Assessment of Creep Damage by NDT

1988 ◽  
Vol 142 ◽  
Author(s):  
Herbert H. Willems
Keyword(s):  
Creep Damage ◽  
Residual Lifetime ◽  
Strain Gages ◽  
Lifetime Analysis ◽  
Creep Cavitation ◽  
Long Time ◽  
Capacitive Strain ◽  
Replication Technique ◽  
Industrial Needs ◽  
Service Inspection

AbstractResidual lifetime analysis of power plant components requires information on the degree of degradation of the material. In case of hightemperature creep, material damage can be related to cavity formation or to the accumulated creep strain. At present, only metallographic replication technique is widely used for in-service inspection to detect creep cavitation. Other NDT-techniques like ultrasonic velocity and electrical resistivity, which have potential for detection of low pore concentrations, are being developed for practical application. The use of capacitive strain gages yields encouraging results for the long-time monitoring of creep deformation. Potential and limits of these NDT-techniques together with industrial needs for creep damage assessment are reviewed.

Quantification of Creep Cavity Evolution Using a Novel Replica Image Processing Technique

2012 ◽  
Author(s):  
Haoliang Yang ◽  
Catrin M. Davies ◽  
John P. Dear
Keyword(s):  
Image Processing ◽  
Creep Damage ◽  
Potential Drop ◽  
Surface Damage ◽  
Practical Method ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Creep Cavitation ◽  
High Temperature Components ◽  
Replication Technique

In industry, the surface replication technique is employed as a practical method for the lifetime assessment of high temperature components. However, the method is limited as it is a time consuming processes, is susceptible to subjective interpretations and is only sensitive to surface damage, whereas creep damage often initiates sub-surface. A replica of a component’s surface is made by applying a softened plastic foil to it. This foil moulds itself to the alloy’s surface when pressed. After its removal from the alloy, the plastic replica provides an exact copy of the etched surface’s microstructure, which can then be examined. A new image processing technique has been developed that provides a reliable and repeatable, quantified measure of creep cavitation using images obtained from replica films. A series of interrupted tests have been performed at the same load on 2.25CrMo (P22) ferritic steel at 650 °C. Post testing, samples were prepared and replication performed. A quantitative 2D map of the cavities across the specimens’ surface has been obtained using a novel image processing technique. The results are related to the specimens’ strain measurements using a displacement gauge and a novel potential drop technique. This new image processing technique may provide a valuable tool for industry.

Preliminary Review of the Influence of Cavitation Behavior in Creep Damage Constitutive Equations

2014 ◽  
Vol 940 ◽  
pp. 46-51 ◽  
Author(s):  
Xin Yang ◽  
Qiang Xu ◽  
Zhong Yu Lu ◽  
Simon Barrans
Keyword(s):  
Reference Value ◽  
Creep Damage ◽  
Preliminary Review ◽  
Current Application ◽  
Cavitation Damage ◽  
X Ray ◽  
Creep Cavitation ◽  
Cr Steels ◽  
Cavitation Behavior ◽  
Damage Equation

This review paper mainly consists of from two aspects: (a) the evolution of the cavitation damage equation from Dyson to current application in high Cr steels by traditional techniques; (b) quantitation analyses of cavitation behavior in brass, copper, dual phase steel from X-ray microtomtograph. Though there is a lack of experimental data for high Cr steels by X-ray microtomography currently, but (b) has provided reference value for studying creep cavitation behavior in high Cr steels. This paper will be the fundamental of development new creep damage constitutive equation through quantitation analyses of X-ray tomography.

Investigation of Strain Gages for Long-Time Static Testing to 650 F

2009 ◽  
pp. 142-142-9
Author(s):  
Herbert Yanowitz ◽  
Irwin Berman ◽  
Alfred Bleiweis
Keyword(s):  
Strain Gages ◽  
Static Testing ◽  
Long Time

scholarly journals Application of Fundamental Models for Creep Rupture Prediction of Sanicro 25 (23Cr25NiWCoCu)

Crystals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 638
Author(s):  
Junjing He ◽  
Rolf Sandström
Keyword(s):  
Grain Boundary Sliding ◽  
Empirical Models ◽  
Creep Rupture ◽  
Solid Solution Hardening ◽  
Physical Parameters ◽  
Brittle Creep ◽  
Creep Cavitation ◽  
Long Time ◽  
Boundary Sliding ◽  
Term Creep

Creep rupture prediction is always a critical matter for materials serving at high temperatures and stresses for a long time. Empirical models are frequently used to describe creep rupture, but the parameters of the empirical models do not have any physical meanings, and the model cannot reveal the controlling mechanisms during creep rupture. Fundamental models have been proposed where no fitting parameters are involved. Both for ductile and brittle creep rupture, fundamental creep models have been used for the austenitic stainless steel Sanicro 25 (23Cr25NiWCoCu). For ductile creep rupture, the dislocation contribution, solid solution hardening, precipitation hardening, and splitting of dislocations were considered. For brittle creep rupture, creep cavitation models were used taking grain boundary sliding, formation, and growth of creep cavities into account. All parameters in the models have been well defined and no fitting is involved. MatCalc was used for the calculation of the evolution of precipitates. Some physical parameters were obtained with first-principles methods. By combining the ductile and brittle creep rupture models, the final creep rupture prediction was made for Sanicro 25. The modeling results can predict the experiments at long-term creep exposure times in a reasonable way.

