Manson Haferd Research Articles

Effects of Cr Carbides Formation on the High Temperature Creep Property of Alloy 690 for Steam Generator Tube Material

The creep properties of Alloy 690, used as a steam generator tube material in nuclear power plants, were evaluated at 650°C, 750°C, and 850°C. The parameters of creep life prediction models were derived using the Larson-Miller (LM), Manson-Haferd (MH), and Orr-Sherby-Dorn (OSD) models, to use as mechanical properties under a virtual severe accident condition like station black out (SBO). The yield strength (YS) and creep property of Alloy 690 were compared with those of Alloy 600, and the effects of the precipitation behavior of Cr carbides on creep properties were analyzed. The YS of Alloy 600 decreased rapidly above the temperature of 750°C, but the YS of Alloy 690 decreased linearly up to the temperature of 850°C because of the formation of M23C6 carbides. The creep stress exponent (n) of Alloy 690 was between 5 and 6, and this indicated that dislocation creep was the major creep mechanism at the test temperatures. The results of creep tests were well matched with the LM, MH, and OSD models for Alloy 690, and there were no significant differences in accuracy between the models. The stress-rupture test results of Alloy 600 and Alloy 690 using the LM model showed that the decrease in creep strength with rupture time of Alloy 690 was steeper than that of Alloy 600 at high temperatures. This indicated that Alloy 690 was more susceptible to creep degradation under longterm creep conditions. The precipitation of Cr carbides in Alloy 690 increased YS, benefitting creep properties for short-term creep. However, the Cr carbides coarsened significantly under loading conditions at high temperature, and this deteriorated the creep properties for long-term creep.

Metamodeling Time-Temperature Creep Parameters

Abstract There exist many time-temperature parameter (TTP) models for creep rupture prediction of components including the Larson–Miller (LM), Manson–Haferd (MH), Manson–Brown (MB), Orr–Sherby–Dorn (OSD), Manson–Succop (MS), Graham–Walles (GW), Chitty–Duval (CD), Goldhoff–Sherby (GS) models. It remains a challenge to determine which model is “best”, capable of accurate interpolation and physically realistic extrapolation of creep rupture data for a given material. In this study, metamodeling is applied to create a unified TTP metamodel that combines and regresses into twelve TTP models (eight existing and four newly derived). An analysis of the mathematical problems that exist in TTP models is provided. A matlab code is written that can: (1) calibrate the material constants of any of the twelve TTP models (using the metamodel); (2) determine the most suitable stress-parameter function; (3) and report the normalized mean square error (NMSE) of rupture predictions for a given material database. Using the metamodel, and code, a design engineer can make an intelligent selection of the “best” TTP model for creep resistant design. This process is demonstrated using four isotherms of alloy P91 creep rupture data. To assess the influence of material, further validation is performed on alloys Hastelloy X, 304SS, and 316SS. It is determined that the “best” model is dependent on material type and the quality and quantity of available data.

Creep Behavior and Life Assessment of a Novel Heat-Resistant Austenite Steel and Its Weldment

In the present study, creep activation energy for rupture was obtained as 221–348 kJ/mol for 22Cr15Ni3.5CuNbN due to the precipitation-hardening mechanism. The extrapolation strength of creep rupture time of 105 h at 923 K for 22Cr15Ni3.5CuNbN is more valid (83.71 MPa) predicted by the Manson–Haferd method, which is superior to other commercial heat-resistant steels. The tensile creep tests ranging from 180 to 240 MPa at 923 K were conducted to investigate creep deformation behavior of welded joint between a novel heat-resistant austenite steel 22Cr15Ni3.5CuNbN and ERNiCrCoMo-1 weld metal. Apparent stress exponent value of 6.54 was obtained, which indicated that the rate-controlled creep occurred in weldment during creep. A damage tolerance factor of 6.4 in the weldment illustrates that the microstructural degradation is the dominant creep damaging mechanism in the alloy. Meanwhile, the welded joints perform two types of deformation behavior with the variation in applied stress, which resulted from the different parts that govern the creep processing. Also, the morphology evolution of the fracture surfaces confirms the effects of stress level and stress state.

