The effect of hydrostatic pressure on the uniaxial creep life of a 2 ¼ % Cr 1% Mo steel

1981 ◽  
Vol 373 (1755) ◽  
pp. 491-509 ◽  
Keyword(s):  
Hydrostatic Pressure ◽  
Cavity Growth ◽  
Pressure Effects ◽  
Time To Failure ◽  
Creep Life ◽  
Creep Tests ◽  
Creep Ductility ◽  
Uniaxial Creep ◽  
Term Creep ◽  
Bainite Microstructure

The effect of a superimposed hydrostatic pressure on the ductility, the creep life and the failure mechanism of a 2 ¼ % Cr 1 % Mo steel, with an over-aged upper bainite microstructure, subject to different uniaxial stresses is described. Creep tests have been made at 923 K with uniaxial stresses in the range 55-80 MPa and superimposed hydrostatic pressures up to 35MPa. Optical and electron optical microscopy have been used to assess the accumulation of grain boundary damage arising from creep deformation. When failure is controlled by intergranular cavitation, increasing the hydrostatic pressure causes an increase in the creep ductility and a decrease in cavitation, and thus an increase in time to failure. In addition, increasing pressure effects a change in failure mode from one controlled by the nucleation and growth of intergranular cavities to one controlled by plastic flow. The results for the creep of this 2¼ % Cr 1 % Mo steel are discussed in terms of a diffusional cavity growth model which includes continuous nucleation. Moreover, these results are compared with data previously obtained for single phase materials tested with a superimposed hydrostatic pressure. The relative contributions of the principal and equivalent stresses to the creep fracture of this low alloy steel are also examined. The estimation of realistic long-term creep life from the results of short-term creep tests is also discussed.

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.

Comparative Creep Life Evaluation of HR3C Using Creep Damage Models

2017 ◽  
Author(s):  
Seok-Jun Kang ◽  
Hoomin Lee ◽  
Moon-Ki Kim ◽  
Jae-Boong Choi
Keyword(s):  
High Temperature ◽  
Power Plant ◽  
Material Properties ◽  
Creep Life ◽  
Creep Tests ◽  
Damage Models ◽  
Life Evaluation ◽  
Uniaxial Creep ◽  
Dyson Model ◽  
Term Creep

Recently, due to both environmental and energy efficiency, the designed life cycle of many power plant have been extended and also their operating temperature increased. When a material is exposed to high temperature over 50% of its melting temperature, it often shows unusual creep behavior in which the long time exposure of high temperature causes a microstructural degradation in the material and leads to creep rupture at a stress much lower than yield. Thus, there is a great significance in evaluating the creep life of high temperature components in power plant. In this study, accelerated uniaxial creep tests have been conducted to obtain material properties of HR3C at high temperature. The material properties of three damage models were derived from the accelerated short term creep tests in different stress conditions and the constitutive equation was the form of a power-law for the Kachanov and Liu-Murakami damage models and a hyperbolic sine function for the Dyson model, respectively. Based on these three damage models, the long term creep life was also evaluated. Using the creep rupture envelope, a modified grain boundary constrained cavitation coefficient function is proposed to resolve the constant failure strain problem. Also another modifications is made to the aging coefficient calculation by suggesting a new type of optimization function. By this, the classical problem of rupture time underestimation in the original Dyson model has been resolved. Consequently, the suggested creep life evaluation technique with a simple uniaxial creep example can be extended to more complicated engineering components at high temperature.

An Improved Omega-Based Method for Creep Life Prediction Using Hyperbolic Sine Stress Correlation

2019 ◽  
Vol 795 ◽  
pp. 130-136
Author(s):  
Xinyu Yang ◽  
Richard Barrett ◽  
Sean B. Leen ◽  
Jian Ming Gong
Keyword(s):  
Life Prediction ◽  
Creep Damage ◽  
Creep Life ◽  
Creep Tests ◽  
Inconel Alloys ◽  
Hyperbolic Sine ◽  
Omega Method ◽  
Creep Life Prediction ◽  
Uniaxial Creep ◽  
Term Creep

This paper is concerned with the creep life prediction of cast 20Cr32NiNb alloy, an alternative candidate material to wrought Inconel alloys for use in the gas collector pipes of CO reformers which suffer from long-term creep damage due to high temperatures and stresses. Uniaxial creep tests of 20Cr32NiNb alloy were performed at 890 °C and 950 °C for different stresses. The Omega method for creep life prediction is applied to the 20Cr32NiNb tests and shown to give reasonably accurate prediction, particularly at low stress levels. A new method, based on the use of a hyperbolic sine function for stress correlation at specific temperatures for identification of the characteristic Omega parameters is presented and validated.

