bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Use of the Notch Master Curve for Apparent Fracture Toughness Predictions of Notched Ferritic Steels Operating Within the Ductile-to-Brittle Transition Zone
Authors: Cicero Sergio , Garcia Tiberio , Madrazo Virginia
Published: November 2015

This paper presents the Notch-Master Curve as a model for the prediction of the apparent fracture toughness of ferritic steels in notched conditions and operating at temperatures corresponding to their ductile-to-brittle transition zone.

The Notch-Master Curve combines the Master Curve of the material in cracked conditions and the notch corrections provided by the Theory of Critical Distances.

In order to validate the model, the fracture resistance results obtained in fracture tests performed on notched CT and SENB specimens are presented. The results gathered here cover four ferritic steels (S275JR, S355J2, S460M and S690Q), three different notch radii (0.25 mm, 0.50 mm and 2.0 mm) and three different temperatures within the corresponding ductile-to-brittle transition zone.

The results demonstrate that the Notch Master Curve provides good predictions of the fracture resistance in notched conditions for the four materials analyzed.
Microstructural Characterization of Alloy 617 Crept Into the Tertiary Regime
Authors: Lillo Thomas M. , Wright Richard N.
Published: November 2015

The dislocation structure and area fraction of creep voids in Alloy 617 were characterized following creep tests interrupted at total creep strains ranging from 2–20%. A range of creep temperatures (750–1000°C) and initial creep stresses (10–145 MPa) produced creep test durations ranging from 1 to 5800 hours. Image analysis of optical photomicrographs on longitudinal sections of the gage length was used to document the fraction of creep porosity as a function of creep parameters. In interrupted creep tests performed at 750°C, minimal levels of creep porosity were found even in samples crept to ∼20% total creep strain. At 1000°C, creep porosity was negligible below total creep strains of 10% and increased thereafter with increasing total creep strain. Also, creep porosity increased with decreasing creep stress for a given total creep strain. TEM performed on the gage sections did not reveal significant creep void formation on grain boundaries or in the grains at the sub-micron level. However, dislocation boundaries exhibited extensive dislocation rearrangement and dislocation-dislocation reactions. It was concluded that the onset of tertiary creep did not result from creep void formation and more likely arose due to the formation of low energy dislocation substructures.
Development and Prospect on Chinese Codes and Standards of Transportable Pressure Vessel
Authors: Xue Xiaolong , Tang Xiaoying , Lu Hongliang , Zhou Weiming
Published: November 2015

Due to hazardous chemicals with pressure inside and service in different areas, the transportable pressure vessels (TPV) are of high risks. Therefore, compulsory supervision should be carried out for the sake of security of TPVs all over the world. In China, TPV contains 5 categories, which are railway tank car, road tanker, tank container, tube trailer and tube container. In this paper, Chinese code and standard system of TPVs were introduced in detail by 5 levels, which are law, regulation, divisional regulation, safety technical regulation and standard. The scope and main content of the documents were presented briefly. The differences of the Chinese code and standard system were compared with that of EU and the United States. The causes of the differences were analyzed and some advices were brought forward. At last, basing on the current situation of the design, manufacture and inspection technology, the trends on development of Chinese codes and standards, tank material, design load, safety factor and allowable stress etc. of TPV were presented.
Evaluation of Stress Intensity Factor Interactions Between Adjacent Flaws With Large Aspect Ratios
Authors: Azuma Kisaburo , Li Yinsheng , Hasegawa Kunio
Published: November 2015

Multiple flaws detected during in-service inspections are evaluated in accordance with the flaw combination rules provided in the ASME B&PV Code Section XI. The rules treat adjacent two flaws as a single combined flaw if the distance between the two flaws is equal to or less than half of the flaw depth. That is, the combination rules are consisted of flaw depth basis. However, its applicability has not been clarified systematically to the flaws with large aspect ratio, the depth of which are greater than half its length. Interactions of stress intensity factors for multiple flaws under membrane stress were investigated using finite element analyses. The numerical results suggest that the flaw combination rules might be better to use flaw length basis, instead of flaw depth, over a wide range of the aspect ratio.
Applicability of a Deterministic Approach to Transfer the Fracture Toughness Jc Between Different Specimen Thicknesses
Authors: Meshii Toshiyuki , Lu Kai
Published: November 2015

