bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Study on Fracture Toughness of CANDU Pressure Tube
Authors: Keim Elisabeth , Nicak Tomas , Wasiluk Bogdan
Published: October 2017

CANDU pressure tubes carry nuclear fuel and belong to the primary heat transport system. They are fabricated from cold-worked Zr-2.5Nb alloy prone to deuterium ingress under normal operating conditions. Increased hydrogen equivalent concentration and reactor pressure-temperature transients result in development of a brittle phase, hydride, changing mechanical behavior. The hydride downgrades fracture toughness properties in the transition region and reduces material ductility.

Canadian Nuclear Safety Commission founded a two-phase project to improve understanding of the parameters governing fracture toughness properties and load carrying capacity of Zr-2.5Nb pressure tubes with elevated hydrogen equivalent concentrations. This paper presents preliminary results obtained in the first phase. The fracture behavior of a curved compact tension specimen (CCTS) and a pressure tube burst specimen (PT) with axial through-wall crack used in destructive burst test were studied in details. The intention was to identify any differences between fracture behavior of the CCTS and the PT potentially affecting fracture toughness estimates.

The stress and deformation states ahead of the crack front, calculated fracture toughness parameters including J-integral and crack tip opening displacement (CTOD), as well as fracture constraint by means of elastic T-stress have been discussed.
Component Testing and Numerical Calculation of a Bolted High Temperature Power Plant Pipe Flange Connection Under Complex, Near-Service Loads
Authors: Leibing Benjamin , Klenk Andreas , Seidenfuss Michael
Published: October 2017

To ensure a reliable power supply with a minimum environmental impact in the future, further increases in efficiency and flexibility of fossil-fired power plants are major challenges to address in recent R&D activities. In order to counterbalance substantial fluctuations in the electricity grid due to the rising share of renewable resources, frequent start-ups and shutdowns of turbomachinery accompanied by quick and heavy load changes will be claimed by the market. Hence, along with the development of advanced materials for elevated steam parameters, contemplations with respect to altered boundary conditions of currently used materials, e.g. for bolted pipe flange connections, are required.

In this paper, a selection of results from a recently finished research project on stress relaxation will be presented. Together with European power plant component manufacturers, a newly developed test rig comprising a scaled IP steam turbine pipe flange now allows investigations under near-service conditions. Before, throughout and after performance of the experiments, an extensive measurement setup enables the examination of effects that cannot be studied in standardized relaxation tests. For example, deformation of the flange plates caused by the interaction of creep and stress relaxation can be considered as such an effect. Within this project, a loss in bolt pretension of up to almost 50% over a comparatively short period of experimental time was observed. By means of numerical calculations, creep deformation in the transition areas between pipe and flange plate sections was identified to be a major originator of these pretension drops. Particularly, good correlations between experiments and FEM-simulations could be achieved through the implementation of enhancements concerning the fitting process of the Graham-Walles-type creep model which was used.
Design and Analysis of Vertical Vessels for Lifting in Fully Dressed Condition
Authors: Doctor Christopher , Stefanovic Radoslav
Published: October 2017

Depending on plant/site location, it may be advantageous to dress a vertical vessel, in horizontal position, prior to erection. Dressing refers to the installation of items attached to the vessel such as internals, insulation, piping, ladders, platforms, electrical cable trays, lighting, etc. The decision to dress a vessel may be due to safety, schedule or economic reasons. Dressing a vessel results in higher lifting loads.

Vessel Codes address loadings to be considered when designing a vessel in its operating position and not necessarily for lifting. Since the Codes do not address erection loadings, engineering judgment must be used in their consideration and analysis in order to avoid overstressing the vessel. In some cases, erection loads govern the design thickness of the vessel.

Lifting analysis in the context of this paper is the evaluation of stresses in the vessel when it is initially picked up from the horizontal position. This paper discusses the compressive stresses which usually govern in the lifting analysis of thin-walled vessels. Different methods used in literature and industry are presented in the paper. Some Owners/Users, engineering firms, and fabricators use the Factor B in ASME Section II, Part D, Subpart 3 as the limiting criterion for compressive stresses. In some cases, this criterion is too conservative. This paper presents the application of alternative buckling criteria for lifting analysis.
Swelling of VVER-1000 Core Baffle: Numerical Modeling and Direct Measurement of its Geometrical Dimensions
Authors: Oryniak Andrii , Orynyak Igor
Published: October 2017

Traditionally, the brittle strength evaluation of reactor pressure vessel was the central issue in lifetime assessment of Ukrainian nuclear power plants (NPPs). The problem of swelling of the reactor core baffle only recently got due attention from the side of operator.

Here the most efforts were given on numerical modeling of austenitic steel 08Kh18N10T swelling and its effect on induced stresses in core baffle and distortion of its geometry. The calculation shows that essential changing of core baffle dimensions is expected after 35–40 years of operation. Eventually this can lead to the contact with the core barrel. Yet, these predictions contain the big number of uncertainties related to the input data used in analysis: fluence distribution; temperature variation due to heat release induced by neutron and gamma radiation; thermal-hydraulic boundary condition between the baffle and coolant; and, especially, the adopted law of swelling in dependence with above factors as well as mechanical stresses.

