Fracture Toughness Assessment of SA508 Gr 3 Steel for KSNP RPV Using Conventional and Bimodal Master Curve Approaches

2014 ◽  
Author(s):  
Jongmin Kim ◽  
Minchul Kim ◽  
Kwonjae Choi ◽  
Bongsang Lee
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Random Parameter ◽  
Random Inhomogeneity ◽  
Curve Analysis ◽  
Large Scatter ◽  
Inhomogeneous Materials ◽  
Quenching Rate ◽  
Material Inhomogeneity ◽  
Rpv Steel

The standard master curve approach has the major limitation, which is only applicable to homogeneous datasets. In nature, steels are macroscopically inhomogeneous and thus the fracture toughness has larger scatters than expected by a conventional master curve approach. RPV steel has different fracture toughness with varying distance from the inner surface of the wall. Regarding this, a clear tendency was reported in that the toughness extracted near the surface had to be higher than in the center region due to the higher quenching rate at the surface (deterministic material inhomogeneity). On the other hand, the T0 value itself behaves like a random parameter when the datasets have a large scatter due to the datasets consisting of several different materials such as welding region (random inhomogeneity). In the present paper, four regions, the surface, 1/8T, 1/4T and 1/2T, were considered for fracture toughness specimens of KSNP (Korean Standard Nuclear Plant) SA508 Gr. 3 steel to provide deterministic material inhomogeneity and random inhomogeneity effect. Specimens were extracted from these four regions and fracture toughness tests were performed at various temperatures in the transition region. Several concepts were provided for the master curve of inhomogeneous materials such as a bimodal and random inhomogeneous master curve scheme, and among them, the bimodal master curve analyses were reviewed and compared with a conventional master curve approach to find the random inhomogeneity. The bimodal master curve considering inhomogeneous materials provides better description of scatter in fracture toughness data than conventional master curve analysis, but it is unclear to provide evidence that the bimodal analysis lines follow the data more closely than the conventional master curve analysis.

Evaluation of Fracture Toughness of a SA580 Gr. 3 Reactor Pressure Vessel Using a Bimodal Master Curve Approach

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Jong-Min Kim ◽  
Seok-Min Hong ◽  
Min-Chul Kim ◽  
Bong-Sang Lee
Keyword(s):  
Fracture Toughness ◽  
Cooling Rate ◽  
Pressure Vessel ◽  
Master Curve ◽  
Random Parameter ◽  
Random Inhomogeneity ◽  
Reactor Pressure Vessel ◽  
Inhomogeneous Materials ◽  
Material Inhomogeneity ◽  
Reactor Pressure

Abstract The standard master curve (MC) approach has a major limitation in that it is only applicable to homogeneous datasets. In nature, steels are macroscopically inhomogeneous. Reactor pressure vessel (RPV) steel has different fracture toughness with varying distance from the inner surface of the wall due to the higher cooling rate at the surface (deterministic material inhomogeneity). On the other hand, the T0 value itself behaves like a random parameter when the datasets have large scatter because the datasets are for several different materials (random inhomogeneity). In this paper, four regions, the surface, 1/8 T, 1/4 T, and 1/2 T, were considered for fracture toughness specimens of Korean Standard Nuclear Plant (KSNP) SA508 Gr. 3 steel to provide information on deterministic material inhomogeneity and random inhomogeneity effects. Fracture toughness tests were carried out for the four regions at three test temperatures in the transition region and the microstructure of each region was analyzed. The amount of upper bainite increased toward the center, which has a lower cooling rate; therefore, the center has lower fracture toughness than the surface so reference temperature (T0) is higher. The fracture toughness was evaluated using the bimodal master curve (BMC) approach. The results of the BMC analyses were compared with those obtained via a conventional master curve analyses. The results indicate that the bimodal master approach considering inhomogeneous materials provides a better description of scatter in the fracture toughness data than a conventional master curve analysis does.

Application of the Master Curve Approach for Abnormal Material Conditions

2007 ◽  
Author(s):  
Tapio Planman ◽  
William Server ◽  
Kim Wallin ◽  
Stan Rosinski
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Master Curve ◽  
Pressure Vessels ◽  
Data Sets ◽  
Inhomogeneous Materials ◽  
Data Set ◽  
Material Inhomogeneity ◽  
Fracture Modes ◽  
Material Conditions

