Long-term creep deformation characteristics of advanced ferritic steels for USC power plants

Recent researches have shown the premature breakdown of creep rupture strength in long term creep region of advanced high Cr ferritic steels. As safe operation of power plants becomes a serious problem we should be able to detect and predict the breakdown transition of creep rupture strength. Some methods for detecting the breakdown transition have been presented till now like the measurement of reduction of area after creep rupture and particle size of laves phase. However it will be more economic if we make use of non-destructive tests, for example, hardness testing. In this paper 3 types of ferritic steels with different Cr concentration have been studied. The results suggest that the hardness of aged structures is constant independently of exposure time in short term region, whereas the hardness breaks down in long term region. The boundary of breakdown in hardness coincides with that of breakdown in creep rupture strength.

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Detecting Long-Term Deformation of a Loess Landslide from the Phase and Amplitude of Satellite SAR Images: A Retrospective Analysis for the Closure of a Tunnel Event

Remote Sensing ◽

10.3390/rs13234841 ◽

2021 ◽

Vol 13 (23) ◽

pp. 4841

Author(s):

Yaru Zhu ◽

Haijun Qiu ◽

Zijing Liu ◽

Jiading Wang ◽

Dongdong Yang ◽

...

Keyword(s):

Local Governments ◽

Surface Deformation ◽

Failure Surface ◽

Deformation Characteristics ◽

Spatiotemporal Evolution ◽

Loess Landslide ◽

Landslide Deformation ◽

Term Creep ◽

Offset Tracking

Information about the long-term spatiotemporal evolution of landslides can improve the understanding of landslides. However, since landslide deformation characteristics differ it is difficult to monitor the entire movement of a landslide using a single method. The Interferometric Synthetic Aperture Radar (InSAR) and pixel offset tracking (POT) method can complement each other when monitoring deformation at different landslide stages. Therefore, the InSAR and improved POT method were adapted to study the pre- and post-failure surface deformation characteristics of the Gaojiawan landslide to deepen understanding of the long-term spatiotemporal evolution characteristics of landslides. The results show that the deformation displacement gradient of the Gaojiawan landslide exhibited rapid movement that exceeded the measurable limit of InSAR during the first disaster. Moreover, the Gaojiawan landslide has experienced long-term creep, and while studying the post-second landslide’s failure stability, the acceleration trend was identified via time series analysis, which can be used as a precursor signal for landslide disaster warning. Our study aims to provide scientific reference for local governments to help prevent and mitigate geological disasters in this region.

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Inherent creep strength and long term creep strength properties of ferritic steels

Materials Science and Engineering A ◽

10.1016/s0921-5093(97)00345-6 ◽

1997 ◽

Vol 234-236 ◽

pp. 1079-1082 ◽

Cited By ~ 29

Author(s):

K. Kimura ◽

H. Kushima ◽

F. Abe ◽

K. Yagi

Keyword(s):

Creep Strength ◽

Strength Properties ◽

Ferritic Steels ◽

Term Creep

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Regulatory Review Results on Allowable Tensile Stress Values of Creep Strength Enhanced Ferritic Steels

Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures ◽

10.1115/creep2007-26512 ◽

2007 ◽

Cited By ~ 4

Author(s):

Kazuo Yoshida ◽

Hirotake Nakai ◽

Minami Fukuda

Keyword(s):

Creep Strength ◽

Rupture Life ◽

Ferritic Steels ◽

Regulatory Review ◽

Tensile Stresses ◽

Life Evaluation ◽

Term Creep ◽

Region Splitting ◽

Review Current

In order to evaluate long-term creep strength and to review current allowable tensile stresses of creep strength enhanced ferritic steels, a committee was organized in Japan Power Engineering and Inspection Corporation. In 2004FY and 2005FY, creep test data of Gr. 122, Gr. 91, Gr. 92, Gr. 23 and KA-SUS410J2TB steels were collected and analyzed by means of region splitting procedure in the committee. Based on the analysis, the allowable tensile stresses were reviewed in accordance with METI regulatory base. And the master curves for creep rupture life evaluation of welds were set forth furthermore based on the data analysis.

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Grades 92 and 23: Weldability Assessment and Long-Term Performances for Power Generation Applications

Materials Science Forum ◽

10.4028/www.scientific.net/msf.580-582.383 ◽

2008 ◽

Vol 580-582 ◽

pp. 383-388

Author(s):

Emmanuel Bauné ◽

E. Galand ◽

B. Leduey ◽

G. Liberati ◽

G. Cumino ◽

...

