bluuebunny/crossref_metadata_2025 huggingface dataset:
Benchmarking PRAISE-CANDU 1.0 With NURBIM Project Fatigue Cases
Authors: Duan Xinjian , Wang Min , Kozluk Michael J.
Published: January 2014

A probabilistic fracture mechanics code, PRAISE-CANDU 1.0, has been developed under a software quality assurance program in full compliance with Canadian Standards Association (CSA) N286.7-99, and was initially released in June 2012. Extensive verification and validation has been performed on PRAISE-CANDU 1.0 for the purpose of software quality assurance. This paper presents the fatigue benchmarking against NURBIM (NUclear Risk Based Inspection Methodology for passive components) fatigue cases between PRAISE-CANDU 1.0 and six other Probabilistic Fracture Mechanics (PFM) codes. This benchmarking is considered to be an important element of the validation of PRAISE-CANDU. Excellent agreement is observed in spite of the differences between the codes. The comparison of the predicted leak probability at the 40th year shows that PRAISE-CANDU not only captures the same trend but also bounds (higher predicted failure probability) the majority of the NURBIM results. In addition to the leak probability, the rupture probability and uncertainty analysis, which were not reported in the NURBIM Project, are also calculated with PRAISE-CANDU and presented.
Validity of Hardness Criteria to Demonstrate Acceptable Temper Bead HAZ Impact Properties for Nuclear Power Applications
Authors: McCracken Steven L. , Smith Richard E. , Barborak Darren
Published: January 2014

Temper bead welding is used routinely for weld repair on low alloy pressure vessel steels in the nuclear power industry. Temper bead procedure qualification is contingent on demonstration that the welding process does not degrade the mechanical properties, including fracture toughness, in the base metal weld heat affected zone (HAZ). Historically for temper bead qualification acceptance, adequate HAZ properties have been verified by tensile, impact, and bend testing, while hardness criteria has not been specified. In fact, temper bead welding has been successfully applied for welding on low alloy steels without any hardness criteria for many years. In 2004, ASME Section IX added hardness testing for temper bead procedure qualification when impact testing is not required. The Eurocode, ISO standards, and numerous other European specifications include maximum hardness criteria for general welding procedure qualification and have invoked these same criteria for temper bead procedures. Test results indicate that imposing maximum hardness criteria can actually lead to acceptance of less than optimum fracture toughness in the temper bead weld HAZ due to rapidly changing microstructures in low alloy steels. Impact properties for such microstructures can vary widely even though similar levels of hardness are exhibited. This paper investigates the legitimacy of using maximum hardness criteria to demonstrate acceptable HAZ fracture toughness in low alloy pressure vessel steels.
Development of 2012 Edition of JSME Code for Design and Construction of Fast Reactors: (5) Creep-Fatigue Evaluation Method for 316FR Stainless Steel
Authors: Nagae Yuji , Takaya Shigeru , Asayama Tai
Published: January 2014

The most important failure mode to be prevented in the design is creep-fatigue at elevated temperatures in fast reactors. 316FR stainless steel is a candidate material for the reactor vessel and internal structures. Development of the procedure for evaluating creep-fatigue life is essential. The method for evaluating creep-fatigue life implemented in the Japan Society Mechanical Engineers code is based on the time fraction rule for austenitic stainless steel such as SUS304. Necessary equations such as fatigue curve and creep rupture curve for calculation of creep-fatigue life are evaluated, and the predicted creep-fatigue life by using the time fraction rule in 316FR stainless steel is compared with experimental data. The longest time to failure is about 100,000 h for evaluating creep-fatigue life. Fatigue curve, creep rupture curve, stress-strain curve and creep strain curve are provided for calculating creep-fatigue life. The creep-fatigue life is predicted within a factor of 2 even the test condition of the longest time to failure. Furthermore, comparison with the ductility exhaustion method was done to investigate the conservatism of the proposed method. Finally, the procedure based on the time fraction rule for evaluation of creep-fatigue life is proposed in 316FR stainless steel.
Effect of Material Microstructure on Creep Damage Formation Behavior for Ni-Base Directionally Solidified Superalloy
Authors: Ozeki Go , Sugiura Ryuji , Yokobori A. Toshimitsu , Nagumo Yoshiko , Takeuchi Hiroaki , Matsuzaki Takashi
Published: January 2014

Ni-base directionally solidified superalloy strengthened by γ′ precipitates have been developed as a gas turbine blade. However, it is difficult to detect creep damage such as creep voids by conventional observation techniques. It is important to clarify the creep damage behavior for Ni-base superalloy.

