bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady-State Response Evaluation of Shape Memory Alloy Wire Under Resistive Heating Using a Newly Developed Element-Free Galerkin Meshless Method
Authors: Ghazavi A. , Sepiani H. A. , Ebrahimi F. , Rastgo A.
Published: July 2008

The studies on shape memory alloys show their much extended application field. Nowadays, many researches are carried out to solve constitutive equations of various models of SMAs. In this research, a macro-scale, phenomenological constitutive model for SMAs is used in conjunction with energy balance equations to study the evolution of temperature and deformation profiles seen in SMA wires under specific thermal and mechanical boundary conditions. In this way, the general fully-coupled thermomechanical formula for resistive heating of an SMA wire-initial detwined martensite leads to strain recovery on heating is used and numerical results are obtained with use of “Meshless” method. Comparisons have been made between the results predicted by proposed EFG method and available reference solutions in the literature, generated either analytically or numerically. A good agreement is obtained between the achieved results and the literature.
Bolt Anti-Seize Performance in a Process Plant Environment
Authors: Brown Warren , Marchand Luc , LaFrance Thierry
Published: July 2008

This paper details recent testing that was performed as an extension of earlier work on nut factor and high temperature Break-out performance of selected anti-seize products. Comparison is made between previous results obtained on C-Si bolts (ASTM A193 B7) with more recent tests on 316 Stainless Steel bolts (ASTM A193 B8M). The bolt nut factor versus temperature and the required Breakout torque after one week at elevated temperature are detailed. In addition, common theories regarding the unsuitability of anti-seize containing graphite on stainless steel and the use of milk of magnesia as an anti-seize are quantitatively tested by comparison with standard anti-seize products. The test methods used are designed to closely mimic actual bolt assembly in a process plant environment. The paper, therefore, presents useful information that will enable more accurate assembly of bolted flanged joints on pressure vessels and piping in any process plant environment.
Evaluation of Contact Stress in Stuffing Box Packings
Authors: Diany Mohammed , Bouzid Abel-Hakim
Published: July 2008

The evaluation of the radial contact stress in a gland packing and its distribution in the axial direction at both the stem and housing interfaces is of major importance when predicting leakage. The method that uses direct measurement of this stress through the use of strain gages installed at the outer surface of the housing is not straightforward. The complexity of the problem is caused by the complex axisymmetric problem with a load variation in the axial direction. The use of analytical and numerical FE modeling can be feasible. This paper examines the contact stress distribution in a gland packing. It shows how strains measurements fixed outside a gland housing coupled with FEM could be used to characterize the compression capacity of packings. The proposed method is used in a stuffing box packing rig under development.
Determination of Optimum Ambient Temperature Re-Torque Dwell Period for PTFE Based Gaskets
Authors: Waterland Alfred F. , Frew James E. B.
Published: July 2008

Gaskets must receive adequate, minimum assembly stress in order to develop the required level of joint tightness. Furthermore, operating stress levels must be maintained above a certain threshold throughout the service life of the connection in order to insure continued joint reliability and tightness (low leakage) performance. PTFE based gasket materials can exhibit significant initial and/or continued compressive flow, which translates into a loss of bolt load. Manufacturers and users of PTFE based gasket materials are advised to re-torque these connections, often after a 24 hour dwell period. The following research was conducted in order to determine if the specific PTFE material selected can influence the need for bolt re-torque, and additionally to determine if the re-torque dwell period can be reduced to a time period less than 24 hours.
Risk-Based Inspection of Relief Valves
Authors: Camburn John , Saunders Kenneth L.
Published: July 2008

Historical methodologies for routine inspections of relief valves involve removing relief valves from service, inspecting, testing and repairing them as needed at some interval that was the same for most or all relief valves. Intuitively, it did not seem right to take this approach. Not all relief valves experience the same severity of service (probability of failure) and not all relief valves are in equally critical service where a failure of the relief valve to perform as intended would have the same effect (consequence of failure). However, until a methodology was developed to provide a logical and consistent approach, it was the best practice available. This paper will discuss a risk based inspection methodology developed for relief valves installed in industrial facilities and its application to two plants. Several benefits have resulted from the application of the risk based inspection program. Inspection resources are now more focused on relief valves that have a higher probability of failure or that are in a more critical service. Inspection intervals for these relief valves, on average, have been reduced so that they will be inspected on a more frequent basis. For the entire population of relief valves, however, the average inspection interval has increased which means that additional inspection resources will now be available to be focused on other critical areas of the plant. Thus producing a safer work environment and a decreased likelihood of a release to the atmosphere.
Test Programs for Degraded Core Shroud and PLR Piping: Simulated Crack Models and Input Seismic Waves for Shaking Test
Authors: Suzuki Kenichi , Kawauchi Hidefumi , Abe Hiroshi
Published: July 2008