In this paper, validity of the deterministic approach to transfer the fracture toughness Jc obtained with different thickness specimens was demonstrated. For this purpose, applicability of the (4δt, σ22c) failure criterion [1] was verified to transfer Jcs obtained for different specimen thicknesses in the fracture toughness database obtained from decommissioned Shoreham reactor vessel steel [2, 3]. The material tested was ASTM A533 Grade B Class 1 ferritic steel tested in the ductile-to-brittle transition temperature region. The critical value σ22c for twelve types of specimens (thickness in the range of 8 to 254 mm) showed only 4% variation. The fact that these critical values were always reached at the specimen mid-plane and the fact that cleavage always initiated at the specimen mid-plane supported the validity of the deterministic approach. Because the (4δt, σ22c) failure criterion requires only “single” set of test data for Jc transfer and because σ22c shows only a few % scatter, it seems to have a possibility to replace what Weibull stress is expected to do.
Measurement of Flow-Induced Forces: A Single Flexible Tube in a Rigid Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow
Authors: Deri Enrico , Nibas Joël , Ries Olivier , Adobes André
Published: November 2015

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to asses risk and thereafter to optimize the SG maintenance policy.

The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is updated in order to cover all existing tube bundle configurations.

Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the result of the first phase of the associated experiments in terms of force coefficients and two-phase flow excitation spectra for both in-plane and out-of-plane vibration.
Thermal-Hydraulic Response of the Secondary Side of a PWR Steam Generator With an Internal Structure to a Main Steam Line Break
Authors: Jo Jong Chull
Published: November 2015

This study addresses a numerical analysis of the thermal-hydraulic response of the secondary side of a steam generator (SG) model with an internal structure to a main steam line break (MSLB) at a pressurized water reactor (PWR) plant. The analysis model is comprised of the SG upper space where steam occupies and the part of the main steam pipe between the SG outlet nozzle and the broken pipe end upstream of the main steam isolation valve. To investigate the effects of the presence of the SG internal structure on the thermal-hydraulic response to the MSLB, the numerical calculation results for the analysis model having a perforated horizontal plate as the SG internal structure are compared to those obtained for a simple analysis model having no SG internal structure. Both analysis models have the same physical dimensions except for the internal structure. The initial operating conditions for both SG models are identical to those for an actual operating plant. To simplify the analyses, it is assumed that steam is constantly generated from the bottom of the SG secondary side space during the blowdown process.

As the results, it has been found that the pressure wave significantly attenuates as it passes through the perforated internal structure and as time elapses. This leads to reduction in instantaneous hydraulic load on the internal structure including tubing. However, it is seen that the presence of the internal structure does not affect the transient velocities of steam passing through the SG tube bundle during the blowdown, which are 2 to 8 times the velocities during the normal reactor operation as in the case for the empty SG. Consequently, the present findings should be considered for the design of the steam generator to ensure the reactor safety as such elevated high steam velocities can cause fluidelastic instability of tubes which results in high cycle fatigue failure of the tubes.
A Numerical Investigation of the Fluidelastic Coupling for a Cell of Flexible Tubes in a Square-in-Line Bundle Subject to Water Cross-Flow
Authors: Berland Julien , Deri Enrico , Adobes André
Published: November 2015

The unsteady flow motions and the force distribution in a normal square tube array subject to cross-flow induced vibrations are investigated by means of large-eddy simulations. The flow configuration and the operating conditions are taken from the experiments of Gosse et al. (PVP Conference, 2001). The set-up is made of 63 (9 rows and 7 columns) straight tube bundle. The tubes are arranged in a square in line pattern, and a cell of 9 flexible tubes, located in the middle of the bundle, may translate in the drag and lift directions.

The LES of cross-flow induced vibrations of a cell of 9 flexible tubes in a normal square tube array is performed. A fully-coupled fluid-structure calculation is hence achieved using Code_Saturne, an open source CFD tool. Turbulence modeling is achieved using the large-eddy simulation framework based on the so-called classical Smagorinsky model. The tube dynamics is modeled by simple mass-spring-damper systems, and the motions of the fluid domain is accounted for by a moving mesh technique (Arbitrary-Lagrangian-Eulerian formulation).

The consistency of the calculations is demonstrated by comparing the numerical data to the experiments of Gosse et al. (PVP Conference, 2001) in terms of tube amplitude and flow-induced force spectra, for various gap velocities.

Investigation of the spectra of the flow-induced forces then shows that the tube motions ignite the emergence of flow phenomena at constant Strouhal numbers. The fluid-structure interactions are also responsible for the existence of a series of tones at rather constant frequencies, corresponding to the vibrational modes of the flexible cell.
Strain Gage and Thermocouple Measurements of Hyper Compressor Packing Cups to Study Pressure Sealing Performance
Authors: Miller Eric S. , Blanding James M.
Published: November 2015

Low Density Polyethylene (LDPE) production involves reactors operating at up to 3,000 bar pressure or even higher. The final stage of gas compression is done with a plunger-type machine called a “Hyper Compressor”. A “packing stack” for pressure sealing consists of multiple bronze packing rings and oil lubrication injection points; which are positioned in place by numerous packing cups. The distribution of pressure drop in a new cylinder and the changes in sealing behavior over its life are critical to design, but have long been prohibitively difficult to verify experimentally.

