Transition Region of Nuclear Vessel Steels: Master Curve Approach Using Small Punch Notched Specimens

The behaviour of the materials in ductile-brittle transition region must be known when performing structural integrity assessments of nuclear reactor vessels working under the effects of neutron irradiation. The characterisation of this region has been usually carried out by means of Charpy impact tests. Just during last few years new approaches based on direct fracture mechanics tests have begun to be used. In most of these cases, the Master Curve methodology, which allows the transition region to be characterised using only one parameter (T0 reference temperature), has been employed. In this paper the transition region of two materials –one vessel steel and one common structural steel-has been characterised by means of Small Punch Tests. First of all, this zone has been characterised using conventional specimens and the results were compared with those of Charpy impact tests. Finally a new approach based on the use of notched Small Punch samples together with Master Curve methodology has been proposed.

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Evaluation of Fracture Toughness From Instrumented Charpy Impact Tests for a Reactor Pressure Vessel Steel

Fatigue, Fracture, and Damage Analysis ◽

10.1115/pvp2003-1982 ◽

2003 ◽

Cited By ~ 1

Author(s):

A. Parrot ◽

P. Forget ◽

A. Dahl

Keyword(s):

Fracture Toughness ◽

Impact Test ◽

Charpy Impact ◽

Charpy Impact Test ◽

Pressure Vessel Steel ◽

Vessel Steel ◽

Impact Tests ◽

Reactor Pressure Vessel Steel ◽

Ductile To Brittle Transition ◽

Reactor Pressure

The monitoring of neutron induced embrittlement of nuclear power plants is provided using Charpy impact test in the surveillance program. However structural integrity assessments require the fracture toughness. Some empirical formulas have been developed but no direct relationship was found. The aim of our study is to determine the fracture toughness of a Reactor Pressure Vessel steel from instrumented Charpy impact test using local approach to fracture. This non-empirical method has been applied in the brittle domain as well as in the ductile to brittle transition for an A508 C1.3 steel. In the brittle domain, fracture occurs by cleavage and can be modeled with the Beremin model. Fracture toughness has been successfully determined from Charpy impact tests results and the influence of several parameters (mesh design, Beremin model with one or two parameters, number of Charpy impact tests results) on the results was considered. In the ductile to brittle transition, cleavage fracture is preceded by ductile crack growth. Ductile tearing has been accounted for in the simulations with the Rousselier model whereas cleavage fracture is still described with the Beremin model. The determination of fracture toughness from Charpy impact tests gave encouraging results but finite element simulations have to be refined in order to improve predictions.

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Validation of the Master Curve Approach With Various Welding Conditions: Groove Shapes, Heat Inputs and Welding Processes

Volume 3: Materials Technology ◽

10.1115/omae2020-18653 ◽

2020 ◽

Author(s):

Jin Ho Lee ◽

Ji Hoon Kim ◽

Myung Hyun Kim

Keyword(s):

Fracture Toughness ◽

Master Curve ◽

Impact Test ◽

Structural Integrity ◽

Charpy Impact ◽

Test Sample ◽

Charpy Impact Test ◽

Theoretical Background ◽

Reference Temperature ◽

Welding Processes

Abstract Engineering critical assessment (ECA) is a procedure for evaluating the soundness of structures with flaws and has been widely applied for assessing the structural integrity. ECA procedure requires reliable fracture toughness data to assess the effect of defects. Ideal data are typically obtained from samples taken during construction of an engineering structure or from the structure afterward, but there are cases in which removal of the test samples is impossible due to the continued operation of the structure. To this end, Appendix J of the BS 7910 provides a procedure for estimating fracture toughness values from appropriate Charpy impact test data. However, the correlation between Charpy impact energy and fracture toughness is known to be overly conservative with not sufficient theoretical background in fracture mechanics perspective. In this regard, the revised BS 7910:2019 provides an improved method for calculating the reference temperature by applying the yield strength and the Charpy upper shelf energy based on empirical data. The target of this study is to validate the master curve approach in the modified BS 7910 for two common offshore grade steels with explicit considerations for various groove shapes, heat inputs and welding processes. For the purpose, the master curves are compared in terms of the reference temperature calculated from Charpy impact test according to BS 7910:2013 and the newly revised 2019 version of BS 7910. The modified master curve resulted in less conservative fracture toughness values anticipated from the decreased reference temperature. The estimated fracture toughness values exhibited a good correlation with experimentally obtained toughness values. The influence of various groove shapes, heat inputs and welding processes in estimating fracture toughness based on the master curve approach is discussed. In addition, the effect of impact test sample locations within weld metals toward estimated fracture toughness values is evaluated.

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Evaluation of Bending Limit of 9Cr-1Mo-V Steel by Master Curve and Failure Assessment Diagram Method: Evaluation of Welded Metal

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2018-84949 ◽

2018 ◽

Author(s):

Mitsuyoshi Nakatani ◽

Kazuo Oda ◽

Tomohiro Tanaka ◽

Masamitsu Abe ◽

Yasuhito Takashima ◽

...