Since the age-related degradation of structures and components in nuclear power plants has been a key issue regarding assessments of seismic safety, the Japan Nuclear Energy Safety Organization (JNES) initiated seismic test programs in fiscal 2004 for the degraded core shroud and primary loop recirculation (PLR) system piping used in old BWR plants. The objectives were to: i) obtain a better understanding of the vibration characteristics and seismic strength of degraded structures and components having cracks due to aging, ii) ensure a margin of seismic design safety by considering age-related cracking, and iii) verify the JSME Code Rules on Fitness-for-Service for Nuclear Power Plants in Japan. Plans were made to test the components of the core shroud and PLR system piping under quasi-static displacement control of monotonous and cyclic load conditions. Plans were also made to test combined components on a shaking table by using a 1/2.5-scale core shroud model and an approximately 1/3-scale PLR piping model. All test models were designed to contain simulated cracking due to aging, involving cracks assumed to have the maximum allowable size according to the JSME Code Rules. The input seismic waves were prepared for the combined component tests of the scaled models based on a modified envelope of broadened response spectra of all S2 design seismic waves in Japan. Final evaluation of the simulated crack models and input seismic waves used for the tests will be conducted in fiscal 2005.
Deployment and Operation of the ES-3100 Type B Shipping Container
Authors: Arbital Jeffrey G. , Tousley Dean R. , Miller Dennis B.
Published: July 2008

The U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) is shipping, for disposition purposes, bulk quantities of fissile materials, primarily highly enriched uranium (HEU). The U.S. Department of Transportation (DOT) specification 6M container has been the workhorse for NNSA and many other shippers of radioactive material since the 1980s. However, the 6M does not conform to the packaging requirements in the Code of Federal Regulations (10 CFR 71) and, for that reason, is being phased out for use in the DOE secure transportation system by the end of 2006. BWXT Y-12 developed and licensed the ES-3100 container to replace the DOT 6M. The ES-3100 was certified by the Nuclear Regulatory Commission (NRC) in April 2006. The process of deploying the new package began in June 2005 and is planned to be completed in July 2006. The package will be fully operational and completely replace the DOT 6M at the Y-12 National Security Complex (Y-12) by October 2006. This paper reviews the deployment process and the mock loading station that was installed at National Transportation Research Center (NTRC) of Oak Ridge National Laboratory. Specialized equipment, tools, and instrumentation that support the handling and loading operations of the ES-3100 are described in detail. Loading options for other user sites are explored in preparation for deployment of this new state-of-the-art shipping container throughout the DOE complex and the private sector.
Preliminary Results of Stainless Steel Impact Bending Tests
Authors: Snow Spencer D. , Morton D. Keith , Rahl Tommy E. , Blandford Robert K. , Hill Thomas J.
Published: July 2008

Stainless steels are used for the construction of numerous spent nuclear fuel or radioactive material containers that may be subjected to high strains and moderate strain rates during accidental drop events. Mechanical characteristics of these materials under dynamic (impact) loads in the strain rate range of concern are not well documented. However, two previous papers [1, 2] reported on impact tensile testing and analysis results performed at the Idaho National Laboratory using 304L and 316L stainless steel specimens that began the investigation of these characteristics. The goal of the work presented herein is to: (1) add the results of additional tensile impact testing for 304L stainless steel specimens, and (2) show that the application of the strain rate-dependent material curves (determined through that tensile impact testing) to specimens designed to respond in bending during impact loading would yield accurate deformation and strain predictions.
Novel Formulation of the Tightening and Breakaway Torque Components in Threaded Fasteners
Authors: Nassar Sayed A. , Yang Xianjie
Published: July 2008

New formulas are developed for the torque-tension relationship, various torque components, and for the break-away torque values in threaded fastener applications. The 3-D aspects of the lead helix and thread profile angles, the kinetic and static friction coefficients are all taken into account. Two scenarios of the contact pressure between threads and under the turning fastener head are considered; namely, uniform distributed and linearly distributed contact pressure scenarios. The effect of thread pitch, lead helix and thread profile angles, friction coefficients, and the fastener geometry is discussed. Results from the new formulas are compared with the approximate torque-tension relationship provided in the literature. A percent difference analysis indicates that the new formulas provide significant improvement that would enhance the reliability and safety of bolted connections, especially in critical applications.
Asset Management Evaluation: The Key Role of Expert Elicitation
Authors: Bauby C. E. , Haik P. , Remy E. , Ricard B. , Billy F.
Published: July 2008