So, the second task was to measure the real geometry of baffle after 27 years of operation, to determine its change and compare these results with the numerically calculated data with accounting for the design tolerances. Thus, the spatial measurement system (SMS) equipped with ultrasonic gages was designed. It contains the central vertical beam which can move in vertical direction and rotate. To the lower end of the beam four horizontal levels are attached, which are equipped with device resistant to the hot water and radiation. The gages are used to measure the shortest distances to the edges of baffle. Two types of results were obtained. The first one are the measurements in the different horizontal planes obtained by rotation the SMS around the vertical axis with angular steps equal to 1 degree. These results were difficult to handle with and required a special mathematical treatment due to the possible shift of the centre of measurement. The second set of measurements was performed by moving the SMS in vertical direction. These data demonstrate the change of distance with the height.

The results clearly show that problem of swelling do exists, and, in general, the measured patterns of the distortions along the vertical and angular coordinates correspond to numerically obtained results. Further work on baffle integrity is however needed.
Hybrid Welding vs Conventional Welding: A Solution to Residual Stress and Distortion Mitigation?
Authors: Gallee Sébastien , Lacroix Rémi , Robin Vincent , Gommez Florence , Jourden Erwan
Published: October 2017

The present paper deals with the hybrid laser/MIG welding process, which allows to assembly high thickness steel sheets. The laser heat source added to the MIG torch improves the process productivity while respecting quality standard.

The multi-pass welding simulation of a plate is presented in this paper and numerical results are compared to experimental measurements (temperature and stresses).
Mechanical Properties of Vanadium Microalloyed High-Strength ASTM A694 Forgings
Authors: Baker K. C. , Thompson R. M. , Gorrell T. C.
Published: October 2017

Recent upstream oil and gas industry experience has raised attention to substandard properties with high strength carbon steel forgings manufactured to the requirements of ASTM A694 and MSS-SP-44. As part of an internal investigation into quality of commodity pipeline flanges, three flanges certified as ASTM A694 grade F60 to F70, were purchased off-the-shelf from three different manufacturers for microstructural and mechanical property investigation. All three flanges were supplied with material test certificates indicating acceptable material properties. Tensile and Charpy impact specimens were extracted from various locations and orientations in each flange. All three flanges failed to meet yield strength requirements for the specified grade. The impact energy and shear area values were well below those reported on the material test certificates. The discrepancy between the sacrificial testing results and the material test certificates is attributed to the use of separately forged test blocks for quality testing instead of integral prolongations or a sacrificial production part, which is permitted by ASTM A694 and MSS-SP-44. Further investigation was made into the chemical composition and heat treating practices. The chemical composition can be characterized as high strength, low alloy steel (HSLA) by virtue of 0.05–0.08 wt. pct. vanadium added to a carbon-manganese steel with CE(IIW) ranging from 0.43 to 0.45. Advanced microscopy showed that the morphology of the vanadium precipitates was inadequate as a strengthener and deleterious to Charpy impact properties for the size of the flanges and the heat treatment practices applied.
Water Hammer Caused by Fast Closing Valves
Authors: Koirala Shesh R. , Telci Ilker T.
Published: October 2017

Operation of fast closing valves in piping systems can create an overpressure condition, resulting in permanent deformation, joint damage, leakage, or rupture. Fast closing valves are used in many piping systems to protect personnel, equipment and the environment from the danger of overpressure. When there is a sudden closure of a piping system valve, the change in the flow velocity produces a transient increase in pipe pressure. This increased pressure is commonly known as transient, fluid hammer waterhammer, or surge pressure. In a very simplistic system, the excess pressure created by this sudden closure of valves can be computed using a simple hand calculation using Joukowsky method. The method is applicable only for the initial pressure wave generated. In complex systems, where there are dead legs (e.g. closed by-pass valves) or branches, there is more chance of the pressure waves being reflected, transmitted and superimposed. The overpressure problem is even more severe if a liquid column separation and re-joining occurs during the transient conditions. The magnitude of the pressure in the system due to these effects may be higher than that estimated by Joukowsky method. Hence a transient analysis needs to be performed to estimate the overpressure in the system.