In this study, creep crack growth tests for Ni-base directionally solidified superalloy CM247LC were conducted using the in-situ observational system. Additionally, the metallographical investigation was conducted on crept specimen using EBSD analysis and relationship between creep crack growth path and material microstructure were clarified. And, in order to clarify the difference of creep crack growth behavior, the designed two-dimensional elastic-plastic creep finite element analyses were conducted for the model with grain distribution obtained by EBSD analysis.
Commissioning Tests for an Experimental Study of Steam Generator Tube Loading During Blowdown
Authors: Hamouda Ouajih , Weaver David S. , Riznic Jovica
Published: January 2014

The goal of this research is to improve our understanding of the effects of a postulated Main Steam-Line Break on the transient loading of nuclear steam generator tubes. The analysis of this problem deals with the complex coupling of rapid transient two-phase flow dynamics and fluid-structural loading processes. A main concern of nuclear reactor safety is to ensure that radioactive materials produced by nuclear fission are safely contained. This type of accident produces a ‘blowdown’ in which the pressurised water in the steam generator is boiled off in a few seconds. The resulting transient loading on the steam generator tubing could lead to their rupture, resulting in the release of radioactive materials out of containment. A better understanding of this phenomenon will permit the development of improved design tools to ensure steam generator safety in the event of such an accident. This paper presents a work in progress, describing the purpose-built experimental facility and a summary of commissioning results, including an evaluation of the instrumentation and data collection methodology. The final results of this research will provide physical insights and guidance for the development of predictive modelling tools.
Assembler Qualification and General Revisions for ASME PCC-1-2013
Authors: Brown Warren , Neely Clyde , Rodery Clay
Published: January 2014

The purpose of this paper is to outline the final approved requirements for assembler qualification that will be published in ASME PCC-1-2013 Appendix A. A brief overview of the requirements and a more detailed look at the intended method of implementation of the requirements by industry are examined. In addition, a series of more general updates and corrections were made to the body of PCC-1, which will be included in the 2013 version. These changes are also briefly outlined within this paper, for the information of the user of ASME PCC-1.
Development of a Residual Stress Evaluation Technique by the Combined Use of Surface Strain Measurements Under the Spherical Indentation Method
Authors: Ozawa Norihiko , Yoshizawa Tomoaki , Watanabe Yutaka , Shoji Tetsuo
Published: January 2014

In this research, a technique was developed for quantitatively evaluating the amount and distribution of tensile and compressive residual stresses by the combined use of strain measurements under the spherical indentation loading together with the finite element method (FEM). When the spherical indentation is applied to the top surface of a welded plate, the elastic strain at an optimized position near the indentation is measured by strain gauges, where the residual and applied indentation stresses are largely superposed. In order to analyze the residual stresses, FEM analysis was conducted to establish the relationship between the elastic strain adjacent to the indentation and the indentation pressure for plates subjected to various uniform tensile and compressive stresses. The critical indentation load was identified, which maximizes the difference between the tensile and compressive residual stresses. A strain energy term (U*) is newly introduced by integrating along the trajectory between the indentation pressure and the elastic strain in a range from 0 to maximum pressure. The application of this technique could contribute to improved reliability in welded parts.
Evaluation of Nonlinear Damping Properties of Magnetorheological Gels Under Shear Loading
Authors: Shibuya Yotsugi , Nasuno Hiroshi , Sakurai Hirohisa , Sunakoda Katsuaki
Published: January 2014

Rheological properties of magnetorheological gels can be changed reversibly by applied magnetic fields. Magnetorheological gels with different material system are characterized the dynamic response of the material by shearing test in magnetic field. Nonlinear behavior is observed in the dynamic response of the material. To understand mechanism of the behavior, dynamic properties of magnetorheological gels are evaluated by experiment and nonlinear viscoelastic model. Magnetorheological gels used in this study consist of three types of paramagnetic particles and a cyclic-poly-siloxane gel matrix. Three material systems of magnetic particles are chosen: Fe-Si-Ni, Si-Fe and Fe-Si-B-Cr types. Shear testing is conducted in magnetic field 0mT, 105mT and 211mT. The stress-strain response under shear deformation is characterized by non-ellipsoidal hysteresis loop due to nonlinearity of the response. To identify the nonlinear properties, analysis in frequency domain is applied to identify the dynamic response of the material. Nonlinear viscoelastic model with high order components is made and phenomenon of the non-ellipsoidal hysteresis loop in the stress-strain relation and damping properties are illustrated.
Study on Piping Response Under Multiple Excitation: Part 1 — Triple Shaking Table Test of Piping Having Three-Supporting Points
Authors: Watakabe Tomoyoshi , Kaneko Naoaki , Aida Shigekazu , Otani Akihito , Moriizumi Makoto , Tsukimori Kazuyuki , Kitamura Seiji
Published: January 2014

The piping in a nuclear power plant is laid across multiple floors of a single building or two buildings, which are supported at many points. As the piping is excited by multiple inputs from the supporting points during an earthquake, seismic response analysis by multiple excitations is needed to obtain the exact seismic response of the piping. However, few experiments involving such multiple excitations have been performed to verify the validity of multiple excitation analysis. Therefore, analysis of the seismic design of piping in Japan is performed by the enveloped Floor Response Spectrum (FRS), which covers all floor response spectra at all supporting points. The piping response estimated by enveloped FRS is conservative in most cases compared with the actual seismic response by multiple excitations. To perform rational seismic design and evaluation, it is important to investigate the seismic response by multiple excitations and verify the validity of the analysis method by multiple-excitation test.

