Characterizing the Influence of Cyclic Re-Priming on the Prediction of Long Term Creep Damage for Gas Turbine Components

2018 ◽  
Author(s):  
Richard Green ◽  
Jonathan Douglas ◽  
Andrew Moffat ◽  
Richard Bellows
Keyword(s):  
Creep Rate ◽  
Gas Turbines ◽  
Hold Time ◽  
Creep Damage ◽  
Creep Tests ◽  
Recovery Potential ◽  
Industrial Gas Turbines ◽  
Actual Operation ◽  
Isothermal Creep ◽  
Term Creep

Industrial Gas Turbines have traditionally been designed for base load operation. However, modern applications require flexibility as well as availability. These requirements lead to components in the hot section experiencing both cyclic and hold time loading, at high temperatures. These loading profiles inevitably lead to damage from both fatigue, due to engine cycles, and creep, due to dwells at load, as well as the interaction of these two damage mechanisms over the duration of the service interval. It is these interactions which can lead to higher average creep rates and more damage than expected. This paper presents the results of a study into the influence of cyclic loading on the average creep rate for a proprietary single crystal nickel based alloy, which is based on the chemistry of INCONEL® 792, a relatively high chromium, gamma/gamma-prime strengthened superalloy. Creep tests have been conducted isothermally with reload cycles of varying duration (or dwell) that result in an unexpected reduction in creep life and an increase in overall creep rate when compared to the continuous isothermal creep tests performed at constant stress without reloading. A hypothesis is presented which attributes the increase in overall creep rate to the influence of a recovery potential stress. The dwell period of each reload cycle is critical to calculating the recovery potential and subsequent creep rate. Results show that tests with relatively short dwell periods exhibited lower lives and higher creep rates than tests with fewer cycles and longer dwell periods. The implication of these findings are significant when considering actual operation, where variations in engine cycles and dwell periods, could influence the accumulation of creep damage. Therefore, an initial approach is presented which accounts for cycles as part of the creep damage calculation.

A Constitutive Model for Predicting Modified Creep Strain Rates due to Cyclic Loading of Gas Turbine Components

2019 ◽  
Author(s):  
Richard Green ◽  
Jonathan Douglas ◽  
Andrew Moffat ◽  
Brent Scaletta
Keyword(s):  
Cyclic Loading ◽  
Creep Rate ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Traditional Approach ◽  
Rate Equations ◽  
Creep Tests ◽  
Subsequent Work ◽  
Recovery Potential ◽  
Dwell Period

Abstract The traditional approach to the design of industrial Gas Turbines considers base load operation. This assumption is no longer applicable as owner operators require more operational flexibility and increased availability and reliability. Flexibility in operation manifests as increased cyclic loading and variations in on and off load dwell periods and thermal loads. These complex loading profiles inevitably lead to damage from both creep and fatigue, and interaction of these two damage mechanisms over the duration of the service interval. These interactions can result in higher average creep rates and more damage than expected. Robust, path dependent modeling approaches are required to better understand the effects of flexible operation on material response and subsequent damage. Moreover, a unified approach to creep-fatigue is significantly more effective at capturing this behavior. There are several types of interactions that can drive additional damage. These include relatively well understood mechanisms, such as the effect of plasticity on primary creep and the effect of creep dwells on cyclic material properties. Other interactions that are less well understood include interruptions to the load during creep dwells and the effects of off-load periods on the overall creep rate. This paper considers a constitutive approach to predict the modified creep rate due to load interruptions and off-load dwells using a backstress model. The backstress model is included in the calculation of inelastic strain rate equations, using a Chaboche type formulation. The model has been fitted to conventional material test data for typical superalloys used in gas turbine applications. To validate the approach, forward creep tests were conducted with varying interruptions to the load during the creep dwell period. These tests show a reduction in creep life and an increase in overall creep rate, when compared with the results for a constant stress and temperature condition. Previous work, presented by the authors [1], outlined a hypothesis that attributes the increase in overall creep rate to the influence of a recovery potential stress. This paper presents the subsequent work which demonstrates that the recovery potential stress can be defined by the difference between the applied stress and the backstress. It is shown that the dwell period between reload cycles is critical for calculating the recovery potential and overall creep rate.