In this case study, the transient conditions initiated due to closure of buckling pin valves (BPVs) are modeled using a proprietary software CE099. The objectives are to calculate the maximum surge pressures, dynamic loads, and to recommend mitigations to reduce transient pressures and loads. The results showed that pressures could be reduced by increasing the pipe size of few segments or adding expansion loops. The most sensitive parameter for transient pressure was pipe size and that for dynamic load was valve closure time. It is recommended that this kind of study be performed in the early phase of engineering design, so that any identified overpressures can be mitigated with simple, cost effective options such as increasing pipe size, altering valve closure times, and adding expansion loops.
Flow Induced Vibration of Equipment Internals in a Two-Phase Gas/Liquid Flow
Authors: Diwakar Philip , Prakash Ajay , Thomas Cyrus
Published: October 2017

The paper describes the use of Fluid-Structure-Interaction (FSI) to evaluate turning vane blades in an inlet distributor with two-phase gas/liquid flow. A fatigue failure mechanism attributed to flow induced vibration (FIV) resulting from vortex shedding and un-steadiness in the flow field is evaluated. This failure mechanism can be missed in a complex flow field that is assumed to be steady. Natural frequency of the turning vanes was found to be well within the flow induced forcing frequency range, which led to structural failure of the vanes.
Nonlinear Finite Element Analysis of Unanchored Steel Liquid Storage Tanks Subjected to Seismic Loadings
Authors: Phan Hoang Nam , Paolacci Fabrizio , Mongabure Philippe
Published: October 2017

Steel liquid storage tanks are widely used in industries and nuclear power plants. Damage in tanks may cause a loss of containment, which could result in serious economic and environmental consequences. For the purpose of the earthquake-resistant design of tanks, it is important to use a rational and reliable nonlinear dynamic analysis procedure. The analysis procedure should be capable of evaluating not only the comprehensive seismic responses but also the damage states of tank components under artificial or real earthquakes. The present paper deals with the nonlinear finite element modeling of steel liquid storage tanks subjected to seismic loadings. A reduce-scale unanchored steel liquid storage tank with the broad configuration from a shaking stable test (i.e., the INDUSE-2-safety project) is selected for this study. The fluid-structure interaction problem of the tank-liquid system is analyzed using the Abaqus software with an explicit time integration approach. In particular, the steel tank is modeled based on a Lagrangian formulation, while an Arbitrary Lagrangian-Eulerian adaptive mesh is used in the liquid domain to permit large deformations of the free surface sloshing. The finite element results in terms of the sloshing of the liquid free surface and the uplift response of the base plate are evaluated and compared with the experimental data that is obtained from the shaking table test for the tank under the INDUSE-2-safety project.
Fitness-for-Service Creep Life Evaluation of a Hot Reheat Piping System at 400,000 Operating Hours
Authors: Cohn Marvin J.
Published: October 2017

This paper discusses a fitness-for-service (FFS) evaluation of a hot reheat (HRH) piping system with about 400,000 hours of operation. It discusses significant differences between the as-designed and simulation as-found piping stress analyses. The significant range of stresses in the piping system illustrates that the few lead-the-fleet girth welds should have significant creep damage decades before many other girth welds.

Since the weldment examination intervals will correspond to scheduled outages, the creep life uncertainties can be grouped into high, medium, and low priorities (e.g., 0–10 years, 10–20 years, and beyond 20 years) with high confidence of rankings among the selected groups.

There are 14 girth welds in this HRH piping system. In this case study, only 2 girth welds were evaluated as high priority nondestructive examination (NDE) locations and 1 girth weld was evaluated as a medium priority location for the next set of NDE reexaminations. Many of the low priority girth welds have predicted creep rupture lives substantially beyond 1,000,000 operating hours.
Fatigue Behavior of Spent Nuclear Fuel Rods in Simulated Transportation Environment
Authors: Wang Hong , Wang Jy-an John , Jiang Hao
Published: October 2017

Nuclear fuel rod is composed of cladding tube and a specified number of fuel pellets contained. In the United States, spent nuclear fuel (SNF) is expected to be transported to at least one storage facility before permanent disposal. The fatigue behavior of spent nuclear fuel (SNF) rods under reversed cyclic bending must be understood in order to evaluate their vibration integrity in a transportation environment. This is especially important for high-burnup SNFs (>45 GWd/MTU). This report presents the experimental results related to Zircaloy (Zry)-4-based surrogate rods and high-burnup SNFs, based on recent work performed at Oak Ridge National Laboratory (ORNL). The surrogate rod was made of Zry-4 cladding and alumina pellets, and high-burnup fuel rods were discharged from H.B. Robinson pressurized water reactor. The reversed cyclic bending testing was conducted at 5 Hz under loading control. The effect of pre-hydriding and burnup or irradiation on the flexural rigidity and fatigue life of cladding-pellet system were discussed. The fatigue data obtained are extremely useful to the future certification of SNF storage and transportation cask.
Statistical Evaluation of Stress Independence of Two Connected Structures
Authors: Johnson Christopher R. , Mann J. Adin , Westwater Gregory D.
Published: October 2017

In ASME B16.34, features included in a control valve geometry that allows connection to standard flanges, referred to as “flange like features”, need to be evaluated as part of the valve design analysis. An analysis approach is presented that evaluates if the stress in the region of the flange like feature is independent of the core control valve structure. When determined to be independent, then the flange like feature can be designed by rule using ASME B16.5. The approach evaluates the stress around the flange like feature with the flange at the designed location and then at an increased distance from the core control valve structure. Because the two geometries result in two different finite element analysis (FEA) meshes, a statistical approach was developed to evaluate how much the linearized stress behind the flange changes between the two different geometries. The result is a procedure and criteria to determine if the flange like feature can be designed by rule or further stress analysis is needed.
Impact Toughness and Brittle Failure of Carbon Steels
Authors: Xu Kang , Rana Mahendra
Published: October 2017