This paper reports on the result of the shaking test using triple uni-axial shaking tables and a 3-dimensional piping model (89.1mm in diameter and 5.5mm thickness). The piping model was fixed to three shaking tables, meaning three. Different inputs were possible. By the shaking test, dynamic behavior under multiple excitations was confirmed, and data to verify multiple-excitation analysis was obtained.
Numerical Simulation of Thermal Stratification in the Upper Plenum of Fast Reactor
Authors: Choi Seok-Ki , Lee Tae-Ho
Published: January 2014

A numerical analysis of the thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained, and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for the steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (∼300 seconds). However, the transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A near homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates.
Damage Process Compared to the Design Standard of the Elbow Subjected to In-Plane Cyclic Bending Load
Authors: Nakamura Izumi , Otani Akihito , Shiratori Masaki
Published: January 2014

Fatigue failure accompanied by ratchet deformation is well known as one of the failure modes of pressurized pipes under high-level cyclic load. In this research, the process of failure of such pipes was investigated based on the experimental result in which an elbow pipe failed by cyclic input of displacement. The strain behavior, moment-deflection relationship, and observed damage were compared with the stress level used in the seismic design of the piping system. As a result, no damage was detected and the moment-deflection relationship remained almost linear within the primary stress intensity limit and the primary plus secondary stress intensity range limit of 3Sm. In the experiment, visible damage was detected at the applied load levels of approximately 5∼6.6Sm of the primary stress intensity. The test results showed that there is a certain time margin before actual failure occurs to piping systems, compared with its designed stress limitation.
Seismic Safety Capacity of a Piping System With Pipe Supports Based on the Shake Table Test
Authors: Nakamura Izumi
Published: January 2014

It is well known that the seismic safety capacity of a piping system itself is considerably high compared to the design limitation from the various preceding studies. But most of the preceding studies focused on the seismic capacity of a piping system without other elements as supports, and the safety capacity may be reduced if the failure at supports, nozzles, or flange connections were precedent to the failure at the body of pipe. Therefore the shake table test on the piping system model with supports was conducted. The piping system model used in the shake table test had three supports, a tank, a valve, and flange connections. Excitations were conducted at several input acceleration intensity, and the response characteristics and the failure mode of the piping system were obtained. The failure mode of the piping system model was the broken damage at a pipe support, and after that the leakage at a flange connection occurred. Though the piping system was damaged at pipe supports, it was shown that the piping system model had a certain seismic capacity compared to the design limitation.
Development of Guideline for Prediction of Inelastic Strain for Creep-Fatigue Evaluation
Authors: Watanabe Osamu , Kobayashi Ken-ichi , Nakamura Kyotada
Published: January 2014

Cyclic thermal and mechanical loads are frequently applied to power plants during their service lives due to the regular operation of start-up and shutdown. Design or actual lives of these high temperature machines and structures have been mainly dominated by the creep-fatigue failure life. Since most of these failures happen at limited local area, namely, it may happen at the geometrical or material discontinuities in structures or components, the detail inelastic analyses with a conservative margin are required at the design and maintenance. However, much time and colossal effort should be avoided at the stage of development to reduce the total cost of designing because the design changes many times until the final configuration is fixed. Many materials in the high temperature components are subjected to inelastic behaviors; plastic or creep strain always cause in the components. In the computational analyses such as Finite Element Analyses, constitutive equations of both plasticity and creep affect analytical results. Neuber’s rule is employed in the present design code to achieve the simplified design of component but its result sometimes provides more conservative margin. Stress Redistribution Locus (Hereinafter denoted as SRL) method is a simplified inelastic analysis and was developed in Japan. ETD committee in HPI has studied its applicability to basic problems and actual components.
Effect of Strain Amplitudes and Mean Strain Values on Fatigue Life at Elevated Temperature
Authors: Watanabe Shin-ichi , Imamura Koh-ichi , Watanabe Osamu , Matsuda Akihiro
Published: January 2014

