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.

Applicability of Miniature-C(T) Specimen for the Master Curve Evaluation of RPV Weld Metal and Heat Affected Zone

2016 ◽  
Author(s):  
Masato Yamamoto ◽  
Naoki Miura
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Master Curve ◽  
Data Sets ◽  
Fracture Toughness Test ◽  
Base Metals ◽  
Master Curve Method ◽  
Surveillance Programs ◽  
Curve Method ◽  
Haz Width

The Master Curve approach is a powerful tool to evaluate material-specific fracture toughness of ferritic steels, such as RPV steels, using a limited number of specimens. However, preparing a sufficient number of standard fracture toughness test specimens is difficult for irradiated RPV steels of existing surveillance programs. Utilization of miniature specimens that can be machined from broken halves of standard Charpy specimens is a possible solution to address this issue. CRIEPI has been working on the test technique utilizing a miniature C(T) (Mini-C(T)) specimens, whose dimensions are 4 × 10 × 9.6 mm (0.16 inch thickness specimen). The basic applicability of the Mini-C(T) Master Curve approach has been confirmed [1] for the base metals of typical Japanese RPV steels. International round robin tests confirmed the reproducibility of fracture toughness data obtained by Mini-C(T) specimens [2–4]. Ensuring the applicability of the Mini-C(T) Master Curve approach to weld metals and heat affected zone materials is of great importance to meet the future demand from the RPV surveillance programs for over 40 or 60 years’ reactor operation. For a weld metal deposit, we verified that valid reference temperature, To, can be estimated using the Mini-C(T) specimens and the statistics of the fracture toughness data [5] show good conformity to the assumption of the Master Curve method [6]. In the present paper, fracture toughness of a weld joint, which consists of two different heats of RPV plate material was examined. Five sets of Mini-C(T) specimens taken from two base metals, their heat affected zones (HAZ) and weld metal deposit, were subjected to the fracture toughness test. 0.5T-C(T) specimens taken from similar locations were also subjected to the fracture toughness tests to investigate specimen size effect. All the Mini-C(T) data sets taken from base metal, HAZ and weld metal were eligible for the determination of valid To with each 12 to 16 Mini-C(T) specimens. The relevance of the specimen size correction in the Master Curve method was confirmed for two base metals and a weld metal. The fracture toughness data for HAZ materials gave a reasonable agreement with the specific Weibull distribution assumed in the Master Curve method. Nevertheless, To values of four data sets of HAZ materials, including two Mini-C(T) datasets and two 0.5T-C(T) datasets, showed larger variation than that of the base metals or the weld metal. The crack initiation sites of HAZ specimens were all within so-called fine grain HAZ. However the HAZ width near the crack initiation site was dependent on the individual specimens. Higher fracture toughness tended to be gained from the specimens with narrower HAZ width. The resulting To values for HAZ material were close to or lower than that for base metals. The results suggest that the HAZ material gives equivalent or higher fracture toughness than in base metals.

Fracture Toughness Evaluation of Reactor Pressure Vessel Steels by Master Curve Method Using Miniature Compact Tension Specimens

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Tohru Tobita ◽  
Yutaka Nishiyama ◽  
Takuyo Ohtsu ◽  
Makoto Udagawa ◽  
Jinya Katsuyama ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Master Curve ◽  
Loading Rate ◽  
Compact Tension ◽  
Master Curve Method ◽  
Toughness Evaluation ◽  
Curve Method ◽  
Fracture Toughness Evaluation ◽  
Reactor Pressure

We conducted fracture toughness testing on five types of commercially manufactured steel with different ductile-to-brittle transition temperatures. This was performed using specimens of different sizes and shapes, including the precracked Charpy-type (PCCv), 0.4T-CT, 1T-CT, and miniature compact tension specimens (0.16T-CT). Our objective was to investigate the applicability of 0.16T-CT specimens to fracture toughness evaluation by the master curve method for reactor pressure vessel (RPV) steels. The reference temperature (To) values determined from the 0.16T-CT specimens were overall in good agreement with those determined from the 1T-CT specimens. The scatter of the 1T-equivalent fracture toughness values obtained from the 0.16T-CT specimens was equivalent to that obtained from the other larger specimens. Furthermore, we examined the loading rate effect on To for the 0.16T-CT specimens within the quasi-static loading range prescribed by ASTM E1921. The higher loading rate gave rise to a slightly higher To, and this dependency was almost the same for the larger specimens. We suggested an optimum test temperature on the basis of the Charpy transition temperature for determining To using the 0.16T-CT specimens.

