Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs: Fatigue Crack Growth Analysis of Hydrogen Flakes

2017 ◽  
Author(s):  
Valéry Lacroix ◽  
Pierre Dulieu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Pressure Vessels ◽  
Simplified Approach ◽  
Integrity Assessment ◽  
The Core

During the 2012 outages at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected, mainly in the lower and upper core shells of the Reactor Pressure Vessels (RPVs). The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, both units remained core unloaded pending the elaboration of an extensive Safety Case demonstrating that they can be safely operated. The Structural Integrity Assessment of the RPVs, through the Flaw Acceptability Assessment, aimed at demonstrating that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions. This demonstration has been done on the basis of a specific methodology inspired by the ASME B&PV Code Section XI procedure but adapted to the nature and the number of indications found in the Doel 3 and Tihange 2 RPVs. As requested by Article IWB-3610(a) of ASME B&PV Code Section XI, one of the parts that have to be addressed through the Flaw Acceptability Assessment is the Fatigue Crack Growth (FCG) Analysis of the flaws in the core shells until the end-of-service lifetime of the RPVs. Due to the large number of flaws in the core shells, a specific methodology has been developed in order not to perform the FCG Analysis of each flaw separately. The paper describes this simplified approach aiming at distributing the flaws according to their inclination and at defining envelope flaws covering the actual flaws to carry out FCG Analysis. Furthermore, the paper highlights and quantifies the conservatisms of this analysis leading finally to demonstrate that the FCG of hydrogen flakes is not a concern in Doel 3 and Tihange 2 RPVs.

Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs Affected by Hydrogen Flakes: Refined X-FEM Analyses

2016 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Extended Finite Element Method ◽  
Structural Integrity ◽  
Pressure Vessels ◽  
Extended Finite Element ◽  
Integrity Assessment ◽  
Safety Case ◽  
Component Manufacturing ◽  
Reactor Pressure

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, specific ultrasonic in-service inspections revealed a large number of quasi-laminar indications in the base metal of the reactor pressure vessels, mainly in the lower and upper core shells. The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, a Flaw Acceptability Assessment had to be performed as a part of the Safety Case demonstrating the fitness-for-service of these units. In that framework, detailed analyses using eXtended Finite Element Method were conducted to model the specific character of hydrogen flakes. Their quasi-laminar orientation as well as their high density required setting up 3D multi-flaws model accounting for flaw interaction. These calculations highlighted that even the most penalizing flaw configurations are harmless in terms of structural integrity despite the consideration of higher degradation of irradiated material toughness.

Technical Basis of Fatigue Crack Growth Rate Curve for Ni-Base Alloy Weld Metal in Air Environment

2011 ◽  
Author(s):  
Takuya Ogawa ◽  
Chihiro Narazaki ◽  
Masao Itatani ◽  
Akihiko Hirano ◽  
Hiroshi Nagase ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Weld Metal ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Structural Integrity ◽  
Base Alloy ◽  
Integrity Assessment ◽  
Alloy Weld

Recently, incidents of SCC in Ni-base alloy weld metal of BWR components have been reported. When the defects are detected by inspection, structural integrity assessment should be performed for the technical judgment on continuous service based on the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers Code (JSME FFS Code). The structural integrity assessment includes fatigue crack growth analysis. However, fatigue crack growth analysis for Ni-base alloy is impossible since the fatigue crack growth rate curves in air and the BWR environment are not prescribed yet in the JSME FFS Code. The curve in air environment is needed for the structural integrity assessment of the flaw when the embedded flaw repair which is one of the repair techniques to isolate the defect from water environment by seal welding is applied. In this study, fatigue crack growth tests in air environment were performed for Ni-base alloy weld metal. Based on the test data, fatigue crack growth rate curves with ΔKth of Ni-base alloy weld metal were investigated. It is found that fatigue crack growth data in the Paris region hardly depend on the test temperature and the stress ratio, whereas data around ΔKth are dependent on them. Hence, the curve in the Paris region was regarded as the same curve despite the difference of the test temperature and the stress ratio. The minimum ΔK of final crack growth data in the ΔK decreasing test was adopted as ΔKth of the curve.

Fatigue Fracture Mechanics Modeling and Structural Integrity Assessment of Offshore Welded Tubular Joints

1989 ◽  
Vol 111 (3) ◽  
pp. 170-176 ◽  
Author(s):  
J. C. P. Kam ◽  
D. A. Topp ◽  
W. D. Dover
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Nondestructive Testing ◽  
Crack Growth ◽  
Large Scale ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Integrity Assessment ◽  
Tubular Joints

Evaluation of the structural integrity of offshore structures requires information on the reliability of nondestructive testing, the accuracy of fatigue crack growth modeling and other data. The University College London Underwater NDE Centre has been set up to provide information on the effectiveness and reliability of different nondestructive testing methods. To achieve this aim, a large library of cracked specimens will be assembled. In the preliminary phase of producing this library, a series of large-scale welded tubular joints were fatigue tested and the crack growth was fully monitored with the ACPD technique. This paper will describe briefly the background to the crack library and present the data obtained from fatigue tests. It will also describe a new model for fatigue crack growth prediction in tubular joints using fracture mechanics. This model allows the prediction of the size effect noted previously in the stress/life curves for tubular joints.

