bluuebunny/crossref_metadata_2025 huggingface dataset:
An Approach for a Statistical Evaluation of Uncertainty in Assessing Fatigue Usage Including Environmental Effects
Authors: Garud Y. S. , Steininger David A. , Wolfe Ken
Published: November 2014

The assessment for adequacy in managing the effects of fatigue in the ASME Code Class-1 (pressure boundary) components is based on a calculated measure of the projected fatigue damage. This measure is the highest cumulative usage factor (CUF) in a given component under a specified set of cyclic loadings and their expected number of repetitions. The Code-based calculation of CUF and its adjustments for potential environmentally-assisted fatigue (EAF) damage accumulation utilize a multitude of inputs, and conservative assumptions and applied margins. To support the extended service life beyond the original design, or longer life of new designs, changes in inputs and/or conservative assumptions used in these deterministically calculated CUFs are often made to meet a deterministic performance criterion. This makes the impact of uncertainty in the inputs and/or changes in the conservative adjustments difficult to assess.

This paper presents a generic, engineering approach for estimation of the uncertainty distribution of CUF based on the expected statistical characteristics of input variables used in the calculation of EAF-based CUF. The approach does not involve Monte Carlo sampling. The proposed statistical approach analytically combines variances of the inputs leading to an acceptable estimation of the total variance of the CUF. The approach does not require specification of full probability distribution(s) for the input variables, nor is the dependence between variables a critical issue from the analytical point of view. Feasibility and limitations of the approach are discussed in relation to the NB-3200 and NB-3600 procedures of the ASME Code and the current Fen-based augmentation for environmental effects. This approach is further examined in the framework of stress–strength interference methodology to account for the uncertainty in the fatigue performance criterion, that can lead to a rational deterministic safety factor interpretation and its relation to a quantifiable measure of the probability of exceeding the fatigue performance criterion.
A Less-Conservative Approach to Simplified Seismic Analysis for Small Bore Nuclear Piping System
Authors: Lee Joon Ho , Kim In Yeung
Published: November 2014

Per guidelines for piping system reconciliation such as EPRI NP-6628 (NCIG-14), simplified seismic design methods have been used by nuclear piping designers to deal with small bore piping for many years. These methods are generally based on enveloping the results of rigorous dynamic or conservative static analysis.

Small bore piping is generally more flexible with larger margin in support design comparing to large bore piping. Consequently, Classes 2 & 3 piping less than 2-1/2 inch NPS that is analyzed by a conservative “cookbook method” is excluded from the as-built verification actions in IE Bulletin 79-14. The ASME code’s Subsection NF and B31.1 provide recommended pipe spans by pipe size considering only piping weight; therefore, the seismically qualified piping span must be developed for the peak acceleration of the applicable amplified or floor response spectra.

Simplified seismic analysis method being considered for the Korean nuclear power plants is based on the Load Coefficient Method provided in Appendix N-1225 of ASME Section III. However, since the simplified analysis method involves conservative and enveloping approach in an effort to comply with applicable requirements and results in an excessive number of supports and unrealistically high support loads, the successful implementation largely depends on how the issues related to the excessive conservatism are resolved when determining allowable pipe spans and support design loads of the piping system.

In this paper, simplified engineering equations are presented as a less-conservative approach based on a detailed computer analysis method, which is alternative to the various handbooks and design charts that are based on the conventional hand calculation method.
Effect of Specimen Size on Elastic-Plastic Fatigue Crack Growth and Resistance Curve of Carbon Steel
Authors: Ikegami Junya , Taniguchi Motoki , Takanashi Masahiro , Hasunuma Shota , Ogawa Takeshi
Published: November 2014

In order to investigate the ultimate strength of structures and components under an unexpected huge earthquake, it is necessary to understand the final fracture condition under static and cyclic loadings. This study compared the crack growth behavior under monotonic and cyclic loading conditions for carbon steel SGV410 used for pressure vessels in nuclear power plants. Fatigue tests were carried out for CT specimens 50 mm wide (1CT), 75 mm wide (1.5CT) and 100 mm wide (2CT) using three kinds of test methods, namely monotonic loading (ML), load line displacement amplitude increasing (V-inc.) and fatigue crack growth (FCG) tests. For the FCG tests, the maximum load was kept constant under cyclic loading with full unloading (R = 0), fully reversed loading (R = −1) and fully reversing the load line displacement (R = −1.5) and the crack growth characteristics were evaluated by the fracture mechanics approach.
Measurement of Residual Stress in Reactor Nozzle Mock-Ups Containing Dissimilar Metal Welds
Authors: DeWald Adrian T. , Hill Michael R. , Benson Michael L. , Rudland David L.
Published: November 2014

