Effects of Secondary Creep Formulation on API 579-1 Residual Life Evaluation

2017 ◽  
Author(s):  
Lorenzo Scano ◽  
Luca Esposito
Keyword(s):  
Life Prediction ◽  
Ad Hoc ◽  
Residual Life ◽  
Creep Damage ◽  
International Standards ◽  
Secondary Creep ◽  
Creep Life ◽  
Life Evaluation ◽  
Level 3 ◽  
The Impact

Although several ad hoc procedures are codified into main international standards, the creep life prediction remains a critical phase of each Fitness-For-Service assessment. Commonly, either a time-fraction or a ductility exhaustion approach can be used. In both cases, conservative predictions within a factor of 2 or 3 are expected [1]. However, since the procedures to determine the creep damage are based upon the results of a stress analysis, the residual life evaluation can be affected by the adopted creep formulation. The choice to use a simple modeling, only accounting for the dislocational creep range, could lead to overestimate the component creep life at low stresses, and this is also subtly true even at concentration points if triaxiality or deformation-controlled loading lead to marked stress relaxation over time. In this paper, the tube to header and the header to hemispherical end joints of a HRSG assembly were assessed by the API 579-1/ASME FFS-1 [2] Level 3 procedure, via inelastic FEA, changing the creep formulation to compare the results. The classical Nortons law was replaced by more sophisticated secondary creep models to account for the complex time-dependent stress-field. In particular, the primary and secondary stress re-distribution/relaxation in the creep range were investigated in order to evaluate the impact of the steady-state creep constitutive equation on the residual life prediction.

Effects of Primary and Secondary Creep Formulations on API 579-1 Residual Life Evaluation

2018 ◽  
Author(s):  
Lorenzo Scano ◽  
Luca Esposito
Keyword(s):  
Constitutive Equation ◽  
Residual Life ◽  
Creep Damage ◽  
Primary Creep ◽  
Secondary Creep ◽  
Time To Rupture ◽  
Life Evaluation ◽  
Omega Method ◽  
Material Constitutive Equation ◽  
Rate Formulation

A sound material constitutive equation is crucial for the residual life evaluation of pressure components operating in the creep range. In a previous work [1], the authors investigated how a secondary creep formulation encompassing both the dislocational and the diffusional range influences the assessment of damage according to API 579-1 [2] within the whole component stress range. In the present paper the work has been extended in order to include the effects of primary creep in the constitutive equation for the ASTM A335 P22 low-alloy steel used for the manufacturing of the HRSG header whose welded details were previously investigated. The creep damage was first calculated according to API 579-1 Section 10 via inelastic, time-dependent FEA and the Larson-Miller approach (LMP) with code-defined, minimum time-to-rupture data. This led to a first reckoning of the primary creep impact in terms of API 579-1 residual life for the components under evaluation. The API 579-1 time-to-rupture was then assessed with a detailed stress analysis implementing the Omega Method and its creep strain rate formulation. The obtained results were finally compared to those previously determined through the LMP procedure and the different creep correlations (secondary and primary+secondary).

scholarly journals Creep Damage Repair of a Nickel-Based Single Crystal Superalloy Based on Heat Treatment

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 623
Author(s):  
Xiaoyan Wang ◽  
Meng Li ◽  
Yuansheng Wang ◽  
Chengjiang Zhang ◽  
Zhixun Wen
Keyword(s):  
Heat Treatment ◽  
Single Crystal ◽  
Creep Damage ◽  
Primary Creep ◽  
Single Crystal Superalloy ◽  
Secondary Creep ◽  
Creep Life ◽  
Phase Coarsening ◽  
Damage Repair ◽  
Creep Time

Taking nickel-based single crystal superalloy DD6 as the research object, different degrees of creep damage were prefabricated by creep interruption tests, and then the creep damage was repaired by the restoration heat treatment system of solid solution heat treatment and two-stage aging heat treatment. The results show that with the creep time increasing, the alloy underwent microstructure evolution including γ′ phase coarsening, N-type rafting and de-rafting. After the restoration heat treatment, the coarse rafted γ′ phase of creep damaged specimens dissolved, precipitated, grew up, and became cubic again. Except for the specimens with creep interruption of 100 h, the γ′ phase can basically achieve the same arrangement as the γ′ phase of the original sample. The comparison of the secondary creep test shows that the steady-state creep stage of the test piece after the restoration heat treatment is relatively increased, and the total creep life can reach the same level as the primary creep life. The high temperature creep properties of the tested alloy are basically recovered, and the restoration heat treatment effect is good.