Predicting long-term creep-rupture property of Inconel 740 and 740H

The prediction of long-term creep-rupture strength values for Inconel 740 and 740H is made at temperatures ranging from 650°C to 850°C by using Larson–Miller (LM) and Manson–Haferd (MH) methodologies. Then, the predicted creep-rupture strength values are compared with the ones reported by Wilshire–Scharning (WS) model, a new approach for life assessment. The results show that the LM method is easy to cause either underestimation or overestimation of long-term properties depending on the selected data. Compared with the LM and WS methods, predictions produced by MH method have a relatively good consistency with the experimental data over 30 000 h, and the 105 hours creep-rupture strength extrapolated from rupture life of 5000 h or more than 30 000 h are almost same. This suggests that the MH method is a better method for predicting the long-term creep-rupture strength of Inconel 740 and 740H alloys.

Estimation of Creep Failure Life of Rotor Grade Steel by Using Time–Temperature Parametric Methods

Creep behavior is one of the most critical factors determining the failure life of components at elevated temperature. Turbine rotor shaft is subjected to such elevated conditions. The creep behavior of rotor grade steel 28CrNiMoV59 was studied at elevated temperatures from 550 to 650 °C and at stress levels varying from 120 to 300 MPa. Tensile tests were conducted to determine the basic properties. Microstructural and chemical analyses were performed to characterize the as received material. Creep rupture data were determined from experimental results. These results were used to calculate the creep constants at elevated temperature which are used in time–temperature parametric (TTP) methods. Different TTP methods like, Larson–Miller, Orr–Sherby–Dorn and Manson–Haferd, were analyzed to check their suitability for extrapolation of creep rupture data of (28CrNiMoV59) steel.

Grade 91 강의 장시간 크리프 수명 예측 방법

Grade 91 steel is used for the major structural components of Generation-IV reactor systems such as a very high temperature reactor (VHTR) and sodium-cooled fast reactor (SFR). Since these structures are designed for up to 60 years at elevated temperatures, the prediction of long-term creep life is very important to determine an allowable design stress of elevated temperature structural component. In this study, a large body of creep rupture data was collected through world-wide literature surveys, and using these data, the long-term creep life was predicted in terms of three methods: Larson-Miller (L-M), Manson-Haferd (M-H) and Wilshire methods. The results for each method was compared using the standard deviation of error. The L-M method was overestimated in the longer time of a low stress. The Wilshire method was superior agreement in the long-term life prediction to the L-M and M-H methods.

Long-term creep data prediction for type 316H stainless steel

Impressive data sets have been produced for 316H stainless steel (18Cr–12Ni–Mo with up to 0.08C) by the National Institute for Materials Science (NIMS), Japan, to reveal the dependencies on stress and temperature of the high-temperature creep and creep fracture behavior of nine batches of tube, six of bar and two of plate. Using these long-term property values, the stresses to produce failure in 100,000h at various plant exposure temperatures have been determined using the Manson–Haferd parameter. However, by incorporating the 0.2% proof stresses and ultimate tensile strengths of each batch of material at the creep temperatures, new relationships allow accurate prediction of the allowable tensile creep stresses using data from tests lasting only up to 5000h. Moreover, all of these results can be interpreted straightforwardly in terms of the dislocation processes controlling creep strain accumulation and the cavitation damage causing creep failure.

Unification of the most commonly used time–temperature creep parameters

The determination of the time to rupture at low stresses and temperatures despite existing methods still remains a challenge. A new unifying time–temperature parameter is proposed. It represents a modification of the efficient, but numerically unstable Manson–Brown parameter. It incorporates the most commonly used time–temperature parameters such as Larson–Miller, Manson–Haferd and Orr–Sherby–Dorn as special cases for the calculation of the master curves. The procedure chooses the most appropriate master curve for the test data and calculates the corresponding coefficients. The inputs for the determination of the master curves are minimised to the least possible amount of test data. The proposed time–temperature parameter is included in a fast creep damage calculation procedure which is a part of a method for evaluating the total damage of the thermomechanically loaded components.

