bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance of Trapped Acoustic Modes of a Ducted Rectangular Cavity
Authors: Bolduc Michael , Ziada Samir , Lafon Philippe
Published: November 2015

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly & Ziada [1–3] investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross-section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.
Progressive Damage Analysis of Full-Wrapped Composite Gas Cylinder Under Overload Condition and Prediction of Its Bursting Pressure
Authors: Wang Zewu , Zhang Guojing , Liu Peiqi , Xia Liangzhi
Published: November 2015

Fiber is widely used as a reinforcing material on the gas cylinder owing to good stiffness-to-weight and designability as well as high strength. However, it is difficult to analyze the failure process of a full-wrapped composite gas cylinder because of the anisotropy of composite material and complexity of a full-wrapped geometric structure. In this study, the three dimensional (3D) numerical model of a full-wrapped gas cylinder was first developed and used for calculating its stress distribution. And then the Hashin failure mode and reduction factor of elastic modulus were integrated into the numerical model by using a user subroutine. Lastly, the progressive damage process of the gas cylinder was analyzed in detail under overload conditions. The results indicated that the proposed progressive damage model could not only reproduce the damage process of the full-wrapped gas cylinder, but also predict the critical bursting pressure. This work will in the future help to guide the calculation of load-carrying capacity and failure analysis of the composite gas cylinder.
RCC-MRX Edition 2015: Overview of Three Years of Developments
Authors: Pétesch C. , Lebarbé T. , de la Burgade F. , Bonne D. , Blat-Yrieix M.
Published: November 2015

The 2015 edition of the RCC-MRx Code will be issued, by the end of the year, in French and English versions by AFCEN (Association Française pour les règles de Conception et de Construction des Matériels des Chaudières Electro-nucléaires). This Code set up rules applicable to research reactor components (coming from the RCC-MX 2008 developed in the context of the Jules Horowitz Reactor project), and to components operating at high temperature and to the Vacuum Vessel of ITER (coming from the RCC-MR 2007).

A significant work has been performed since 2012, first edition of the RCC-MRx, in order to improve the rules, to facilitate its use and understandability, and also to have a better fit with the feedbacks of the main projects (ASTRID, JHR, ITER).

This paper presents the technical evolutions in the 2015 edition and also the other initiatives led upstream (prenormative works) and downstream (publication of the rules background - criteria) of the publication of rules.
B31.1 Compliant Design of CFRP Buried Piping Systems
Authors: Stoeva Neda , Adams Timothy M. , Jimenez Tomas , Arnold Scott , Uhland John
Published: November 2015

This paper presents the implementation of a Carbon Fiber Reinforced Polymer (CFRP) composite system as a long term replacement for a non-safety, non-seismic, non-QA, low pressure service water buried pipeline. The existing pipeline (to be replaced) consists of approximately 1800 feet of large diameter (primarily 54in.), carbon steel, spiral wound, seam welded pipe, which was built and installed using AWWA standards, but is maintained in accordance with the B31.1 Power Pipe Code [1]. The CFRP pipe installation is to be done as an internal repair, and designed to comply with ASME B31.1 as a stand-alone pipe (pressure boundary). In lieu of using the limited evaluation of PCC-2 [2], which is focused on local repairs; a complete design evaluation of the entire piping system to B31.1-2010 is conducted, which is consistent with and acceptable under PCC-2. Since B31.1 does not provide detailed guidance on the design of buried piping systems, the criteria presented in this paper use the base design requirements of B31.1 adjusted to include applied soil and surcharge loads. The selected CFRP repair is the TYFO® Fiberwrap® system which consists of a carbon fiber fabric (CFRP, TYFO SCH-41-2X), and glass fiber fabric (GFRP/dielectric barrier, TYFO SHE-51A), saturated with epoxy. This composite system is built up of unidirectional CFRP layers; thus, the presented design approach also considers anisotropic material behavior, and evaluates the hoop and axial loads and capacities separately. The criteria are presented for plants considering alternative repair and replacement techniques for buried and above ground non-safety pipes.
Nonlinear Guided Waves for Monitoring Microstructural Changes in Metal Structures
Authors: Choi Gloria , Liu Yang , Lissenden Cliff J.
Published: November 2015

The capability of third harmonic generation to indicate material degradation at the microstructural level is demonstrated for strain ratcheting in Alloy 617. Specifically, mechanical experiments on Alloy 617 having constant axial stress and shear strain controlled cycling were conducted to failure and damage fractions of 0.58 and 0.71 based on the total axial strain. The tubular specimens were then nondestructively tested using magnetostrictive transducers to send and receive finite amplitude torsional guided waves. These primary waves generated third harmonics that are sensitive to the microstructural state. These results demonstrate the potential of nonlinear ultrasonics for early detection of degradation, which is needed for life cycle management based on condition-based maintenance.
Design of Cross Ties in Steel Plate Concrete Structures
Authors: Tan Sinjaya , Sawab Jamshaid , Li Mo , Mo Y. L. , Qin Feng
Published: November 2015