Weld residual stresses can significantly impact the performance of structural components. Tensile residual stresses are of particular concern due to their ability to accelerate failure. For example, the presence of tensile residual stress can cause initiation and accelerate growth of primary water stress corrosion cracking (PWSCC). The contour method is a residual stress measurement technique capable of generating two dimensional maps of residual stress, which is particularly useful when applied to welds since they typically contain spatially varying residual stress distributions. The two-dimensional capability of the contour method enables detailed visualization of complex weld residual stress fields. This data can be used to identify locations and magnitude of tensile residual stress hot-spots. This paper provides a summary of the contour method and presents detailed results of contour method measurements made on a mock-up from the NRC/EPRI weld residual stress (WRS) program [1].
Effect of Aspect Ratio on the Flow Field Above the Free End of a Finite Circular Cylinder
Authors: Rostamy Noorallah , Sumner David , Bergstrom Donald J. , Bugg James D.
Published: November 2014

The flow above the free end of a surface-mounted finite-height circular cylinder was studied in a low-speed wind tunnel using particle image velocimetry (PIV). The cylinder was mounted vertically in the wind tunnel, normal to a ground plane. The approaching flow was in the x-direction and the cylinder axis was aligned in the z-direction. Velocity measurements were made above the free-end surface in several vertical (x-z) planes and several horizontal (x-y) planes, for finite circular cylinders of aspect ratios AR = 9, 7, 5 and 3, at a Reynolds number of Re = 4.2×104. The relative thickness of the boundary layer on the ground plane was δ/D = 1.7. In the vertical symmetry plane, the mean velocity measurements show the prominent separation from the circumferential leading edge, the mean recirculation zone above the free-end surface, the arch vortex inside the recirculation zone, and reattachment of the flow onto the free-end surface. Experimental evidence is found for a leading-edge separation bubble, a flow structure which has been reported in some numerical simulations in the literature. As AR decreases, the reattachment point and the centre of the arch vortex move downstream, the recirculation zone becomes thicker, and the centre of the arch vortex moves higher above the free end. Away from the symmetry plane, the recirculation zone becomes thinner, the arch vortex centre moves upstream and closer to the free-end surface, and the reattachment point moves upstream. In the horizontal planes, measurements made very close to the surface can approximate the mean surface streamline topology, revealing the pair of foci representing the termination points of the arch vortex, the prominent curved reattachment line, reverse flow beneath the mean recirculation zone, and the reattachment and separation saddle points on the free-end centerline.
Investigation on Fatigue Curve Against Cyclic Loads of an Earthquake for Piping Components
Authors: Uesaka Masao , Kojima Nobuyuki , Muroya Itaru , Nomura Hiroshi , Yamazaki Junichi , Otani Akihito
Published: November 2014

In Japan, seismic assessments considered aging phenomena have been conducted as part of activities for aging measures of nuclear power plants. In the activities, it is found that FAC (Flow Accelerated Corrosion) of piping components made of carbon steel impact on seismic integrity because of decreasing a cross section of piping. Therefore, many destructive tests of piping have been conducted in Japan and the other countries.

At first, factors on which did not focus in the past destructive test have been extracted in this investigation. displacement controlled cyclic tests of piping components which focused on extracted factors have been conducted additionally in order to provide enough test data for past destructive test data of piping components. Moreover, fatigue curve for practical evaluation of piping components made of carbon steel has been settled after obtained test data were put in order including past destructive test data of piping components from a point of fatigue.
Mechanical Properties Estimation of Materials With Different Grain Sizes by Small Punch Test at Elevated Temperature
Authors: Yang Sisheng , Ling Xiang , Yang Xinjun , Lu Shuhua
Published: November 2014

As an effective method for performance analysis of in-service component, small punch test (SPT) can be used in various situations to analyze material characterization of structural component. In order to improve stress distribution and fatigue strength of materials, ultrasonic impact treatment (UIT) has been widely researched in recent years. However, the nanocrystalline layer is so thin that can not be analyzed by the conventional tests. In this paper, the mechanical properties of AISI304 which were improved by ultrasonic impact treatment were evaluated by small punch test. Meanwhile, as two important factors, the temperature and grain size were considered. The influence of impact time on surface treatment of AISI304 was analyzed. It can be found that the grain size decreases with the increase of impact time. Based on the variation of Load-Displacement (L-D) curves obtained by small punch test, the strengths of treated specimens were obtained. Finally, the mechanical property evolutions with different surface grain sizes were discussed at elevated temperature.
Experimental Verification of Finite Element Approach for Designing Robust Bolted Joints Using Titanium and Titanium Alloy Bolts at Elevated Temperature
Authors: Fukuoka Toshimichi , Nomura Masataka , Hirai Takao
Published: November 2014

When bolted joints are subjected to thermal load, variations of the bolt clamping force are of great concern from the view point of joint safety. It is considered that titanium and titanium alloy bolts have high possibility for clamping machines and structures subjected to thermal load. Its specific characteristic of low thermal expansion expectantly works well to mitigate the reduction of bolt clamping force caused by thermal expansion. Low weight, low Young’s modulus and high resistance to corrosion of titanium and titanium alloy are also highly attractive.