A Study on Estimation of Internal Pressure Creep Life Using Small Punch Creep (SPC) Tests for Boiler Pipes

2009 ◽  
Author(s):  
Toshimi Kobayashi ◽  
Toru Izaki ◽  
Junichi Kusumoto ◽  
Akihiro Kanaya
Keyword(s):  
Internal Pressure ◽  
Residual Life ◽  
Test Results ◽  
Creep Life ◽  
Creep Tests ◽  
Good Correspondence ◽  
Small Punch ◽  
Uniaxial Creep ◽  
Wide Range ◽  
The Relationship

The small punch creep (SPC) test is possible to predict residual creep life at a high accuracy. But, the results of SPC tests cannot be compared with uniaxial creep or internal pressure creep results directly. In this report, the relationship between SPC test results and uniaxial creep test results in ASME A335 P11 (1.25Cr-0.5Mo Steel) was studied. The obtained relationship between SPC load and equivalent uniaxial creep stress formed a simple linear equation under the wide range of test temperature and test period. Then, the SPC results can be compared with uniaxial results by converting SPC loads to the equivalent uniaxial creep stresses. The relationship between SPC test results and internal pressure creep tests results was also studied. The internal creep life of as-received P11 pipe was almost same as SPC result when the hoop stress was converted to the SPC load. The creep lives of internal pressure creep influenced materials also showed good correspondence with SPC results. Therefore SPC can estimate the residual life of internal pressure creep influenced materials.

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.

Microstructure and Creep Properties of AISI 316LN Steels with Niobium Additions

2005 ◽  
Vol 482 ◽  
pp. 275-278 ◽  
Author(s):  
Vlastimil Vodárek ◽  
Gabriela Rožnovská ◽  
Jaromír Sobotka
Keyword(s):  
S Phase ◽  
Creep Life ◽  
Creep Ductility ◽  
Niobium Content ◽  
Creep Properties ◽  
Size Refinement ◽  
Tertiary Stage ◽  
Type Aisi ◽  
Term Creep

The long-term creep rupture tests have been carried out on three casts of a type AISI 316LN steel at 600 and 650°C. Two of the casts investigated contained additions of 0.1 and 0.3 wt.% of niobium. The growing niobium content strongly reduced the minimum creep rate and prolonged the time to the onset of the tertiary stage of creep and also shortened this stage. The enhanced creep resistance of niobium containing steels is not accompanied by the longer creep life that might have been expected. At both temperatures of creep exposure the niobium-bearing casts displayed an inferior creep ductility. Microstructural investigations revealed that niobium provoked significant grain size refinement and the formation of Z-phase. Particles of this phase were considerably dimensionally stable. Furthermore, niobium accelerated the formation and coarsening of s-phase, h-Laves and M6(C,N). The coarse intergranular particles facilitated the formation of cavities which resulted in intergranular failure mode.

Effect of Hydrogen on Creep Properties of SUS304 Austenitic Stainless Steel

CORROSION ◽  
10.5006/3678 ◽  
2020 ◽  
Author(s):  
Daisuke Takazaki ◽  
Toshihiro Tsuchiyama ◽  
Ryosuke Komoda ◽  
Mohsen Dadfarnia ◽  
Brian Somerday ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Life Time ◽  
Hydrogen Gas ◽  
Dislocation Creep ◽  
Absolute Pressure ◽  
Carbide Formation ◽  
Time To Failure ◽  
Creep Life ◽  
Creep Ductility

The objective of this study is to derive mechanistic insight into the degradation of metals in high-temperature hydrogen in order to enable the safety of evolving hydrogen technologies that operate at elevated temperature. Creep testing was carried out in argon and hydrogen gases under absolute pressure of 0.12 MPa at 873 K. The material was JIS SUS304 austenitic stainless steel. Results revealed that the creep life (time-to-failure) and creep ductility (strain-to-failure) of the SUS304 in hydrogen gas and in argon displayed opposite trends. While the creep life (time-to-failure) of the SUS304 in hydrogen gas was significantly shorter than that in argon, creep ductility (strain-to-failure) was higher in hydrogen. Associated with the relatively higher creep ductility, evidence of transgranular microvoid coalescence was more prevalent on fracture surfaces produced in hydrogen compared to those produced in argon. In addition, analysis of the steady state creep relationships in hydrogen and argon indicated that the same creep mechanism operated in the two environments, which was deduced as dislocation creep. Regarding the mechanisms governing reduced creep life in hydrogen, the effects of decarburization, carbide formation and the hydrogen-enhanced localized plasticity (HELP) mechanism were investigated. It was confirmed that these effects were not responsible for the reduced creep life in hydrogen, at least within the creep life range of this study. Alternately, the plausible role of hydrogen was to enhance the vacancy density, which led to magnified lattice diffusion (self-diffusion) and associated dislocation climb. As a consequence, hydrogen accelerated the creep strain rate and shortened the creep life.