Cross ties have been widely used in Steel plate Concrete (SC) structures. It is considered as one of the most effective methods in ensuring the integrity of the SC module when subjected to both flexure and out-of-plane shear. Although there are no specific guidelines for the design of cross ties as shear reinforcement in the current practice, the requirements for reinforced concrete structures specified in ACI 349 has been generally adopted in design. The experimental studies completed at the University of Houston show that a minimum amount of cross ties is required for the SC structures to preserve shear ductility. This amount was found to be greater than the ACI 349 recommendations. In addition, the strength of SC beams could not be predicted by the ACI 349 code. This paper evaluates the applicability of the present shear design methods of reinforced concrete beams to steel plate concrete beams and proposes a set of shear design equations.
Experimental Investigation of Post-Fire Mechanical Properties of Q345R Steel
Authors: Shao Shanshan , Jia Guodong , Cao Luowei , Du Chenyang
Published: November 2015

The degeneration of mechanical properties is one of the main concerns in assessment of fire damaged pressure vessels. This study investigates the influence of fire exposure on mechanical properties of Q345R steel which is widely used for pressure vessels in China. Heat treatment with different temperatures and holding times was conducted to simulate various heat exposure conditions in fire event. Hardness testing, metallographic analysis and tensile tests were carried out to investigate the effects of fire exposure temperature and duration. The experimental results indicate that the inflection temperature for mechanical property degeneration of Q345R steel is 700 °C. The decline of hardness, yield and tensile strengths due to spheroidization become more obvious with increasing heat exposure duration. A linear correlation is indicated by fitting the tensile strength and hardness. For the assessment of fire damaged component, the mechanical properties of Q345R steel at room temperature can be determined combining on-situ field metallographic examination and hardness testing with.
Hydrogen-Assisted Cracking Threshold of High-Strength Low-Alloy Steel
Authors: Yanagisawa Yusuke , Yoru Wada , Ohmi Toshihito , Yokobori A. Toshimitsu
Published: November 2015

Threshold stress intensity factor Kih would be an appropriate index parameter for the cut-off limit in fatigue crack growth analysis in order to prevent hydrogen storage tanks from suffering brittle fractures at hydrogen stations. The Kih factors were evaluated using rising load and constant displacement tests conducted in high-pressure gaseous hydrogen. The following results were obtained:

1. Kih measured under rising load was less than Kih measured under constant displacement.

2. The difference of Kih increased as tensile strength decreased.

3. The difference of Kih may be attributed to the plastic wake of propagating cracks.

Hydrogen diffusion behavior at crack tips was also estimated by a finite difference method analysis.
Low Cycle Fatigue Behavior of Original Ferritic P92 Steel at High Temperature: Experiments and Simulations
Authors: Wang Xiaowei , Gong Jianming , Jiang Yong , Zhao Yanping
Published: November 2015

Low cycle fatigue tests of original ferritic P92 steel at high temperatures and different strain amplitudes were conducted to investigate its cyclic softening behavior and fracture behavior. LCF tests of strain amplitudes ranging from ±0.2% to ±0.8% were performed in fully reversed manner with constant strain rate at 600 °C and 650 °C. In order to represent the different hysteresis stress-strain curves and the cyclic softening behavior of P92 steel, a cyclic plastic material model was used. In the model, improved nonlinear isotropic hardening parameter was proposed to make better simulation of the cyclic softening behavior. Based on the simulated stress-strain hysteresis loops, an energy-based life prediction model was used to predict the low cycle fatigue life. When compared with experimental responses, the simulations and predicted life were found to be quite reasonable. Low cycle fatigue fractography of the P92 steel was also observed, and it was found to be associated with the different strain amplitudes imposed on the specimen, the larger strain amplitude the more amounts of crack initiation sites could be found.
Effects of Plasticity on the Stress Intensity Factor Evaluation for Underclad Crack Under Pressurized Thermal Shock Events
Authors: Katsuyama Jinya , Huang Ling , Li Yinsheng , Onizawa Kunio
Published: November 2015

When the structural integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) events is assessed, an underclad crack is postulated at the inner surface of RPV and the stress intensity factor (SIF) corresponding to the driving force of non-ductile crack propagation, is evaluated for this crack. On the inner surface of RPV, cladding of the stainless steel is overlay-welded as a means for corrosion protection. Because the cladding is a ductile material, it is important to evaluate the SIF for postulated underclad crack considering the plasticity of cladding. A SIF evaluation method, which takes the effect of plasticity into account using a plastic correction method, has been established in France. In this study, we examined the SIF evaluation method established in France for underclad cracks during PTS transients. The elastic and elastic-plastic analyses based on the finite element method considering PTS events and inner pressure were performed using three-dimensional models including an underclad semi-elliptical crack with different geometry. We discussed the conservativeness of plastic correction method based on the analysis results.
Creep Simulation of the Hydroprocessing Reactor Using a Physically-Based CDM Model
Authors: Zhou Yu , Xuedong Chen , Zhichao Fan , Dong Jie
Published: November 2015