Brittle failure of pressure containing equipment can lead to catastrophic consequences and must be prevented. ASME pressure vessel codes have developed clear rules on toughness requirements based on both long term safe and reliable experience and fracture mechanics concepts. The essence of the toughness rules in ASME Boiler and Pressure Vessel (B&PV) Codes Section VIII, Division 1 and Division 2 is a set of impact test exemptions curves and impact toughness requirements as a function of materials’ yield strength and thickness. Considering the limitations of the impact toughness in characterizing the resistance to brittle fracture, a high level of conservatism is built into the toughness rules. It should be emphasized that impact tests are satisfactory as a rule making tool for quality control, but impact toughness values by themselves cannot be reliably used to predict materials’ resistance to brittle failure. Fracture mechanics analysis should be performed to investigate the root cause of a brittle failure, instead of relying solely on impact toughness values.
Improving Ultrasonic Examination Procedures for Detection of Thermal Fatigue
Authors: Spanner Jack
Published: October 2017

This paper describes improvements to the ultrasonic procedures to be used for the detection of thermal fatigue in nuclear power plants in accordance with the requirements of the Electric Power Research Institute (EPRI) Material Reliability Program (MRP) inspection and evaluation guidelines. These examinations have been performed at nuclear plants in the USA since the 1980s with very few detections of degradation. However, since 2013 there have been ten instances of thermal fatigue cracks. The MRP formed a thermal fatigue focus group to analyze these leaks and flaws related to thermal fatigue inspection programs. Then the group developed recommendations to address these recent operational experiences. The MRP has been developing improvements to the ultrasonic examination process and this paper will share these. A computer based training program for the ultrasonic personnel has been developed that will be described. And finally, the MRP has fabricated a variety of thermal fatigue mockups that are loaned to member utilities prior to an outage so the ultrasonic personnel can practice detecting thermal fatigue just prior to the examinations. Implementation of these mockups will also be described.
Is it Possible to Get-Rid of S-N Curve for Fatigue Evaluation?: A Fully Mechanistic Model of 316SS Reactor Steel for Fatigue Life Evaluation
Authors: Barua Bipul , Mohanty Subhasish , Soppet William K. , Majumdar Saurindranath , Natesan Krishnamurti
Published: October 2017

The present methods for fatigue life evaluation of nuclear reactor components have large uncertainties due to the overdependence on approaches that involve empirical fatigue life estimation, such as use of test-based curves of stress/strain versus life (S∼N) and Coffin-Manson type empirical relations. To reduce the uncertainty in fatigue life evaluation, we are trying to develop a fully mechanistic modeling approach. The aim is to capture the time/cycle-dependent material ageing behavior such as stress hardening/softening through multi-axial stress-strain evolution of the components based on which the life of the component can be predicted. In this paper, we introduce an implementation of the ANL developed evolutionary cyclic plasticity model for 316 SS reactor steel within the commercial finite element (FE) software ABAQUS. A user subroutine is developed to enable the incorporation of the ANL developed evolutionary cyclic plasticity model [1] into ABAQUS. The FE model, developed in this work, can be used for predicting the time-dependent stress hardening/softening of 3D structure. A strain-controlled constant amplitude fatigue experiment scenario is 3D modeled using the developed ABAQUS based FE modeling framework and is verified through experimental data.
Design of Series Multiple Tuned Mass Dampers for Response Control of Asymmetric Buildings
Authors: Wang Jer-Fu , Li Jie-Chun , Lin Chi-Chang
Published: October 2017

Series multiple tuned mass dampers (SMTMD), comprising of serially interconnected multi-degree-of-freedom TMDs, for response control of torsionally coupled (TC) buildings were studied. A design theory was developed for the optimization of the SMTMD parameters. Considering the features of floor response of TC buildings, the performance of SMTMD was measured by indices that were established with more than one significant vibration modes of the primary structures. The total mass of SMTMD was assumed to be linearly distributed to each TMD unit with a mass-distribution factor. Both uniform and variant TMD damping and stiffness coefficients were considered. The characteristic and corresponding performance of optimal SMTMD under various parametric conditions were investigated and compared with those of the single TMD. The optimal location of SMTMD on the floor was also investigated. It concludes that an SMTMD is capable of reducing the TC response of multiple modes, while more than one TMD are needed to achieve the similar control effectiveness.
An Experimental Investigation of the Dynamics of a Loosely Supported Tube Array
Authors: Elhelaly Amro , Hassan Marwan , Mohany Atef , Moussa Soha
Published: October 2017

The integrity of tube bundles is very important especially when dealing with high-risk applications such as nuclear steam generators. A major issue to system integrity is the flow-induced vibration (FIV). FIV is manifested through several mechanisms including the most severe mechanism; fluidelastic instability (FEI). Tube vibration can be constrained by using tube supports. However, clearances between the tube and their support are required to allow for thermal expansion and for other manufacturing considerations. The clearance between tubes may allow frequent impact and friction between tube and support. This in turn may cause fatigue and wear at support and potential for catastrophic tube failure.