Fracture Toughness Evaluation of Reactor Pressure Vessel Steels by Master Curve Method Using Mini-CT Specimens

2013 ◽  
Author(s):  
Tohru Tobita ◽  
Yutaka Nishiyama ◽  
Takuyo Ohtsu ◽  
Makoto Udagawa ◽  
Jinya Katsuyama ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Loading Rate ◽  
Rate Effect ◽  
Master Curve Method ◽  
Toughness Evaluation ◽  
Curve Method ◽  
Temperature Reference ◽  
Fracture Toughness Evaluation ◽  
Reactor Pressure

To examine the applicability of Mini-CT (0.16T-CT) specimens to fracture toughness evaluation by Master Curve method, we conducted fracture toughness tests using specimens with different size and shapes such as pre-cracked Charpy-type, 0.4T-CT and 1T-CT in addition to 0.16T-CT specimens for commercially manufactured five kinds of SA533B Cl.1 steels with different ductile-to-brittle transition temperature. Reference temperature To determined by 0.16T-CT specimens were approximately equal to those of 1T-CT specimens for all materials. The Weibull slope of 0.16T-CT specimens was similar to those of other larger specimens. We also examined a loading rate effect on To of 0.16T-CT specimens within the quasi-static loading range prescribed by ASTM E1921. There was no loading rate effect peculiar to 0.16T-CT specimens, while the higher loading rate gave rise to slightly higher To.

Prediction of Fracture Toughness for WWER RPV Integrity Assessment on the Basis of the Unified Curve Approach and Surveillance Specimens Testing

2009 ◽  
Author(s):  
Boris Margolin ◽  
Victoria Shvetsova ◽  
Alexander Gulenko ◽  
Valentin Fomenko
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Present Report ◽  
Temperature Shift ◽  
Curve Shape ◽  
Integrity Assessment ◽  
Master Curve Method ◽  
Curve Method ◽  
Unified Curve ◽  
Surveillance Specimens

For construction of the fracture toughness temperature curve that may be used for WWER RPV integrity assessment on the basis of tests of cracked surveillance specimens, the issues have to be solved as follows. First of all, it is important to determine how fracture toughness varies as a function of temperature, and how the fracture toughness vs. temperature dependence, KJC(T), changes with in-service material degradation due to neutron irradiation. These variations of KJC(T) curve are known to be the shift of KJC(T) curve to higher temperature range and change in the KJC(T) curve shape. At present, two advanced engineering methods are known that allow the prediction of KJC(T) curve on the basis of small-size fracture toughness specimens (for example, pre-cracked Charpy specimens), namely, the Master Curve and the Unified Curve methods. Procedures of test result treatment for the Master Curve and the Unified Curve are very similar. The Master Curve method uses the lateral temperature shift condition and, therefore, does not describe possible change in the KJC(T) curve shape. The Unified Curve method has an advantage as compared with the Master Curve as the Unified Curve describes a variation of the KJC(T) curve shape when degree of embrittlement increases. This advantage becomes important for RPV integrity assessment when the reference KJC(T) curve is recalculated to the crack front length of the postulated flaw that is considerable larger than thickness of surveillance specimens. Application of the KJC(T) curve determined from test results of cracked surveillance specimens to RPV integrity assessment requires also to introduce some margins. These margins have to take into account the type and number of tested specimens and the uncertainty connected with spatial non-homogeneity of RPV materials. Indeed, there is sufficient number of experimental data showing variability in fracture toughness for various parts of RPV. Therefore, situation is possible when the material properties near the postulated flaw will be worse than the properties of surveillance specimens. In the present report, advanced approaches are considered for prediction of fracture toughness for WWER RPV integrity assessment that allow one: • to construct the KJC(T) curve for irradiated RPV steels with any degree of embrittlement; • to provide transferability of fracture toughness data from cracked surveillance specimens to calculation of resistance to brittle fracture of RPV with a postulated flaw.

Fracture Toughness Transferability Study Between the Master Curve Method and a Pressure Vessel Nozzle Using Local Approach

2003 ◽  
Author(s):  
Anssi Laukkanen ◽  
Pekka Nevasmaa ◽  
Heikki Keina¨nen ◽  
Kim Wallin
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Master Curve ◽  
Structural Integrity ◽  
Reference Temperature ◽  
Cleavage Crack ◽  
Local Approach ◽  
Master Curve Method ◽  
Curve Method ◽  
Constitutive Parameters

Local approach methods are to greater extent used in structural integrity evaluation, in particular with respect to initiation of an unstable cleavage crack. However, local approach methods have had a tendency to be considered as methodologies with ‘qualitative’ potential, rather than quantitative usage in realistic analyses where lengthy and in some cases ambiguous calibration of local approach parameters is not feasible. As such, studies need to be conducted to illustrate the usability of local approach methods in structural integrity analyses and improve upon the transferability of their intrinsic, material like, constitutive parameters. Improvements of this kind can be attained by constructing improved models utilizing state of the art numerical simulation methods and presenting consistent calibration methodologies for the constitutive parameters. The current study investigates the performance of a modified Beremin model by comparing integrity evaluation results of the local approach model to those attained by using the constraint corrected Master Curve methodology. Current investigation applies the Master Curve method in conjunction with the T-stress correction of the reference temperature and a modified Beremin model to an assessment of a three-dimensional pressure vessel nozzle in a spherical vessel end. The material information for the study is extracted from the ‘Euro-Curve’ ductile to brittle transition region fracture toughness round robin test program. The experimental results are used to determine the Master Curve reference temperature and calibrate local approach parameters. The values are then used to determine the cumulative failure probability of cleavage crack initiation in the model structure. The results illustrate that the Master Curve results with the constraint correction are to some extent more conservative than the results attained using local approach. The used methodologies support each other and indicate that with the applied local approach and Master Curve procedures reliable estimates of structural integrity can be attained for complex material behavior and structural geometries.

