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.

Re-Evaluation of Stress Rupture Factors for Grade 91 Weldments Based on the Extended Database With the Data Collected in Japan

2019 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Masatsugu Yaguchi
Keyword(s):  
Base Metal ◽  
Rupture Strength ◽  
Stress Rupture ◽  
Creep Rupture ◽  
Weld Strength ◽  
Creep Rupture Strength ◽  
Premature Failure ◽  
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 was incorporated in the creep database collected in Japan which was used for the previous study. Time and temperature dependent stress rupture factors for Grade 91 steel have been re-evaluated based on the extended database as a ratio of average creep rupture strength of cross weld test specimen to the average creep rupture strength of base metal.

Evaluation of Stress Rupture Factors for Grade 91 Weldments

2018 ◽  
Author(s):  
Kazuhiro Kimura
Keyword(s):  
Base Metal ◽  
Rupture Strength ◽  
Stress Rupture ◽  
Creep Rupture ◽  
Weld Strength ◽  
Creep Rupture Strength ◽  
Premature Failure ◽  
Type Iv ◽  
Grade 91

Stress rupture factors and weld strength reduction factors for Grade 91 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 the 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 weldments in the long-term, however, is caused by Type IV failure which takes place in the fine grained 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. Time and temperature dependent stress rupture factors for Grade 91 have been estimated based on the average creep rupture strength of cross weld test specimen to the average creep rupture strength of base metal.

A Postassessment Test of 100,000 h Creep Rupture Strength of Grade 91 Steel at 600 °C

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
K. Maruyama ◽  
N. Sekido ◽  
K. Yoshimi
Keyword(s):  
Rupture Strength ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Data Points ◽  
Predicted Values ◽  
Grade 91 ◽  
Term Creep ◽  
Term Data ◽  
Grade 91 Steel

Predictions as to 105 h creep rupture strength of grade 91 steel have been made recently. The predicted values are examined with long-term creep rupture data of the steel. Three creep rupture databases were used in the predictions: data of tube products of grade 91 steel reported in National Institute for Materials Science (NIMS) Creep Data Sheet (NIMS T91 database), data of T91 steel collected in Japan, and data of grade 91 steel collected by an American Society of Mechanical Engineers (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 (multiregion 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 h (cutoff time of 1000 h). In the case of NIMS T91 database, a time–temperature parameter (TTP) analysis of a dataset selected by multiregion analysis can properly describe the long-term data points and gives the creep rupture strength of 68 MPa at 600 °C. However, TTP analyses of datasets selected by σ0.2/2 criterion and cutoff time of 1000 h from the same database overestimate the data points and predict the strength over 80 MPa. Datasets selected by the same criterion from the three databases provide similar values of the strength. The different criteria for data selection have more substantial effects on predicted values of the strength of the steel than difference of the databases.

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.

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.

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 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.

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.

Microstructural Evaluation of 9Cr-3W-3Co-Nd-B Heat-Resistant Steel (SAVE12AD) After Long-Term Creep Deformation

2017 ◽  
Author(s):  
Tomoaki Hamaguchi ◽  
Hirokazu Okada ◽  
Shinnosuke Kurihara ◽  
Hiroyuki Hirata ◽  
Mitsuru Yoshizawa ◽  
...  
Keyword(s):  
Base Metal ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Rupture Strength ◽  
Large Diameter ◽  
Creep Rupture ◽  
Martensite Lath ◽  
Creep Rupture Strength ◽  
Term Creep

The new ferritic heat-resistant steel composed of 9Cr-3W-3Co-Nd-B, registered as ASME Code Case 2839, has been developed for large diameter and heavy wall thickness pipes and forgings of fossil-fired power boilers. The steel, which contains 0.01 mass% boron, a small amount of neodymium, and optimized amounts of nitrogen, is characterized by the superior long-term creep strengths of both the base metal and welded joint. P92 had equiaxed subgrain structures changed from martensite lath structures and coarsened M23C6 type carbides after long-term creep. In contrast, the developed steel, SAVE12AD, maintained martensite lath structures with fine M23C6 along the boundaries even after the long-term creep stage. The addition of high amounts of boron suppressed the coarsening of M23C6 along the boundaries, thereby stabilizing the martensite lath structure in the base metal of the steel. Consequently, SAVE12AD had higher creep rupture strength than other high chromium ferritic steels. To investigate the creep rupture strength of welded joints, two welded joints with Ni-based alloy and Grade 92 welding filler wires were prepared by automatic gas tungsten arc welding. The creep rupture strength of each welded joint showed small degradation compared with the base metal in the long-term creep stage over 10,000 hours. These were ruptured 1.5 mm away from the fusion line, which was the same area as Type IV cracking. Microstructural observations were carried out by electron back scatter diffraction analysis using simulated heat-affected zone samples at different peak temperatures from 750 °C to 1350 °C in order to clarify the microstructure in the heat-affected zone. No fine grain area was observed in the microstructure after the simulated heat-affected zone at 910 °C just above AC3 transformation temperature, although there were fine grains along prior austenite grain boundaries, which seemed to form with the diffusion transformation. The creep cracks seemed to have initiated from the fine grain structures, resulting in the rupture at the same area as Type IV cracking. However, the creep rupture strength degradation of the welded joints against the base metal was significantly smaller than that of conventional steel welded joints owing to the suppression of fine grains found in the heat-affected zone heated around AC3 temperature. The developed 9Cr-3W-3Co-Nd-B steel (SAVE12AD) will be used for large diameter and heavy wall thickness pipes and forgings in 600 °C ultra super critical power plants.

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