scholarly journals Improvement of Creep Strength of Ferritic Steels for Coal-fired Power Plants.

2001 ◽  
Vol 70 (8) ◽  
pp. 756-761
Author(s):  
Fujio ABE
Keyword(s):  
Creep Strength ◽  
Power Plants ◽  
Ferritic Steels

Creep Failure Behavior of Creep-Strength Enhanced Ferritic Steels

2004 ◽  
Author(s):  
F. Masuyama ◽  
N. Komai
Keyword(s):  
Creep Strength ◽  
Power Plants ◽  
Void Formation ◽  
Thick Wall ◽  
Failure Behavior ◽  
Ferritic Steels ◽  
Physical Damage ◽  
Creep Failure ◽  
Type Iv ◽  
Microstructural Morphology

Creep-strength enhanced ferritic steels such as Gr.92, Gr.122, Gr.23 and Gr.91 have recently been introduced for power plant applications, and some of these have experienced creep failure in boiler tubes and thick wall components after several years of operation. In order to use these steels safely in power plants, understanding of creep failure behavior is essential. In this study the creep failure of Gr.91 and Gr.92 boiler tube base metal and Type IV cracking of Gr.92, Gr.122, Gr.23 and Gr.91 welds were reproduced in test piece of actual components size. Creep failure mode was investigated, as was microstructural morphology during creep, particularly in the weldment, with discussion based on evidence of void formation and changes in the physical damage in terms of creep life.

Prediction of Breakdown Transition of Creep Strength in Advanced High Cr Ferritic Steels by Hardness Measurement of Aged Structures at High Temperature

2007 ◽  
Vol 345-346 ◽  
pp. 553-556 ◽  
Author(s):  
Hassan Ghassemi Armaki ◽  
Kouichi Maruyama ◽  
Mitsuru Yoshizawa ◽  
Masaaki Igarashi
Keyword(s):  
Power Plants ◽  
Rupture Strength ◽  
Hardness Measurement ◽  
Creep Rupture ◽  
Ferritic Steels ◽  
Creep Rupture Strength ◽  
Cr Concentration ◽  
Reduction Of Area ◽  
Term Creep

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.

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

1997 ◽  
Vol 234-236 ◽  
pp. 1079-1082 ◽  
Author(s):  
K. Kimura ◽  
H. Kushima ◽  
F. Abe ◽  
K. Yagi
Keyword(s):  
Creep Strength ◽  
Strength Properties ◽  
Ferritic Steels ◽  
Term Creep

EPRI Guidelines for Fabrication of Components Manufactured From Grade 91 Steel

2012 ◽  
Author(s):  
Jonathan Parker ◽  
Kent Coleman
Keyword(s):  
Quality Assurance ◽  
Creep Strength ◽  
Ferritic Steels ◽  
Factors Affecting ◽  
Critical Information ◽  
Grade 91 ◽  
Recommended Guidelines ◽  
Grade 91 Steel

Over the last 10 years EPRI has been researching critical information on the factors affecting the performance of creep strength enhanced ferritic steels in general and Grade 91 steel in particular. This work has resulted in a major new report which provides recommended guidelines for fabrication and the associated quality assurance to ensure that component properties meet or exceed the minimum expectations of ASME design approaches. The present paper outlines the recommendations in the report and provides technical background for specific aspects of the guide.

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

2007 ◽  
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.

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

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.

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

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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