The range of applicability of Master Curve testing Standard ASTM E 1921 is limited to macroscopically homogeneous steels with “uniform tensile and toughness properties”. A majority of structural steels appear to satisfy this requirement by exhibiting fracture toughness data which comply with the assumed KJc vs. temperature dependence and scatter within the specified validity area. As indicated in ASTM E 1921 a criterion for material macroscopic inhomogeneity is often applied using the 2% lower bound (possibly also the 98% upper bound). Data falling below this 2% lower-limit curve may be an indication of material inhomogeneity or susceptibility to grain boundary fracture. When this situation occurs, it is recommended to analyze the material with the so-called SINTAP procedure, which is intended for randomly inhomogeneous materials to assure a conservative lower-bound estimate. When a data set distinctly consists of two or more different data populations instead of one (due to variation of irradiation dose or specimen extraction depth, for instance) adoption of a bimodal (or a multimodal) Master Curve model is generally appropriate. These modal models provide information if the deviation of distributions is statistically significant or if different distributions truly exist for values of reference transition temperature, T0, characteristic of separate data populations. In the case of data sets representing thick-walled structures (i.e., reactor pressure vessels), indications of abnormal fracture toughness data can be encountered such that material inhomogeneity or fracture modes other than pure cleavage should be suspected. A state-of-the-art review for extended, non-standard Master Curve data and techniques highlights limits of applicability in situations where the basic ASTM E 1921 procedure is not appropriate for material homogeneity or different fracture modes.

Fracture toughness master-curve analysis of the tempered martensitic steel Eurofer97

2009 ◽  
Vol 386-388 ◽  
pp. 323-327 ◽  
Author(s):  
Pablo Mueller ◽  
P. Spätig ◽  
R. Bonadé ◽  
G.R. Odette ◽  
D. Gragg
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Martensitic Steel ◽  
Curve Analysis

Assessment of Master Curve Material Inhomogeneity Using Small Data Sets

2018 ◽  
Author(s):  
Kim Wallin
Keyword(s):  
Modal Analysis ◽  
Master Curve ◽  
Large Data ◽  
Large Data Sets ◽  
Small Data ◽  
Data Sets ◽  
Inhomogeneous Materials ◽  
Material Inhomogeneity ◽  
Analysis Methods ◽  
Small Data Sets

The standard Master Curve (MC) deals only with materials assumed to be homogeneous, but MC analysis methods for inhomogeneous materials have also been developed. Especially the bi-modal and multi-modal analysis methods are becoming more and more standard. Their drawback is that these methods are generally reliable only with sufficiently large data sets (number of valid tests, r ≥ 15–20). Here, the possibility of using the multi-modal analysis method with smaller data sets is assessed, and a new procedure to conservatively account for possible inhomogeneities is proposed.

Fracture Toughness Analysis of the China RPV Steel with Miniaturized Specimen

2016 ◽  
Vol 850 ◽  
pp. 41-46 ◽  
Author(s):  
Yun Lin ◽  
Wen Yang ◽  
Zhen Feng Tong ◽  
Guang Sheng Ning
Keyword(s):  
Fracture Toughness ◽  
Nuclear Power ◽  
Master Curve ◽  
Initiation Site ◽  
Cleavage Crack ◽  
Test Technique ◽  
Rpv Steel ◽  
Specimen Test ◽  
Relationship Of ◽  
The Relationship

Reactor pressurized vessel (RPV), which determines the lifetime of the nuclear power plant (NPP), is mainly forged using A508-3 steel in China. In order to meet the requirement of the small specimen test technique in the nuclear application, the fracture toughness of A508-3 steel was tested under-100°C using 1/4 CT specimens, and analyzed using Master Curve according to ASTM E 1921. In this work, the relationship of the KIC and the distance between the cleavage crack initiation site and the front of the fatigue crack is studied, and the transition temperature T0 of A508-3 is-98.7 oC, which is quite close to the test temperature.

Applicability of Miniature C(T) Specimens for the Master Curve Evaluation of RPV Weld Metal

2015 ◽  
Author(s):  
Masato Yamamoto ◽  
Naoki Miura
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Master Curve ◽  
Master Curve Method ◽  
Rpv Steel ◽  
Steel Base ◽  
Toughness Evaluation ◽  
Curve Method ◽  
The Difference