Experimental and Analytical Studies on the Effect of Excessive Loading on Fatigue Crack Propagation in Piping Materials

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Yoshihito Yamaguchi ◽  
Jinya Katsuyama ◽  
Kunio Onizawa ◽  
Yinsheng Li ◽  
Genki Yagawa
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Nuclear Power ◽  
Power Plants ◽  
Large Scale ◽  
Structural Integrity ◽  
Large Earthquake ◽  
Retardation Effect ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Test

The seismic design review guide in Japan was revised in September 2006 to address the occurrence of a large earthquake beyond the design basis. In addition, Japanese nuclear power plants (NPPs) experienced multiple large earthquakes, such as Niigata-ken Chuetsu-Oki Earthquake in 2007 and the Great East Japan Earthquake in 2011. Therefore, it is very important to assess the structural integrity of reactor piping under such a large earthquake when a crack exists in the piping. In this work, crack growth behavior after excessive loading during the large-scale earthquake were experimentally and analytically evaluated for carbon steel and austenitic stainless steel. Some cyclic loading patterns with increasing and decreasing load amplitudes and maximum loads were applied to fatigue crack growth test specimens. From the results, the retardation of crack growth rate was clearly observed after excessive loading. In addition, the applicability to the retardation effect of the modified Wheeler model was confirmed. It is also concluded that the retardation effect has little influence on the failure probability due to seismic loading using probabilistic fracture mechanics (PFM) analyses with the modified Wheeler model.

Study on Banded Structure in Low Carbon Vessel Plate for Nuclear Power Plant

2010 ◽  
Vol 44-47 ◽  
pp. 1763-1766
Author(s):  
Fei Xue ◽  
Zhi Feng Luo ◽  
Wei Wei Yu ◽  
Zhao Xi Wang ◽  
Lu Zhang
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Nuclear Power ◽  
Power Plants ◽  
Fatigue Tests ◽  
Crack Growth Behavior ◽  
Low Carbon ◽  
Banded Structure ◽  
Crack Retardation

In this paper, the role of the pearlite-banded structure on fatigue crack growth behavior was investigated on carbon vessel plate material SA516, which is commonly used in the nuclear power plants. Along pearlite-banded orientation, in situ fatigue tests indicate that the crack initiated and propagated in the ferrite and then extended along the ferrite-pearlite interface when it met pearlitic colony. For comparison, the cyclic loading was also carried out perpendicular to the banding direction of the microstructure, and an intense crack branching was observed which led to fatigue crack retardation. Besides, the orientation perpendicular to banded pearlite in the investigated ferrite-pearlite steel was found to have a lower fatigue crack growth rate.

Effect of Specimen Size on Elastic-Plastic Fatigue Crack Growth and Resistance Curve of Carbon Steel

2014 ◽  
Author(s):  
Junya Ikegami ◽  
Motoki Taniguchi ◽  
Masahiro Takanashi ◽  
Shota Hasunuma ◽  
Takeshi Ogawa
Keyword(s):  
Fatigue Crack ◽  
Carbon Steel ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Power Plants ◽  
Pressure Vessels ◽  
Crack Growth Behavior ◽  
Load Line ◽  
Load Line Displacement

In order to investigate the ultimate strength of structures and components under an unexpected huge earthquake, it is necessary to understand the final fracture condition under static and cyclic loadings. This study compared the crack growth behavior under monotonic and cyclic loading conditions for carbon steel SGV410 used for pressure vessels in nuclear power plants. Fatigue tests were carried out for CT specimens 50 mm wide (1CT), 75 mm wide (1.5CT) and 100 mm wide (2CT) using three kinds of test methods, namely monotonic loading (ML), load line displacement amplitude increasing (V-inc.) and fatigue crack growth (FCG) tests. For the FCG tests, the maximum load was kept constant under cyclic loading with full unloading (R = 0), fully reversed loading (R = −1) and fully reversing the load line displacement (R = −1.5) and the crack growth characteristics were evaluated by the fracture mechanics approach.

Effects of Load Sequence on Fatigue Crack Growth in Pressure Vessels

2010 ◽  
Vol 160-162 ◽  
pp. 1217-1222 ◽  
Author(s):  
Shahrum Abdullah ◽  
S.M. Beden ◽  
Ahmad Kamal Ariffin ◽  
Zulkifli Mohd Nopiah
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Test Data ◽  
Life Prediction ◽  
Power Plants ◽  
Pressure Vessels ◽  
Low Alloy Steels ◽  
Variable Amplitude

Low alloy steels such as ASTM A508 and A533 and their equivalent materials have been extensively applied in fabricating pressure vessels due to their relatively excellent mechanical properties and moderately good weldability. The integrity of such materials governs the safety of the power plants. These vessels mainly are subjected to random loading in service and the load cycle interactions can have a significant effect in fatigue crack growth. Studying of fatigue crack growth rate and fatigue life calculation under spectrum loading is important for the reliable life prediction of vessels. Many models have been proposed, but as yet no universal model exists. In this paper, a fatigue life predicted under various load spectra, using three different fatigue crack growth models namely the Austen, modified Forman and NASGRO models. These models are validated with fatigue crack growth test data under various variable amplitude loadings. This application is performed with aids of three-point bend specimens. The results show clearly the load sequences effect and the predicted results agree with some discrepancies between the different models as well as with the test data. Neglecting, the cycle interaction effects in fatigue calculation under variable amplitude loading lead to invalid life prediction.

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