The life management of a nuclear power plant raises several major issues amongst which ranks the aging management of the key components of the plant, both from a technical and an economic point of view. Decision-makers are thus faced with the need to define the best strategy in order to achieve the best possible performance which requires both a very precise modeling of the plant and a detailed analysis of all risks potentially incurred. In this paper, we wish to provide the reader with an overview of how advanced expert elicitation techniques can help identify, structure, quantify and feed sensitive data into a risk-based information system which can then be used for risk-based asset management evaluation. First we focus on the way knowledge management techniques allow EDF to structure and collect life-cycle management data into knowledge-based information systems. The elicitation of component experts is key, particularly in order to get technical information on the future behavior of the component (“anticipation” of whatever events may occur on the plant). We then detail how expert elicitations allow to quantify the probabilities of occurrence of the events: whether there is feedback data, models or not, expert opinion has to be taken into account and mixed, for instance with Bayesian procedures, to this information. Lastly we describe how the information elicited from experts can help top level decision makers get a transverse, long term view on how life management investment strategy translates into plant availability, avoided costs and improved component durability.
Three-Dimensional Mode Separation to Obtain Stress Intensity Factors
Authors: Gu Pei , Asaro R. J.
Published: July 2008

For mixed-mode loading at a crack tip under small-scale yielding condition, mode I, mode II and mode III stress intensity factors control the crack propagation. This paper discusses three-dimensional mode separation to obtain the three stress intensity factors using the interaction integral approach. The 2D interaction integral approach to obtain mode I and mode II stress intensity factors is derived to 3D arbitrary crack configuration for mode I, mode II and mode III stress intensity factors. The method is implemented in a finite element code using domain integral method and numerical examples show good convergence for the domains around the crack tip. A complete solution for the three stress intensity factors is obtained for a bar with inclined crack face to the cross-section from numerical calculations. The solution for the bar is plotted into curves in terms of a set of non-dimensional parameters for practical engineering purpose. From the solution, mode mixity along the crack front and its implication to the direction of crack propagation is discussed.
Inelastic Analysis of Sealing Characteristics of Flanges With Metal Ring Joint Gasket at Elevated Temperature
Authors: Sato Takuya , Kado Kenichiro
Published: July 2008

In a previous paper(1) presented in 2005 ASME PVP Conference, the authors investigated the elastic plastic behavior of dissimilar material flanges with a metal ring joint gasket operated at elevated temperature using FEA. Case studies were performed to study the effects of load path, material combination and flange size on the contact pressure and the plastic strain distribution in the ring joint gasket. In that paper, the authors concluded that the load path has a large impact on both, the contact pressure and the plastic strain, and, on the other hand, the material combination of the flanges and their size have small effects. In this paper, the authors present further FEA-based investigation on this mechanism. The first issue is the effects of meteorological changes, such as wind velocity, ambient temperature and rain, as is often the case with real energy and process plants. These meteorological changes result in the temperature change of bolts and flanges. The bolt temperature change causes different thermal expansion in the ring joint gasket and the bolts. This may affect the sealing performance. In this paper, the wind velocities were changed to investigate meteorological changes as a typical such change. The second issue is the behavior of the metal ring joint gasket after the second operation cycle. The metal ring joint gaskets are usually replaced after the first operation cycle, i.e., from start up to shut down. However, it is said that all ring joint gaskets are not replaced. In the previous paper, the behavior of the ring joint gasket during the first operation cycle was investigated. Increase of plastic strain in the sequential operation cycles is an important issue in terms of sealing performance. Therefore the behavior of the ring joint gasket in the second operation cycle was investigated. Finally the sealing mechanism and characteristics of this dissimilar material flanges under elevated temperature operation cycles were made clear.
Experimental Evaluation of Screw Thread Loosening in Bolted Joint With Some Parts for Preventing the Loosening Under Transverse Repeated Loadings
Authors: Sawa Toshiyuki , Ishimura Mitsutoshi , Yamanaka Hiroshi
Published: July 2008