This paper shows randomness effects of loading amplitude and mean value of displacement-controlled loading history for perforated plates made of SUS304 stainless steel at elevated temperature of 550°C. Under the random wave of strain amplitude, the fracture behavior at elevated temperature environment is clarified by measuring the load-deflection curve at all cycles. The data of experiments were evaluated by Miner’s rule, which has been established as an evaluation method for load variation problem. Number of cycles to fracture is compared to show the good agreement with the Best Fit Fatigue curve (BFF). Peak count method also was used in calculating frequency of the strain in order to evaluate Miner’s rule, and the local strain concentration is calculated based on Stress Redistribution Locus (SRL) method. The other object of this study is to evaluate effect of mean value of strain in loading diagram on fatigue life. The mean strain were used for the cases of R = −0.0, −0.2, −0.4, −0.8 and −1.0. The crack length is measured by using photographs with the CCD video camera at a constant frequency. From the measurement, it is found that the number of cycles to failure is reduced when the absolute of value of mean strain is decreased. And cracks develop at both sides around the hole, but the growth of each crack may not be symmetric. By using these inelastic strain amplitude and crack initiation cycle, the experimented results are shown at the present study.
Relevance of a Size Effect Correction on a Minimum Toughness Value in the Ductile-to-Brittle Transition of Ferritic Steel to Study the French PWR RPV Resistance
Authors: Delvallée-Nunio Isabelle , Balestreri François
Published: January 2014

The integrity of Reactor Pressure Vessel (RPV) which ensures radioactivity confinement is reevaluated regularly to take into account updated knowledge and to verify the high level of safety required for this component. The French 900-MWe RPV integrity demonstration was reviewed by the French Safety Authority (ASN) and the Institute for Radiological Protection and Nuclear Safety (IRSN).

This paper focuses on the validity of the fracture criterion used in this demonstration realized by the operator.

In the RPV operating temperature range, ferritic steel can have a ductile-to-brittle behaviour due to irradiation embrittlement. In this range, toughness results from normalized test specimens exhibit a size effect that could be related to the crack length. According to this, the operator has considered that the toughness of the RPV containing a given crack is equal to the minimum toughness defined on the RCC-M curve —similar to the ASME curve— reduced by a factor function of the crack length. For IRSN, this criterion is not relevant. This conclusion is based on the statistical analysis of toughness results available in the literature which shows that although taking into account a crack length correction is relevant on the average toughness, it is not the case for the minimum toughness which is the value used in the mechanical analysis: There is no size effect on the minimal toughness. Following the IRSN’s recommendation, the RPV service ability of the 900-MWe reactors has been demonstrated by the operator without applying a crack length correction on the toughness.
Effect of Strain Rate and Hold Time in Creep-Fatigue Test
Authors: Kojima Masakazu , Funai Madoka , Dozaki Takashi , Watanabe Osamu , Matsuda Akihiro
Published: January 2014

The present paper shows the two experimental results for creep-fatigue interaction effects of perforated plate at elevated temperature. (1) The loading history is assumed to be triangle form in fatigue tests, and that in creep-fatigue loading history, the loading rate from compressive strain to tensile strain is assumed to be constant, which vary from fast rate to slow rate in 5 types of strain rate. The slow strain rate loading includes the creep effects to reduce the life span, which is shown to be predicted if the constant loading assumption is assumed. (2) The holding time effect is also investigated. The tensile strain is held to be constant, and holding time is elongated in the present experiments, which is investigated by the fracture analysis.
Instability of a Simply-Supported Cylinder Subjected to Annular Flow Over a Finite-Length at its Mid-Length
Authors: Kang Heung Seok , Lee Kang Hee , Mureithi Njuki W.
Published: January 2014

A few analytical models for a simply-supported cylinder subjected to a concentric annular flow have been developed considering small perturbations in the flow components. The flow perturbation is believed to play a key role in causing instabilities or reducing the effective tube damping. However, it is generally accepted that there is no dynamic instability of a simply-supported cylinder subjected to concentric annular flows; the dynamic instability may materialize only with a very flexible rod where traveling wave solutions are expected. The dynamic behavior of a concentric annular flow in a finite-length-narrow gap at the mid-span of a cylinder is studied to investigate the possibility of a dynamic instability in the case of a simply-supported cylinder. In this study, typically used stainless steel tubing and geometry in engineering application are applied with some fluid boundary conditions at the finite-length-narrow gap such as a contraction entrance and a diffuser exit. The research results from this study are as follows: (1) determination of an analytical solution for tube dynamics in terms of fluid boundary conditions such as contraction loss at the entrance and pressure recovery at the exit of the finite-length-annular gap, (2) confirmation of the effect of leakage-flow to system dynamics, and (3) confirmation of flutter instability (negative damping type) at the fluid boundary conditions.
Study on Plastic Collapse Load of Steel Elliptical Heads Under Internal Pressure
Authors: Sun Liang , Deng Guide , Zhao Jiufeng
Published: January 2014