Evaluation of Microstructures and Creep Damages in HAZ of P91 Steel Weldment

2007 ◽  
Author(s):  
Masaaki Tabuchi ◽  
Hiromichi Hongo ◽  
Yongkui Li ◽  
Takashi Watanabe ◽  
Yukio Takahashi
Keyword(s):  
Damage Mechanics ◽  
Early Stage ◽  
Rupture Life ◽  
Creep Damage ◽  
Specimen Thickness ◽  
Creep Tests ◽  
Steel Weldment ◽  
Type Iv ◽  
Damage Process ◽  
Term Creep

The present paper aims to clarify the Type IV creep damage process of Mod.9Cr-1Mo (Gr.91) steel weldment. Long-term creep tests for base metal and simulated fine-grained HAZ and welded joints were conducted at 550, 600 and 650 °C. Furthermore, creep tests of thick welded joint specimens were interrupted at 0.2, 0.5, 0.7, 0.8, 0.9 of rupture life, and damage distributions were measured quantitatively. It was found that creep voids initiated at the early stage of life inside the specimen thickness, and grew into cracks at the later stage of life. Experimental creep damage distributions were compared with computed ones using FEM and damage mechanics analysis. The effect of multiaxial stress condition on creep damage evolution is discussed.

3D Imaging Using X-Ray Tomography and SEM Combined FIB to Study Non Isothermal Creep Damage of (111) Oriented Samples of γ / γ ' Nickel Base Single Crystal Superalloy MC2

2012 ◽  
Vol 706-709 ◽  
pp. 2400-2405 ◽  
Author(s):  
Mustapha Jouiad ◽  
J. Ghighi ◽  
Jonathan Cormier ◽  
E. Ostoja-Kuczynski ◽  
G. Lubineau ◽  
...  
Keyword(s):  
Single Crystal ◽  
Ion Beam ◽  
Creep Damage ◽  
Creep Tests ◽  
Deformation Localization ◽  
X Ray ◽  
Oriented Samples ◽  
Isothermal Creep ◽  
Nickel Base ◽  
Observed Damage

An unprecedented investigation consisting of the association of X-Ray tomography and Scanning Electron Microscopy combined with Focus Ion Beam (SEM-FIB) is conducted to perform a 3D reconstruction imaging. These techniques are applied to study the non-isothermal creep behavior of close (111) oriented samples of MC2 nickel base superalloys single crystal. The issue here is to develop a strategy to come out with the 3D rafting of γ’ particles and its interaction whether with dislocation structures or/and with the preexisting voids. This characterization is uncommonly performed away from the conventional studied orientation [001] in order to feed the viscoplastic modeling leading to its improvement by taking into account the crystal anisotropy. The creep tests were performed at two different conditions: classical isothermal tests at 1050°C under 140 MPa and a non isothermal creep test consisting of one overheating at 1200°C and 30 seconds dwell time during the isothermal creep life. The X-Ray tomography shows a great deformation heterogeneity that is pronounced for the non-isothermal tested samples. This deformation localization seems to be linked to the preexisting voids. Nevertheless, for both tested samples, the voids coalescence is the precursor of the observed damage leading to failure. SEM-FIB investigation by means of slice and view technique gives 3D views of the rafted γ’ particles and shows that γ corridors evolution seems to be the main creep rate controlling parameter.

scholarly journals A 3D Creep Model considering Disturbance Damage and Creep Damage and Its Application in Tunnel Engineering

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Geng-Feng Wang ◽  
Fan Sun ◽  
Xiao-Hui Xiong ◽  
Lei He ◽  
Ke-Hong Zhang
Keyword(s):  
Space Dimension ◽  
Creep Damage ◽  
Wave Theory ◽  
Creep Model ◽  
Time Dimension ◽  
Creep Tests ◽  
Railway Tunnel ◽  
Damage Theory ◽  
Term Creep

Based on the Kachanov damage theory and elastic wave theory, considering the long-term creep damage from time dimension and instantaneous disturbance damage from space dimension, we presented a 3D damage creep model and converted it to difference expressions in order to write into the finite difference software FLAC3D. Then, according to the results of creep tests, we conducted parameter inversion of our damage creep model with the help of the particle swarm optimization (PSO) method. Finally, the damage creep model was applied in a railway tunnel project in Yunnan to simulate the tunnel deformation. Compared with the Burgers model and the model considering only creep damage, our model which considers both creep damage and disturbance damage yielded more reasonable results.