Four cylinders were extensively instrumented; two in each of two successive test campaigns over four years’ time. Strain gages were located at the outside diameter of each packing cup to infer internal dynamic pressure across the packing stack. Included also in the high-speed data acquisition were strain gages on numerous additional components, thermocouples on packing cup faces, a pressure transducer in the low-pressure lubrication line, and existing eddy-current proximity probes on the plunger rods. Continuous monitoring was performed from the initial installation to final removal of each cylinder. Analysis of this high speed data along with long-term trends led to several conclusions regarding the design and operation of the Hyper cylinder. Testing also revealed various unusual events that can be further studied to better understand some of the unique behaviors that take place in the highly complex cylinder design of Hyper compressors.
Flaw Tolerance Assessment for Low-Cycle Fatigue of Stainless Steel
Authors: Kamaya Masayuki
Published: November 2015

According to Appendix L of the BPVC Section XI, flaw tolerance assessment is performed using the stress intensity factor even for low-cycle fatigue. On the other hand, in Section III, the fatigue damage is assessed using the design fatigue curve, which has been determined from strain-based fatigue tests. Namely, the stress is used for the flaw tolerance assessment, whereas the strain (Ke factor) is quoted for the design. In order to resolve this inconsistency, in the present study, the strain intensity factor was used for crack growth prediction. First, it was shown that the strain range was the key parameter for predicting the fatigue life and crack growth. The crack growth rates correlated well with the strain intensity factor even for the low-cycle fatigue. Then, the strain intensity factor was applied to predict the crack growth under uniform and thermal cyclic loading conditions. The estimated fatigue life for the uniform cyclic loading condition agreed well with that obtained by the low-cycle fatigue tests, while the fatigue life estimated for the cyclic thermal loading condition was longer. It was shown that the inspection result of “no crack” can be reflected to determining the future inspection time by applying the flaw tolerance analysis. It was concluded that the flaw tolerance concept is applicable not only to the plant maintenance but also to plant design. The fatigue damage assessment using the design fatigue curve can be replaced with the crack growth prediction.
Development of the Extremely Low Probability of Rupture (xLPR) Version 2.0 Code
Authors: Rudland D. , Harrington C. , Dingreville R.
Published: November 2015

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals.

US NRC staff, working cooperatively with the Electric Power Research Institute through a memorandum of understanding, conducted a multi-year project that focused on the development of a viable method and approach to address the effects of PWSCC in primary piping systems approved for LBB. This project, called eXtremely Low Probability of Rupture (xLPR), defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations.

As reported in previous technical papers, the first version of the xLPR code was developed as part of a pilot study, which leveraged existing fracture mechanics based models and software coupled to both a commercial and open source code framework to determine the framework and architecture requirements appropriate for building a modular-based code with this complexity. Using the lessons learned from the pilot study, the production version of this code, designated as Version 2.0, focuses on those primary piping systems previously approved for LBB. In this version, the appropriate fracture mechanics-based models are employed to model the physical cracking behavior and a variety of computational options are provided to characterize, categorize and propagate problem uncertainties.

This paper examines the xLPR Version 2.0 model by presenting a brief overview of the xLPR scope, the code structure, computational framework and fracture mechanics-based models. As a demonstration of the xLPR Version 2.0 capabilities, an example is presented that focuses on PWSCC in large-bore piping systems. This example exercises some functionalities of the xLPR code to demonstrate its application to assess compliance with 10CFR50 Appendix A, GDC-4. This paper concludes with a brief discussion on the path forward and plans for the control and maintenance of the xLPR code.
Computation of a Loosely Supported Tube Under Cross-Flow by a Hybrid Time-Frequency Method
Authors: Piteau Philippe , Borsoi Laurent , Delaune Xavier , Politopoulos Ioannis , Antunes Jose
Published: November 2015

Flow-induced vibrations of heat-exchanger tubes are particularly analyzed in the nuclear industry for safety reasons. Adequate designs, such as anti-vibration bars in PWR steam generators, prevent any excessive vibrations provided the tubes are well supported. Nevertheless degraded situations, where the tube/support gaps would widen, must also be considered. In such a case, the tubes become loosely supported and may exhibit vibro-impacting responses due to both turbulence and fluid-elastic coupling forces induced by the cross-flow.

This paper deals with the predictive analysis of such a situation, based on a time-frequency hybrid method, given the necessity of taking into account both the strong impact nonlinearity due to the gap and the linearized fluid-elastic forces defined in the frequency domain. It comprises four parts.

1) The experimental campaign carried out at CEA Saclay on this issue, with a rigid square bundle surrounding a flexible cantilever tube under water cross-flow, is briefly recalled.