A general formula for plastic collapse load of elliptical heads under internal pressure is useful in plastic collapse design and integrity assessment of pressure vessels. Plastic collapse load of steel elliptical heads with different shapes and thickness was computed by finite element analysis using elastic-perfectly plastic constitutive model, and a formula with maximum relative error less than 6% was derived from the numerical results. The formula is a function of the yield strength of materials, the ratio of major axis Di to minor axis 2hi and that of outer diameter Do to inner diameter Di, and is applicable to steel elliptical heads with Di/2hi within 1–2.6 and Do/Di within 1.001–1.300.
Estimates of Plastic J-Integral and Crack Opening Displacement Considering Circumferential Transition Crack From Surface to Through-Wall Crack in Cylinder
Authors: Cho Doo-Ho , Choi Young-Hwan , Surh Han-Beom , Choi Jae-Boong , Huh Nam-Su , Shim Do-Jun
Published: January 2014

The present paper provides the enhanced estimation of plastic J-integral and crack opening displacement (COD) for circumferential transition crack from surface to through-wall crack in cylinder based on detailed finite element analysis. The effects of circumferential transition crack on plastic J-integral and crack opening displacement have been systematically investigated for practical ranges of cylinder geometries and materials of interest. Then, the plastic influence functions (h1, h2) employed in the GE/EPRI method have been proposed to quantify those effects on plastic J-integral and COD. Furthermore, the J-integral and COD estimations based on the reference stress method using optimized reference load have also been introduced for circumferential non-idealized TWC in cylinder. Then, in order to gain the confidence in the proposed methods, the results from those proposed estimates were compared with elastic-plastic FE results by using actual stress-strain data and Ramberg-Osgood fit constants for TP 316 stainless steel. The present results can be expected to apply on various structure integrity assessments and to accurate plastic J-integral and COD estimation for circumferential non-idealized TWC in cylinder.
Uncertainty Analysis of a Cross-Ply Composite Cylinder Subject to External Pressure by Convex Modeling
Authors: Radebe Isaac Sfiso , Adali Sarp
Published: January 2014

Quite often the values of the elastic constants of composite materials can be estimated with some error due to manufacturing imperfections, defects and misalignments. This introduces some level of uncertainty in the computation of the buckling loads, frequencies, etc. In the present study an ellipsoidal convex model is employed to study the buckling of long cross-ply cylinders subject to external pressure with the material properties displaying uncertain-but-bounded variations around their nominal values. This approach determines the lowest buckling pressure and as such provides a conservative answer. Method of Lagrange multipliers is applied to compute the worst-case variations of the elastic constants and an explicit expression is obtained for the critical buckling pressure for a given level of uncertainty. Expressions for the relative sensitivities of the buckling pressure to uncertain elastic constants are derived.
Experimental Fatigue Evaluation of Aluminum Brazed Plate Fin Heat Exchangers
Authors: Hölzl Reinhold , Flüggen Rainer
Published: January 2014

For the verification of a finite element based calculation procedure for the strength and fatigue design of aluminum brazed Plate Fin Heat Exchangers (PFHE) an extensive experimental investigation program was planned and executed.

In the first step high temperature loadings as single events were applied to the PFHEs to recognize, whether damage (a leak) can be produced by a severe single loading. After various tests on different geometries the investigations were enlarged to thermal cycling tests on small PFHEs until leaks were detected.

The tests were executed with three blocks in parallel to cover a statistical influence and the tests were repeated with three new blocks under identical conditions. All six blocks gave nearly the same number of load cycles until first detection of leaks. In addition three blocks of the same geometry were loaded with lower thermal stress, giving higher load cycle numbers until a leak occurred.

The experimentally determined cycle numbers were compared to calculated cycle numbers out of the finite element modeling and showed very good agreement. Those tests and comparisons are a strong basis for fatigue and lifetime considerations on large scale PFHEs in the process industry.
Research and Development of Distributed Multistage TMD for Long Period Structure Using Coil Spring
Authors: Furuya Osamu , Kurabayashi Hiroshi
Published: January 2014

The response control techniques are mainly divided into two categories. One is a storey installation damper type using a damping element such as oil, elasto-plastic, viscoelastic, and so on. The other is an additional mass damper type such as a active and passive type tuned mass damper including a hybrid type. The device configuration of later damper type becomes larger into high-rise structure and long natural period structure because of increase of additional mass in the same case of mass ratio and necessary design stroke of moving mass. In generally, however, it is desired to be a compact size with a same vibration attenuation performance because of that there is a limitation of installation space for the device, and also it is important to be realize the application of the damper with low cost and with a necessary specification for damper performance. This study has been conducted to develop the passive tuned mass damper system using coil spring for long period structure considering a design indexes such as compact size, low cost and robustness. Although a coil spring has been well used by the tuned mass damper system as one way of solving a cost problem and performance stability, the problem of compact size still remains in case of the application to a long period structure. Multistage type is therefore proposed to the system in this time. Furthermore, the distributed TMD theory is applied to the system for robustness of the system. This paper summarizes from a basic theory to the application of proposed device to the real scale long period structure.
Residual Stress Measurement of a Hipped Bonded Valve Seat Using the Contour Method
Authors: Hosseinzadeh Foroogh , Bouchard P. John
Published: January 2014