Fundamental Modelling of Mechanisms Contributing to Tertiary Creep in Copper at 215 and 250°C

2018 ◽  
Author(s):  
Fangfei Sui ◽  
Rolf Sandström
Keyword(s):  
Spent Nuclear Fuel ◽  
Creep Damage ◽  
Back Stress ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Creep Tests ◽  
Long Time ◽  
Higher Temperature ◽  
Good Agreement

Extensive creep tests have been performed on oxygen free copper with 50 ppm phosphorus at both low and high temperatures. It is the candidate material for storage of spent nuclear fuel in Sweden. Basic models without fitting parameters have been formulated to reproduce primary and secondary creep. For a long time, only empirical models existed for fitting of tertiary creep. To understand the role of creep damage, including recovery, cavitation and necking, basic models that do not involve adjustable parameters are in urgent demand. Only recently, basic models taking the relevant mechanisms into account have been developed. These models were used to predict the tertiary creep for copper at 75°C. The modelled results were compared with experimental creep curves and good agreement has been found. In the present paper, the models are applied to creep tests at higher temperatures (215 and 250°C). A similar representation with good accuracy is obtained. This demonstrates that the fundamental model for back stress is applicable for the higher temperature tests as well.

scholarly journals Prediction of creep failure time using machine learning

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Soumyajyoti Biswas ◽  
David Fernandez Castellanos ◽  
Michael Zaiser
Keyword(s):  
Machine Learning ◽  
Creep Rate ◽  
Failure Time ◽  
Learning Algorithm ◽  
Acoustic Emissions ◽  
Creep Damage ◽  
Machine Learning Algorithms ◽  
Supervised Machine Learning ◽  
Residual Lifetime ◽  
Complex Nature

Abstract A subcritical load on a disordered material can induce creep damage. The creep rate in this case exhibits three temporal regimes viz. an initial decelerating regime followed by a steady-state regime and a stage of accelerating creep that ultimately leads to catastrophic breakdown. Due to the statistical regularities in the creep rate, the time evolution of creep rate has often been used to predict residual lifetime until catastrophic breakdown. However, in disordered samples, these efforts met with limited success. Nevertheless, it is clear that as the failure is approached, the damage become increasingly spatially correlated, and the spatio-temporal patterns of acoustic emission, which serve as a proxy for damage accumulation activity, are likely to mirror such correlations. However, due to the high dimensionality of the data and the complex nature of the correlations it is not straightforward to identify the said correlations and thereby the precursory signals of failure. Here we use supervised machine learning to estimate the remaining time to failure of samples of disordered materials. The machine learning algorithm uses as input the temporal signal provided by a mesoscale elastoplastic model for the evolution of creep damage in disordered solids. Machine learning algorithms are well-suited for assessing the proximity to failure from the time series of the acoustic emissions of sheared samples. We show that materials are relatively more predictable for higher disorder while are relatively less predictable for larger system sizes. We find that machine learning predictions, in the vast majority of cases, perform substantially better than other prediction approaches proposed in the literature.

scholarly journals Review of Creep Cavitation and Rupture of Low Cr Alloy and its Weldment

2013 ◽  
Vol 744 ◽  
pp. 407-411
Author(s):  
Qi Hua Xu ◽  
Qiang Xu ◽  
Yong Xin Pan ◽  
Michael Short
Keyword(s):  
High Temperature ◽  
Constitutive Equation ◽  
Damage Mechanics ◽  
Experimental Approach ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Safe Operation ◽  
Computational Approaches ◽  
Creep Cavitation

This paper presents a review of creep cavitation and rupture of low Cr alloy and its weldment, particular in the heat-affected zone (HAZ). Creep damage is one of the serious problems for the high temperature industry. One of the computational approaches is continuum damage mechanics which has been developed and applied complementary to the experimental approach and assists in the safe operation. However, the existing creep damage constitutive equations are not developed specifically for low stress. Therefore, in order to form the physical bases for the development of creep damage constitutive equation, it is necessary to critically review the creep cavitation and rupture characteristics of low Cr alloy and its weldment.