Creep failure is one of the most important failure modes in the design of hydroprocessing reactors at elevated temperatures, and the accurate prediction of the creep behavior in structural discontinuities is a critical issue for component design. A physically-based continnum damage mechanics (CDM) model was adopted to describe all three creep stages of 2.25Cr-1Mo-0.25V ferritic steel widely used in manufacturing modern hydroprocessing reactors. The material constants in the damage constitutive equations were identified using an efficient optimization scheme based on genetic algorithm (GA). The user-defined subroutine implementing the CDM model was developed using user programmable features (UPFs) in ANSYS. Three-dimensional finite element analysis of the hydroprocessing reactor was conducted to determine the critical regions, and the studies on the stress redistribution and the prediction of damage evolution in these regions during creep were carried out. The results show that FE modelling based on CDM theory can provide a good tool for creep design of complex engineering components.
Fracture Threshold Measurements of Hydrogen Precharged Stainless Steel Weld Fusion Zones and Heat Affected Zones
Authors: Ronevich Joseph A. , Somerday Brian P. , San Marchi Chris W. , Balch Dorian K.
Published: November 2015

Austenitic stainless steels are used in hydrogen environments because of their generally accepted resistance to hydrogen embrittlement; however, hydrogen-assisted cracking can occur depending on the microstructures or composition of the stainless steel. One area that has not been well researched is welds and in particular heat affected zones. The goal of this work was to measure the subcritical cracking susceptibility of hydrogen precharged gas tungsten arc (GTA) welds in forged stainless steels (21Cr-6Ni-9Mn and 304L). Welds were fabricated using 308L filler metal to form 21-6-9/308L and 304L/308L weld rings, and subsequently three-point bend specimens were extracted from the fusion zone and heat affected zone and precharged in high-pressure hydrogen gas. Crack growth resistance curves were measured in air for the hydrogen precharged fusion zones and heat affected zones under rising-displacement loading, revealing significant susceptibility to subcritical cracking. Fracture thresholds of 304L/308L welds were lower than 21-6-9/308L welds which was attributed to higher ferrite fractions in 304L/308L since this phase governed the crack path. Fracture thresholds for the heat affected zone were greater than the fusion zone in 21-6-9/308L which is likely due to negligible ferrite in the heat affected zone. Modifications to the weld joint geometry through use of a single-J design were implemented to allow consistent testing of the heat affected zones by propagating the crack parallel to the fusion zone boundary. Despite low hydrogen diffusivity in the austenitic stainless steels, effects of displacement rates were observed and a critical rate was defined to yield lower-bound fracture thresholds.
Stress Intensity Factors for Complex-Cracked Pipes Based on Elastic Finite Element Analyses
Authors: Jeong Jae-Uk , Choi Jae-Boong , Huh Nam-Su , Kim Yun-Jae
Published: November 2015

A complex crack is one of severe crack that can occur at the dissimilar metal weld of nuclear piping. A relevant fracture mechanics assessment for a pipe with a complex crack has become interested in structural integrity of nuclear piping. A stress intensity factor is not only an important parameter in the linear elastic fracture mechanics to predict the stress state at the crack tip, but also one of variables to calculate the J-integral in the elastic plastic fracture mechanics. The accurate calculation of stress intensity factor is required for integrity assessment of nuclear piping system based on Leak-Before-Break concept.

In the present paper, stress intensity factors of complex-cracked pipes were calculated by using detailed 3-dimensional finite element analysis. As loading conditions, global bending, axial tension and internal pressure were considered. Based on the present FE works, the values of shape factors for stress intensity factor of complex-cracked pipes are suggested according to a variables change of complex crack geometries and pipes size. Furthermore, the closed-form expressions based on correction factor are newly suggested as a function of geometric variables. These new solutions can be used to Leak-Before-Break evaluation for complex-cracked pipes in the step of elastic J calculation.
Effectiveness of Retightening in Maintaining Higher Residual Bolt Loads and Tightness of Bolted Flanged Connections
Authors: Kobayashi Takashi , Zenyoji Chihiro
Published: November 2015

Bolt loads reduce significantly after tightening of bolted flanged connections in which expanded PTFE (Polytetrafluoroethylene) gaskets are used. Bolts are often retightened after a while to compensate for the reduction of bolt loads in practice. The visco-elastic characteristic of PTFE gaskets is the main cause for the phenomenon. The flexibility of the bolt-flange system also affects the phenomenon. However, effects of the retightening on the residual bolt loads and the tightness of flanged connections have not been clarified yet.

