scholarly journals The Huge Missing Factor in LBB Analysis - How A Circumferential Through-Wall-Crack in A Pipe System Changes the Flexibility and Reduces the Applied Moments

2021 ◽  
Author(s):  
Mohammed F Uddin ◽  
Gery Wilkowski ◽  
Sureshkumar Kalyanam ◽  
Frederick W. Brust
Keyword(s):  
Crack Size ◽  
Nuclear Industry ◽  
Fe Model ◽  
Critical Crack ◽  
Pipe System ◽  
Normal Operating ◽  
Loss Of Coolant Accident ◽  
Seismic Loadings ◽  
Critical Crack Size ◽  
Leak Before Break

Abstract In typical leak-before-break (LBB) analyses in the nuclear industry, the uncracked piping normal operating forces and moments are applied in a cracked-pipe analytical procedure to determine normal leakage, and the combined forces and moments under normal operating condition and safe shutdown earthquake seismic loading are used in a fracture analysis to predict margins on "failure". The International Piping Integrity Research Program (IPIRG) performed in 1990 to 1998 provided some insights to typical LBB behaviors where pipe system tests were conducted with simulated seismic loadings. The test results showed a large margin on LBB which was also recognized in 2011 when the Argentinian Atucha II plant was analyzed using a robust full FE model. It was found that when circumferential through-wall cracks were put in the highest stressed locations, the applied moment dropped for both normal operating and N+SSE loading as the crack length increased. The through-wall crack size for causing a double ended guillotine break (DEGB) was greater than 90%-percent of the circumference. Similar results were also found for a petrochemical pipe system where thermal expansion stresses are much higher than the primary stresses. Even with very low toughness materials, the critical crack size leading to DEGB was greater than 80% of the circumference. The implication of this work is that pragmatically there is much higher margin for DEGB failure in nuclear plant operation, and efforts would be better focused on the potential for a small-break loss-of-coolant accident (SB-LOCA).

Comparison of Leak-Before-Break Assessment of Main Loop Piping Lines Fabricated of Different Materials

2016 ◽  
Author(s):  
Linwei Ma ◽  
Xiaotao Zheng ◽  
Yan Wang ◽  
Jiasheng He ◽  
Anqing Shu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Material Properties ◽  
Plastic Instability ◽  
Crack Size ◽  
Critical Crack ◽  
Main Loop ◽  
Critical Crack Size ◽  
Leak Before Break

Leak-Before-Break (LBB) assessment is used for the design of nuclear reactor coolant system main loop piping to lower the cost of construction and operation in China. In these applications, the materials of main loop piping lines are cast austenitic stainless steel (CASS) or wrought stainless steel (WSS) due to the different type of reactor design. According to US.NRC SRP3.6.3, LBB assessment includes two major calculations, such as critical crack size calculation and leakage flaw size calculation. The elastic-plastic instability analysis or plastic instability analysis is chosen to perform critical size calculation depending on material properties, especially fracture toughness. In this paper, LBB assessment in the guidance of SRP 3.6.3 was performed to evaluate main loop piping lines of CASS and WSS. The JR curve tests and the adjustment due to thermal aging are performed to achieve reasonable material properties. J integral/tearing modulus approach is used to determine critical crack size of CASS pipe and net section collapse (NSC) approach is used to determine critical crack size of WSS pipe. Leakage flaw size under 1gpm leakage detection capability is determined based on Henry’s homogeneous nonequilibrium critical flow model. In order to demonstrate that fatigue crack growth is not a potential source of pipe rupture for the evaluated piping lines, the fatigue crack growth of a postulated circumferential part-through-wall crack under nuclear power plant full life time operating transients and the fatigue crack growth of a circumferential through-wall crack under one time safe shutdown seismic are analyzed. And the LBB assessment procedure and results of CASS pipe and WSS pipe are compared.