Predicting the Time to Failure in Heavily Loaded Masonry Specimens with the Acoustic Emission Technique

2010 ◽  
Vol 133-134 ◽  
pp. 217-222 ◽  
Author(s):  
Els Verstrynge ◽  
Luc Schueremans ◽  
Dionys Van Gemert
Keyword(s):  
Acoustic Emission ◽  
Failure Time ◽  
Event Rate ◽  
Creep Damage ◽  
Time To Failure ◽  
Creep Tests ◽  
Strain Monitoring ◽  
Specimen Processing ◽  
Term Creep

This paper presents the results of a research project in which the knowledge on testing of creep damage in masonry and acoustic emission (AE) monitoring are combined. Results from different types of creep tests are combined to investigate whether AE monitoring could predict the failure time of the masonry specimens. In previous work, it was observed that the AE event rate is related to the time to failure of the specimen. Processing of the results of new tests enables to update the previously found relation between AE event rate and failure time and to indicate a confidence interval for predictions made with this model. Additionally, the question can be raised whether temporary monitoring could detect unstable damage accumulation and predict failure. Therefore, the results of long-term creep tests are analysed and compared with data from strain monitoring. The results indicate that in most cases, the failure can be predicted.

Modeling and Experimental Study of Long Term Creep Damage in Austenitic Stainless Steels

2013 ◽  
Vol 592-593 ◽  
pp. 83-86 ◽  
Author(s):  
Yi Ting Cui ◽  
Maxime Sauzay
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
Cavity Growth ◽  
High Stress ◽  
Austenitic Stainless Steels ◽  
Creep Damage ◽  
Future Generation ◽  
Creep Tests ◽  
Term Creep

Austenitic Stainless Steels (SSs) are presently being investigated as appropriate candidates for structural components for the future Generation IV nuclear reactors. Austenitic SSs of different grades will operate at high temperature and suffer low stress loading for decades. At the laboratory, austenitic SSs have been subjected to creep tests at various stresses and temperatures between 500°C to 700°C, up to nearly 50·103h. Interrupted creep tests show an acceleration of the reduction in cross-section only during the last 15% of creep lifetime which may be called macroscopic necking. The modeling of necking using a modified Norton power-law allows lifetime predictions in agreement with experimental data up to a few thousand hours only. And the experimental results show that, the extrapolation of the 'stress lifetime curves obtained at high stress leads to large overestimations of lifetimes at low stress. After FEGSEM observations, these overestimates are mainly due to additional intergranular cavitation along grain boundaries. The modeling of cavity growth by vacancy diffusion along grain boundaries coupled with continuous nucleation proposed by Riedel has been carried out. Lifetimes for long term creep are rather correctly predicted with respect to experimental lifetimes. The lifetime curves predicted by either the necking model or the creep cavity one cross each other, defining transition times of five to ten thousand hours for temperatures between 600°C and 700°C, in agreement with experimental curves.

A Dynamic Systems Based Approach to Estimate Cyclic and Creep Damage of a Power Turbine Blade Subjected to a Random Transient Operation

2021 ◽  
Author(s):  
Dipankar Dua ◽  
Quang Le ◽  
Anthony Saladino ◽  
Deepak Thirumurthy ◽  
Jaskirat Singh
Keyword(s):  
Dynamic Systems ◽  
Gas Turbines ◽  
Creep Damage ◽  
Continuous Assessment ◽  
Computationally Efficient ◽  
Operating Cycle ◽  
Engine Operation ◽  
Power Turbine ◽  
Actual Operation ◽  
Stage 1

Abstract The Paper presents a novel computationally efficient physics based framework for continuous assessment of cyclic and time dependent damage consumption for Siemens Aeroderivative power turbine components based on actual engine operation. The framework discussed in paper provides the capability for Siemens’ customers to move away from fixed overhaul schedule to a customized schedule which is based on a given gas turbines actual operation and inspection findings. This customized overhaul schedule enables the customers a flexibility to maximize the unit availability and minimize operating costs. Semi-empirical framework discussed in this paper, utilizes dynamic systems theory-based approach to estimate the cyclic & creep damage as a response to transient engine operation; characterized by relevant installed engine instrumentation data from the Engine Health Monitoring system. To estimate damage response through any given complex transient operating cycle, algorithm solves a set of ordinary differential equations (ODEs), that have been calibrated to the engine control and safety instrumentation parameters such as shaft speed, turbine temperatures, pressures etc. by pre-analyzed operating envelope cases. The framework can be setup for predicting accumulated cyclic and creep damage for all type of turbine components (Aerofoils, disks, casings, diffusers etc.), transient stress state complexity (in-phase, out-of-phase, uniaxial, multiaxial stress profiles) and is capable to handle unit specific ramp rates, start-up times, restart/cooldown effects specific and random changes in load, history. The framework for discussion in this paper has been demonstrated as applied to the stage-1 blade of an A-35 RT62 power turbine as an example.

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.

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