2) The hybrid time-frequency method is presented. The technique consists in an iterative solving, going back and forth from the frequency domain to the time domain, until convergence. Focus is made on the key points that are the algorithm convergence, and the non-causality of fluid-elastic forces stemming from the extrapolation of the frequency-limited experimental data.

3) The experimental and computational results are compared for a large range of flow velocities and three values of gaps, with a satisfying overall agreement. The comparison includes also previous results obtained from a simplified method based on the concept of “instantaneous” frequency.

4) Finally two a priori surprising behaviors are noted in the energy balances that have been computed: the sometimes dissipative aspect of turbulence forces, and the “mirror effect” between the work of turbulence and fluid-elastic forces.
Prediction of Dynamic Break-Opening Area Under Beyond Design Basis Seismic Loading
Authors: Uddin M. , Kurth E. , Brust F. W. , Wilkowski G. M. , Betervide A. A. , Mazzantini O. , Fernandez R. A.
Published: November 2015

The thermal-hydraulics computer code, RELAP (Reactor Excursion and Leak Analysis Program) is used to analyze loss of coolant accidents (LOCAs) and system transients in PWRs and BWRs. However, RELAP requires the knowledge of break-opening area versus time history for Double-Ended Guillotine Break (DEGB) of a pipe fracture event as an input to calculate pressure drops at critical locations in the primary pipe loop. Previously authors conducted a detailed dynamic FE analyses to determine the condition for DEGB that provided moment versus rotation of the cracked-pipe and time histories for DEGB under beyond design basis seismic loading.

In this paper, crack-opening area was calculated using the moment-rotation-time history obtained from dynamic FE analyses. In the LBB.ENG2 J-estimation scheme for circumferentially cracked pipe, the rotation at the cracked-pipe cross-sectional location (rotation due to the crack) is uniquely related to the total crack length and crack-opening displacement at the center of the crack. However, the relationship is only valid when the moment versus rotation from the FE analyses corresponds to the ductile tearing curve from the LBB.ENG2 ductile fracture analysis. During any unloading (and reloading) parts of the applied seismic history, the rotation can drop down from the upper-envelope for the tearing resistance of the cracked pipe in an elastic unloading manner from the seismic/cyclic unloading. During this part of the seismic time-history, the crack length remains constant but the center-crack-opening displacement decreases, i.e., there is crack closure with a constant crack length which needs to be included in predicting crack-opening area. Based on a number of past cyclic pipe fracture tests with large amounts of ductile tearing, a procedure was developed to predict the crack-opening area that included crack closure during cyclic loading of the seismic event. The resulting opening-area versus time history then becomes the input to the RELAP analysis for determination of emergency core cooling/safety processes.
Probabilistic Structural Integrity Evaluation on a Pressurized Water Reactor Pressure Vessel Under Pressure–Temperature Limit Operations
Authors: Chou Hsoung-Wei , Huang Chin-Cheng
Published: November 2015

The normal reactor startup (heat-up) and shut-down (cool-down) operation limits are defined by the ASME Code Section XI-Appendix G, to ensure the structural integrity of the embrittled nuclear reactor pressure vessels (RPVs). In the paper, the failure risks of a Taiwan domestic pressurized water reactor (PWR) pressure vessel under various pressure-temperature limit operations are analyzed. Three types of pressure-temperature limit curves established by different methodologies, which are the current operation limits of the domestic RPV based on the KIa fracture toughness curve in 1998 or earlier editions of ASME Section XI-Appendix G, the recently proposed limits according to the KIC fracture toughness curve after the 2001 edition of ASME Section XI-Appendix G, and the risk-informed revision method proposed in MRP-250 report that provides more operational flexibility, are considered. The ORNL’s probabilistic fracture mechanics code, FAVOR, is employed to perform a series of fracture probability analyses for the RPV at multiple levels of embrittlement under such pressure-temperature limit transients. The analysis results indicate that the pressure-temperature operation limits associated with more operational flexibility will result in higher failure risks to the RPV. The shallow inner surface breaking flaw due to the clad fabrication defect is the most critical factor and dominates the failure risk of the RPV under pressure-temperature limit operations. Present work can provide a risk-informed reference for the safe operation and regulation of PWRs in Taiwan.
Crack Initiation and Growth Simulation for CRDM Nozzles by eXtended Finite Element Method
Authors: Lee Sung-Jun , Chang Yoon-Suk
Published: November 2015