This study aims to investigate the dynamics of loosely supported tube array subjected to cross-flow. The work is performed experimentally in an open-loop wind tunnel to address this issue. A loosely-supported single flexible tube in both triangle and square arrays subjected to cross-flow with a pitch-to-diameter ratio of 1.5 and 1.733, respectively were considered. The effect of the flow approach angle, as well as the support clearance on the tube response, are investigated. In addition, the parameters that affect tube wear such as impact force level are presented.
Assessment, Mitigation, Management and Extension of Coke Drum Life Through Equipment Health Monitoring Systems and On Line Inspection
Authors: Seijas Antonio J. , Bedoya Julian J. , Stoller Alex P. , Perez Oscar A. , Marcano Luis M.
Published: October 2017

The reliability of coke drums has become a central theme to many refineries worldwide as high value products are recovered from refinery residuum. The severe thermal gradients inherent in the coking process have led to ever more frequent failures from cracks in bulges, skirts and cones, which reduce productivity and jeopardize the safe and reliable operation of coke drums. An intrinsically-safe coke drum health monitoring system rated for operation in hazardous environments, consisting of high temperature strain gauges and thermocouples was installed on a coke drum at a refinery in the United States. Specific locations identified as high risk areas through a combination of engineering analyses, inspections and historical repairs were targeted for monitoring. The health monitoring system calculates the cumulative damage and damage rates at critical locations through the quantification of thermal transient gradients and measured strains, and analyzes the trends over time. Of particular interest are two high damage events recorded with the health monitoring system that closely preceded the propagation of a through wall crack, approximately one week after the events. This paper performed a post-mortem analysis of the event, and shows how the data obtained via health monitoring systems can be used for prioritizing inspections and the potential for anticipation of failures. By analyzing damage accumulation trends from specific operational practices, the impacts of process changes on the expected life of the coke drum can be assessed. Finally, a detailed review of the maintenance and inspection records, results of the on-line Non-Destructive Examination (NDE), laser mapping, and bulged severity assessment were used to prepare a detailed inspection and repair plan for a forthcoming turnaround. The damage accumulation trends captured with an Equipment Health Monitoring System (EHMS) were used to optimize operating parameters of the coke drums referred to in this paper. This together with the execution of detailed inspection plan and comprehensive repairs are allowing a safe and reliable operation of these drums.
Variable Inertia Damper Using MR Fluid: Part II — Improvement of Inertia Effect
Authors: Matsuoka Taichi , Abe Naoto , Hiramoto Kazuhiko , Sunakoda Katsuaki
Published: October 2017

The authors have developed fluid inertia damper using MR fluid in order to obtain a variable inertia effect. From the experiments, it seemed to be that the inertia effect was slightly switched, but very small. In this paper, to get much inertia effect, the damper was improved by using long bypass pipe of stainless steel, and 24 electromagnets were installed along the long by-pass pipe. Dynamic property was investigated experimentally and theoretically.
Creep Life Prediction of HR3C Steel Using Creep Damage Models
Authors: Lee Hoomin , Kang Seok-Jun , Choi Jae-Boong , Kim Moon-Ki
Published: October 2017

The world’s energy market demands more efficient power plants, hence, the operating conditions become severe. For thermal plants, Ultra Super Critical (USC) conditions were employed with an operating temperature above 600°C. In such conditions, the main failure mechanism is creep rupture behavior. Thus, the accurate creep life prediction of high temperature components in operation has a great importance in structural integrity evaluation of USC power plants. Many creep damage models have been developed based on continuum damage mechanics and implemented through finite element analysis. The material constants in these damage models are derived from several accelerated uniaxial creep experiments in high stress conditions.

In this study, the target material, HR3C, is an austenitic heat resistant steel which is used in reheater/superheater tubes of an USC power plant built in South Korea. Its creep life was predicted by extrapolating the creep rupture times derived from three different creep damage models. Several accelerated uniaxial creep tests have been conducted in various stress conditions in order to obtain the material constants. Kachanov-Rabotnov, Liu-Murakami and the Wen creep damage models were implemented. A comparative assessment on these three creep damage models were performed for predicting the creep life of HR3C steel. Each models require a single variable to fit the creep test curves. An optimization error function were suggested by the authors to quantify the best fit value. To predict the long term creep life of metallic materials, the Monkman-Grant model and creep rupture property diagrams were plotted and then extrapolated over an extended range. Finally, it is expected that one can assess the remaining lifetime of UCS power plants with such a valid estimation of long-term creep life.
Advances in Nuclear Non-Metallic Repair/Replacement Activities
Authors: O’Sullivan J. E. (Jim)
Published: October 2017