Life Prediction of Power Turbine Components for High Exhaust Back Pressure Applications: Part I — Disks

2015 ◽  
Author(s):  
Dipankar Dua ◽  
Brahmaji Vasantharao
Keyword(s):  
Steady State ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Life Prediction ◽  
Creep Damage ◽  
Back Pressure ◽  
System Level ◽  
Cyclic Life ◽  
Power Turbine ◽  
The Impact

Industrial and aeroderivative gas turbines when used in CHP and CCPP applications typically experience an increased exhaust back pressure due to pressure losses from the downstream balance-of-plant systems. This increased back pressure on the power turbine results not only in decreased thermodynamic performance but also changes power turbine secondary flow characteristics thus impacting lives of rotating and stationary components of the power turbine. This Paper discusses the Impact to Fatigue and Creep life of free power turbine disks subjected to high back pressure applications using Siemens Energy approach. Steady State and Transient stress fields have been calculated using finite element method. New Lifing Correlation [1] Criteria has been used to estimate Predicted Safe Cyclic Life (PSCL) of the disks. Walker Strain Initiation model [1] is utilized to predict cycles to crack initiation and a fracture mechanics based approach is used to estimate propagation life. Hyperbolic Tangent Model [2] has been used to estimate creep damage of the disks. Steady state and transient temperature fields in the disks are highly dependent on the secondary air flows and cavity dynamics thus directly impacting the Predicted Safe Cyclic Life and Overall Creep Damage. A System-level power turbine secondary flow analyses was carried out with and without high back pressure. In addition, numerical simulations were performed to understand the cavity flow dynamics. These results have been used to perform a sensitivity study on disk temperature distribution and understand the impact of various back pressure levels on turbine disk lives. The Steady Sate and Transient Thermal predictions were validated using full-scale engine test and have been found to correlate well with the test results. The Life Prediction Study shows that the impact on PSCL and Overall Creep damage for high back pressure applications meets the product design standards.

Extrapolation of Creep Curve and Creep Life Prediction From Secondary Creep by Evaluation of Strain Rate Change

2010 ◽  
Author(s):  
Hiroyuki Sato
Keyword(s):  
Strain Rate ◽  
Creep Curve ◽  
Life Prediction ◽  
Temperature Reconstruction ◽  
Rate Change ◽  
Secondary Creep ◽  
Creep Life ◽  
Strain Rate Change ◽  
Creep Life Prediction ◽  
Creep Curves

New method of creep life prediction by Strain-Acceleration-Parameter, SAP, is presented. Sato has found that shapes of creep curves can be characterized by the SAP that reflects magnitude of strain-rate change in secondary creep [1–4]. The SAP values are defined at minimum creep rates, and show the shapes of a creep curve, that depends on stress and temperature. Reconstruction of creep curves by a combination of SAP and a minimum-creep rate is successfully performed, and the extrapolated curves agree well with experiment. The predicted life times also reasonably agree with that obtained by experiment. The possibility of precise life prediction by SAP is pronounced. One of an important advantage of the proposed method is that the required parameters evaluated by individual creep curve are simpler than that are used in methods previously proposed, i.e., the theta projection concept, for example. Possibilities of wide application on many kinds of heat resistant materials should be investigated with the method of SAP.

The Significance of Thermo-Mechanical Fabrication on Long Term Creep Life of Type 316H Austenitic Stainless Steel Components

2016 ◽  
Vol 853 ◽  
pp. 384-388
Author(s):  
Ana Isabel Martinez-Ubeda ◽  
Alexander D. Warren ◽  
Ian Griffiths ◽  
Peter E.J. Flewitt
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Nuclear Power ◽  
Energy Dispersive Spectrometer ◽  
Creep Damage ◽  
Ion Milling ◽  
Creep Life ◽  
Thin Foils ◽  
The Impact

The UK’s Advanced Gas Cooled Reactor (AGR) nuclear power generating plant operates at temperatures up to 550 °C, where creep life is important. We consider Type 316H austenitic stainless steel headers and tubes with thermo-mechanical fabrication histories that result in significantly different initial microstructures. The heat affected zone of weldments, in these thick section headers and thin walled boiler tubes, have been found to be susceptible to creep damage leading to cracking during service. In this work we explore these differences in the long term service aged microstructure and the link to overall creep life of these components. To achieve this, samples containing weldments have been removed from plant after extended periods of service. Specifically parent and HAZ regions have been examined to determine the types of precipitates arising from the long term ageing. In particular, thin foils have been examined in a JEOL ARM transmission electron microscope operating at 200KeV fitted with an Oxford Instruments energy dispersive spectrometer to allow comparison between high resolution images and chemical composition. The thin foils were removed from predetermined locations using gallium ion milling and finally thinned using a low ion current to minimise ion damage. Differences between the distributions and types of precipitates are considered in the context of the initial microstructure arising from the thermo-mechanical history on the loss of creep strength and initiation of creep cavities at grain boundaries. The impact on overall service life is addressed.