Keyword(s):

Heat Treatment ◽

Master Curve ◽

Postweld Heat Treatment ◽

Charpy Impact ◽

Fracture Probability ◽

Absorbed Energy ◽

Diagram Method ◽

Impact Tests ◽

Master Curve Method ◽

Bending Process

In this study, the bending and rolling limit of 9Cr-1Mo-V steel plate welded using submerged arc welding (SAW) was investigated. Hereafter in this report, the bending limit refers to bending by press or by roller. Since heat treatment after welding and before the bending process may be effective in preventing brittle fracture during bending, the effect of postweld heat treatment (PWHT) for improving toughness was evaluated by Larson-Miller parameter (LMP). Charpy impact tests of SAW welded parts made of 9Cr-1Mo-V steel plates were performed, and the absorbed energy of the weld metal was lower than that of the heat affected zone (HAZ) and the base metal, however the absorbed energy was recovered by PWHT. The absorbed energy increased as LMP increased. The reference temperature T0 for the master curve method was estimated by the results of Charpy impact tests. The bending limit was estimated by the method proposed in the previous study. The fracture probability during the bending process seems to decrease as LMP increases.

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CURVE FITTING IN THE TRANSITION REGION OF CHARPY IMPACT DATA

International Journal of Modern Physics B ◽

10.1142/s0217979208046980 ◽

2008 ◽

Vol 22 (09n11) ◽

pp. 1496-1503 ◽

Cited By ~ 2

Author(s):

HYUNG-SEOP SHIN ◽

JONG-SEO PARK ◽

HAE-MOO LEE

Keyword(s):

Transition Region ◽

Research Work ◽

Charpy Impact ◽

Data Fitting ◽

Hyperbolic Function ◽

Impact Tests ◽

Fitting Procedure ◽

General Mathematical Model ◽

Fitting In ◽

Impact Data

The toughness data obtained from Charpy impact tests are presented by a temperature-energy relationship. Data fitting for quantitative evaluation of the transition temperature, upper shelf energy and ductile-brittle transition, in other words, the representation with general mathematical model equation for energy variation according to the temperature is necessary. In this study, the Charpy impact tests to two representative steels were carried out as a research work for the material property standardization technique development. The fitting procedure of the scattering in data according to materials and temperature in the transition region was described. The data fitting procedure using the tangent hyperbolic function was established through variances treatment in the transition region.

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Embrittlement Trend Curves for Notch and Fracture Toughness of 15Kh2MFAA Type Steel

Volume 1A: Codes and Standards ◽

10.1115/pvp2017-65174 ◽

2017 ◽

Author(s):

Milan Brumovsky ◽

Radim Kopřiva ◽

Miloš Kytka

Keyword(s):

Fracture Toughness ◽

Temperature Dependence ◽

Pressure Vessel ◽

Master Curve ◽

Charpy Impact ◽

Type Steel ◽

Impact Tests ◽

Surveillance Programs ◽

Vessel Integrity ◽

Reactor Pressure

Reactor pressure vessel integrity and lifetime evaluation is based on the use of fracture mechanics apparatus but most of the material vessel material data and their degradation during operation are based on results from Charpy V-notch impact tests. Then, empirical correlations between transition shift of temperature dependence of notch toughness and fracture toughness are applied. Elaboration of „Master Curve“ approach for fracture toughness experimental data analysis allows to use fracture toughness data directly to the reactor pressure vessel integrity evaluation. Wider use of this approach is limited by the lack of appropriate database from surveillance specimen test data, as mostly only Charpy impact specimen are included into the Surveillance specimen programs. Fortunately, all WWER Surveillance programs contain also fracture toughness specimens, either pre-cracked Charpy size or CT-0.5. Thus, database of fracture toughness data from Surveillance programs of WWER-440/V-213C type reactor pressure vessels, operated in the Czech Republic, Slovakia and Hungary and manufactured only by one manufacturer - SKODA JS, was collated and analyzed. These vessels were manufactured from 15Kh2MFAA type steel and appropriate weld metal, both of Cr-Mo-V type with low content of detrimental impurities — P and Cu. Analysis of the data in fluence interval up to 6×1024 m−2 (with neutron energies En larger than 0.5 MeV) show that transition temperature shifts in fracture toughness temperature dependence are higher than for Charpy impact tests. Several formulae have been applied for fitting these shift dependencies with chemical composition of materials and finally new Embrittlement Trend Curves for Charpy shifts have been corrected. Additionally, new Embrittlement Trend Curves for fracture toughness shifts based on “Master Curve” approach have been also proposed. Both trends are using simple power law on fluence with exponents around 0.6 and depend on phosphorus and copper contents even though effect of other elements has been also checked.

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The Use of Charpy/Fracture Toughness Correlations in the FITNET Procedure

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 3 ◽

10.1115/omae2005-67569 ◽

2005 ◽

Author(s):

E. Lucon ◽

K. Wallin ◽

P. Langenberg ◽

H. Pisarski

Keyword(s):

Fracture Toughness ◽

Structural Integrity ◽

Historical Data ◽

Charpy Impact ◽

Charpy Impact Energy ◽

Empirical Correlations ◽

Actual Structure ◽

Ideal Situation ◽

Integrity Assessments ◽

Actual Test

In an ideal situation, fracture toughness data to be used in structural integrity assessments are generated through the use of appropriate fracture mechanics-based toughness tests. In reality, such data are often not available or cannot be easily obtained due to lack of material or the impracticability of removing material from the actual structure. In such circumstances, and in the absence of appropriate historical data, the use of correlations between Charpy impact energy and fracture toughness can provide the fracture toughness value to be used in the assessment. The FITNET (Fitness-for-Service) procedure, presently being developed in the frame of a European Thematic Network, includes a section which deals with the use of empirical correlations between Charpy and fracture toughness data. This paper will outline the contents of this chapter, along with some examples of application of selected correlations to actual test data.

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