This paper discusses the current status of ASME Section XI Code activities associated with two methods employing non-metallic materials for repair or replacement of metallic piping: high-density polyethylene (HDPE) and carbon fiber reinforced composites (CFRC).
Simulation of Fatigue Crack Initiation in Heat Affected Zone Microstructure Using Crystal-Plasticity Finite Element Method
Authors: Hiraide Takashi , Igi Satoshi , Tagawa Tetsuya , Ikeda Rinsei , Tsutsumi Seiichiro
Published: October 2017

It is well known that fatigue fracture of welded joints can depend on many factors such as residual stress, stress concentration and an inhomogeneous microstructure in the HAZ (Heat Affected Zone). Some solutions to improve fatigue properties, for example, hammer peening (1), have been developed to mitigate effects related to stress. Improvement from mechanical view point is not only applied, but optimized microstructure design of the base metal and HAZ should be also considered. However, microstructural effects on fatigue crack initiation behavior have not been fully understood because systematic experimental evaluation of them takes much efforts with difficulty. An analytical method is a useful idea to specify the optimum microstructure against fatigue crack initiation before experimental examinations. CP-FEM (Crystal-Plasticity Finite Element Method) is expected to describe fatigue crack initiation behavior, because it can express strain localizations caused by an inhomogeneous microstructure.

In the present study, a simulation model using CP-FEM is developed to describe strain localizations under cyclic loading. Microstructural effects on plastic strain localization and accumulation were investigated by changing microstructural factors.
Orientation Effects on Fatigue Behavior of Additively Manufactured Stainless Steel
Authors: Smith Thale R. , Sugar Joshua D. , San Marchi Chris , Schoenung Julie M.
Published: October 2017

Direct energy deposition (DED) is an additive manufacturing process that can produce complex near-net shape metallic components in a single manufacturing step. DED additive manufacturing has the potential to reduce feedstock material waste, streamline manufacturing chains, and enhance design flexibility. A major impediment to broader acceptance of DED technology is limited understanding of defect populations in the novel microstructures produced by DED and their relationship to process parameters and resultant mechanical properties. A design choice as simple as changing the build orientation has been observed to result in differences as great as ∼25% in yield strength for type 304L austenitic stainless steel deposited with otherwise identical deposition parameters. To better understand the role of build orientation and resultant defect populations on fatigue behavior in DED 304L, tension-tension fatigue testing has been performed on circumferentially notched cylindrical test specimens extracted from both vertical and horizontal orientations relative to the build direction. Notched fatigue behavior was found to be strongly influenced by the manufacturing defect populations of the material for different build orientations.
Verification Methodology and Results of Probabilistic Fracture Mechanics Code PASCAL
Authors: Masaki Koichi , Miyamoto Yuhei , Osakabe Kazuya , Uno Shumpei , Katsuyama Jinya , Li Yinsheng
Published: October 2017

A probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed by Japan Atomic Energy Agency (JAEA). PASCAL can evaluate failure frequencies of Japanese reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events based on domestic structural integrity assessment models and data of influence factors. In order to improve the engineering applicability of PFM to Japanese RPVs, we have performed verification of the PASCAL. In general, PFM code consists of many functions such as fracture mechanics evaluation functions, probabilistic evaluation functions including random variables sampling modules and probabilistic evaluation models, and so on. The verification of PFM code is basically difficult because it is impossible to confirm such functions through the comparison with experiments. One of the verification methodologies of PFM codes is that the result evaluated by using each function of PFM code is compared with a theoretical value. When a PFM code is applied for evaluating failure frequencies of RPVs, verification methodology of the code should be clarified and it is important that verification results including the region and process of the verification of the code are indicated. In this paper, our activities of verification for PASCAL are presented. We firstly represent the overview and methodology of verification of PFM code, and then, some verification examples are provided. Through the verification activities, the applicability of PASCAL in structural integrity assessments for Japanese RPVs was confirmed with great confidence.
Numeric Study on Propellant Leakage in Atmospheric Environment
Authors: Ma Denglong , Tan Wei , Zhang Zaoxiao
Published: October 2017

Leakage risk management is very important for propellant storage because of its poisonousness. Numerical method was used to study the leakage, volatilization and dispersion of liquid propellant. The results of CFD (Computational Fluid Dynamics) simulation show that leaked liquid UDMH (unsymmetrical dimethylhydrazine) will jet on the ground under the pressure of storage tank and then it disperses forward slowly with the liquid film. Therefore, it is necessary to set a safety cofferdam around the storage tank. Based on the Gaussian dispersion model, the dispersion process of liquid propellant in pools under different atmospheric conditions was simulated. The results show that atmospheric stability and wind speed influence the risk distance after UDMH leaking. The less stability of atmosphere and lower wind speed , the longer the risk distance is. Hence, the field atmosphere condition should be considered when the risk distance is determined.
Thermal Aging Behavior of Grade CF3M Cast Austenitic Stainless Steels
Authors: Miura Yasufumi , Sawabe Takashi , Betsuyaku Kiyoshi , Arai Taku
Published: October 2017