Development on Stress Monitoring Method for Measurement of Cyclic Stress of Railway Axles

2005 ◽  
Vol 297-300 ◽  
pp. 84-89
Author(s):  
Seok Jin Kwon ◽  
Kazuhiro Ogawa ◽  
Tetsuo Shoji
Keyword(s):  
Electrical Resistance ◽  
Stress Measurement ◽  
Cyclic Stress ◽  
Railway Vehicle ◽  
Strain Gages ◽  
Stress Monitoring ◽  
Monitoring Method ◽  
Use Of Data ◽  
Copper Electroplating ◽  
Long Time

In general, the S-N curve in railway axles was mainly carried out under 107-108 cycles, while the service area of a railway axle is 108-109 cycles. The strain gages using electrical resistance have been used to measure stresses in railway vehicle wheelsets. However, there are some problems with strain gages using electrical resistance for railway axles. For example, the measured data is for special or limited intervals only. Strain gage installation is complicated, that is, it requires lead wires for measurement. The design of railway axles makes use of data that was obtained many years ago. The applied stresses in wheelsets running for a long time and in new railway vehicle wheelsets have not been studied clearly yet. It is necessary to carry out stress monitoring for more than 108 cycles to evaluate the safety of railway wheelset. Therefore, it is necessary to develop new stress monitoring techniques that can easily measure the working stress of the wheelset. In the present paper, the stress measurement technique of copper electroplating is considered because of its high potential for this purpose.

Quantification of Creep Cavitation in Welded Joint and Evaluation of Material Characteristics of Simulated Heat-Affected Zone in X 20 CrMoV 12 1 Steel

2000 ◽  
Vol 123 (1) ◽  
pp. 112-117 ◽  
Author(s):  
Yong-Keun Chung ◽  
Cheol-Hong Joo ◽  
Jong-Jin Park ◽  
Ik-Man Park ◽  
Hyo-Jin Kim
Keyword(s):  
Base Metal ◽  
Heat Affected Zone ◽  
Power Plants ◽  
Welded Joint ◽  
Charpy Impact ◽  
Creep Damage ◽  
Average Diameter ◽  
Damage Mechanism ◽  
Creep Rupture ◽  
Creep Cavitation

X 20 CrMoV 12 1(DIN 17 175) steel has been used for components subjected to high temperature in power plants and chemical and petroleum industries. Therefore, extensive studies have been made on this steel. However, these studies focused mainly on the base metal, and few studies on the welded joint have been reported. Actually, a large number of failures have occurred at the welded joint, so there is increasing need to investigate the characteristics of X 20 CrMoV 12 1 weldment. In this study, the interrupted and creep rupture tests were carried out and quantification of the creep damage was attempted for the X 20 CrMoV 12 1 welded joint. The interrupted and creep rupture tests were performed at four conditions\M650-60, 600-100, 600-120, and 575-150(|SDC-MPa)\Mon the X 20 CrMoV 12 1 welded joint specimens, respectively. It was revealed from the experimental results that creep damage mechanism of a welded joint was mainly creep cavitation, and that the intensively damaged area by creep cavitations was the transition region from fine-grained heat-affected zone (HAZ) to unaffected base metal, namely intercritical HAZ. For both the interrupted and ruptured specimens, quantification of creep damage was attempted by evaluating cavitated area fraction, average diameter, and the number of cavities with creep life fraction. In addition, on the basis of the heat input during the welding, microstructure, microhardness, and grain size of the actual intercritical HAZ, simulated HAZ was made in order to evaluate its material properties. For the simulated HAZ specimens, tensile, charpy impact, and creep rupture tests were carried out. As a result, yield, tensile strength, and elongation of simulated HAZ were similar to those of base metal, respectively, and impact property of simulated HAZ was slightly above base metal. Also, it was found that creep strength of simulated HAZ was inferior to that of the base metal.

Life Prediction of T91 Welded Joint and its Engineering Application Under Consideration of Welding Residual Stresses

2011 ◽  
Author(s):  
Changyu Zhou ◽  
Guodong Zhang
Keyword(s):  
Residual Stresses ◽  
Life Prediction ◽  
Welded Joint ◽  
Engineering Application ◽  
Prediction Method ◽  
Bending Moment ◽  
Creep Damage ◽  
Initial Stage ◽  
Long Time ◽  
Distribution Of Stress

Welding residual stresses (WRS) of welded joint have been a problem for long time. At present experiment and numerical simulation technology can be used to determine the distribution of WRS. ABAQUS codes were used to calculate WRS for welded joint of T91 tube and obtain the stress distribution under internal pressure (IP) and bending moment (BM) with WRS. ABAQUS user subroutine of the modified Kachanov-Rabotnov (K-R) constitutive equations was developed to calculate creep damage of welded joint on consideration of WRS. The distribution of stress and creep damage was obtained for the tube at different service time. Although the WRS relax at initial stage rapidly at high temperature condition, the accumulative damage caused by initial stress has much effect on the welded joint. Finally life prediction method of T91 welded joint with WRS on the basis of creep damage was proposed, which was compared with the results by DL/T 940-2005, API 579, and L-M method. The results in present paper are in good agreement with experiment result.

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