In mechanical structures, a lot of bolts and nuts have been used. Sometimes loosening accidents happen in the structures under several types of loadings. Recently, the cause of the screw thread loosening is being elucidated. However, the effect of some parts for preventing the loosening in bolted joints such as spring washer, double nut and so on is not fully elucidated. In this study, the experiments were carried out to measure the reduction of axial bolt force in the bolted joint with some parts for preventing the loosening such as the spring washer, the toothed washer, the double nuts, the eccentric nut, and so on under the transverse repeated loadings. The test machine used was Junker’s type loosening machine. Then, the effects of the washers and some types of nuts are evaluated on the loosening of bolted joints. It is shown that the performance for loosening is getting better as the initial clamping force increases and the effect of the washers is not found on the loosening. However, the effect of eccentric nut is substantial on the loosening. In addition, the loosening tests according to NAS were also carried out. No effect of all the washers mentioned above is found due to NAS testing. Discussion is made on the effect of the parts for preventing the loosening mentioned above.
Improving the Properties of Materials With Laser-Peening: An Overview on French Activities
Authors: Peyre P. , Berthe L. , Fabbro R.
Published: July 2008

Extensive work was carried out in France since 1986 on all the fields relevant to laser-shock processing (or laser-peening), including plasma physics, laser shock-waves detonics, surface modifications (residual stresses ...), and improvement of materials properties such as fatigue, corrosion or wear. The paper aims at presenting an overview on the most recent works about LP, with a special focus on FE modeling aspects for residual stress predictions, on pitting corrosion properties of a 316L steel after LP treatment, and on different fatigue applications, mainly on aluminium alloys. For most of the applications considered, the benefits of LP will be discussed, compared with usual mechanical treatments such as shot-peening.
Fracture Toughness Characterization of Midland Beltline Weld After High Dose of Irradiation
Authors: Sokolov Mikhail A. , Nanstad Randy K.
Published: July 2008

The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory includes a task to investigate the shape of the fracture toughness master curve for reactor pressure vessel steel highly embrittled as a consequence of irradiation exposure, and to examine the ability of the Charpy 41-J shift to predict the fracture toughness shift. As part of this task, a low upper-shelf WF-70 weld obtained from the beltline region of the Midland Unit 1 reactor pressure vessel was characterized in terms of static initiation and Charpy impact toughness in the unirradiated and irradiated conditions. Irradiation of this weld was performed at the University of Michigan Ford Reactor at 288°C to neutron fluence of 3.4×1019 neutron/cm2 in the HSSI irradiation-anneal-reirradiation facility. This reusable facility allowed the irradiation of either virgin or previously irradiated material in a well-controlled temperature regime, including the ability to perform in-situ annealing. This was the last capsule irradiated in this facility before reactor shut down. Thus, the Midland beltline weld was irradiated within the HSSI Program to three fluences — 0.5×1019; 1.0×1019; and 3.4×1019 neutron/cm2. It was anticipated that it would provide an opportunity to address fracture toughness curve shape and Charpy 41-J shift compatibility issues at different levels of embrittlement, including the highest dose considered to be in the range of the current end of life fluence. It was found that the Charpy 41-J shift practically saturated after neutron fluence of 1.0×1019 neutron/cm2. The transition fracture toughness shift after 3.4×1019 neutron/cm2 was only slightly higher than that after 1.0×1019 neutron/cm2. In all cases, transition fracture toughness shifts were lower than predicted by the Regulatory Guide 1.99, Rev. 2 equation.
Flaw Proximity Rules for Parallel Surface Cracks Based on Elastic, Elastic-Plastic Fracture Mechanics and Limit Load Analyses
Authors: Kamaya Masayuki
Published: July 2008

When multiple cracks approach one another, the stress intensity factor, J integral value of cracks and limit load of cracked component are likely to change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks must be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Sec. XI, adjacent cracks are replaced by a coalesced single combined crack if they are located within the distance of half depth of deeper crack. However, the criterion for offset distance is given by an absolute value, although magnitude of the interaction is inevitably dependent on the crack size. In current study, an alternative criterion for the offset distance is examined. The linear-elastic fracture, elastic-plastic fracture and limit load analyses are performed for interacting semi-circular and semi-elliptical surface cracks by using the finite element method under a tensile and bending load. Based on the relationship between fracture strength and relative position of the two cracks, the allowable condition for the offset distance is discussed.
Use of an Offset in Assessing Radiation Embrittlement Data and Predictive Methods
Authors: Soneda Naoki , English Colin , Server William
Published: July 2008