Benchmark Evaluations to Compare R6 Calculations to European Engineering Assessment and Leak-Before-Break Methods Based on STYLE Mock-Up Experiments

2014 ◽  
Author(s):  
Colin Madew ◽  
John Sharples ◽  
Peter Budden ◽  
Dana Lauerova
Keyword(s):  
Nuclear Power ◽  
Large Scale ◽  
Crack Opening ◽  
Limit Load ◽  
Crack Size ◽  
Opening Displacement ◽  
Critical Crack ◽  
Four Point Bending ◽  
Critical Crack Size ◽  
Leak Before Break

As part of the recent STYLE European project, three large scale mock-up experiments (Mock-up 1, Mock-up 2 and Mock-up 3) were performed. The Mock-ups were representative of nuclear power plant locations containing welds or cladding and contained an initial defect, either through-wall or surface breaking, and were loaded under four point bending conditions. Benchmarks based on each of these experiments were launched to investigate current Engineering Assessment Methods (EAMs) and Leak-before-Break (LbB) procedures used throughout Europe and how the application of these methods compare to each other and to the experimental data. Parameters that were specified for the benchmark participants to evaluate included crack opening displacement (COD), critical crack size, limit load, and load vs various amounts of ductile tearing. This paper presents and compares the results of the calculations performed by the participants in the benchmark. It focuses on the AMEC calculations using R6 and draws conclusions regarding its relative conservatism compared with each of the other methods and through comparison with the results of the Mock-up experiments.

Effect of Rotational Stiffness Evolution at Crack Part on Critical Crack Size in SFR

2012 ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Shinji Yoshida
Keyword(s):  
Evaluation Method ◽  
Large Diameter ◽  
Crack Size ◽  
Evolution Model ◽  
Piping System ◽  
Rotational Stiffness ◽  
Critical Crack ◽  
Rotational Spring Model ◽  
Size Evaluation ◽  
Critical Crack Size

This paper describes the efficiency of the deployment of rotational stiffness evolution model in the critical crack size evaluation for Leak Before Break (LBB) assessment of Sodium cooled Fast Reactor (SFR) pipes. The authors have developed a critical crack size evaluation method for the thin-walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, since the SFR pipe is mainly subjected to displacement controlled load caused by thermal expansion, the stress at the crack part is estimated taking stiffness evolution due to crack into account. The stiffness evolution is evaluated by using the rotational spring model. In this study, critical crack sizes for several pipes having some elbows were evaluated and discuss about the effect of the deployment of the stiffness evolution model at the crack part on critical crack size. If there were few elbows in pipe, thermal stress at the crack part was remarkably reduced by considering the stiffness evolution. In contrast, in the case where the compliance of the piping system was small, the critical crack size could be estimated under displacement controlled condition. As a result, the critical crack size increases by employing the model and LBB range may be expected to be enlarged.

Determination of Critical Crack Size Utilizing a Fracture Mechanics Test in Equipment Under Fatigue

2009 ◽  
Author(s):  
Irene Garcia Garcia ◽  
Radoslav Stefanovic
Keyword(s):  
Heat Treatment ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Operational Experience ◽  
Element Analysis ◽  
Critical Crack ◽  
Circumferential Welds ◽  
Fea Model ◽  
Critical Crack Size

Equipment that is exposed to severe operational pressure and thermal cycling, like coke drums, usually suffer fatigue. As a result, equipment of this sort develop defects such as cracking in the circumferential welds. Operating companies are faced with the challenges of deciding what is the best way to prevent these defects, as well as determining how long they could operate if a defect is discovered. This paper discusses a methodology for fracture mechanics testing of coke drum welds, and calculations of the critical crack size. Representative samples are taken from production materials, and are welded employing production welding procedures. The material of construction is 1.25Cr-0.5Mo low alloy steel conforming to ASME SA-387 Gr 11 Class 2 in the normalized and tempered condition (N&T). Samples from three welding procedures (WPS) are tested: one for production, one for a repair with heat treatment, and one for repair without heat treatment. The position and orientation of test specimen are chosen based on previous surveys and operational experience on similar vessels that exhibited cracks during service. Fracture mechanics toughness testing is performed. Crack finite element analysis (FEA) model is used to determine the path-independed JI-integral driving force. Methodology for the determination of critical crack size is developed.

Critical crack size in the fracture of metals

2007 ◽  
Vol 52 (7) ◽  
pp. 937-939
Author(s):  
V. A. Ivanskoĭ
Keyword(s):  
Crack Size ◽  
Critical Crack ◽  
Critical Crack Size

scholarly journals On the fracture toughness of snow

2004 ◽  
Vol 38 ◽  
pp. 1-8 ◽  
Author(s):  
Jürg Schweizer ◽  
Gerard Michot ◽  
Helmut O.K. Kirchner
Keyword(s):  
Fracture Toughness ◽  
Crack Size ◽  
Laboratory Measurements ◽  
Critical Crack ◽  
Arrhenius Relation ◽  
Linear Fracture ◽  
Different Temperatures ◽  
Increasing Temperature ◽  
Critical Crack Size ◽  
Key Parameter