In this paper, an analytical model of a bolted flanged connection, in which the flanges, the bolts and the gasket are represented by spring constants, is proposed. The residual bolt forces and the deflection of the gasket were estimated based on the analytical model of the bolted flanged connection and a creep characteristic of the gasket. Thus, the relationship between gasket deflection and the tightness of the bolted flanged connection are clarified. Based on the analytical method, the effectiveness of retightening was discussed from the view points of the residual bolt load and the tightness.
Finite Element Analysis for the Evaluation of Cracks at a Pipe-Flange Welded Part by the Direct-Current Potential Difference Method
Authors: Tada Naoya , Kosaka Masaki
Published: November 2015

The use of a flange joint is a popular method to close the end of pipes or connect pipes in manufacturing industries. As the pipes are often subjected to vibrations and cyclic bending, fatigue cracking may occur at the welded part between the pipe and flange. It is therefore important to detect and monitor the cracking in this part to ensure safety of the whole piping system. The direct-current potential difference method (DC-PDM) is known as a suitable non-destructive technique to monitor the initiation and growth of cracks and it has been applied to cracks and wall thinning on the inner surface of pipes. In this study, finite element analyses were carried out to clarify the relationship between the size and location of cracks at the pipe-flange welded part and the potential difference. An evaluation method of circumferential crack length angle by DC-PDM was proposed.
Study on Dimensional Tolerances Required for Miniature C(T) Specimens
Authors: Miura Naoki , Momoi Yasunori , Yamamoto Masato
Published: November 2015

The Master Curve approach using the miniature C(T) specimens with 4 mm-thickness is a promising method for the direct determination of the reference temperature of reactor pressure vessel steels, because they can be taken from the broken halves of the Charpy specimens used for surveillance program to monitor neutron irradiation embrittlement. The dimensional tolerances of standard C(T) specimens are relatively provided in the present standard, ASTM E1921, consequently, absolute dimensional tolerances are severer for smaller specimens. In this paper, the effect of the tolerances of key dimensions on the elastic-plastic equivalent stress intensity factor derived from the J-integral, KJ, was calculated using three-dimensional finite element analysis. Even if the dimensional tolerances for the miniature C(T) specimens based on the present standard were mitigated in some degree (as examples, the tolerance of specimen thickness of ±0.08 mm was mitigated to ±0.1 mm, the tolerance of specimen width of ±0.04 mm was mitigated to ±0.1 mm), the variations of KJ and reference temperature were negligibly small. The use of the mitigated dimensional tolerances with adequate accuracy of fracture toughness evaluation was ascertained.
Uncertainty Quantification of Aeroacoustic Power Sources in Corrugated Pipes
Authors: Swamy Maharudrayya , Omrani Pejman Shoeibi , Diez Nestor Gonzalez
Published: November 2015

Gas transport in corrugated pipes often exhibit whistling behavior, due to periodic flow-induced pulsations generated in the pipe cavities. These aero-acoustic sources are strongly dependent on the geometrical dimensions and features of the cavities. As a result, uncertainties in the exact shape and geometry play a significant role in determining the singing behavior of corrugated pipes. While predictive modelling for idealized periodic structures is well established, this paper focusses on the sensitivity analysis and uncertainty quantification (UQ) of uncertain geometrical parameters using probabilistic models. The two most influential geometrical parameters varied within this study are the cavity width and downstream edge radius. Computational Fluid Dynamics (CFD) analysis was used to characterize the acoustic source. Stochastic collocation method was used for propagation of input parameter uncertainties. The analysis was performed with both full tensor product grid and sparse grid based on level-2 Clenshaw-Curtis points. The results show that uncertainties in the width and downstream edge radius of the cavity have an effect on the acoustic source power, peak Strouhal number and consequently the whistling onset velocity. Based on the assumed input parameters distribution functions, the confidence levels for the prediction of onset velocity were calculated. Finally, the results show the importance of performing uncertainty analysis to get more insights in the source of errors and consequently leading to a more robust design or risk-management oriented decision.
Utilization of SPT Techniques for Evaluation of Changes in the Properties of the VVER-440 Reactor Pressure Vessel Steels After Their Irradiation in the Research and Power Reactors
Authors: Březina Martin , Petzová Jana , Kupča Ľudovít , Kapusňák Michal
Published: November 2015

The paper describes the testing procedures and the basic results of the evaluation of the Small Punch Test (SPT) specimens after their irradiation in the Halden reactor in Norway. The SPT technique was used for estimation of basic mechanical properties as ultimate tensile strength and yield stress of the tested materials as well as the Fracture Appearance Transition Temperature (FATT).

The main aim of the work was to compare the SPT results obtained from the surveillance specimen programs implemented in the Slovak power reactors with the SPT results from the specimens irradiated in the research reactor in Halden. For the project there were chosen 3 types of steels used for construction of the reactor VVER 440/213 type in Bohunice NPPs in the Slovak Republic. The experimental materials were two bainitic steels — base metal and weld metal of the reactor pressure vessel wall and austenitic cladding of the reactor wall.