Keyword(s):

Creep Strength ◽

Welded Joints ◽

Power Plants ◽

Product Family ◽

Base Material ◽

Advanced Materials ◽

Creep Properties ◽

Steam Parameters ◽

Term Creep

Increased efficiency and emission reduction in modern power plants lead to the use of new advanced materials with enhanced creep strength, with the objective to increase the steam parameters of power plants. With over ten years on market and wide experience related to its use, ASTM Grade 92 is becoming one of the most required materials when high service temperatures are reached (max. 610°C). Its composition, with 9%Cr and 1.5%W, gives rise to martensitic microstructures which offer very high creep strength and long term stability. The improved weldability and creep-strength between 500 and 580°C of the low alloy ASTM Grade 23, as well as a cost advantage over higher Cr materials in this temperature range, make it one of the possible candidates to meet the stringent requirements of modern power plants. Air Liquide Welding (ALW) has optimized and distributes a complete product family for the welding of Grades 23 and 92. TenarisDalmine (TD) focused on the development of Grade 23 tubes and pipes and is working on the development of Grade 92. A deep characterization work of the microstructural evolution and long term creep performances of these high temperature resistant materials was thus undertaken by ALW and TD, in collaboration with the Centro Sviluppo Materiali (CSM). The joint characterization program consisted in the assessment of welded joints creep properties. Welded joints were produced using the gas tungsten (GTAW), shielded metal (SMAW) and submerged arc welding (SAW) processes. Mechanical and creep properties of weldments were measured both in the as welded and post weld heat treated conditions and proper WPS’s were designed in a manner such that industrial production needs were satisfied. Short term creep resistance of cross weld specimens was measured to be within the base material acceptance criteria. Long term base material and cross weld creep performance evaluation are now in progress.

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Atomic Resolution Investigations of Phase Transformation from TaN to CrTaN in a Steel Matrix

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.823 ◽

2012 ◽

Vol 706-709 ◽

pp. 823-828

Author(s):

Hilmar Kjartansson Danielsen ◽

John Hald

Keyword(s):

Crystal Structure ◽

Creep Strength ◽

Power Plants ◽

Atomic Resolution ◽

Double Layers ◽

Steel Matrix ◽

Phase Precipitation ◽

Direct Transformation ◽

Term Creep

In development of 12%Cr high temperature steels used for fossil fired power plants, the precipitation of large Z-phase particles, CrMN, has been identified as a major problem since they replace small and finely distributed MN particles. This causes a premature breakdown in the long-term creep strength of the steel. The Cr content promotes Z-phase precipitation, making MN strengthening of these materials unfeasible, since 12%Cr is necessary for oxidation resistance. The authors have suggested an acceleration of Z-phase precipitation to obtain a fine and stable distribution of CrMN instead of MN, thus preserving long-term creep strength. This can be done by alloying with Ta instead of Nb and V. Recent investigations have indicated a direct transformation of MN into CrMN to take place, not the traditional nucleation/dissolution process. In this paper atomic resolution microscopy shows how Cr atoms diffuse from the steel matrix into TaN precipitates and physically transform them into CrTaN. The crystal structure of the precipitates changes from that of a typical MN NaCl type crystal structure to a Z-phase crystal structure with alternating double layers of Cr and TaN. Since there is a large contrast between heavy Ta atoms and light Cr atoms, the ordering of the Cr layers inside the TaN particles can clearly be observed.

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Cr concentration dependence of overestimation of long term creep life in strength enhanced high Cr ferritic steels

International Journal of Pressure Vessels and Piping ◽

10.1016/j.ijpvp.2010.03.012 ◽

2010 ◽

Vol 87 (6) ◽

pp. 276-281 ◽

Cited By ~ 25

Author(s):

K. Maruyama ◽

H. Ghassemi Armaki ◽

R.P. Chen ◽

K. Yoshimi ◽

M. Yoshizawa ◽

...

Keyword(s):

Concentration Dependence ◽

Ferritic Steels ◽

Creep Life ◽

Cr Concentration ◽

Term Creep

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Assessment of Creep Rupture Strength for New Martensitic 9% Cr Steels

Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures ◽

10.1115/creep2007-26332 ◽

2007 ◽

Cited By ~ 1

Author(s):

Walter Bendick ◽

Jean Gabrel ◽

Bruno Vandenberghe

Keyword(s):

Power Plants ◽

Rupture Strength ◽

Strength Properties ◽

Creep Rupture ◽

Assessment Procedure ◽

Creep Rupture Strength ◽

Raw Data ◽

Cr Steels ◽

Term Creep

The application of new heat resistant steels in power plants requires reliable long term creep rupture strength values as basis for design. Modern martensitic 9% Cr-steels have complex microstructures that change with service exposure. That is why extrapolations of long term strength properties will be most difficult. Due to new long term test results, re-assessments became necessary for grades 911 and 92. Different methods have been used. Good agreement was obtained between a graphical and the numerical ISO 6303 method. In both cases a two-step assessment procedure was used. First the raw data was prepared in a suitable way, which was followed by mathematical averaging procedures. For comparison a Larson-Miller analysis on the raw data was performed, too. The results turned out to be too optimistic at temperatures higher than 575°C (1050°F). It is shown that a suitable preparation of data can improve the Larson-Miller assessment. As a result of the new assessments the design values had to be reduced for both grades. With respect to previous assessments the new values are up to almost 10% lower. In the case of grade 92 the difference from the former ASME values are even higher. Consequences concerning design and service operation are discussed.

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Heterogeneous Recovery and Precipitation of Z Phase during Long Term Creep Deformation of Modified 9Cr-1Mo Steel

Tetsu-to-Hagane ◽

10.2355/tetsutohagane1955.86.8_550 ◽

2000 ◽

Vol 86 (8) ◽

pp. 550-557 ◽

Cited By ~ 36

Author(s):

Kenta SUZUKI ◽

Shinji KUMAI ◽

Hideaki KUSHIMA ◽

Kazuhiro KIMURA ◽

Fujio ABE

Keyword(s):

Creep Deformation ◽

Term Creep

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