The Master Curve approach for the fracture toughness evaluation is expected to be a powerful tool to ensure the reliability of long term used reactor pressure vessel (RPV) steels. In order to get sufficient number of data for the Master Curve approach coexistent with the present surveillance program for RPVs, the utilization of miniature specimens that can be taken from the broken halves of the surveillance Charpy specimens is important. CRIEPI has developed the test technique for the miniature C(T) specimens, whose dimensions are 4 × 10 × 9.6 mm, and has verified the basic applicability of the Master Curve approach by means of the miniature C(T) for the determination of the fracture toughness of typical Japanese RPV steel base metals [1]. A series of round robin tests on RPV steel base metals [2–4] demonstrated that the miniature C(T) specimen can be used for the determination of the reference temperature (To) with no specific difficulties in test techniques. The present paper addresses the applicability of the fracture toughness evaluation by the miniature C(T) specimens on a RPV weld metal with multi-layer weld bead structure. The distribution of the fracture toughness and the trend in fracture toughness change with temperature were confirmed to show a good agreement with the assumption of the Master Curve method [5]. Fracture surface of the specimens were in cleavage fracture mode regardless of the difference in fracture toughness level. The relevance of the specimen size correction in the Master Curve method was confirmed. The difference of To values were only in a few degrees Celsius between the data obtained with 0.5 inch-thickness C(T) specimens and the miniature C(T) specimens. The effect of local loss of constraint nearby the specimen side surface was examined by comparing with the datasets from the specimens with and without side grooves. The difference of To was only 3 degree centigrade and no remarkable effect of side grooving could be seen. From overall examination results, it was concluded that the miniature C(T) specimen can be used for the Master Curve evaluation of tested PRV weld metal.

IAEA Coordinated Research Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Applicability for Highly Embrittled Materials

2007 ◽  
Author(s):  
Tapio Planman ◽  
Kunio Onizawa ◽  
William Server ◽  
Stan Rosinski
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Fracture Mode ◽  
Master Curve ◽  
Material Behavior ◽  
Curve Shape ◽  
Inhomogeneous Materials ◽  
Research Project ◽  
Energy Agency ◽  
Transition Range

In the Master Curve (MC) fracture model, a universal temperature dependence is assumed for ferritic steels, including those used in reactor pressure vessel (RPV) applications. The assumed curve shape also has been observed to be generally valid for highly irradiated or thermally aged materials that exhibit a high value of reference transition temperature, To. Lower than predicted fracture toughness behavior occasionally has been observed, however, in the upper transition range. It has been suggested that this behavior possibly may be associated with a lowered upper shelf toughness due to high irradiation doses. One objective of the present International Atomic Energy Agency (IAEA) Coordinated Research Project 8 (CRP-8) is to clarify the MC shape issue by collecting and analyzing relevant fracture toughness data measured on irradiated (or thermally aged) RPV and corresponding steels. For thermally aged or highly irradiated materials the fracture mode typically tends to gradually change from cleavage to one of intergranular fracture (IGF) which, if the IGF proportion is high, may significantly affect both the scatter and temperature dependence of fracture toughness. The data reviewed to date in this CRP show, in general, a very consistent fracture behavior with the basic Master Curve model that further confirms the applicability of the assumed curve shape. In cases where the basic homogeneity or fracture mode assumptions of the MC model were not satisfied due to high proportions of IGF, correspondence with the measured and predicted behavior could be markedly improved by applying available models developed to address inhomogeneous materials (e.g., SINTAP or the multi-modal model). The onset of upper shelf (TUS) and its correlation with To is presented as a possible approach for characterizing material behavior in the upper transition region when sufficient upper shelf fracture toughness data are available.

Validity of the Master Curve Temperature Dependence Assumption for Highly Embrittled RPV Materials: Results From the IAEA Coordinated Research Project (CRP-8)

2009 ◽  
Author(s):  
Tapio Planman ◽  
Kunio Onizawa ◽  
William Server
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Master Curve ◽  
Shape Change ◽  
Transition Curve ◽  
Curve Shape ◽  
Topic Area ◽  
Material Inhomogeneity ◽  
Realistic Description ◽  
Definition Of

The fracture toughness temperature dependence (transition curve shape) has been discussed almost since the original empirical definition of the curve in 1991. The data sets showing anomalous fracture behaviour of highly irradiated VVER-1000 pressure vessel steels presented in 2000’s have further enhanced this discussion and even a special model has been proposed for highly irradiated steels, including a mathematical definition of the curve shape change. Although in most cases the standard Master Curve (MC) approach, assuming a constant transition curve shape, has proven to give a realistic description for also highly irradiated ferritic steels, there are grades which show for example abnormally weak temperature dependence. In these cases, however, an obvious reason for the behaviour may be that the material does not fail by the mechanism assumed in the MC model. The fracture toughness data collected and analysed in the CRP-8 Topic Area 3 supports the validity of the curve shape assumption of ASTM E1921 also in case of irradiated steels and gives no rise to change the present definition. The Master Curve C-parameter (the shape parameter) estimation is proposed as an appropriate analysis method when there is need to estimate also the temperature dependence, whereas the SINTAP procedure is recommended for ensuring conservative lower bound estimates when material inhomogeneity is suspected. The results show that irradiation may slightly lower the fracture toughness in the upper transition region in relation to that predicted by ASTM E1921, but the effect after moderate T0 shift values (up to about 100°C) seems to be negligible. The investigated steels exhibit no or very weak correlation between the C-parameter and T0.

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