Application of Manson–Haferd and Larson–Miller Methods in Creep Rupture Property Evaluation of Heat-Resistant Steels

The current paper discusses the selection of Manson–Haferd and Larson–Miller constants on correlation results of creep rupture property in several heat-resistant steels. It indicates that the change in Larson–Miller constant CLM has obvious effect on the predicting result of rupture life and the optimal CLM values will depend on materials and the optimal ranges of the values are narrow. However, for Manson–Haferd constants Ta and log ta, they are at least phenomenally not independent variables but show a linear relationship: log ta=27.015−0.0267Ta. It is shown that the values of Manson–Haferd constants (Ta,log ta) can be selected in a wide range with desirable correlation accuracy and a set of Manson–Haferd constant (Ta=450, log ta=15) is recommended to correlate the creep rupture data.

A New Approach of Reliability Design For Creep Rupture Property

Generally, creep rupture data of a heat-resistant steel can be compressed into a narrow band by using a temperature-time parametric method such as the Larson–Miller or Manson–Haferd method. In order to describe the scattering of the data, the current paper proposes a “Z parameter” method to represent the magnitude of the deviation of the rupture data to master curve. Statistical analysis shows that the scattering of the Z parameter for several types of steels is supported by normal distribution. Using this method, it is possible to achieve unified analysis of the creep rupture data in various temperature and stress conditions. Stress-time temperature parameter-reliability curves (σ-TTP-R curves), stress-rupture time-reliability curves (σ-tr-R curves), and allowable stress-temperature-reliability curves ([σ]-T-R curves) are proposed, which could embrace the reliability concept into creep rupture property design.

New ECCC assessment of creep rupture strength for steel grade X10CrMoVNb9-1 (Grade 91)

A first assessment of creep rupture strength for steel grade X10CrMoVNb9-1 (Grade 91) was performed by ECCC in 1995. The results were included in the European standard EN 10216. Due to a significant increase of test data and test duration it was decided in 2005 to make a re-assessment of the extended database. Different procedures have been used independently by different assessors. The method with the best overall fit of the data set has found to be the ISO CRD method. This is characterized by a two steps procedure: in the first step the mean isotherms are evaluated from the test data, afterwards the evaluated isotherms are used for averaging by a Manson–Haferd master-curve. The results have been chosen as the basis to specify long term creep rupture strength values in a new ECCC data sheet for X10CrMoVNb9-1 (Grade 91).

A numerical approach to determine creep constants for Time-Temperature Parametric methods

This study dealt with how to mathematically obtain creep constants of C, Q/2.3R, T a and t a used in Time-Temperature Parametric (TTP) methods. A number of creep rupture data from 550 °C to 800 °C for Type 316LN stainless steel were collected through a worldwide literature survey and experimental data produced at KAERI. It was found that the creep rupture data revealed a linear relationship when the data were plotted by the semilogarithmic coordinates of log (t r ) versus stress. On the basis of this linear relationship, the creep constants of C, Q/2.3R, T a and t a used in the Larson-Miller (LM), the Orr-Sherby-Dorn (OSD), and the Manson-Haferd (MH) methods were obtained by a new numerical method. This approach can be utilized as a useful method to predict the long-term creep life of Type 316 stainless steel.

Alloy 617의 장시간 크리프 수명 예측을 위한 다중회귀 선형 모델의 제안 및 평가

Creep life prediction has been commonly used by a time-temperature parameter (TTP) which is correlated to an applied stress and temperature, such as Larson-Miller (LM), Orr-Sherby-Dorn (OSD), Manson-Haferd (MH) and Manson-Succop (MS) parameters. A stress-temperature linear model (STLM) based on Arrhenius, Dorn and Monkman-Grant equations was newly proposed through a mathematical procedure. For this model, the logarithm time to rupture was linearly dependent on both an applied stress and temperature. The model parameters were properly determined by using a technique of maximum likelihood estimation of a statistical method, and this model was applied to the creep data of Alloy 617. From the results, it is found that the STLM results showed better agreement than the Eno’s model and the LM parameter ones. Especially, the STLM revealed a good estimation in predicting the long-term creep life of Alloy 617.