Graded Creep Deformation Properties of 316H Welds and its Impact on Creep

2018 ◽  
Author(s):  
S. Dey ◽  
D. M. Knowles ◽  
C. E. Truman
Keyword(s):  
Stress Distribution ◽  
Base Metal ◽  
Creep Deformation ◽  
Creep Damage ◽  
Impression Creep ◽  
Uniform Stress ◽  
Creep Tests ◽  
Creep Ductility ◽  
Uniaxial Creep ◽  
Deformation Properties

The creep damage evolution in multi-pass welds is believed to be influenced by the variation of creep rates from the weld to the base metal and through the HAZ. Material heterogeneity in a multi-pass weld leads to a non-uniform stress distribution resulting in non-uniform evolution of creep strains with strain localisation. Also, a non-uniform stress distribution may lead to highly multiaxial stress states in the weld resulting in a lower creep ductility. Since creep damage in metallic components is influenced by creep strain rate and creep ductility of the material amongst other factors, creep inhomogeneity in a weldment may significantly affect creep damage accumulation. Therefore, in order to predict creep behaviour of a multi-pass weld, it is important to take into account the gradation of creep deformation properties through the weld HAZ. Impression creep tests are useful in revealing localised creep properties in a material, where test results can be directly correlated to uniaxial creep tests. In this paper, a 2D finite element model of a multipass 316H weld with three different material sections (weld, HAZ, parent) is used to demonstrate the effects of creep deformation mismatch on stress and strain distributions. The paper also describes a series of impression creep tests planned and being conducted on an ex-service 316H weldment from a power plant steam generator with specimens taken from locations in the HAZ and at varying proximities to the weld fusion line. One specimen from the far away base metal and one from the weld centerline were also taken to serve as reference since the uniaxial creep deformation properties for the weld and the base material are known from uniaxial creep tests. By comparing the minimum creep rates for the HAZ specimens against the reference specimens from the weld and the base metal, Norton’s law creep coefficients and stress exponents will be derived for the HAZ specimens thereby revealing the gradation of creep deformation properties as a function of distance from the weld fusion line.

Residual Life Assessment of 2.25Cr-1Mo Boiler Pipe by Small Punch Creep Test

2006 ◽  
Author(s):  
Junichi Kusumoto ◽  
Akihiro Kanaya ◽  
Toshimi Kobayashi
Keyword(s):  
Residual Life ◽  
Life Assessment ◽  
Creep Life ◽  
Creep Tests ◽  
Assessment Technique ◽  
Small Punch ◽  
Creep Stress ◽  
Uniaxial Creep ◽  
Residual Life Assessment ◽  
Creep Life Assessment

The non-destructive techniques such as the microstructural assessment are usually performed for residual creep life assessment of plant components. Since these techniques have limited accuracy, destructive assessment techniques such as uniaxial creep tests are required to improve the accuracy of the assessment. However, if this type of destructive assessment technique are applied, the sampling and the weld repair damages the material, and also the assessment will become expensive. On the other hand, small punch creep (SPC) test [1,2], which uses miniature-sized specimens, does not cause any serious sampling damages, and its assessment accuracy is high since it is a mechanical assessment technique. However, in applying the SPC test to the residual creep life assessment of the boiler in service, there are some issues to be studied [1,3,4]. In order to apply SPC test to the residual creep life assessment of the 2.25Cr-1Mo steel boiler pipe, the relationship between uniaxial creep stress and the SPC test load has been studied. And the Omega method [5] by SPC test was also studied.

Creep Life Prediction of HR3C Steel Using Creep Damage Models

2017 ◽  
Author(s):  
Hoomin Lee ◽  
Seok-Jun Kang ◽  
Jae-Boong Choi ◽  
Moon-Ki Kim
Keyword(s):  
Life Prediction ◽  
Power Plants ◽  
Creep Damage ◽  
Creep Rupture ◽  
Creep Life ◽  
Damage Models ◽  
Creep Life Prediction ◽  
Uniaxial Creep ◽  
Term Creep

The world’s energy market demands more efficient power plants, hence, the operating conditions become severe. For thermal plants, Ultra Super Critical (USC) conditions were employed with an operating temperature above 600°C. In such conditions, the main failure mechanism is creep rupture behavior. Thus, the accurate creep life prediction of high temperature components in operation has a great importance in structural integrity evaluation of USC power plants. Many creep damage models have been developed based on continuum damage mechanics and implemented through finite element analysis. The material constants in these damage models are derived from several accelerated uniaxial creep experiments in high stress conditions. In this study, the target material, HR3C, is an austenitic heat resistant steel which is used in reheater/superheater tubes of an USC power plant built in South Korea. Its creep life was predicted by extrapolating the creep rupture times derived from three different creep damage models. Several accelerated uniaxial creep tests have been conducted in various stress conditions in order to obtain the material constants. Kachanov-Rabotnov, Liu-Murakami and the Wen creep damage models were implemented. A comparative assessment on these three creep damage models were performed for predicting the creep life of HR3C steel. Each models require a single variable to fit the creep test curves. An optimization error function were suggested by the authors to quantify the best fit value. To predict the long term creep life of metallic materials, the Monkman-Grant model and creep rupture property diagrams were plotted and then extrapolated over an extended range. Finally, it is expected that one can assess the remaining lifetime of UCS power plants with such a valid estimation of long-term creep life.

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