The head penetration nozzles of control rod driving mechanisms (CRDMs) are susceptible components on primary water stress corrosion cracking (PWSCC) due to the dissimilar metal welds. The accurate integrity assessment of the CRDM head penetration nozzles is important for the safe operation of nuclear power plants. To resolve the integrity issue, conventional finite element methods, a cohesive zone model, and a virtual crack closure technique have been employed; however, there are still many uncertainties in accuracy and efficiency. In the present study, a specific Strain Rate Damage Model (SRDM) with stress and thermal dependent parameters was adopted to calculate crack initiation time. Also, a level set method, which defines the crack location based on the crack surface and vertical surface of crack tip, was considered to simulate arbitrary crack growth. By taking into account these two features, the eXtended Finite Element Method (XFEM) was implemented to simulate the PWSCC initiation and growth with a user subroutine code. Finally, the validity of the proposed method was evaluated by comparing the reference cracks that occurred in the CRDM head penetration nozzles.
Strain Prediction for X80 Steel Pipeline Subjected to Strike-Slip Fault Under Compression Combined With Bending
Authors: Liu Xiaoben , Zhang Hong , Chen Yanfei
Published: November 2015

Strike-slip fault is one main kind of PGD faced by long distance gas pipelines. Based on non-linear finite element method, a numerical model for buried pipeline under strike-slip fault was proposed. The model was proven to be reasonable by comparing the numerical results with previous researcher’s experiment results. By using the FE model, peak compressive strain of X80 steel pipeline subjected to strike-slip fault under compression combined with bending was studied. The sensitivities of the diameter, wall thickness, soil rigidity, fault displacement and crossing angle on the peak compressive strain of the pipeline are examined in detail. Furthermore, based on numerous numerical results, a regression equation for predicting peak compressive strain of X80 steel pipeline is proposed. The applicable range of the formula is given. 15 true design cases in the Second West to East pipeline Project in China were investigated to demonstrate the accuracy and applicability of the proposed methodology by comparing the predicting peak compressive strain results with FEM results. The proposed method can be referred in the strain-based and reliability-based design for X80 steel pipelines subjected to strike-slip fault.
Application of XFEM to Model Crack Initiation and Propagation During a PTS Event
Authors: Nicak Tomas , Mutz Alexander , Keim Elisabeth , Meier Gottfried
Published: November 2015

The integrity of a reactor pressure vessel (RPV) has to be ensured throughout its entire life in accordance with the applicable regulations. Typically an assessment of the RPV against brittle failure needs to be conducted by taking into account all possible loading cases. One of the most severe loading cases, which can potentially occur during the operating time, is the loss-of-coolant accident (LOCA), where cold water is injected into the RPV at operating conditions. High pressure in combination with a thermal shock of the ferritic pressure vessel wall caused by the injection of cold water leads to severe loading conditions at the beltline area known as Pressurized Thermal Shock (PTS).

Usually the assessment against brittle failure is based on a deterministic fracture mechanics analysis, in which common parameters like the J-integral or stress intensity factor are employed to calculate the load path during the PTS event for an assumed (postulated) flaw. Subsequently the results of the fracture mechanics analysis are compared with material properties obtained from the irradiation surveillance program of the RPV to demonstrate the exclusion of brittle fracture initiation.

In this paper an alternative novel method for the calculation of the crack initiation and possible crack propagation by means of the eXtended Finite Element Method (XFEM) will be introduced and compared with results of the standard PTS analysis.
Further Validation of the Technical Basis of Code Case N-838 for Flaw Tolerance Evaluation of CASS Piping
Authors: Griesbach Timothy J. , Dedhia Dilip , Harris David O. , Cofie Nathaniel G. , Alleshwaram Aparna , Amberge Kyle
Published: November 2015

ASME Code, Section XI Code Case N-838 provides analyses methods that may be used when performing flaw tolerance evaluation of Class 1 and 2 cast austenitic stainless steel (CASS) piping components with ferrite content exceeding 20%. Tolerable flaw sizes are provided in the Code Case that cannot be exceeded during the evaluation period from an initial postulated flaw. The tolerable flaw sizes were determined based on probabilistic fracture mechanics (PFM) techniques employing toughness and flow strength correlations developed at Argonne National Laboratory (ANL) that estimated the crack growth resistance (J-R) curve using material composition with the room temperature Charpy energy as an intermediate variable. Since the publication of the technical basis for this Code Case, additional toughness data have been identified, some of which are significantly lower than the toughness for CASS CF-8M materials considered in the ANL model.