Influence of Microstructural Variation in Thick Section Steels on the Characterisation of Fracture Toughness Using Sub-Size Specimens

2019 ◽  
Author(s):  
Philippa Moore ◽  
Borislava Yordanova ◽  
Yong Lu ◽  
Yin Jin Janin
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Plate Thickness ◽  
High Strength ◽  
Steel Plates ◽  
Full Thickness ◽  
Master Curve Method ◽  
Sampling Locations ◽  
Curve Method ◽  
Thick Material

Abstract The challenges of performing full-thickness fracture toughness tests on steel plates of 100mm thickness and greater means that the use of sub-size specimens is desirable. In this work, 100mm thick parent plate of S690 high strength steel was characterised using SENB fracture toughness specimens with thickness of 12mm, 25mm, 50mm and 100mm. Sub-size specimens were extracted at two different locations through the plate thickness; mid-wall and quarter wall. Sufficient specimens were tested to apply the Master Curve method in ASTM E1921 to predict the behaviour of 100mm thick material from each set of sub-size specimens. The through-thickness microstructural variation in these heavy-wall steel plates meant that significantly different predictions of full-thickness fracture toughness were obtained from the two sampling locations. However, when sampled from the mid-wall location, sub-size specimens down to 25mm thick were able to conservatively predict full-thickness fracture toughness using Master Curve methods.

Adjustments to Master Curve Methodology and Development of Fracture Toughness Estimation

2011 ◽  
Author(s):  
R. S. Kulka
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Driving Force ◽  
Master Curve ◽  
Structural Components ◽  
Fracture Test ◽  
Element Analysis ◽  
Master Curve Method ◽  
Curve Method ◽  
Constraint Effects

In conventional fracture mechanics assessments, there is often an inadequate treatment of in-plane constraint effects on the apparent toughness of structural components, leading to significant conservatism. Modifications to the Master Curve method, to account for these effects, have previously been suggested. A study of these proposed modifications has identified that less conservative toughness estimates could be made from the analysis of fracture mechanics test specimens. An approach has been developed for allowing a comparison of a variation of fracture toughness values throughout a component, to a variation of the localised effective driving force. Cracked-body finite element analysis has been used to assess fracture test specimens with varying levels of in-plane constraint, to provide fracture mechanics data for use with the approach that has been developed.

The Master Curve Fracture Toughness Evaluation of Irradiated Plate Material JRQ Using Miniature-C(T) Specimens

2017 ◽  
Author(s):  
Masato Yamamoto
Keyword(s):  
Fracture Toughness ◽  
Master Curve ◽  
Technical Difficulty ◽  
Plate Material ◽  
Test Technique ◽  
Toughness Evaluation ◽  
Standard Plate ◽  
Surveillance Programs ◽  
International Round ◽  
The Difference

The Master Curve approach is a powerful tool to evaluate material-specific fracture toughness of ferritic steels, such as RPV steels, using a limited number of specimens. However, preparing sufficient volume of material for the generally used 25.4mm-thickness fracture toughness specimens is difficult for irradiated reactor pressure vessel (RPV) steels of existing surveillance programs. Utilization of miniature specimens, which can be machined from broken halves of standard Charpy specimens, is a possible solution to address this issue. CRIEPI has been working on the development of test technique utilizing a miniature C(T) (Mini-C(T)) specimens, whose dimensions are 4×10×9.6 mm (0.16 inch thickness specimen). The basic applicability of the Mini-C(T) Master Curve approach on un-irradiated materials had been confirmed for the base metals of typical Japanese RPV steels [1]. International round robin tests [2–4] confirmed the reproducibility of fracture toughness data obtained by Mini-C(T) specimens. Applicability of the Mini-C(T) specimen on neutron irradiated materials is of another important subject to be ensured. In the present study, the European standard plate material JRQ, which is in irradiated state up to the fluence of 1.85×1019 n/cm2 was subjected to the Master Curve evaluation with Mini-C(T) specimens. Two laboratories, A and B, as well as CRIEPI were involved in this study. Both of the laboratories separately and successfully carried out machining, pre-cracking and fracture toughness testing without excessive technical difficulty even though the material was highly irradiated. Consistent reference temperature, To was estimated as 40°C (Lab. A) or 32°C (Lab. B). The difference between the two laboratories was reasonably small. To was also consistent with that by pre-cracked Charpy V-notch specimens (PCCv), or 1-inch thickness C(T) specimens examined in the former IAEA Coordinated Research Program [5]. As a results of the investigation, the relevance of using Mini-C(T) specimens for irradiated JRQ material was demonstrated.

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