Two sets of SPT specimens together with mini-tensile specimens prepared from the experimental materials were irradiated in the Halden reactor. The samples were irradiated at 275°C to two fluence values which are equivalent to approximately of 4 and 6 campaigns in the power reactor. Obtained results are compared to up-to-date SPT results from the surveillance specimen program applied at Bohunice NPP in the Slovak Republic.
The Effect of the Size and Orientation of Corrosion Damage on the Residual Strength of Steel Pipes: Analytical Validation of a Numerical Model
Authors: Abi Shdid Caesar , Hajali Masood
Published: November 2015

Corrosion is the main culprit responsible for the failure of steel pipes. The catastrophic nature of the failure of such critical infrastructure facilities makes the determination of the residual strength of pipelines with corrosion damage a subject of interest to inspectors, owners, and operators alike. Given that it is the only structural component of a steel pipe, any loss of the cross-sectional area of the steel due to corrosion has a direct and an immediate impact on the overall strength of the pipe. There are some existing techniques used to evaluate the corrosion damage of steel pipelines and to estimate their residual strength. Some methods consider only the longitudinal extent of corrosion, but ignore its circumferential extent; other methods consider both effects, simultaneously. This study presents the numerical modeling of a steel pipe with corrosion damage, and examines the effects of the size and orientation of the corroded area on the residual strength without considering the external loading. The extent of both, the longitudinal and circumferential, defect extension is examined, and their effects on the static and cyclic strength of a pipeline are presented. The numerical model uses the finite elements method to predict the pipe’s elastic-plastic and rupture behaviors. The numerical model is validated using classical and accepted analytical theory. The numerical results show good agreement with the analytical solution, and the model is shown to be a reliable approach to be used in a utility’s asset management program.
Origin and Effect of Back Stress on Cyclic Creep Deformation of 316H Stainless Steel
Authors: Mamun Abdullah Al , Moat Richard James , Bouchard P. John
Published: November 2015

Components in power generation plants operate at high temperature and often go through complex cyclic loading sequence during its operations. ‘Back stress’ is generated during such cyclic loading due to inhomogeneity in deformation at micro scale and significantly affects the overall creep lifetime of the materials of these components. Using a time of flight neutron diffraction facility, we studied the origin of back stress and its effects on creep deformation rate of AISI type 316H austenitic steel during cyclic creep at 650 °C. The result shows, during high temperature cyclic loading of this material for any given level of stress, the magnitude of back stress vary significantly depending on the point in the cycle being observed. The effective back stress levels associated with dwells introduced at different points in the cycle shows good co-relation with the measured macroscopic secondary creep deformation rate. Moreover, a simplified approach using modified power law creep equation is proposed to quantify back stress from a known creep deformation rate.
Numerical Investigations of Seam Welds Under Low Cycle Fatigue: Proposal for Lifetime Estimation and Recommendations for Design With Commonly Used Guidelines
Authors: Bosch Alexander , Rudolph Jürgen , Vormwald Michael
Published: November 2015

Seam welds in technical plants are often subjected to thermal loading conditions, e.g. thermal transients in the low cycle fatigue range. Corresponding to this fact, the failure of seam welds under Low Cycle Fatigue (LCF) must be predictable, to avoid cases of damage. A commonly used material for pipelines of power plants is the austenitic stainless steel of type X6CrNiNb18-10 (1.4550). Based on experimental investigations on machined and as-welded seam welds by Lang and co-authors, a parametric model was developed to consider geometrical and metallurgical notches in finite element analyses. Through additional experimental investigations (including several specimen shapes and temperature levels on 20°C, 200°C and 350°C) by Langschwager, Bosch and co-authors the assumptions and model parameters have been validated. The consideration of the microstructural support effect at the sharp notch on as-welded seam welds was realized by the reduction of local strain amplitudes by averaging stresses over a structural support length. The additional surface influence was determined on specimens with machined seam welds and is describable by a factor on local strain amplitudes. Using a local approach by using measured geometry-parameters, the selected distribution of material parameters and in consideration of the additional influences, acceptable accordance between experimentally and numerically calculated fatigue lives was obtained. Moreover, the results of the experimental investigations were used to compare them to allowable loading cycles, calculated by the simplified elastic plastic fatigue analysis (Ke-procedure) of the German KTA 3201.2 standard (similar to the procedure in ASME Section III and French RCC-M Code). The results of this comparison were not satisfactory, because the allowable number of loading cycles was mostly higher than the experimental number of loading cycles. The simplified elastic plastic fatigue analysis was modified in order to correct the results of the numerical lifetime estimation.
Investigation of ASME Code Case N-513 Square Root RT Limit on Evaluation of Butt Welded Elbows as Straight Pipe
Authors: Dawson Brad , Houston Eric
Published: November 2015