In this paper, the effectiveness of the numerical method proposed in the previous study is validated by experiments using bolted joints composed of titanium bolts and carbon steel plates. Then, thermal and mechanical behaviors of titanium and titanium alloy bolts are analyzed by finite element analysis in order to examine the applicability of those bolts for the joints under elevated temperature. Numerical analyses are executed as in the manner introduced in the previous paper, i.e., by incorporating the thermal contact coefficient into the finite element formulation. Numerical results suggest that titanium and titanium alloy bolts are favorably applied to the joints made of carbon steel whose clamping forces are likely to decrease under elevated temperature.
Creep Wave Testing Technology Application on In-Service Pressure Pipe
Authors: Chen Yubao
Published: November 2014

For many in-service pressure pipe welds with thinner thickness (less than 10mm), the conventional pulse echo testing technique is difficultly used for its less thickness and the radiographic testing is not conveniently performed because of the pipe position limitation. But, the creeping wave (CW) technology can play an important role in these pipe welds inspection because of its special characteristics. In the paper, the generation and attenuation feature of CW are detailed and the probe configuration and comparative block of CW testing are discussed. Finally, successful application of CW in pipe welds is demonstrated.
Leakage Analysis of a High Pressure Flange Connection Under Bending Moments: An Analytic Procedure
Authors: Bortz Matthias , Wink Rolf
Published: November 2014

High pressure flange connections for LDPE plants are designed using lens ring gaskets and bolted flange connections. The sealing principle is to achieve a high contact pressure between the spherical lens shape and the conical tube end. This contact pressure must exceed the fluid pressure by a safety margin under all operating conditions. Bending moments acting on the flange connection will create an uneven distribution of contact pressure over the lens ring surface.

In this paper a procedure is shown to analyse the influence of the bending moment under consideration of internal pressure on a flange connection using 3-dimensional finite element models. The variations in bolt stress and distribution of contact pressures due to the bending moment are of specific interest. A first approach will be provided to derive some simplified design rules regarding leakage assessment of such flange connections.
Developing an Engineering Based Integrity Management Program for Piping, Pipelines, and Plant Equipment
Authors: Alexander Chris , Bedoya Julian
Published: November 2014

Establishing integrity for piping and pipelines requires an understanding of the specific threats, their relationship to the overall condition of the system, and the mitigating measures required to assure safe operation. In the past, industry has relied on years of research and experience to develop a set of tools to analyze these threats and apply conservative solutions to ensure integrity and fitness for service. An effective integrity management program as discussed in this paper, known as the Engineering Based Integrity Management Program (EB-IMP), provides operators with a resource for integrating inspection results, analysis, and testing to qualify the components within a pressurized system.

This paper presents a detailed discussion on how experience, advances in analytical techniques, experimental methods, and engineering rigor are combined to develop a tool to characterize and ensure system integrity. Several case studies are included to demonstrate how the EB-IMP method was used to evaluate the integrity of a piping system, as well as rail gondola cars used to transport coal. The intent with the approach presented in this paper is to foster further developments for advanced integrity management efforts.
Status of Proposed Updates to the Weld Residual Stress Guidance for Flaw Assessments in API 579-1/ASME FFS-1
Authors: Dewees Dave J. , Smith Katelyn J.
Published: November 2014

Guidance for weld residual stress (WRS) in flaw assessments of in-service equipment is given in Annex E of the Fitness-for-Service (FFS) standard, API 579-1/ASME FFS-1. Recent progress in the simulation of weld residual stress, and in its verification and validation has provided the opportunity to both simplify and supplement Annex E. Specifically, a tiered approach is recommended with the baseline guidance simplified and harmonized with other existing guidance, while more complicated cases are recommended to be handled with an explicitly described simulation method. The simulation method is the subject of related papers, while this paper focuses on comparison and evaluation of existing guidance for the common cases of cylinder girth and seam welds. A complete draft of recommended guidance has been completed, and intended for publication in the 2014 revision of API 579-1/ASME FFS-1. A supporting basis document which details the underlying methodologies for recommendations has also been completed.
Effect of Indentation Load on Vickers Hardness of Austenitic Stainless Steel After Hydrogen Charging
Authors: Takakuwa Osamu , Mano Yuta , Soyama Hitoshi
Published: November 2014

In order to reveal the effect of indentation load on Vickers hardness of austenitic stainless steel after hydrogen charging, the Vickers hardness measurements have been conducted with three different indentation load of 0.49, 1.96 and 9.80 N on the surface of type 316L austenitic stainless steel after hydrogen charging. Relationship between plastic deformation behavior during indentation process and hydrogen absorption behavior was revealed. In the Vickers hardness test, Vickers hardness keeps same value though the indentation load varies. Needless to say, the value did not depend on magnitude of the indentation load before hydrogen charging in the present study. However, the Vickers hardness increased along with hydrogen charging time and, interestingly, the increase in the Vickers hardness due to the presence of hydrogen depends on magnitude of the indentation load. In the load of 0.49 N and 9.80 N, the Vickers hardness has a maximum value of 3.04 and 2.04 GPa which is 1.58 and 1.15 times larger than value of 1.73 and 1.70 GPa before hydrogen charging, respectively. The hydrogen-induced hardening behavior observed by the Vickers hardness tests employing different indentation load would be evaluated by the relationship between the plastic deformation depth and the hydrogen absorption depth.
Effect of Dissimilar Leading Edges on the Flow Structures Around a Square Cylinder
Authors: Nair Arunkumar Kumaran , Kumar R. Ajith , Many Hariprasad Chakkalaparambil
Published: November 2014