In this study, CASSs which were thermally aged at 275–400°C for up to 30000 hrs were investigated using atom probe tomography, Charpy impact test, hardness test, and fracture toughness test in order to evaluate the effects of chemical composition and ferrite content on thermal aging embrittlement. Test materials were 4 types of statically casted grade CF3M stainless steels which are used in Japanese BWR plants. As a result of the tests, Charpy absorbed energy at room temperature of all thermal aging conditions were obtained. We also obtained the microstructural evolution in ferrite phase, hardness of ferrite phase, and J–R curves of several aging conditions. The fracture toughness and the Charpy absorbed energy of all materials aged at 275°C for up to 15000 hrs were approximately same as those of unaged materials. On the other hand, reduction of the fracture toughness and the Charpy absorbed energy were observed in the materials aged at 300°C, 320°C, 350°C and 400°C. For the Charpy impact test in this study, the absorbed energy of the material with highest molybdenum was lower than that of the material with highest ferrite content. After the tests, the fracture toughness estimation model for grade CF8M in NUREG/CR-4513 and the method in PVP2005-71528 (H3T model) were discussed in order to confirm the applicability of the prediction methods to CF3M.
Application of Computed Radiography in Pressure Vessel Welds: ASME Sec V Requirements and Recommendations of ASTM E2007
Authors: Saha Santanu
Published: October 2017

Computed radiography or CR has been used in the Radiography NDT industry for quite a long time. Use of CR in the pressure vessel welds has not been so popular or common industry practice, particularly in this region, may be because of cost and to some extent acceptance by the client. However ASME BPV Code has already approved use of CR and DR techniques in pressure vessel welds in place of film Radiography. The latest edition of ASME BPV Code Sec V has added some new requirements for qualification and certification of NDT personnel in Computed Radiography (ASME Sec V: 2015 Article I; Mandatory Appendix II). Typically, as we all know, CR or computed radiography uses a storage phosphor imaging plates, known as SPIP, which emits photo-stimulable luminescence in place of Silver Bromide coated films, that luminescence or light radiation is amplified by photomultiplier tubes and passes through A/D converter and several filters which produce an image on the suitable computer monitor. Most of the requirements of ASME Sec V for CR are similar to that of film radiography except in some cases as resolution, brightness and contrast in place of density and contrast used for film radiography. Although it requires expertise for processing the images, but the technique is very useful in replacing film radiography particularly in terms of chemical hazards and environmental issues of film processing, exposed film archiving and computer assisted image enhancement. But more than in traditional radiography, the use of digital images is a trade-off between the speed and the required quality. Better image quality is obtained by longer exposure times, slower phosphor screens and higher scan resolutions. Therefore, different kinds of storage phosphor screens are needed in order to cover every application. ASTM E2007 & E2033 provide excellent information and guidance of the process and application of computed radiography. Here in this presentation, we have described our understanding and experience of using computed radiography in lieu of film radiography for a pressure vessel meeting all the requirements of ASME Code.
Retardation Effect of Cyclic Overload on Stress Corrosion Crack Growth in Stainless Steel
Authors: Saito Toshiyuki , Hayashi Takahiro , Narazaki Chihiro , Itow Mikiro
Published: October 2017

Stress Corrosion Cracking (SCC) has been observed in some components of austenitic stainless steels in the Boiling Water Reactors (BWRs). The structural integrity evaluation for flawed component is performed for continued service for a specified time period based on the Rules on Fitness-for-Service (FFS) for Nuclear Power Plants, such as JSME FFS Code or ASME Section XI. SCC growth evaluation is generally performed only by taking into account steady loads, such as welding residual stress. It is important to examine various factors affecting SCC growth behavior for further understanding and improvement in predicting growth behavior in the BWR environment. Cyclic overloading due to such as earthquake force is one of the important factors to be evaluated. In this study, the effect of cyclic overload on SCC growth in simulated BWR environment has been examined by using CT specimens of cold-rolled stainless steels (Type 316L). The retardation phenomenon was observed in SCC growth behavior immediately after the cyclic overloading was applied. It was considered that SCC propagation was retarded due to the compressive plastic region at the crack tip, introduced by overloads. The method of predicting the SCC growth behavior after cyclic overloading was also discussed.
Modified GTAW Orbital Tube-to-Tubesheet Welding Technique, and the Effect of a Copper Weld Retainer During Welding of Alloy 825
Authors: Krustev Angel , Alexandrov Boian , Kovacich Jerry
Published: October 2017

Tube-to-tubesheet welds are an essential part of the design of heat exchangers used in power generation, petro-chemical, chemical processing, pharmaceutical, and food processing industries. The tube-to-tubesheet welds are typically produced using gas tungsten arc welding (GTAW) with or without the addition of filler wire, and involve carbon steels and various creep and corrosion resistant alloys. The weld heat input in tube-to-tubesheet welds is an essential parameter that controls the productivity and weld quality, in terms of weld bead geometry and heat affected zone microstructure and properties.

