying the New UK Procedure for Creep Rupture Data Assessment to Gas Turbine Materials

1998 ◽  
Vol 120 (3) ◽  
pp. 588-594
Author(s):  
C. K. Bullough
Keyword(s):  
Gas Turbine ◽  
Linear Models ◽  
Rupture Strength ◽  
Statistical Tests ◽  
Error Variance ◽  
Creep Rupture ◽  
Data Sets ◽  
Data Assessment ◽  
Rupture Data ◽  
Turbine Blading

A new procedure being developed in British Standards for the assessment of creep-rupture data is described and evaluated with trial data sets of gas turbine blading materials. The procedure is applied in phases. An important development by statistical experts is a framework for the main assessment phase that uses maximum-likelihood fitting methods for the treatment of unfailed test points and error variance. The framework selects models from a standard suite (together with any other linear models supplied by the assessor) using statistical criteria, but also incorporates metallurgical judgement. The improved representation of the experimental data compared with previous fitting methods and the associated statistical tests indicate that the new procedure can be used to derive rupture strength values for gas turbine materials with confidence.

Experience in Applying the New UK Procedure for Creep Rupture Data Assessment to Gas Turbine Materials

1997 ◽  
Author(s):  
Chris K. Bullough
Keyword(s):  
Gas Turbine ◽  
Linear Models ◽  
Rupture Strength ◽  
Statistical Tests ◽  
Error Variance ◽  
Creep Rupture ◽  
Data Sets ◽  
Data Assessment ◽  
Rupture Data ◽  
Turbine Blading

A new procedure being developed in British Standards for the assessment of creep-rupture data is described, and evaluated with trial data sets of gas turbine blading materials. The procedure is applied in phases. An important development by statistical experts is a framework for the main assessment phase which uses maximum-likelihood fitting methods for the treatment of unfailed test points and error variance. The framework selects models from a standard suite (together with any other linear models supplied by the assessor) using statistical criteria, but also incorporates metallurgical judgement. The improved representation of the experimental data compared with previous fitting methods, and the associated statistical tests indicate that the new procedure can be used to derive rupture strength values for gas turbine materials with confidence.

scholarly journals Identifying a Dynamic Model for a GE Frame 7 Gas Turbine

1994 ◽  
Author(s):  
Howard Kaufman ◽  
R. Ravi
Keyword(s):  
Gas Turbine ◽  
Linear Models ◽  
Controller Design ◽  
Guide Vane ◽  
Selection Criterion ◽  
Inlet Guide Vane ◽  
Data Sets ◽  
Similar Work ◽  
Identification Techniques ◽  
Vane Angle

Several tests were conducted on a GE Frame 7 gas turbine to determine its dynamic characteristics. The objective is to obtain a model that can be used for controller design. The tests consisted of adding sequences of square waves to the two inputs — the fuel reference and the inlet guide vane angle reference — and recording the inputs and the outputs. This method of exciting the system afforded us with a way of separating the data sets into two categories, the first, in which the fuel reference was changed, and the second, in which the guide vane angle reference was changed. Least-squares system identification techniques were used to obtain linear models using a selection criterion that was a measure of how well a model fit both the sets of data. This brought in a measure of robustness to the models thus making them ideal for use in controller design. This paper summarizes the results from these tests, contains plots that show how well the linear models are able to fit the recorded data, and finally, provides some recommendations for others doing similar work.

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.

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.

Evaluation of Creep Strength Reduction Factors for Welded Joints of Modified 9Cr-1Mo Steel (P91)

2006 ◽  
Author(s):  
Masaaki Tabuchi ◽  
Yukio Takahashi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Creep Rupture ◽  
Type Iv ◽  
Rupture Data ◽  
Term Creep

In order to review the allowable creep strength of high Cr ferritic steels, creep rupture data of base metal and welded joints have been collected and long-term creep strength have been analyzed in the SHC committee in Japan since 2004. In the present paper, the creep rupture data of 370 points for welded joint specimens of modified 9Cr-1Mo steel (ASME Grade 91) offered from seven Japanese companies and institutes were analyzed. These data clearly indicated that the creep strength of welded joints was lower than that of base metal due to Type IV fracture in HAZ at or above 600°C. From the activities of this committee, the master curve for life evaluation of welded joints of Gr.91 steel could be represented as follows: LMP==34154+3494(logσ)−2574(logσ)2,C=31.4 The reduction factor of 100,000 hours creep rupture strength of welded joint to base metal was concluded to be 0.75 at 600°C and 0.70 at 650°C for the Gr.91 steel.

The European Creep Collaborative Committee (ECCC) Approach to Creep Data Assessment

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Stuart Holdsworth
Keyword(s):  
Rupture Strength ◽  
Large Data ◽  
Small Data ◽  
Data Sets ◽  
Creep Data ◽  
Data Set ◽  
Data Assessment ◽  
Long Time ◽  
Small Data Sets ◽  
Material Conditions

The European Creep Collaborative Committee (ECCC) approach to creep data assessment has now been established for almost ten years. The methodology covers the analysis of rupture strength and ductility, creep strain, and stress relaxation data, for a range of material conditions. This paper reviews the concepts and procedures involved. The original approach was devised to determine data sheets for use by committees responsible for the preparation of National and International Design and Product Standards, and the methods developed for data quality evaluation and data analysis were therefore intentionally rigorous. The focus was clearly on the determination of long-time property values from the largest possible data sets involving a significant number of observations in the mechanism regime for which predictions were required. More recently, the emphasis has changed. There is now an increasing requirement for full property descriptions from very short times to very long and hence the need for much more flexible model representations than were previously required. There continues to be a requirement for reliable long-time predictions from relatively small data sets comprising relatively short duration tests, in particular, to exploit new alloy developments at the earliest practical opportunity. In such circumstances, it is not feasible to apply the same degree of rigor adopted for large data set assessment. Current developments are reviewed.

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.

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.

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