ASME Code Case N-513-3 allows evaluation of flaws in elbows to be evaluated as straight pipe if the flaw is located within a distance √Rt from the weld, provided the elbow is welded to straight pipe. The recently published revision to N-513-3 (N-513-4) provides guidance for evaluation of flaws in elbows when the flaw is remote from the butt weld, but this approach may be overly conservative for flaws near the butt weld. This paper will utilize finite element models to examine the stress distribution in elbows with uniform wall thickness. The results of this paper may be used as supporting evidence to modify the √Rt limit in evaluation of flaws in butt welded elbows in a pending revision to Code Case N-513-4 (N-513-5).
An Examination of the Role of the Assumed Young’s Modulus Value at the High Cycle End of ASME Code Fatigue Curve for Stainless Steels
Authors: Ranganath Sampath , Mehta Hardayal S.
Published: November 2015

When the ASME Code fatigue curves (S-N curves) are used in the assessment of high frequency cyclic stresses (such as those produced by flow-induced vibrations), the question arises as to the need for an E correction (i.e., multiplying the calculated cyclic stress by the ratio of the E value at the room temperature and the E value at the temperature used in the stress analysis). This question becomes significant for materials such as stainless steels when the two sets of S-N curves up to the 2007 Edition of the Code [1] are specified: i) the first curve covered the cyclic range of 10 to 106 cycles and specified an E value. This curve covered mostly the strain controlled fatigue data for which the correction for E is required. ii) The second curve covered the cyclic range of 106 to 1011 cycles and didn’t provide a specific E value. This curve covered mostly the load controlled fatigue test data for which the correction for E is not required since the stress was independent of E (stress was either P/A for axial loading or Mc/I for bending). However the 2010 and subsequently the 2013 Editions of the Code [2] combined the two curves into a single curve with a cycle range of 10 to 1011 cycles with E value specified at room temperature. This means that the E correction applies across the board for the entire cyclic range of 10 to 1011 cycles including the high cycle end where the test results are independent of E. The inclusion of the E correction for the high cycle fatigue range presents a problem for the evaluation of components with vibratory loading. The present paper describes the results of a thorough review of the past technical basis papers for the ASME Code S-N curves and examines the necessity for E correction at the high cycle end of the Code S-N curves for stainless steels.
Optimization of NDE Reexamination Locations and Intervals for Grade 91 Piping System Girth Welds
Authors: Cohn Marvin J. , Cronin Michael T. , Faham Fatma G. , Bosko David A. , Liebl Erick
Published: November 2015

It has become apparent with the development of creep strength enhanced ferritic steels, the mandatory ASME B31.1 Chapter VII and the non-mandatory ASME B31.1 Appendix V guidelines require a more rigorous method to manage the Grade 91 piping integrity at Genesee Unit 3. Given the relatively young age of Genesee Unit 3, three questions have been asked: 1) when do the examinations start, 2) what locations should be examined first, and 3) how often should the same location be reexamined? To ensure that the best value is obtained from the reexamination budget, a five-step process can be effectively used to define and categorize the scope of each set of reexaminations in the girth weld integrity management program. The five processes are performing the following analyses: 1) an evaluation of the historical information, 2) piping system hot and cold walkdowns, 3) as-designed and as-found piping stress analyses, 4) creep life consumption evaluations, including elastic and inelastic axial and radial stress redistributions, and 5) creep crack growth curve analyses. Reexaminations of the few critical lead-the-fleet weldments are performed with lower examination costs and higher confidence.

Evaluations of the Genesee Unit 3 main steam (MS) piping system revealed that the applicable weldment stress is probably the most significant parameter in determining the Grade 91 girth weld critical reexamination locations and intervals. ASME B31.1 piping stress analyses of the MS piping system have sustained load stress variations of more than 100% among the girth welds. The lower bound American Petroleum Institute (API) 579 creep rupture equation for Grade 91 operating at 1,060°F (571°C) indicates that the creep life is a function of stress to the power of 8.9; consequently, a 15% stress increase results in about 2/3 reduction of creep rupture life. Creep crack growth analyses of several of the MS piping system weldments revealed that the creep crack growth time to grow from 1/8 inch to through-wall is a function of stress to the power of 8.8; consequently, a 15% stress increase results in about 2/3 reduction of time for a 1/8-inch crack to grow through-wall.

This evaluation reveals that a few critical lead-the-fleet locations should be reexamined most frequently and justification can be provided for much longer reexamination intervals of the remaining girth welds with much lower applied stresses.
Development of Residual Stress Simulation and Experimental Measurement Tools for Stainless Steel Pressure Vessels
Authors: Reynolds Thomas B. , Brown Arthur A. , Beghini Lauren L. , Kostka Timothy D. , San Marchi Chris W.
Published: November 2015