In the present study, results of a flow visualization study on the flow around a square cylinder with dissimilar leading edges are presented. The radii of the leading edges of the cylinder ‘r1’ and ‘r2’ are such that the ratio r1/ r2 is systematically varied from 0 to 1. The flow structures around the cylinder with different leading edge radii particularly the vortex shedding mode and mechanism are investigated. For studies with stationary as well as oscillated cylinder cases, the results are taken at a Reynolds number value of 2100. For the oscillated case, a special mechanism is made to oscillate the cylinders at a desired amplitude and frequency. That is, the cylinder undergoes forced oscillation in this case. Results indicate that dissimilar leading edges bring notable changes in the near-wake flow structures of a square cylinder. For the stationary cylinder cases, the vortex formation length decreases with increase in the r1/ r2 ratio. Flow structures are also found to be influenced by the amplitude ratio (amplitude to body size ratio); the higher the amplitude, the larger the size of vortices shed per cycle of cylinder oscillation. In view of marine structures and building sections with similar geometries, the present results carry considerable practical significance.
Applying Finite Element Based Limit Load Analysis Methods to Structures Under Dynamic Loads
Authors: Booth Martin R.
Published: November 2014

To conduct an ASME III NG-3200 limit load strength assessment, it is required to determine the structure’s limit load under a particular loading configuration, and compare it against the applied loading represented as a static equivalent. Typically, the process is applied to static problems which have well-defined loading characteristics. When the limit load has been determined, often through the use of finite element (FE) based methods, the margin against plastic collapse is simple to calculate. For dynamically loaded structures, however, the process is more complicated since there are no ASME guidelines for expressing dynamic loads as their static equivalent. Thus, relating limit load analyses to dynamic events is not clear. This paper proposes an analysis technique which makes use of FE methods to apply the principles of limit load analysis to dynamically loaded structures. The primary benefit is that reserve factors against plastic collapse, in accordance with ASME III NG-3200 assessment criteria, can be calculated.
Study of Acoustic Vibration in Piping Systems by Energy-Based Finite Element Analysis
Authors: Dweib Ahmed H.
Published: November 2014

Finite Element Analysis (FEA) and Statistical Energy Analysis (SEA) methods have been applied recently to the study of acoustic induced vibration (AIV) in piping systems.

In this paper, the acoustic vibration in the piping systems is studied by performing FEA of a model of the structural pipe with the application of the acoustic excitation as stationary acoustic modes to the structural pipe model. This approach provides an alternative to performing FEA using a combined model for the acoustic fluid and the pipe. The analysis is used for the evaluation of the power flow from the acoustic medium to the pipe. The acoustic part of the system is modeled as a series of acoustic modes that are taken to act on the pipe FEA model. The Coupling Loss Factor (CLF), required for the formulation of the SEA model, is identified and plotted against pipe parameters.
A Fracture-Toughness Based Transition Reference Temperature for Use in the ASME Code With the Crack Arrest (KIA) Curve
Authors: Kirk Mark , Hein Hieronymus , Erickson Marjorie , Server William , Stevens Gary
Published: November 2014

In the early 2000s, ASME adopted Code Cases N-629 and N-631 [1–2], both of which permit the use of the Master Curve reference temperature (To) to define an reference temperature RTTo, as follows (in SI units, as are used throughout the paper):RTTo=To+19.4℃The Code Cases state that “this reference temperature … may be used as an alternative to [the] indexing reference temperature RTNDTfor the KIcand KIatoughness curves, as applicable, in Appendix A and Appendix G [of Section XI of the ASME Code].” KIa is now only used in Appendix A. The functional form of the ASME KIc and KIa curves dictate that the temperature separation between them remains constant irrespective of the degree of neutron radiation embrittlement, as quantified by ΔRTNDT or ΔRTTo. However, data collected from the literature and new data reported by Hein et al. show that radiation embrittlement brings the KIc and KIa curves closer together as embrittlement increases. As a result, current Code guidance will not produce a bounding KIa curve in all situations when RTTo is used as an reference temperature. To reconcile this issue, this paper summarizes available data and, on that basis, concludes that use of the following reference temperature will ensure that the ASME KIa curve bounds currently available KIa data:RTKIa=RTTo-19.4+44.97×exp⁡−0.00613×RTTo-19.4
Flow Around a Leading Edge Slat: Part II — Cove Flow Dynamics via Snapshot POD
Authors: Wilkins Stephen J. , Richard Patrick R. , Hall Joseph W.
Published: November 2014