AbstractThe release of a dry-snow slab avalanche involves brittle fracture. It is therefore essentially a non-linear fracture mechanics problem. Traditional snow-stability evaluation has mainly focused on snow strength measurements. Fracture toughness describes how well a material can withstand failure. The fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity, and hence snows lope stability. Fracture toughness in tension KIc and shear KIIc was determined with notched cantilever-beam experiments in a cold laboratory. Measurements were performed at different temperatures and with different snow types of density ρ = 100–300 kgm–3, corresponding to typical dry-snow slab properties. The fracture toughness in tension KIc was found to be larger (by about a factor of 1.4) than in shear KIIc. Typical values of the fracture toughness were 500–1000 Pam1/2 for the snow types tested. This suggests that snow is one of the most brittle materials known to man. A power-law relation of toughness KIc on relative density was found with an exponent of about 2. The fracture toughness in tension KIc decreased with increasing temperature following an Arrhenius relation below about –8°C with an apparent activation energy of about 0.16 eV. Above –6°C the fracture toughness increased with increasing temperature towards the melting point, i.e. the Arrhenius relation broke down. The key property in dry-snow slab avalanche release, the critical crack size under shear at failure, was estimated to be about 1 m.

Fracture Resistance in GFRP-BMC Composites Induced by Sub-Millimeter Length Fiber Dispersion

2012 ◽  
Vol 706-709 ◽  
pp. 907-913
Author(s):  
Michael C. Faudree ◽  
Yoshitake Nishi
Keyword(s):  
Fracture Resistance ◽  
Unsaturated Polyester ◽  
Glass Fibers ◽  
Acoustic Emissions ◽  
Crack Size ◽  
Critical Crack ◽  
Fiber Dispersion ◽  
Static Tensile ◽  
Styrene Butadiene ◽  
Critical Crack Size

Based on previous results of both an increase of nearly 40% in static tensile strain by shortening fiber length from commercial 6.4 mm to 0.44 mm in an unsaturated polyester/styrene-butadiene GFRP-BMC composite containing 20 mass% short E-glass fibers and their acoustic emissions (AE), the fracture resistance mechanics of sub-mm length fiber dispersion reinforcement is proposed. Since the 40% strain increase acts to improve strength and toughness, the mechanics is useful. This paper aims to present the mechanism of strain-driven improvement where microcracks are prevented from propagating beyond the critical crack size (2ac) for thermoset polymers, resulting in an increased and more dispersed total microcrack surface area as recorded by AE raising fracture strain.

NUMERICAL METHODS RESEARCH AND FRACTURE FAILURE ANALYSIS FOR CRITICAL CRACK SIZE

2019 ◽  
Vol 2019.27 (0) ◽  
pp. 1542
Author(s):  
Kaikai SHI ◽  
Xiaoming BAI ◽  
Yanli YUAN ◽  
Liangang ZHENG ◽  
Jianguo CHEN ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Failure Analysis ◽  
Crack Size ◽  
Critical Crack ◽  
Fracture Failure ◽  
Critical Crack Size

Influence of Predetermined Surface Defect to the Bendability of Ultra-High-Strength Steel

2012 ◽  
Vol 504-506 ◽  
pp. 901-906 ◽  
Author(s):  
Antti Määttä ◽  
Antti Järvenpää ◽  
Matias Jaskari ◽  
Kari Mäntyjärvi ◽  
Jussi A. Karjalainen
Keyword(s):  
Surface Defects ◽  
High Strength Steels ◽  
Steel Structures ◽  
High Strength ◽  
Crack Size ◽  
Critical Crack ◽  
Bending Radius ◽  
Ultra High Strength Steels ◽  
Materials Used ◽  
Critical Crack Size

The use of ultra-high-strength steels (UHS) has become more and more popular within last decade. Higher strength levels provide lighter and more robust steel structures, but UHS-steels are also more sensitive to surface defects (e.g. scratches). Practically this means that the critical crack size decreases when the strength increases. The aim of the study was to study if the formula of critical crack size is valid on forming processes of UHS-steels. Surface cracks with different depths were created by scratching the surface of the sheet by machining center. Effect of the scratch depth was determined by bending the specimens to 90 degrees. Bents were then visually compared and classified by the minimum achieved bending radius. Test materials used were direct quenched (DQ) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). Results from the bending tests were compared to the calculated values given by the formula of critical crack size.

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