The work presented in this paper explores the through-thickness distribution of residual stresses in a valve seat of complex geometry where a Tristelle insert was HIP-bonded to a Type 316 stainless steel body. The contour method was conducted in a novel way to measure a full cross-sectional map of hoop stress at an axial-radial plane along the length of the valve seat. Special care was applied to control and optimise the cutting step of the measurement technique in order to produce cut surfaces of high quality thereby minimising potential associated errors in stress. The innovation in the present work was to use sacrificial material to avoid any cutting artefacts introduced by the cutting process. High levels of residual stresses were measured in the region where an insert was HIP-bonded to the main body. The excellent correlation between the stresses measured using the contour and incremental centre hole drilling methods demonstrates the importance of controlling the quality of a contour cut and that care should be taken to avoid cutting artefacts particularly when stresses close to the surface are of interest.
Structural Integrity Evaluation of Reactor Pressure Vessels During PTS Events Using Deterministic and Probabilistic Fracture Mechanics Analysis
Authors: Osakabe Kazuya , Nishikawa Hiroyuki , Masaki Koichi , Katsuyama Jinya , Onizawa Kunio
Published: January 2014

To assess the structural integrity of reactor vessels (RVs) during pressurized thermal shock (PTS) events, a deterministic fracture mechanics (DFM) approach has been widely used such as the procedure in JEAC4206-2007. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of RV has become attractive recently because uncertainties related to input parameters can be incorporated rationally. The probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. In this paper, in order to verify the applicability of a PFM method to JEAC4206-2007, deterministic and probabilistic analyses have been performed, and the effects of initial crack size defined in JEAC4206-2007 on the temperature margin obtained from DFM and the probability of crack initiation obtained from PFM have been evaluated. With regard to the PTS event variation, a stuck open valve scenario (SO) has been considered in addition to large- and small-break loss of coolant accident (LBLOCA, SBLOCA) and main steam line break (MSLB).
Research on the Temperature Model of CNG Cylinders for Vehicle During Bonfire Test
Authors: Ma Hongbo , Xu Weipu , Li Qian , Luo Xiaoming
Published: January 2014

The bonfire test is an important method to verify the active of pressure relief device (PRD) of compressed natural gas (CNG) cylinders for vehicle. However, the change law of the surface temperature of the CNG cylinders during bonfire test is still unknown. In order to make sure the requirement of surface temperature, a dynamical model is proposed to predict the surface temperature of the CNG cylinders during bonfire test. By comparing the predicted value of this model with the practical value gauged by thermocouples, the effectiveness of the dynamical model is verified.
Improving the Traditional RCA Methodology to Design a Most Efficient and Reliable Valve for LDPE Hypercompressors Leveraging Experimental Data From Test Bench Simulation: A Real Case Study
Authors: Maggi Carmelo , Tognarelli Leonardo , Bagagli Riccardo , Wojnar Jan
Published: January 2014

The behavior of the valves of Hypercompressors on LDPE plants is challenging to predict because it depends on many factors and often the expected and macroscopic gas parameters, such as pressure, temperature and gas composition are not sufficient to properly evaluate the valve behavior in the field.

In fact valve operation is highly dependent on local phenomena such as localized pressure losses and presence of vortexes which are in turn influenced by the geometry of the valve and by its behavior.

To better understand all these phenomena it is needed to characterize these valves through experimental tests aimed at defining, with a good accuracy, the valve dimensionless parameters Cd (drag coefficient) and Ks (flow coefficient) as a function of the geometry of the valve itself.

If the coefficients Cd and Ks are not accurate, the expected behavior of the valve may be completely different from the evidence of the field and could not properly explain certain types of failure modes.

With a more accurate evaluation of Cd and Ks, some types of damage which in first hypothesis would seem caused by factors external to the valve, in reality are proven to be intrinsically related to valve design and often dependent on valve malfunctioning.

As a final step, through to a deep understanding of the valve behavior in the field an improvement of valve reliability and efficiency can be achieved through optimization of the design for various operating conditions.
A Round Robin Program of Master Curve Evaluation Using Miniature C(T) Specimens — 2nd Report: Fracture Toughness Comparison in Specified Loading Rate Condition
Authors: Yamamoto Masato , Onizawa Kunio , Yoshimoto Kentaro , Ogawa Takuya , Mabuchi Yasuhiro , Miura Naoki
Published: January 2014

