Microstructures of Grade 91 Steels Under Long-Term Creep Conditions

2018 ◽  
Author(s):  
Kenji Kako ◽  
Susumu Yamada ◽  
Masatsugu Yaguchi ◽  
Yusuke Minami
Keyword(s):  
Remaining Life ◽  
Martensitic Steels ◽  
Creep Data ◽  
Creep Life ◽  
Creep Tests ◽  
Microstructural Observation ◽  
Type Iv ◽  
Grade 91 ◽  
Term Creep

Type IV damage has been found at several ultra-supercritical (USC) plants that used high-chromium martensitic steels in Japan, and the assessment of the remaining life of the steels is important for electric power companies. The assessment of the remaining life needs long-term creep data for over 10 years, but such data are limited. We have attempted to assess the remaining life by creep tests and by microstructural observation of Grade 91 steels welded pipes which were used in USC plants for over 10 years. Following the results of microstructural observation of USC plant pipes, we find that microstructures, especially distribution of MX precipitates, have large effect on the creep life of Grade 91 steels.

Modified Dyson Continuum Damage Model for Austenitic Steel Alloy

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Seok Jun Kang ◽  
Hoomin Lee ◽  
Jae Boong Choi ◽  
Moon Ki Kim
Keyword(s):  
Damage Model ◽  
Life Time ◽  
Continuum Damage ◽  
Creep Life ◽  
Creep Tests ◽  
Continuum Damage Model ◽  
Thermal Plant ◽  
Uniaxial Creep ◽  
Term Creep

Ultrasuper critical (USC) thermal plants are now in operation around the globe. Their applications include superheaters and reheaters, which generally require high temperature/pressure conditions. To withstand these harsh conditions, an austenitic heat-resistant HR3C (ASME TP310NbN) steel was developed for metal creep resistance. As the designed life time of a typical thermal plant is 150,000 h, it is very important to predict long-term creep behavior. In this study, a three-state variable continuum damage model (CDM) was modified for better estimation of long-term creep life. Accelerated uniaxial creep tests were performed to determine the material parameters. Also, the rupture type and microstructural precipitation were observed by scanning electron microscopy. The creep life of HR3C steel was predicted using only relatively short-term creep test data and was then successfully verified by comparison with the long-term creep data.

Short-Term Creep Data Based Long-Term Creep Life Predictability for Grade 92 Steels and Its Microstructural Basis

2018 ◽  
Vol 25 (3) ◽  
pp. 713-722 ◽  
Author(s):  
Seen Chan Kim ◽  
Jae-Hyeok Shim ◽  
Woo-Sang Jung ◽  
Yoon Suk Choi
Keyword(s):  
Creep Data ◽  
Creep Life ◽  
Short Term ◽  
Term Creep ◽  
Short Term Creep

scholarly journals Predictions of long-term creep life for the family of 9–12 wt% Cr martensitic steels

2020 ◽  
Vol 815 ◽  
pp. 152417 ◽  
Author(s):  
Amit K. Verma ◽  
Jeffrey A. Hawk ◽  
Vyacheslav Romanov ◽  
Jennifer L.W. Carter
Keyword(s):  
Martensitic Steels ◽  
Creep Life ◽  
The Family ◽  
Term Creep

Long Term Creep Life Prediction of New and Service Exposed P91 Steel

2018 ◽  
Author(s):  
Muneeb Ejaz ◽  
Norhaida Ab Razak ◽  
Andrew Morris ◽  
Scott Lockyer ◽  
Catrin M. Davies
Keyword(s):  
Tensile Strength ◽  
Creep Behaviour ◽  
Equivalent Stress ◽  
Practical Reasons ◽  
Creep Data ◽  
Short Term ◽  
Creep Tests ◽  
High Temperature Components ◽  
Term Creep

P91 steels are widely used in high temperature components for power generation. Creep data is often generated through accelerated short term creep tests, for practical reasons, via increasing stress or temperature though this may alter the creep behaviour. Through normalising the creep test stress by tensile strength the Wilshire models reduce the batch to batch scatter in the creep data and enable the prediction of long term creep data from relatively short term test results. In this work it is shown that the Wilshire models fitted to uniaxial creep rupture data can be used to predict failure in both as cast and service exposed multiaxial tests. This is provided that the equivalent stress is the rupture controlling stress, as is the case for the P91 tests examined, and the tensile strength is measured as part of the test programme.

scholarly journals Use of the Wilshire Equations to Correlate and Extrapolate Creep Data of Inconel 617 and Nimonic 105

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2534 ◽  
Author(s):  
Vito Cedro III ◽  
Christian Garcia ◽  
Mark Render
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Creep Strength ◽  
Goodness Of Fit ◽  
Creep Data ◽  
Creep Life ◽  
Self Diffusion ◽  
Inconel 617 ◽  
Term Creep

Advanced power plant alloys must endure high temperatures and pressures for durations at which creep data are often not available, necessitating the extrapolation of creep life. A recently developed creep life extrapolation method is the Wilshire equations, with which multiple approaches can be used to increase the goodness of fit of available experimental data and improve the confidence level of calculating long-term creep strength at times well beyond the available experimental data. In this article, the Wilshire equation is used to extrapolate the creep life of Inconel 617 and Nimonic 105 to 100,000 h. The use of (a) different methods to determine creep activation energy, (b) region splitting, (c) heat- and processing-specific tensile strength data, and (d) short-duration test data were investigated to determine their effects on correlation and extrapolation. For Inconel 617, using the activation energy of lattice self-diffusion as Q C * resulted in a poor fit with the experimental data. Additionally, the error of calculated rupture times worsened when splitting regions. For Nimonic 105, the error was reduced when heat- and processing-specific tensile strengths were used. Extrapolating Inconel 617 creep strength to 100,000 h life gave conservative results when compared to values calculated by the European Creep Collaborative Committee.