This paper reports the results of evaluations and sensitivity studies performed to examine the additional toughness and tensile data and determine the effects on the Code Case tolerable flaw size tables. The current study directly employs an expanded set of data of actual measured fully saturated high-temperature crack growth resistance curve, thereby bypassing the material composition-to-Charpy-to-toughness correlations in the ANL model. In this study, both deterministic fracture mechanics and PFM analyses were performed using the assembled data of toughness and tensile properties. The results obtained in the current PFM and deterministic analysis which use the actual toughness and tensile data are found to always provide larger tolerable flaw sizes than those obtained from the previous analyses which used ANL material correlations, thereby demonstrating the conservative nature of the technical basis for the Code Case.
Multiple Inner Crack Growth Simulation Using S-Version FEM
Authors: Kikuchi Masanori , Serizawa Ryosuke , Li Yulong
Published: November 2015

Growth behaviors of multiple inner cracks, which are located near to structure surface, are simulated using S-FEM. Coalescence of cracks occurs before penetration to surface in some condition. In other condition, penetration occurs before coalescence. By changing relative locations of two inner cracks, these phenomena are observed, and criteria for coalescence and penetration are discussed.
Integrity and Life Assessment of Cast Duplex Stainless Steel Elbows of EDF PWR Main Coolant Piping
Authors: Le Delliou Patrick , Saillet Sébastien
Published: November 2015

Thermal ageing of cast duplex stainless steel elbows is a concern for long-term operation of EDF nuclear power plants. The thermal ageing embrittlement results from the micro-structural evolution of the ferrite phase (spinodal decomposition), and can reduce the fracture toughness properties of the steel. In addition, it is necessary to consider manufacturing quality and the possible occurrence of casting defects such as shrinkage cavities. In a context of life extension, it is important to assess the safety margins to crack initiation and crack propagation instability.

This paper reports the present integrity and life assessment methodologies as carried out by EDF. The approach is based on the in-service inspection and surveillance RSE-M Code and on French regulation requirements for NPPs in operation. This work is supported by an extensive R&D programme on one hand and on field experience analysis on the other hand.

The paper details the three main topics of the life assessment methodology:

- estimation of the fracture toughness of the steel with predictive formulae using the chemical composition and ageing conditions,

- definition of a reference crack size based on an inventory of the manufacturing quality of the elbows,

- fracture mechanics evaluation based on the J parameter, computed either by an engineering estimation method or by a finite element analysis. The calculated J parameter is then compared with the estimated fracture toughness of the material. Partial safety coefficients are included in the calculation process as required by the RSE-M Code.
Analysis of Pressurization of Plutonium Oxide Storage Vials During a Postulated Fire
Authors: Laurinat James E. , Kesterson Matthew R. , Hensel Steve J.
Published: November 2015

The documented safety analysis for the Savannah River Site evaluates the consequences of a postulated 1000 °C fire in a glovebox. The radiological dose consequences for a pressurized release of plutonium oxide powder during such a fire depend on the maximum pressure that is attained inside the oxide storage vial. To enable evaluation of the dose consequences, pressure transients and venting flow rates have been calculated for exposure of the storage vial to the fire. A standard B vial with a capacity of approximately 8 cm3 was selected for analysis. The analysis compares the pressurization rate from heating and evaporation of moisture adsorbed onto the plutonium oxide contents of the vial with the pressure loss due to venting of gas through the threaded connection between the vial cap and body. Tabulated results from the analysis include maximum pressures, maximum venting velocities, and cumulative vial volumes vented during the first 10 minutes of the fire transient. Results are obtained for various amounts of oxide in the vial, various amounts of adsorbed moisture, different vial orientations, and different surface fire exposures.
Measurements of Fatigue Crack Growth Rates of the Heat-Affected Zones of Welds of Pipeline Steels
Authors: Slifka Andrew J. , Drexler Elizabeth S. , Amaro Robert L. , Lauria Damian S. , Hayden Louis E. , McCowan Christopher N. , Sowards Jeffrey W.
Published: November 2015

Pipelines are widely accepted to be the most economical method for transporting large volumes of hydrogen, needed to fuel hydrogen-powered vehicles. Some work has been previously conducted on the fatigue crack growth rates of base metals of pipeline materials currently in use for hydrogen transport and on pipeline materials that may be used in the future. However, welds and their heat-affected zones are oftentimes the source and pathway for crack initiation and growth. The heat-affected zones of welds can exhibit low resistance to crack propagation relative to the base metal or the weld itself. Microstructural irregularities such as chemical segregation or grain-size coarsening can lead to this low resistance. Therefore, in order to have adequate information for pipeline design, the microstructures of the heat-affected zones must be characterized, and their mechanical properties must be measured in a hydrogen environment. With that in mind, data on the fatigue crack growth rate is a critical need. We present data on the fatigue crack growth rate of the heat-affected zones for two girth welds and one seam weld from two API 5L X52 pipes. The materials were tested in hydrogen gas pressurized to 5.5 MPa and 34 MPa at a cyclic loading rate of 1 Hz, and an R ratio of 0.5.
Development of Integrated Numerical Analysis Model for Unsteady Phenomena in Upper Plenum and Hot-Leg Piping System of Japan Sodium-Cooled Fast Reactor
Authors: Takaya Shigeru , Tanaka Masaaki , Fujisaki Tatsuya
Published: November 2015