The dynamics of flow within the cove of a leading edge slat has been investigated using Proper Orthogonal Decomposition by the method of snapshots. The shear-layer that originates from the slat cusp contains a large proportion of the turbulent kinetic energy within the flow. Reconstructions performed with the first 10 POD eigenmodes illustrates that several smaller regions of vorticity persist within the shear-layer. Depending on the Reynolds number and the angle of attack, the shear-layer can impinge upon the leading edge of the main wing element, roll up within the slat cove, or be ejected through the gap between the slat trailing edge and the leading edge of the wing. This unsteady impingement of both the shear-layer, and the smaller features within the shear-layer could result in a very strong acoustic dipole source.
A Strategy for Development of a Mechanistic Understanding of Environmental Fatigue
Authors: Twite Marius
Published: November 2014

There has been much focus in recent years on development of an empirical understanding of the effects of a range of variables on fatigue performance of nuclear plant materials in relevant operating environments — for example, the influences of surface finish, temperature, and cyclic waveform. To complement these empirical studies, a well-developed mechanistic understanding of Environmental Fatigue initiation behaviour is required to allow extrapolation of results beyond the variable ranges tested and to provide insight into the margins incorporated into fatigue analysis methods, including fatigue design curves.

Mechanistic understanding may be defined as a multi-scale description of physical and chemical effects determining fatigue behaviour through the stages of crack nucleation, small crack (Stage I) growth and the transition to long crack (Stage II) growth.

A review of literature related to mechanistic understanding of Environmental Fatigue initiation in nuclear plant materials in air and PWR primary coolant environments has been carried out. Detailed findings of that review are not presented here; however, high level conclusions are discussed. It was found that very little literature specific to these combinations of material and environment is available, although there exists a substantial body of work related to generic mechanistic understanding of fatigue and environmental effects in metallic materials.

Based on the conclusions of this literature review, a strategy for improvement of mechanistic understanding of Environmental Fatigue initiation has been developed by Rolls-Royce. This strategy is based around three strands of work: metallurgical investigation; numerical modelling; and laboratory testing.

Improvements in mechanistic understanding of Environmental Fatigue initiation offer significant opportunities for collaboration between interested parties. Indeed, attainment of a well-developed mechanistic understanding that may be used, in combination with empirical understanding, to inform advances in fatigue analysis methods is likely to be achievable only through collaborative effort.
Four Points Bending Test on an EPR Type DMW Pipe Containing a Through-Wall Defect: Experimental and Numerical Analysis From Small Specimens Until Pipe Scale
Authors: Bourgeois M. , Chapuliot S. , Marie S. , Ancelet O. , Kayser Y.
Published: November 2014

Within the framework of European project STYLE [1], a fracture test on a pipe containing a through wall crack in a narrow gap Inconel Dissimilar Metals weld (welds named hereafter DMW) has been performed. The work is focusing on the Inconel - ferritic steel interface which is the weakest area of such welded pipes in front of ductile tearing. The study temperature is 300°C, which covers typical temperatures in components like hot pipes in the primary coolant system of pressurized water reactors.

The four point bending test was carried out by the French Atomic Energy Commission and Alternative Energies (CEA), in order to study the mechanical properties and integrity of component such as the DMW pipes provided and designed by AREVA France. The observations made post-mortem showed a small 2.5 mm ductile tearing at the interface of Inconel and ferritic steel, and after this point, a large crack that has deviated from the interface to propagate in the Inconel and then in the stainless steel.

The DMW Mock-up is presented with previous results concerning the mechanical characterizations of his constitutive materials. The second part of this paper is devoted to the four point bending test at 300°C: procedure, instrumentation and interpretation of large-scale test in terms of initiation and propagation of cracks. A comparison is made with tests performed at a smaller scale on multi-material CT specimens. The third part deals with first numerical analysis of fracture test. The results are interpreted on a small scale using finite element analysis to obtain the parameters of damage models that are needed for global approach. Finally, numerical approaches is presented and applied to simulate the fracture of the large-scale pipe.

The aim of this paper is to propose and discuss the validity of new assessment methods of ductile propagation in a large scale pipe containing a through wall crack in a narrow gap dissimilar metal weld.
An Engineering Procedure for Calculating Cleavage Fracture Toughness From Charpy Specimen Data Using a Mechanistic Approach for Ferritic Steels
Authors: Smith Robin J. , Sherry Andrew H. , Horn Anthony J. , Bannister Adam C.
Published: November 2014

This research develops an engineering approach which permits the treatment of Charpy specimen absorbed energy data in the lower transition of Charpy specimen fracture behaviour. The procedure has been shown to be applicable to a ferritic steel study material. The calculation method comprises several steps to correct the input Charpy data to the equivalent material fracture toughness of a ferritic steel under consideration. The engineering procedure develops existing methods for constraint and notch correction to data [Sherry et al, EFM 2005] [Horn and Sherry, IJPVP 2012].