A modified GTAW tube-to-tubesheet orbital welding head that utilizes a copper weld retainer is described in this paper. The copper weld retainer provides a heat sink during welding, and supports the molten weld metal. This permits the use of a relatively high heat input, required for a single pass welding with filler wire addition. Furthermore, the copper retainer limits the amount of weld overlap into the tube bore.

The application of the modified orbital welding technique, which helped for resolving a suspected liquation cracking problem in Alloy 825 tube to 316L stainless steel tubesheet welds, is presented.
Proposed Approach of Scenario Analysis Using a Probabilistic Code
Authors: Sallaberry Cédric J. , Kurth Robert E. , Brust Frederick W. , Kurth Elizabeth A.
Published: October 2017

The following paper presents a global methodology to analyze the set of results generated by a probabilistic analysis. The approach regroups traditional analyses such as Sensitivity Analysis (SA), Uncertainty Analysis (UA), and stability analysis as well as sensitivity studies (both deterministic and probabilistic) with enhanced sampling techniques (double loop to separate aleatory from epistemic uncertainty, importance sampling, adaptive sampling) in an incremental set of steps, with the goal to give the analyst and decision maker the most comprehensive and defensible collection of results.

An example using the xLPR code and a selected scenario is used to illustrate each step of the approach.
Thermal Mechanical Finite Element Simulation of Additive Manufacturing: Process Modeling of the Lens Process
Authors: Stender Michael E. , Beghini Lauren L. , Veilleux Michael G. , Subia Samuel R. , Sugar Joshua D.
Published: October 2017

Laser engineered net shaping (LENS) is an additive manufacturing process that presents a promising method of creating or repairing metal parts not previously feasible with traditional manufacturing methods. The LENS process involves the directed deposition of metal via a laser power source and a spray of metal powder co-located to create and feed a molten pool (also referred to generically as Directed Energy Deposition, DED). DED technologies are being developed for use in prototyping, repair, and manufacturing across a wide variety of materials including stainless steel, titanium, tungsten carbide-cobalt, aluminum, and nickel based superalloys. However, barriers to the successful production and qualification of LENS produced or repaired parts remain. This work proposes a finite element (FE) analysis methodology capable of simulating the LENS process at the continuum length scale (i.e. part length scale). This method incorporates an element activation scheme wherein only elements that exceed the material melt temperature during laser heating are activated and carried through to subsequent analysis steps. Following the initial element activation calculation, newly deposited, or activated elements and the associated geometry, are carried through to thermal and mechanical analyses to calculate heat flow due to radiation, convection, and conduction as well as stresses and displacements. The final aim of this work is to develop a validated LENS process simulation capability that can accurately predict temperature history, final part shape, distribution of strength, microstructural properties, and residual stresses based on LENS process parameters.
Temperature Measurement of an Array of Heated Rods Subjected to Vacuum Drying Conditions
Authors: Maharjan Dilesh , Hadj-Nacer Mustafa , Greiner Miles
Published: October 2017

During vacuum drying of used nuclear fuel canister, helium pressure is decreased to as low as 67 Pa to promote evaporation and removal of water remaining in the canister following draining operation. At low pressures associated with vacuum drying, there is a temperature jump (thermal resistance) between the solid surfaces and helium in contact with them. This temperature jump increases as the pressure decreases (rarefied condition), which contributes to the fuel assembly’s temperature increase. It is important to keep the temperature of the fuel assemblies below 400°C during vacuum drying to ensure their safety for transport and storage.

In this work, an experimental apparatus consisting of a 7×7 array of electrically heated rods maintained between two spacer plates and enclosed inside a square cross-section stainless steel pressure vessel is constructed to evaluate the temperature of the heater rods at different pressures. This geometry is relevant to a BWR fuel assembly between two consecutive spacer plates. Thermocouples are installed in each of the 49 heater rods, spacer plates and enclosure walls. They provide a complete temperature profile of the experiment. Different pressures and heat generation relevant to vacuum drying conditions are tested. The results showed that the maximum temperature of the heater rods increases as the pressure decreases. The results from these experiments will be compared to computational fluid dynamics simulations in a separate work.
Probabilistic Fracture Mechanics Analysis Models for Japanese Reactor Pressure Vessels
Authors: Lu Kai , Katsuyama Jinya , Uno Shumpei , Li Yinsheng
Published: October 2017

Probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed by Japan Atomic Energy Agency for structural integrity assessments of reactor pressure vessels (RPVs) by considering the inherent probabilistic distributions of various influence factors. For practical applications, several evaluation models are improved, and have been implemented into the current PASCAL code. In this paper, the improvements of PASCAL are introduced firstly, such as the evaluation method for underclad cracks, treatments of the complicated welding residual stress distribution, and evaluation models for the warm pre-stressing effect. In addition, the effects of these improvements on failure probability or failure frequency of RPVs are investigated by performing PFM analyses for domestic RPVs using PASCAL. From the analysis results, the effects of the improved evaluation models are discussed.