Flow-induced vibration of hot-leg pipings is one of concerns for the design of Japan Sodium-cooled Fast Reactor (JSFR) which is now being developed. The flow field in the hot-leg pipings is supposed to be affected by flow disturbances at the entrance, so it is important to evaluate flow fields including the upper plenum. In this study, a simulation model of the upper plenum and the hot-leg piping system of JSFR was developed. Unsteady fluid flow analyses were then conducted by unsteady Reynolds averaged Navier-Stokes simulation (URANS) with Reynolds stress model. The appropriateness of the calculated results was discussed by comparing available scale model test results. Furthermore, a prototype model for vibration analysis of the hot-leg piping was developed. In the model, the transient pressure data predicted by the URANS were used as input data for the vibration analysis. The number of element was significantly reduced from that of CFD model by considering the correlation length of stress fluctuation. In addition, a stress mapping tool from a CFD model to a model for vibration analysis was created.
An Experimental Study of Steam Generator Tube Loading During Blowdown
Authors: Hamouda Ouajih , Weaver David S. , Riznic Jovica
Published: November 2015

If the main steam line from a nuclear steam generator were to break, the water in the steam generator would rapidly flash off in what is called a blowdown. Such an event could produce significant loading on the steam generator tubes, which if fractured, could lead to a loss of radioactive materials from containment. Thus, knowing the tube loading during such an event is an important input for safe design. This paper presents the results of an experimental laboratory study of the transient tube loading during a simulated blowdown. The working fluid was R-134a and the sectional tube model was a normal triangular array with a pitch ratio of 1.36. Tests were conducted with various levels of liquid R-134a and various numbers of tube rows. The transient tube loading is explained in terms of the associated flow physics and the maximum load is compared with existing models for tube loading obtained under steady flow conditions.
Modal Analysis of a Clamped-Free Plate in a Duct
Authors: Zhao Xiaochen , Liu Gongmin
Published: November 2015

When a rigid wall is replaced by a cavity covered by a flexible plate, the plate can cause broadband sound reflection in a duct. In this paper, analytical formulations in previous studies are extended to the plate with clamped-free boundary conditions. A set of static beam functions, which are a combination of sine series and third-order polynomial, is employed as the trial functions of the plate vibration velocity. Optimization is carried out in order to obtain the widest sound reflection bandwidth. Further studies with regard to the plate under several different classical boundary conditions based on the validated model show that, a clamped-free plate in the duct has the narrowest sound reflection bandwidth. In order to understand the precise mechanism of the spectra change, the behavior of each clamped-free plate mode is also analyzed. It is found that the weak first modal response in a clamped-free plate leads to its performance degradation.
Introduction of a Research Activity on the Seismic Safety Evaluation of Nuclear Piping Systems Taking the Effect of Elastic-Plastic Behavior Into Account
Authors: Nakamura Izumi , Shiratori Masaki , Otani Akihito , Morishita Masaki , Shibutani Tadahiro , Nakamura Hitoshi
Published: November 2015

According to investigations of several nuclear power plants (NPPs) hit by actual seismic events and a number of experimental researches on the failure behavior of piping systems under seismic loads, it is recognized that piping systems used in NPPs include a large seismic safety margin until boundary failure and the current code design allowable stresses are very conservative. Since the stress assessment based on the elastic analysis does not reflect actual response of piping systems including plastic region, rational procedures to estimate the elastic-plastic behavior of piping systems under a large seismic load are expected to be developed for piping seismic design applications.

With the aim of establishing a procedure that takes into account the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, a research activity has been planned. Through the activity, the authors intend to establish two kinds of guidelines; 1) a guideline of a standard analysis procedure to evaluate elastic-plastic behavior of piping systems under extreme seismic loads with rational and conservative margins, and 2) a guideline that provide criteria for the seismic safety assessment of piping systems by the standard analysis to evaluate elastic-plastic behavior established by the above guideline. As the first step of making out the analysis guideline, benchmark analyses are conducted for a pipe element test and a piping system test.