Research on a New Secondary Creep Model and Creep Damage Evolution for P92 Steel

2013 ◽  
Vol 690-693 ◽  
pp. 157-163 ◽  
Author(s):  
Jun Yuan ◽  
Hong Xu ◽  
Yong Zhong Ni
Keyword(s):  
Experimental Data ◽  
Stress Exponent ◽  
Creep Damage ◽  
Creep Model ◽  
Secondary Creep ◽  
Creep Life ◽  
P92 Steel ◽  
Tertiary Stage ◽  
Creep Constitutive Model ◽  
Damage Equation

In the traditional Norton-Bailey model, the stress exponent is a constant value when the temperature keeps constant, But for some materials, this situation can’t be suitable. Based on the analysis of the experimental data, a secondary creep constitutive model which can be used in the stress exponent changing situation has been proposed. By introducing Kachanov-Rabotnov damage equation, the modified creep model has been established for P92 steel at 610°C and 670°C, which can describe the second and tertiary stage. And the method to determine creep parameters of tertiary stage has been derived. The new model was embedded into ANSYS interface program, and used for calculating the creep life of P92 steel. The results show that the model is in agreement with the experimental data.

Stress Relaxation Damage Analysis for High Temperature Bolting

2012 ◽  
Vol 455-456 ◽  
pp. 1429-1433
Author(s):  
Jin Quan Guo ◽  
Xiao Hong Sun ◽  
Hui Chao Shi
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Stress Relaxation ◽  
Life Prediction ◽  
Creep Damage ◽  
Damage Analysis ◽  
Damage Mechanisms ◽  
Life Evaluation ◽  
Relaxation Characteristics ◽  
Life Prediction Model

The paper analyzes the stress relaxation damage mechanisms of high temperature (HT) bolts of ultra-supercritical steam turbine units. Based on creep damage mechanisms and relaxation characteristics, the paper proposes a life prediction model, and by which to predict relaxation damage life of HT bolting material 1Cr10NiMoW2VNbN. Validation results indicate that the developed model has led to better consistent results with experimental data and thus can be recommended in relaxation life evaluation of HT materials.

Improving Component Life Prediction Accuracy and Reliability Through Physics Based Prognosis: A Probabilistic Turbine Blade Case Study

2008 ◽  
Author(s):  
Ashok K. Koul ◽  
Saurabh Bhanot ◽  
Ajay Tiku ◽  
Brent Junkin
Keyword(s):  
Life Prediction ◽  
Residual Life ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Life Extension ◽  
Inlet Temperature ◽  
Damage Analysis ◽  
Creep Life ◽  
Critical Locations

The paper presents the results of a probabilistic creep life study on RRA 501 KB turbine blades and demonstrates the importance of using physics based probabilistic damage modeling techniques to deal with life prediction uncertainty in cast equiaxed components. It is shown that physics based damage analysis yields accurate results and considerably less mechanical properties data is needed for life prediction of cast components. In physics based damage analysis, it is also easy to quickly assess the life limiting damage modes and to establish fracture critical locations in components. In physics based modeling, the influence of individual microstructural or thermal-mechanical loading factors on metallurgical crack nucleation can also be studied with relative ease. Residual life of service exposed parts and effectiveness of life extension techniques can also be predicted because the state of microstructure due to prior service and repair can be taken into account. In this study, Life Prediction Technologies Inc.’s (LPTi’s) prognosis tool known as XactLIFE™ was successfully used to establish the fracture critical location of RRA 501KB first stage gas turbine blades under steady state loads. Deterministic analysis was first used to compute the lower bound airfoil nodal creep life of the various finite element nodes and this was followed by probabilistic creep life analysis to take into account the variability of microstructure from one blade to another. The analysis used typical engine operating data from the field in terms of engine speed and average turbine inlet temperature (TIT). The primary objectives of the case study are to show how prognosis can allow a user to predict component fracture critical locations, establish inspection intervals to avoid failures and establish fleet reliability for engine specific operating conditions.

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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