Micromechanical modeling of cleavage fracture behaviour has been applied in conjunction with sequential experimental testing. This work addresses the important geometric differences between a single edge notch bend, SEN(B), fracture toughness specimen and the standard Charpy V-notch specimen. The engineering approach is demonstrated using a suitable study ferritic steel material and by undertaking an experimental laboratory testing programme comprising standard fracture toughness specimens and non-standard U-notch and V-notch Charpy sized specimens with a range of notch geometries.

It has been found that constraint and notch assessment methodologies premised upon micro-mechanical modeling of cleavage fracture offer an accurate probabilistic description of fracture behaviour in these specimen geometries. Refinement of a notch angle correction is necessary within the procedure. These findings permit the extension of the approach to develop a material specific guidance to practitioners undertaking structural integrity assessments. The final extension of the research to Charpy impact data requires the measurement of ferritic steel material flow behaviour under dynamic conditions and represents further research.
An Experimental Study of Ductile Failure Under Multi-Axial Loading
Authors: Lu Wei-Yang , Jin Helena
Published: November 2014

Recent experimental investigations show that most models are not able to capture the ductile behavior of metal alloys in the entire triaxiality range, especially at low triaxiality. Modelers are moving beyond stress triaxiality as the dominant indicator of material failure and developing constitutive models that incorporate shear into the evolution of the failure model. Available data that cover low triaxiality range are rare and a series of critical experiments is needed. Here, experiments of smooth thin as well as notched tubular specimens of Al6061-T651 under combined tension-torsion loading were conducted. This provides a very basic set of data for phenomenological models. A full-field deformation technique, digital image correlation (DIC), was applied to these tests to allow measurement of the field deformation, including the notched area. The microstructural features of the tested specimens were characterized to better understand the different failure mechanisms which led to ductility variation in the aluminum alloy.
Palladium Hydride Atomic Potentials for Hydrogen Storage/Separation
Authors: Park Y. H. , Hijazi I.
Published: November 2014

Palladium is capable of storing a large atomic percent of hydrogen at room temperature and allows for hydrogen to diffuse with a high mobility. These unique properties make it an efficient storage medium for hydrogen and hydrogen isotopes, such as tritium, a byproduct of nuclear reaction. Palladium thus can be used for applications where fast diffusion and large storage density are important. Better understanding of molecular level phenomena such as hydride phase transformation in the metal and the effect of defects in the materials provides clues to designing metal hydrides that perform better. Atomic simulations are useful in the evaluation of palladium-hydrogen systems as changes in composition can be more easily explored than with experiments. In this paper, we present the palladium hydride potentials to investigate and identify the relevant physical mechanisms necessary to describe the absorption of hydrogen within a metal lattice.
The Failure Evaluation and Application of Power Plant Boiler Membrane Type Water-Cooled Wall Based on Risk-Based Inspection
Authors: Yan Zhenrong , Yang Yuqing , Han Jun , Si Jun , Wang Huanan , Luo Xiaoming
Published: November 2014

In recent years, Ultra supercritical power plant boiler in China is developing very rapidly, therefore, using the RBI risk evaluation method to carry out inspection of large power station boiler is very necessary. Operation practice shows that the membrane type water-wall is one of the main risk parts of large power plant boiler. Research has shown that typical failure area of membrane type water-wall is layer nearby the burner; Most of failure positions are in high heat flux region, the fins weld joint; Failure mechanism is comprehensive factors, such as, the welding deformation, weld defects and fins weld crack, foreign bodies blocked, blowing loss thinning, short-term over temperature overheating. On this basis, the application of RBI risk assessment method, analyzed the risk level and failure consequences of a power plant boiler membrane type water-wall, the risk matrix is obtained, proposed the corresponding test strategy, for the RBI technology application to evaluation of power plant boiler components provides a new method of failure risk.
Smoothed Particle Hydrodynamics for Hypervelocity Impacts Into Inhomogeneous Materials
Authors: Zisis Iason , van der Linden Bas , Giannopapa Christina , Dam Jacques
Published: November 2014

Smoothed Particle Hydrodynamics numerical method is extensively used in the study of hypervelocity impacts and subsequent shock propagation into solids. During impacts into inhomogeneous materials, effects produced on the interface of adjacent materials by shock waves need to be resolved. The present study discusses an SPH mutliphase scheme for compressible processes, that is based on the number density estimate and exhibits the scheme’s performance at shock propagation through inhomogeneous materials. In specific, a one-dimensional Riemann problem with known solution validates the scheme and results of two-dimensional hypervelocity impact scenarios into materials with (large-scale and small-scale) inhomogeneities are studied.
Research Plan on Failure Modes by Extreme Loadings Under Design Extension Conditions
Authors: Kasahara Naoto , Nakamura Izumi , Machida Hideo , Nakamura Hitoshi
Published: November 2014

As the important lessons learned from Fukushima-nuclear power plant accident, preparation based on Probabilistic Risk Assessment (PRA) with adequate scenario is strongly recognized as essential countermeasures against severe accidents, which are possible in nuclear plants. IAEA requires design extension conditions (DEC) for considering severe accidents. From a view point of structural design, the strength evaluation approach for DEC is somewhat different from conventional one for design basis accident (DBA). There are additional failure modes by extreme loadings under DEC. Best estimation with possible scenarios is necessary for PRA and planning of accident management (AM).