In this paper, the outline of the research activity and the preliminary results of benchmark analyses for a pipe element test are described.
FEM Stress Analysis and Sealing Performance of Bolted Flanged Connections Using PTFE Blended Gaskets Under Internal Pressure
Authors: Sato Koji , Muramatsu Akira , Kobayashi Takashi , Sawa Toshiyuki
Published: November 2015

The objective of the paper is to examine mechanical characteristics of bolted flanged connection with newly developed PTFE blended gaskets under internal pressure such as the contact gasket stress distribution, the sealing performance, the load factor, reduction in axial bolt load due to creep and the flange hub stress. The relationship between the leak rate and the contact gasket stress for newly developed PTFE blended gasket were measured according to JIS B 2490 as well as the stress - displacement relationship of the gaskets. Then, the leak rate for bolted flanged connection with the PTFE blended gaskets (2inch nominal flange) was measured under internal pressure while changing the bolt preloads. In addition, the load factor and the hub stress were measured experimentally. The changes in each axial bolt force were measured using the strain gauges taking into account gasket creep. Using FEM, the gasket stress distribution, the load factor and the hub stress are analyzed taking into account the creep phenomenon of the PTFE blended gasket. The optimal maximum bolt preload is determined and the FEM results of the load factor and hub stress are in a fairly good agreement with the measured results. The predicted leak rate is fairly coincided with the measured results.
A Joint Research Project to the Control of Rapid Temperature Changes in Industrial Components
Authors: Trieglaff Ralf , Rieck Detlef , Schulz Axel
Published: November 2015

The control of rapid and numerous temperature changes is an urgent requirement in many industrial processes, particularly for thermal power plants in flexible operation.

The paper describes objectives, partners and methodical approaches of the ongoing German research project THERRI.

The project scope is to establish essential Fracture Mechanics basics for an industrial application of a Damage Tolerance concept to thick-walled components of thermal power plants.

One key issue of the stipulated works is to provide an experimental data base for fatigue crack propagation in high-temperature ferritic-martensitic steels in the relevant temperature range from 300°C to 600°C. This will be supplemented by simulation calculations (XFEM) and the further development of ultrasonic measurement techniques.

The research project has been started but not finished yet. Therefore this paper is a snapshot of the ongoing project work and shows — besides the methodological work — first but not final results.
Investigations on Crack Propagation Under Cyclical Isothermal and Thermo-Mechanical Loadings for a Type 304-L Stainless Steel Used for Pressurized Water Reactor
Authors: Gourdin C. , Rossillon F. , Le Delliou P. , Perez G. , Fissolo A.
Published: November 2015

The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR) has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, RSE-M introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in strength-controlled conditions.

To this end, a new device called PROFATH was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the cycle, a high frequency induction coil heats the external wall. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load.

To obtain a very precise thermal mapping, a specific specimen with dedicated instrumentation is used: 20 thermocouples are appropriately located on the outer surface and along the wall thickness. During the test, the crack-propagation is estimated through crack-opening measurements (compliance method).

Now, three first tests have been carried out. These tests allow having an evaluation of the pertinence of the correction proposed by the RSE-M for a significant plasticity. Following tests are planned in order to have a confirmation or to propose an extension of the validity domain.
Lateral Influence Coefficients for a Thin Conical Shell Frustum
Authors: Liepins Atis A. , Arnez Javier
Published: November 2015

Thin conical shell components are often used in vertical process vessels, bins, and water storage tanks. When exposed to the elements, such structures may be subjected to lateral wind forces and seismic accelerations. For calculations of lateral response of such structures with simplified models, in the form of vertical beams, lateral influence coefficients for thin conical frustum shells are useful.

To compute lateral influence coefficient for conical frusta, asymmetric solutions of shell equations for cones are needed. The literature on asymmetric solutions for conical shells is sparse. Hoff [1] derived equations suitable over a limited range of parameters for asymmetric response of conical shells and indicated possible solutions using Fourier and power series. In his discussion of Hoff’s work, Pohle [2] indicated that an asymptotic solution of the equations is useless because of its validity over an impractical range of parameters. Seide [3] derived equations that removed the limitations of Hoff’s equations. Wilson [4] proposed solutions by separation of variables and power series. The slowly converging power series were summed using a computer for a conical panel under distributed loading. Chandrashekhar and Karekar solved the equations for a conical frustum under wind loading by expanding the solution in Fourier series in the circumferential direction, and applying finite differences in the meridional direction. The difference equations were solved using a computer.

Derived here are closed-form expressions for thin conical shell frusta based on the membrane theory of shells. These influence coefficients are compared with finite element results for a conical shell, with specific geometry and material properties, for which wall bending is included.
Low Cycle Fatigue Evaluation Using Cyclic Loading Test Data
Authors: Hojo Kiminobu , Kawabata Shinichi
Published: November 2015

The JSME Codes and Standards Committee have a plan to make a guideline for excessive cyclic loading after Fukushima accident. The special task group of the JSME C&S Committee conducted two kinds of benchmark analyses for simulating the test results of an elbow model under cyclic loading and a pipe system model under seismic loading. The authors participated in the analysis group using an elbow model. The Chaboche model was used for a constitutive law and three displacement levels were applied to the model separately. The crack was estimated to initiate at the flank of the center cross section of the elbow. The estimated cyclic number for fatigue crack initiation by Manson’s universal slope method conservatively agreed with the experimental result.