Master Curve approach for the fracture toughness evaluation is expected to be a powerful tool to ensure the reliability of long term used RPV steels. In order to get sufficient number of data for the Master curve approach coexistent with the present surveillance program for RPVs, the utilization of miniature specimens, which can be taken from broken halves of surveillance Charpy specimens, is important. CRIEPI had developed the test technique for the miniature C(T) specimens (Mini-CT), whose dimensions are 4 × 10 × 10 mm, and verified the basic applicability of the Master Curve approach by means of Mini-CT and larger specimens for the determination of fracture toughness of typical Japanese RPV steels. A round robin program was organized with the participation of a university, industries and a government institute in Japan. The first-round test results (PVP2012-78661[1]) with limited number of reference temperature To data points indicated the possible loading rate dK/dt dependence in To. However, increasing number of data points in second-round test, which was conducted in specified loading rate of 0.5 MPa m0.5 /sec, ensures that there is no clue of such a remarkable dK/dt dependency. Concerning the effect of large plastic deformation on dK/dt, dK/dt calculated by several definitions were compared with each other. Maximum one order difference was found between dK/dts with and without consideration of plastic deformation. dK/dt - T0 relationships showed similar amount of scatter in T0 regardless of dK/dt definitions. Difference in dK/dt definition seems less effective on scatter of T0 in the present results.
Simulating Residual Stresses Using a Modified Wedge-Loaded Compact Tension Specimen
Authors: Kapadia P. , Zhou H. , Davies C. M. , Wimpory R. C. , Nikbin K. M.
Published: January 2014

Residual stresses are induced in components when fabrication processes produce internal stresses or local deformation and cause accelerated creep damage and cracking during service at elevated temperatures. A method of inducing residual stresses in laboratory fracture specimens is proposed where an oversized wedge is inserted into the crack mouth of a compact tension, C(T), type specimen. In this way the extent of internal stresses can be controlled in order to minimise the level of crack tip plasticity which inherently reduces the remaining strain to failure. Numerical simulations of wedge insertion into specimens made of 316H austenitic stainless steel have been developed to calibrate the wedge insertion process. These models have been experimentally validated using surface strains measured during the wedge insertion, using Digital Image Correlation (DIC), and Neutron Diffraction (ND) measurements. The validated Finite Element (FE) model is used to determine the wedge insertion depth required to maximise the residual stresses without causing significant crack tip plasticity. The validated numerical simulation is used to determine the wedge insertion depths of further wedge-loaded C(T) specimens made from uniformly pre-compressed 316H stainless steel. The reduced creep ductility of this material increases the rate of crack growth under creep conditions. This method of inducing residual stresses with limited crack tip plasticity allows creep crack growth under simulated secondary loading conditions to be investigated without the influence of non-uniform creep ductility caused by work hardening.
Limit Analysis Interaction Formulae for Thin-Walled and Moderately Thick-Walled Pipes Subjected to Pressure and Pipe Bending
Authors: Möller Mikael , Hallin Lars , Veljkovic Milan
Published: January 2014

The primary stress pipe equations in the ASME code, subsection III, Ref. [1], and similar codes add stress contributions from pressure and bending and impose a limit on this sum, while a limit on the pressure hoop stress is imposed separately. The equations constitute interaction formulae for the resistance of the pipe cross-section to the combined action of pressure and bending, similar to the limits on primary membrane and primary membrane plus primary bending stress for a rectangular section. For the latter, an analytical limit load solution is found e.g. in Ref. [2]. In this paper, closed-form limit analysis collapse interaction formulas are derived by means of limit analysis for thin-walled as well as moderately thick-walled straight pipes subjected to internal pressure and pipe bending. The analytical solutions are confirmed by means of non-linear finite element analysis. Moreover, the resistance to combined loading as predicted from the derived interaction formulas is compared to the resistance according to the ASME code primary stress pipe equations and the deviations are elaborated.
Crack Arrest Test Results of Unirradiated and Irradiated German RPV Steels
Authors: Obermeier Florian , Barthelmes Julia , Keim Elisabeth , Hein Hieronymus , Schnabel Hilmar , Kaiser Marco
Published: January 2014

In the CARISMA[1] and CARINA[2] projects comprehensive tensile, Charpy-impact and fracture toughness tests were performed for unirradiated and irradiated original reactor pressure vessel (RPV) steel specimens from German pressurized water reactors (PWR) up to neutron fluences in the range of 60 operational years and beyond.

In addition, crack arrest fracture toughness tests were performed to demonstrate the crack arrest behavior of the materials. To determine the crack arrest properties of ferritic steels, the designated test method according to ASTM E1221 [3] was used. However, in particular for irradiated reactor pressure vessel materials with higher irradiation embrittlement, the prescribed standard test specimen does not always provide adequate test results. During starter notch preparation annealing effects occurred in the heat affected zone (HAZ) of the brittle weld of the starter notch causing crack arrest in the HAZ after unstable crack initiation. Therefore a modified test method to perform crack arrest tests with so called duplex specimens was investigated.