The Performance of Creep-Strengthened Ferritic Steels in Power Generating Plant

2007 ◽  
Author(s):  
Jonathan Parker ◽  
Jeff Henry
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Ferritic Steels ◽  
Stress Concentrations ◽  
Actual Case ◽  
Type Iv ◽  
Temperature Performance ◽  
Grade 91 ◽  
Term Creep

Creep-strengthened ferritic steels, such as Grade 91, offer the potential for excellent high-temperature performance. To realize the benefits for these alloys requires careful control of original composition and manufacturing processes, such as welding and bending, as well as the associated heat treatments. Laboratory tests indicate that long-term lives may be below the original estimates made based on Larson Miller extrapolation. Furthermore, accelerated rates of damage accumulation in in-service Grade 91 components can occur due to a number of factors including: • Problems associated with design, for example with reinforcement at nozzles and with stress concentrations in piping systems. • Incorrect heat treatment, in addition to proper instrumentation appropriate heat treatment schedules should consider specific compositions. • Bending, problems may be introduced following both hot or cold bending. • High-temperature operation in tubing leading to excessive scale formation and overheating. • Type IV cracking in welds which results from the local reduction in the heat affected zone strength resulting from welding thermal cycles. Review of key information regarding the high-temperature performance of creep strengthened ferritic steels shows that the long-term creep strength may not achieve the levels expected from simple extrapolation of short term data. The problems experienced are highlighted with reference to actual case histories. The additional challenges associated with the development of creep-fatigue damage in high-temperature plant operated in a cyclic mode are also discussed.

scholarly journals Estimation of Creep Strength of Grade 91 Steel Welded Joint in Time Region Over 100,000 Hours

2018 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Sosuke Nakahashi ◽  
Koji Tamura
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Base Metals ◽  
Creep Life ◽  
Initial State ◽  
Creep Tests ◽  
Grade 91 ◽  
Grade 91 Steel

A creep strength of welded joint of ASME Grade 91 steel in a region exceeding 100,000 hours was examined in this work. Creep tests were conducted on the steel used at USC plants for long-term, and remaining creep life of the material for operating condition was calculated on a fitting curve using Larson-Miller parameter. Total creep life of the material, which means a creep life at initial state, was presumed to be a summation of the service time at the plants and the remaining creep life. The estimation was conducted for welded joints used at five plants for long-term, and all results lay within 99% confidential band by the creep life evaluation curve of the material proposed by Japanese committee in 2015, while a significant heat-heat variation of creep strength was found even in the region exceeding 100,000 hours. Creep tests on base metals related to each welded joint were also conducted, and the estimation results of the total creep life of the base metals were compared to those of the welded joints. It was suggested that the heat-heat variation of the welded joints eminently depends on the creep life property of the corresponding base metal.

Creep Properties of Hastelloy-X Alloy for the High Temperature Gas-Cooled Reactor

2006 ◽  
Vol 326-328 ◽  
pp. 1105-1108 ◽  
Author(s):  
Woo Gon Kim ◽  
Sang Nan Yin ◽  
Woo Seog Ryu ◽  
Jong Hwa Chang
Keyword(s):  
High Temperature ◽  
Creep Data ◽  
Creep Life ◽  
Statistical Process ◽  
Hastelloy X ◽  
Creep Properties ◽  
Rupture Data ◽  
Term Creep ◽  
High Temperature Gas

The creep properties for the Hastelloy-X alloy which is one of candidate alloys for a high temperature gas-cooled reactor are presented. The creep data was obtained with different stresses at 950oC, and a number of the creep data was collected through literature surveys. All of the creep data were combined together to obtain the creep constants and to predict a long-term creep life. In the Norton’s creep law and the Monkman-Grant relationship, the creep constants, A, n, m, and m’ were obtained. Creep master curves based on the Larson-Miller parameter were presented for the standard deviations of 1σ, 2σ and 3σ. Creep life at each temperature was predicted for a longer-time rupture above 105 hours. Failure probability was also estimated by a statistical process of all the creep rupture data.

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.

The behaviour of friction piles in ice and ice-rich soils

1980 ◽  
Vol 17 (3) ◽  
pp. 405-415 ◽  
Author(s):  
N. R. Morgenstern ◽  
W. D. Roggensack ◽  
J. S. Weaver
Keyword(s):  
Test Data ◽  
Upper Bound ◽  
Creep Data ◽  
Creep Tests ◽  
Comprehensive Review ◽  
Flow Law ◽  
Term Creep ◽  
Good Agreement

A comprehensive review of long-term creep tests on ice has been undertaken and a flow law for ice has been proposed. Creep tests on ice-rich soils have also been reviewed, and it is concluded that the flow law for ice constitutes an upper bound to these test data. Using this flow law, pile velocities in ice and ice-rich soils have been predicted and the predictions are shown to be in good agreement with available long-term creep data for piles in ice and ice-rich soils.

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