시간-온도 파라미터법과 최소구속법에 의한 크리프 수명예측과 오차 분석

To predict long-term creep life from short-term creep life data, various parametric methods such as Larson-Miller (L-M), Orr-Sherby-Dorn (O-S-D), Manson-Haferd (M-H) parameters, and a Minimum Commitment Method (MCM) were suggested. A number of the creep data were collected through literature surveys and experimental data produced in KAERI. The polynomial equations for type 316LN SS were obtained by the time-temperature parameters (TTP) and the MCM. Standard error (SE) and standard error of mean (SEM) values were obtained and compared with the each method for various temperatures. The TTP methods showed good creep-life prediction, but the MCM was much superior to the TTP ones at 700℃ and 750℃. It was found that the MCM were lower in the SE values when compared to the TTP methods.

Method for improving parametric creep rupture life of 2·25Cr–1Mo steel using artificial neural networks

A number of well known parametric models and a multilayer neural network are subjected to an ‘acid test’ of extrapolation to determine whether the latter can produce improved long term rupture life predictions for 2·25Cr–1Mo steel. Linear and non- linear least squares analysis was used to estimate the parametric models and genetic algorithms were used to identify and train the network. All the parametric models produced lifetime predictions for stresses below 60 MPa that were in error by some 20–40% on average. This reflected their tendency to overfit the data sets used for their estimation. Standard statistical measures of model inadequacy were of little use in overcoming this problem and the more non-linear models (e.g. Manson–Haferd) produced implausible extrapolations. In contrast, the optimised neural network was able to identify general patterns in the training data that were useful for extrapolation purposes and this was reflected in an average error of some 4–5%.

Physical significance and reliability of Larson–Miller and Manson–Haferd parameters

Both the Larson–Miller and the Manson–Haferd parameters are used to extrapolate rupture data from high temperature creep. The first of these is in agreement with the theoretical equation for low temperature deformation only, and cannot describe the high temperature properties accurately. The second parameter has no physical basis. Starting from data taken from a theoretical stress–rupture time diagram, both extrapolation methods are tested. At the lower stresses the Larson–Miller method considerably overestimates the resistance of the material to rupture. Despite the lack of physical significance, the Manson–Haferd parameter coincidentally describes to some extent the complex deformation patterns due to the different deformation mechanisms, and is more reliable for high temperature predictions.MST/1882

Creep-Rupture Reliability Analysis

A probablistic approach to the correlation and extrapolation of creep–rupture data is presented. Time–temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson–Miller and on the Manson–Haferd parameters, but it can be applied to any of the TTP’s. A method is developed for evaluating material dependent constants for TTP’s. It is shown that “optimized” constants can provide a significant improvement in the correlation of the data, thereby reducing modeling error. Attempts were made to quantify the performance of the proposed method in predicting long-term behavior. Bias and uncertainty in predicting long-term behavior from short-term tests were derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state-of-the-art reliability methods to the design of components under creep.

Time-temperature relationship for long-term and fatigue strength of some partially crystalline polymers

1. The investigation was concerned with the time-temperature relationship for the long-term strength of PEVP. The maximum test length was 1400 h. 2. It was shown that the use of the Manson—Haferd parametric equation and the Kovpak physical similarity method in processing experimental data produced better results than other relations. 3. The observed deviations of experimental data from the parametric relationship observed at medium loads may be attributed to the changes in the mutual relationship of the two steps of the fatigue rupture of PEVP, to the reduction (increase) in the incubation period of crack formation, and to the changing nature of the fracture. 4. In the long-term strength curve characterizing the brittle fracture, two sections were observed which can be attributed to the existence of two mechanisms of rupture of PEVP in this region. 5. For the phenomenological description of two fatigue rupture stages of PEVP two scales of vulnerability were introduced which, in contrast to the theory of cumulative damage, had made possible the consideration of the effect of loading history.