In forged, welded, and machined components, residual stresses can form during the fabrication process. These residual stresses can significantly alter the fatigue and fracture properties compared to an equivalent component containing no residual stress. When performing lifetime assessment, the residual stress state must be incorporated into the analysis to most accurately reflect the initial condition of the component. The focus of this work is to present the computational and experimental tools that we are developing to predict and measure the residual stresses in stainless steel for use in pressure vessels. The contour method was used to measure the residual stress in stainless steel forgings. These results are compared to the residual stresses predicted using coupled thermo-mechanical simulations that track the evolution of microstructure, strength and residual stress during processing.
Fabrication, Welding, and Inspection Techniques in Preparation for In-Reactor Testing of Accident Tolerant Fuels
Authors: Barrett Kristine , Teague Michael , Moore Glenn , Woolum Connor , Archibald Kip
Published: November 2015

After the Fukushima events in 2011, DOE-NE in collaboration with nuclear industry shifted R&D emphasis to accident performance of LWR fuels under extended loss of active cooling and steam exposure. DOE-NE has created a roadmap for the “Development of Light Water Reactor Fuels with Enhanced Accident Tolerance.” The mission of the Accident Tolerant Fuel (ATF) Roadmap is to develop the next generation of LWR fuels with improved performance, reliability, and safety characteristics during normal operations and accident conditions and with reduced waste generation. The ultimate goal of the ATF roadmap is to support the insertion of lead fuel rods (LFRs) or lead fuel assemblies (LFAs) of an Accident Tolerant Fuel into a commercial LWR within 10 years (i.e., by the end of FY-2022). As a step toward this goal, an irradiation test series has been developed to assess the performance of proposed ATF concepts under normal LWR operating conditions. Data generated by this test program will be used to establish the feasibility of certain aspects of proposed ATF concepts, as well as provide information to support screening among concepts; as such, it is an integral part of Phase I: Feasibility Assessment and Down-Selection outlined in the ATF Roadmap. This irradiation test series is planned to be performed as a series of drop-in capsule tests to be irradiated in the Advanced Test Reactor (ATR) operated by the Idaho National Laboratory (INL), and it has been designated as the ATF-1 test series.

Current fission reactors use zirconium-based fuel cladding because of its extremely low macroscopic thermal neutron absorption cross-section, good high temperature strength, and decent corrosion resistance. However, advanced, innovative materials may provide these same benefits while increasing reactor safety margin, core power density, and fuel utilization. These advanced fuel cladding systems will allow revolutionary cladding performance and enhanced fuel mechanical designs, however, challenges exist in design, analysis and fabrication of innovative, never before tested, fuel cladding systems for in-reactor testing. This paper highlights the challenges associated with design, fabrication and welding, and inspection of innovative materials and actions taken to address those challenges in preparation for the Phase I ATR irradiation testing. The lessons learned from Phase I of this experiment can be used to guide researchers for design and analysis of future in-reactor testing of advanced fuel cladding systems.
Fatigue Monitoring System and Post-Processing of Temperature Measurements: Surge Line Under Stratification Loading
Authors: Jouan Benoit , Rudolph Jürgen , Bergholz Steffen
Published: November 2015

The ageing management of power plants is nowadays a main issue for all nuclear industry actors: states, regulatory agencies, operators, designers or suppliers. Consequently, lots of operators have to deal with demanding safety requirements to ensure the operation of power plants particularly in the context of lifetime extension. With regard of the fatigue assessment of nuclear components, stringent safety standards are synonymous of new parameters to take into account in the fatigue analysis process such as for instance: new design of fatigue curves particularly for austenitic stainless steels, the consideration of environmentally assisted fatigue (EAF) and stratification effects. In this context AREVA developed within the integral approach AREVA Fatigue Concept (AFC) new tools and methods to live up to operators expectations. The last mentioned stratification issue will be focused on in the framework of this dedicated paper. Based on measured thermal loads, the Fast Fatigue Evaluation (FFE) process allows for highly-automated and reliable data processing to evaluate time-dependent cumulative usage factors of mechanical components. This method has recently been extended to the consideration of stratification loading with surge line application. The paper presents the latest AREVA research and development activities on the FFE method applied to a surge line under stratification thermal loading. An additional CFD analysis was performed in order to calculate realistic thermal loadings during start-up conditions of nuclear power plant conditions. The FFE methodology was used to calculate thermal stress at all relevant locations. This approach opens the possibility of a realistic CUF calculation. The methodology, the principle results and benefits are presented in the paper.
Basis of the Upcoming Changes to the Piping Inelastic Fatigue Design Rules in the ASME Boiler and Pressure Vessel Code Section III, Division 1, Article NB-3600
Authors: Adams Timothy M.
Published: November 2015

