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.

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.

Master Curve Approach for Some Japanese Reactor Pressure Vessel Steels

2008 ◽  
Author(s):  
Minoru Tomimatsu ◽  
Takashi Hirano ◽  
Seiji Asada ◽  
Ryoichi Saeki ◽  
Naoki Miura ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Power Plant ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Master Curve ◽  
Reactor Pressure Vessel ◽  
Pressure Vessel Steels ◽  
The World ◽  
Reactor Pressure ◽  
Plant Components

The Master Curve Approach for assessing fracture toughness of reactor pressure vessel (RPV) steels has been accepted throughout the world. The Master Curve Approach using fracture toughness data obtained from RPV steels in Japan has been investigated in order to incorporate this approach into the Japanese Electric Association (JEA) Code 4206, “Method of Verification Tests of the Fracture Toughness for Nuclear Power Plant Components”. This paper presents the applicability of the Master Curve Approach for Japanese RPV steels.

Application of Master Curve Data for Reactor Vessel Steels

2003 ◽  
Author(s):  
William L. Server ◽  
Timothy J. Griesbach ◽  
Stan T. Rosinski
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Master Curve ◽  
Reactor Pressure Vessel ◽  
Material Behavior ◽  
Data Sets ◽  
Master Curve Method ◽  
Curve Method ◽  
Curve Fracture ◽  
Reactor Pressure

The Master Curve method has been developed to determine fracture toughness of a specific material in the brittle-to-ductile transition range. This method is technically more descriptive of actual material behavior and accounts for the statistical nature of fracture toughness properties as an alternative to the current ASME Code reference toughness curves. The Master Curve method uses a single temperature, To, as an index of the Master Curve fracture toughness transition temperature. This method has been successfully applied to numerous fracture toughness data sets of pressure vessel steels contained in the Master Curve database, including the beltline materials for the Kewaunee reactor pressure vessel. The database currently contains over 5,500 toughness data records for vessel weld, plate and forging materials, and it is currently being updated to include more recent fracture toughness data. Application of Master Curve fracture toughness data to reactor pressure vessel (RPV) integrity evaluations requires some assumptions relative to the degree of constraint in the fracture toughness test specimens versus the actual assumed RPV flaw. An excessive degree of conservatism can be introduced if the constraint levels are substantially different. In performing a Master Curve evaluation, the analysis may be restricted by the type of fracture toughness data available. Any excess conservatism should be appropriately considered when the overall safety margin is applied. For example, the precracked Charpy three-point bend specimen actually has some advantages over the compact tension specimen when the application involves a shallow surface flaw in a RPV wall. This paper analyzes some key fracture toughness results from several weld data sets containing both unirradiated and irradiated data to evaluate constraint effects in fracture toughness and pre-cracked Charpy specimens. The evaluated To values were compared to determine if there is any difference in bias from specimen geometry between the unirradiated and irradiated data.

Alternative Reference Temperature Based on Master Curve Approach in Japanese Reactor Pressure Vessel Steel

2013 ◽  
Author(s):  
Takatoshi Hirota ◽  
Takashi Hirano ◽  
Kunio Onizawa
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Master Curve ◽  
Reactor Pressure Vessel ◽  
Test Method ◽  
Reference Temperature ◽  
Ferritic Steels ◽  
Pressure Vessel Steel ◽  
Reactor Pressure

Master Curve approach is the effective method to evaluate the fracture toughness of the ferritic steels accurately and statistically. The Japan Electric Association Code JEAC 4216-2011, “Test Method for Determination of Reference Temperature, To, of Ferritic Steels” was published based on the related standard ASTM E 1921-08 and the results of the investigation of the applicability of the Master Curve approach to Japanese reactor pressure vessel (RPV) steels. The reference temperature, To can be determined in accordance with this code in Japan. In this study, using the existing fracture toughness data of Japanese RPV steels including base metals and weld metals, the method for determination of the alternative reference temperature RTTo based on Master Curve reference temperature To was statistically examined, so that RTTo has an equivalent safety margin to the conventional RTNDT. Through the statistical treatment, the alternative reference temperature RTTo was proposed as the following equation; RTTo = To + CMC + 2σTo. This method is applicable to the Japan Electric Association Code JEAC 4206, “Method of Verification Tests of the Fracture Toughness for Nuclear Power Plant Components” as an option item.