This paper introduces study plan on failure modes and their mechanisms by extreme loadings under DEC.

First step is the list-up of possible failure modes which should be assumed for extreme loadings such as very high temperature, high pressure and great earthquakes. Next is clarification of failure mechanism and relevant limit strength.

One of examples is the failure modes of structural discontinuities under high pressure such as ductile fracture and local failure. Another example is ones of pipes under severe earthquake such as collapse and low cycle fatigue.

To clarify above questions, such different scale tests were planned and conducted as the fundamental tests with simulated materials, structural element tests and structural tests. Preliminary results of above tests and next plans are explained.
Earthquake Load Reduction Effects of Boiler Structures by High Energy Absorbing Seismic Ties
Authors: Aida Kiyoshi , Kawate Kodai , Hiyoshi Yuichi , Kawamura Kotaro , Fujita Satoshi
Published: November 2014

Seismic ties are steel energy absorbing devices installed between the boiler and its support structure. This paper deals with the relationship between the energy absorption of a new type of seismic tie (made of low yield strength steel and with an optimized I-sectional shape) and its reduction effect on the resultant shear force of the support structure. To quantify the relationship between the energy absorption and the reduction effect on the resultant shear force, time-history analyses using a lumped mass vibration model that simulates the boiler structure, were performed for three representative design seismic waves (The largest class (level 2) waves of Taft, El Centro and Hachinohe earthquakes). The time-history analysis results demonstrated that the energy absorption increasing rates of the new seismic ties were correlated quantitatively with the shear force reduction rates of the support structure for the three design seismic waves.
Development of Pressure Vessels Made of 9Cr-1Mo-V Steels for High-Temperature Processes in Refining Industries
Authors: Nakanishi Tomoaki , Ikeuchi Tadashi , Terada Susumu , Yamada Masato , Miyamura Takeo , Nanba Shigenobu , Shinozaki Tomoya , Nakashima Hiroki , Ikeda Tetsunao , Yamashita Ken
Published: November 2014

Due to the increasing demands for light oil in newly industrializing countries and depletion of conventional oil resources, upgrading of heavy oil and coal-to-liquid processes have been a focus in recent years. The efficiency of these processes depends on temperature and pressure conditions, where a higher temperature, around 500°C, is likely to be used. However, 2¼Cr-1Mo-V steels which have been widely used for heavy-wall pressure vessels for many years cannot be applied to a high temperature process around 500°C since the design temperature of this material is limited to 482°C by ASME Code Section VIII, Division 2 [1].

On the other hand, 9Cr-1Mo-V steels (Grade 91), which has an excellent performance at high temperature in mechanical properties and hydrogen resistance, has been used for tubing and piping materials in power industries and it can be a candidate material for the high temperature processes. However it has not been used for pressure vessels in refining industries.

In order to manufacture heavy-wall pressure vessels using 9Cr-1Mo-V steels, essential techniques including manufacture of large forged shell rings, thick wall welding and overlay welding have been developed.
Experience of Work for Replacing Reactor Recirculation Piping in Narrow Space of MARK-I Containment Vessel
Authors: Shiraki Keisuke , Taniguchi Akira , Fujino Takushi , Nakama Shouhei , Suzuki Osamu , Kobayashi Hiroyuki
Published: November 2014

Tsuruga unit-1, the first Japanese commercial BWR (BWR-II, 357MWe) started its operation in 1970, has a Mark-I type containment vessel and 3-loop reactor recirculation piping.

In the 33rd planned outage of 2011, most parts of the reactor recirculation piping were replaced to improve corrosion resistance and inspectability. This replacement work dealing with long pipe pieces had to be conducted in limiting condition and severe environment such as the narrow work space, only one small entrance hatch, and high dose rate. In addition, other maintenance works by four contractors were concurrently being carried out in the same area. Therefore, these work processes in the containment vessel were controlled carefully through close coordination with contractors and using advanced construction technique. As a result, it was achieved that efficient process which contributed to shortening work period and injury-free work in this challenging environment and condition.

Regarding radiation management, radiation dose rate was reduced substantially by applying chemical decontamination using ozone as chemical agent.

Experience obtained from this work is valuable in the current situation that many operators are trying to operate their aging nuclear plants continuously as long as economically viable.
Semianalytical Method for the SIF Calculation for a Crack of Arbitrary Shape in Infinite Body
Authors: Batura Anatolii , Orynyak Igor , Oryniak Andrii
Published: November 2014

The exact analytical approach for stress intensity factor calculation for an arbitrary shape mode I crack loaded by the polynomial stresses is proposed. The approach is based on the calculation of the crack faces displacement at given loading. The displacement field is presented as a shape function multiplied by an adjustment polynomial. At that the key problem is the solution of well-known inverse task: obtaining the stresses field at the crack faces on the base of a given displacements field. Multiply solution of such task for a whole set of certain displacements base functions (e.g., for the single terms of the adjustment polynomial) allows to get analytical expression which connects stresses and displacements fields.