In this paper this modified method and the test results of five base and four weld metals with a fluence up to 4,69E+19 cm−2 (E >1 MeV) are discussed.

The available test results show that the duplex specimen is an appropriate alternative to the standard compact crack arrest (CCA) specimen. The measured KIa fracture toughness data are enveloped by the “lower bound” of the ASME KIa-curve indexed with RTNDTj or TKIa but not all data are enveloped by indexing the “lower bound” curve with RTT0 like described in the ASME Code Case N-629 [4]. Furthermore correlations of the crack arrest test results with Charpy-impact and fracture toughness test results will be shown.
Singing Mitigation in Corrugated Tubes With Liquid Injection
Authors: Belfroid S. P. C. , Golliard J. , Vijlbrief O.
Published: January 2014

Pipes with a corrugated inner surface, as used in flexible pipes for gas production and transport, can generate a high amplitude tonal sound (singing). Small quantities of liquid can result in a significant amplitude reduction or total mitigation of this sound production. To evaluate different potential mechanisms, liquid injection tests were done in both a horizontal and vertical small scale (49 mm) setup including high speed camera recordings using a transparent corrugated section.

The singing amplitude decreased linearly with the liquid injection rate for both orientations, although the effect in the vertical setup was even faster. Liquid injection resulted also in higher onset velocities.

The video recordings showed partially filled corrugations. For horizontal corrugations, liquid crept upward in the corrugations. In the vertical test, liquid accumulated at the upward edge with intermitted liquid spill over to downstream corrugations. The liquid fill up did not change significantly with higher liquid loads. Taking the fill-up grade and additional damping into account, a match could be made between the measured singing amplitude and a predicted singing amplitude as function of liquid rate. However, no model has been found to predict the liquid fill-up yet.
Experimental and Numerical Investigation of Pressurized Pipe Elbows Under Strong Cyclic Loading
Authors: Varelis George E. , Ferino Jan , Karamanos Spyros A. , Lucci Antonio , Demofonti Giuseppe
Published: January 2014

The present work examines the behavior of pipe elbows subjected to strong cyclic in-plane bending loading in the presence of internal pressure. In the first part of this work the experimental procedure is presented in detail. The tests are conducted in a constant amplitude displacement-controlled mode resulting to failures in the low-cycle fatigue range. The overall behavior of each tested specimen, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. Different internal pressure levels are used in order to examine their effect on the fatigue life of the specimens.

The above experimental investigation is supported by rigorous finite element analysis. Using detailed dimensional measurements and material testing obtained prior to specimen testing, detailed numerical models are developed to simulate the conducted experiments. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the local strain development at the critical part of the elbow where cracking occurs. Finally, the results of the present investigation are compared with available design provisions in terms of both ultimate capacity and low-cycle fatigue.
Numerical and Experimental Testing of Composite Rings for Reciprocating Compressor Valves
Authors: Annicchiarico Claudio , Babbini Alberto , Capitani Renzo , Tozzi Pierluigi
Published: January 2014

Valves are one of the most critical class of components for the reliability of reciprocating compressors. Many failures of reciprocating compressor valves are due to valve ring failure. Investigating the failure mode of rings is complicated because of the ring composite material properties, which randomly and locally range from orthotropic to anisotropic due to the random disposition of the reinforcement, usually consisting of short fibers.

In this paper, a cooperation between GE Oil & Gas and the University of Florence, the results of a numerical simulation campaign will be presented, along with its correlation with the experimental evidence arising from a purpose-built test rig. This work guided the design of a new material for rings, whose characteristics have been tailored based on the results of this experimental and numerical campaign.
Mesh Convergence Studies for Thick Shell Elements Developed by the ASME Special Working Group on Computational Modeling
Authors: Molitoris David P. , Bjorkman Gordon S. , Tso Chi-Fung , Yaksh Michael
Published: January 2014

The ASME Special Working Group on Computational Modeling for Explicit Dynamics was founded in August 2008 for the purpose of creating a quantitative guidance document for the development of finite element models used to analyze energy-limited events using explicit dynamics software. This document will be referenced in the ASME Code Section III, Division 3 and the next revision of NRC Regulatory Guide 7.6 as a means by which the quality of a finite element model may be judged. One portion of the document will be devoted to a series of element convergence studies that can aid designers in establishing the mesh refinement requirements necessary to achieve accurate results for a variety of different element types in regions of high plastic strain. These convergence studies will also aid reviewers in evaluating the quality of a finite element model and the apparent accuracy of its results.

In this paper, the authors present the results of a convergence study for an impulsively loaded propped cantilever beam constructed of LS-DYNA thick shell elements using both reduced and selectively reduced integration. A large load is applied to produce large deformations and large plastic strains in the beam. The deformation and plastic strain results are then compared to similar results obtained using thin shell elements and hexahedral elements for the beam mesh.