Study on Applicability of Master Curve Methodology Using Miniature C(T) Specimen to a Reactor Pressure Vessel With Low Upper Shelf Energy

2018 ◽  
Author(s):  
Kentaro Yoshimoto ◽  
Takatoshi Hirota ◽  
Hiroyuki Sakamoto ◽  
Masato Oshikiri ◽  
Kazuya Tsutsumi ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Neutron Irradiation ◽  
Pressure Vessel ◽  
Master Curve ◽  
Energy Use ◽  
Reactor Pressure Vessel ◽  
Test Method ◽  
Shelf Energy ◽  
Irradiation Embrittlement ◽  
Reactor Pressure

Miniature compact tension (Mini-C(T)) specimen can be an effective tool by utilizing together with Master Curve (MC) methodology for fracture toughness evaluation of irradiated reactor pressure vessel (RPV) steels. Recently, Mini-C(T) specimen has been incorporated into the Japanese standard test method related to MC methodology, JEAC4216-2015 and several studies were found focusing on applicability of Mini-C(T) specimen to irradiated RPV materials. However, there exist some other issues to be resolved considering application to irradiated materials. One of them is violation against the limitation criteria for ductile crack growth (DCG) specified in the standards. In general, upper shelf energy (USE) of RPV materials tends to decrease as well as shift in Charpy transition temperature due to neutron irradiation embrittlement. It may cause reduction in resistance of material against DCG and this leads to the problem peculiar to low USE materials such that the limitation for DCG might be dominant rather than that for KJclimit. Therefore, it is possible to fail to obtain valid KJc data even within valid temperature range of MC methodology, i.e. −50°C ≤ T-To ≤ 50°C, for low USE materials using Mini-C(T) specimens. In this study, the RPV steel with USE lower than 68J was made simulating reduction of USE due to neutron irradiation. Fracture toughness tests were performed using Mini-C(T) specimens as well as the standard 1T-C(T) specimens. Based on the test results, the validity for DCG limitation was also evaluated for each datum by post-test observation of fracture surface. Additionally, effectiveness of added side grooves and double thickness of specimen was examined as a countermeasure for Mini-C(T) specimen.

Validation of RTT0 for German Reactor Pressure Vessel Steels

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Dieter Siegele ◽  
Elisabeth Keim ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Master Curve ◽  
Reactor Pressure Vessel ◽  
Reference Temperature ◽  
Data Sets ◽  
Asme Code ◽  
Definition Of ◽  
Size Adjustment ◽  
Reactor Pressure

For the introduction of the new reference temperature RTT0 of the ASME Code Cases N-629 and N-631 into the German Standard KTA 3201.2, the applicability of RTT0 was validated by the reevaluation of the existing fracture toughness database of German reactor pressure vessel. (RPV) steels including unirradiated and irradiated base materials and weld metal data. The test temperatures of the database were standardized to the reference temperature T0 of the master curve of the data sets and the database was compared with the ASME KIC-curve as adjusted by RTT0. The KIC-curve adjusted by RTT0 enveloped both the 1T-size adjusted database and also the as-measured database, corresponding to the definition of RTT0. Thus, the results also prove the validity of the KIC(RTT0)-curve for allowable flaw sizes and up to the crack length spectrum of the ASME KIC-database without size adjustment of T0. The results of both investigations confirmed the validity of RTT0 for German RPV steels. The majority of existing fracture toughness data are based on KIC-values. More recent data are (KJC) related to the issuing of ASTM E 1921 in 1997 and to the success of the master curve-based T0 approach. Therefore, the possible difference between T0 determined from KJC and from KIC was investigated with available databases for RPV steels. The comparison of T0(KJC) and T0(KIC) showed a 1:1 correlation proving the equivalence of KJC and KIC in the determination of T0.

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