The original semi-analytical technique for integration with subsequent differentiation of well-known singular integral equation of the flat crack problem is developed. The excellent accuracy of the method is confirmed for an elliptic crack as well as for a rectangular one in the infinite 3D body. New results are given for an inner semi-elliptic crack in the infinite body which surfaces are loaded by polynomial stresses up to the 6th order. The importance of choosing the appropriate shape function is demonstrated.
Study on the Failure Assessment of Small Diameter Pipe With Circumferential Crack Under Monotonic and Cyclic Multi-Axial Loading
Authors: Itatani Masao , Saito Toshiyuki , Akiniwa Yoshiaki , Naito Keita
Published: November 2014

Failure behaviors of small diameter pipe of austenitic stainless and carbon steels with circumferential crack under monotonic and cyclic multi-axial loading were observed and the criteria of failure under these conditions were investigated. For the failure under monotonic loadings, it was observed that the maximum load was attained when the net section von Mises equivalent stress almost reached to the flow stress of the material. For the cyclic loading, Pa/Pmax or Ta/Tmax seems to be a good parameter to estimate failure life irrespective of specimen thickness, initial crack size and loading pattern, especially for STPT410. Here, Pa and Ta are load and torque amplitude respectively, and Pmax and Tmax are the maximum load and torque under monotonic loading with the same loading pattern for cyclic loading.
Development of an Automatic 3D Finite Element Crack Propagation System
Authors: Doi Hiroaki , Nakamura Hitoshi , Gu Wenwei , Okada Hiroshi
Published: November 2014

When cracks are detected in piping in nuclear power plants during in-service inspections, the crack propagation is usually calculated using approximation formulas of stress intensity factor (SIF) provided in the ASME Code, the JSME Rules or the literature. However, when the crack is detected in complicated-shaped locations in components, finite element analysis (FEA) needs to be used to calculate the SIFs. Accordingly, a method of automatically conducting FEA for crack propagations in nuclear power plants is needed. Therefore, we, the Nuclear Regulation Authority (NRA, Japan) have developed an automatic 3D finite element crack propagation system (CRACK-FEM) for nuclear components. The developed CRACK-FEM uses three methods of SIF calculation: the Virtual Crack Extension Method (VCEM), the Virtual Crack Closure-Integral Method (VCCM) and the Domain Integral Method (DIM). Each method uses different meshes, so users can select a method which uses a suitable mesh for the problem. The software includes a geometry generator to create complicated weld models, and a mesh generator which can deal with interior boundaries formed between different materials. The functions and accuracy of the new software are demonstrated by solving several sample problems involving crack propagation.

The contents of this paper were conducted as a research project of the Japan Nuclear Energy Safety Organization (JNES) when one of the authors (Doi) belongs to JNES. After this project, JNES was abolished and its staff and task were absorbed into NRA on March 1, 2014.
Treatment of Stresses Exceeding Material Yield Strength in ASME Code Section XI Appendix G Fracture Toughness Evaluations
Authors: Mehta Hardayal S. , Stevens Gary L. , Sommerville Daniel V. , Benson Michael , Kirk Mark , Griesbach Timothy J. , Kusnick Joshua
Published: November 2014

A previous PVP paper [1] identified suggested improvements to be made to ASME Code, Section XI, Nonmandatory Appendix G, “Fracture Toughness Criteria for Protection Against Failure” [2]. That paper also identified that the current version of Appendix G does not have any provisions for when the calculated operating stress (pseudo stress) exceeds the material yield strength. The treatment of stresses exceeding yield was included in earlier versions of Appendix G, but it was removed via Code Action ISI-94-40 in 1995. The specific reasons for removal of these provisions were not documented.

In some Appendix G postulated flaw evaluations for pressure-temperature (P-T) limits, the calculated total linear-elastic (or pseudo) stress (i.e., including the primary stress due to pressure loading and thermal stress) may exceed the material yield stress. The ASME Section XI Working Group on Operating Plant Criteria (WGOPC) decided that this provision needed to be more fully considered, with appropriate benchmarking and possible adjustments to Appendix G made consistent with the current state of knowledge in elastic-plastic fracture mechanics (EPFM) methods. This is appropriate since the state of knowledge in EPFM has significantly advanced since the time the technical basis for Appendix G was established, as documented in Welding Research Council (WRC) Bulletin No. WRC-175, which was published in 1972. Furthermore, EPFM provides an improved method for evaluating the effects of high stresses.

This paper describes the results of preliminary investigations of stresses exceeding the material yield stress in fracture toughness assessments associated with Appendix G. Also included in the technical evaluations presented are the temperature conditions for which upper shelf conditions are present and where EPFM methods are applicable.