In conducting a Class 1 piping analysis per the simplified rules of the ASME Boiler and Pressure Vessel Code, Section III, Division 1, Article NB-3600, a fatigue analysis is required per paragraph NB-3653 for both Service Level A and Service Level B. The fatigue analysis provides two options. The options are dependent on Equation 10 of subparagraph NB-3653.1. If this equation is met for a given load set pair under consideration, then the analysis proceeds directly to subparagraphs NB-3653.2 through NB-3653.5. If however, Equation 10 is exceeded, the Code allows the use of a simplified Elastic Plastic Analysis as delineated in subparagraph NB-3653.6. The first requirement of NB-3653.6 is that both Equation 12 and Equation 13 must be met. The changes in the seismic design in the last 25+ years have not been appropriately reflected in the subparagraph NB-3653.6(b) Equation 13. Also, the Code provides no clear guidance on seismic anchor motions in paragraph NB-3650. In 2012 ASME Code Committees undertook an action to address these issues. This paper provides the background and basis for Code changes that are anticipated will be implemented in the near future in paragraph NB-3653.6 of the ASME Boiler and Pressure Vessel Code, Section III, Division 1 that will address both of these issues. This implementation will make the Elastic Plastic Fatigue rules of NB-3653.6 consistent with the design by analysis approach of NB-3228.5.
Effect of Scatter in Axial Bolt Force on the Sealing Performance of 20” Inch Pipe Flange Connections With CSG Under Internal Pressure
Authors: Omiya Yuya , Itano Koji
Published: November 2015

Since a scatter in axial bolt force exists in assembling the pipe flange connections, it is important to evaluate the effect of scatter in axial bolt force on the sealing performance of pipe flange connection. The FE and experimental analyses were done to evaluate the effect of scatter in axial bolt force on the sealing performance of pipe flange connection with 20 “nominal diameter. The results revealed that the large diameter pipe flange connection was sensitive to the scatter in axial bolt force. Besides, the large diameter pipe flange affected more by flange rotation when internally pressurized. As a result, a larger diameter pipe flange connection with scattered bolt preload showed poor sealing performance. The experimentally obtained scatter in axial bolt force as assembled was taken into account in FE analyses and the effect of the scatters on the contact gasket stress distributions was shown numerically. FE results show that the sealing performance is reduced due to the distributed gasket stress and bolt force scatter in the axial direction.
Effects of Side Groove on Fracture Toughness
Authors: Ryu Ho-Wan , Kim Hune-Tae , Han Jae-Jun , Kim Yun-Jae , Kim Jong-Sung , Choi Myung-Rak , Kim Jin-Weon
Published: November 2015

This paper describes ductile tearing simulation for compact tension (C(T)) specimens using FE damage analysis based on the stress-modified fracture strain model. The side groove effect on J-resistance curve was estimated by experimental and analytical ways. In this paper, SA508 Grade 1A low alloy steel pipe material was considered. Tensile and C(T) specimens are simulated to determine the failure criteria with finite element method. Then, different shapes of C(T) specimens are analysed and the results from simulations are compared with test data for verification of proposed method. Overall, the predicted simulation results show good agreement with test data.
Estimation and Visualization of the Probability of Failing an Assessment When Using a Failure Assessment Diagram
Authors: Cochran Jeffrey D. , Guo Ruohua Z. , Panzarella Charles H.
Published: November 2015

Codes and standards are often filled with deterministic equations and relationships that are presented without explicit quantification of the uncertainty inherent in their application or derivation. That is not to say that such equations and relationships are not conservative, but to the contrary, that whatever conservatism is dutifully included sometimes goes unquantified. The gamut of Failure Assessment Diagrams (FAD) used for assessing the risk of crack-like flaws provides an excellent example of useful criteria that may benefit from uncertainty quantification. The Level 2 FAD from API 579-1/ASME FFS-1 is used as an exemplar in the probabilistic extension of existing codes and standards. As a first step toward modeling the true probability of failure for assessment points nominally below the FAD envelope, assumptions are made regarding the variance of operating conditions, geometry, and flaw sizes, and these assumptions are utilized to estimate the probability that a nominal assessment point will in fact correspond to conditions exceeding the FAD envelope. This estimation procedure is used to generate contour lines of constant probability within the existing FAD envelope, providing an easily interpretable visualization of the results that may be coupled with risk matrices or other risk-based inspection methodologies.
Effect of Strain Hardening Constitutive Relations on Weld Residual Stress Simulation of Dissimilar Metal Weld
Authors: Chen Jian , Chen Gaoqiang , Yu Xinghua , Feng Zhili , Crooker Paul
Published: November 2015

Weld residual stress (WRS) in dissimilar metal welds (DMWs) has been identified as an important driver for primary water stress corrosion cracking, which is observed in nuclear power plant safety-related components. In this work, a newly developed dynamic strain hardening rule is implemented in finite element (FE) thermal-mechanical model to simulate the residual stress distribution in a dissimilar metal weld studied in a recent NRC/EPRI Round Robin study. This new dynamic strain hardening constitutive rule takes into account the effect of dynamic recovery and recrystallization at elevated temperatures on the strain hardening behavior during welding. Weld residual stresses calculated using the new dynamic strain hardening rule are compared to those with the conventional strain hardening ones (isotropic and kinematic), as well as the experimental measurement data. The new dynamic strain hardening rule results in improvements in WRS prediction.