Analyses of reactor pressure vessel (RPV) surveillance data from Charpy V-notch shift results coupled with our latest knowledge of the mechanisms of radiation embrittlement have led to new predictive correlations/models that have a strong technical underpinning. In this paper we examine how well the new CRIEPI embrittlement predicts US RPV surveillance data. Secondly, we note that within the US surveillance data sets there are indications that the data may follow the same form as the predictive models, but the data may be offset by a constant amount (either positive or negative) from the predictive values. This offset can be attributed in some cases to inadequate baseline data. In other cases, there does not appear to be a constant offset, or such an offset is hidden by data scatter. This paper also reviews the potential use of an offset adjustment and focuses on several surveillance datasets for comparisons.
Modelling of Irradiation Embrittlement in the Ductile to Brittle Transition Range for an A508 Pressure Vessel Steel
Authors: Tanguy B. , Besson J. , Bugat S.
Published: July 2008

The aging behavior of structural steels used to manufacture nuclear pressure vessels is surveyed using Charpy V-notch specimens located in capsules inside the pressure vessel. The Charpy data are then used to assess the safety integrity of the structures based on semi-empirical relations relating Charpy impact transition curve shifts and the fracture toughness shifts due to irradiation. Using a computational strategy proposed in [1] which combines a deterministic model for ductile fracture and a statistical description of brittle fracture, this work aims at the prediction of the whole Charpy transition curve of irradiated steels. The actual strain hardening behavior of an A508 Cl.3 steel from the french surveillance program is considered in the simulations, contrarily to a previous work where a shift of the un-irradiated stress-strain curve to higher stress values was considered. Comparison with Charpy energy data for two levels of irradiation shows that irradiation possibly also affect brittle fracture. It is also shown that if a low increase of the yield stress is considered, the ductile fracture energy can decrease as a result of a compensation between the increase of dissipated energy due to a higher yield stress and a decrease of dissipated energy due to a faster ductile crack propagation.
Prediction of Forming Limit Diagrams for Aluminum Alloy Sheet Using Finite Element Analysis
Authors: Li Bing , Nye Tim J.
Published: July 2008

Prediction of forming limit diagram (FLD) for aluminum alloy sheet using finite element analysis without implementing pre-defined geometrical imperfections or material imperfections was studied. The limit strains of the FLD were determined by applying a new proposed localization criterion in the dome stretching test. The elements just outside the necking area, where their major and minor principal strains have no simultaneous change after localized necking happens, were chosen as the reference elements for measurement of limit strains. Simulations were carried out for various strain paths ranging from balanced biaxial stretching to uniaxial stretching. The effects of material properties, sheet thickness, anisotropic parameter and friction coefficient at the sheet punch interface on the locus of FLD were investigated. It was found that the material yield stress and average anisotropic parameter value has almost no effect on forming limits; larger strain-hardening exponent and higher sheet thickness result in higher level of forming limit strains; the friction coefficient has little influence on the locus of FLD but does affect the strain path taken during the deformation. The predicted FLD of AA 5182-O was compared with an experimentally determined FLD and very good agreement has been achieved. It was demonstrated that forming limit diagrams can be predicted by the finite element method without requiring any assumed geometric or material imperfections in the numerical model.
Reactor Pressure Vessel and Reactor Coolant Circuit Cast Duplex Stainless Steel Components: Contribution of the Expertise for Life Management Studies
Authors: Bezdikian Georges
Published: July 2008

The life management of French Nuclear Power Plants is a major stake from an economic and a technical point of view considering the aging management assessment of the key components of the plant. The actual life evaluation is the results of prediction of life assessment from important program of expertises for the 3-loop PWR and 4-loop PWR plants in operation. To optimize the strategic in order to achieve the best possible performance and to prepare the technical and economical choice and decision, the paper presents the association of life management strategy and the program of expertises considering: • the identification of degradation for different components and prediction criteria proposed, • the large database from cast reactor coolant and component removed from nuclear power plants and expertised to confirm the prediction, • the life evaluation of RPV with radiation surveillance program based on the expertises of irradiation capsules, it is particularly shown how the expertise is in the center of the strategic choice. The French utility has organized the life management of Nuclear Plant in function of several program of expertises of knowledge on the long term experience feedback and the maintenance program for life. This paper shows updated on RPV and reactor coolant equipments activities engaged by utility on: • periodic maintenance and volume of expertise, • Alternative maintenance actions, • Large volume of expertises and how are managed these results to predict the aging management.
Effect of Chemistry Variations in Plate and Weld Filler Metal on the Corrosion Performance of Ni-Cr-Mo Alloys
Authors: Fix David V. , Rebak Rau´l B.
Published: July 2008

The ASTM standard B 575 provides the requirements for the chemical composition of Nickel-Chromium-Molybdenum (Ni-Cr-Mo) alloys such as Alloy 22 (N06022) and Alloy 686 (N06686). The compositions of each element are given in a range. For example, the content of Mo is specified from 12.5 to 14.5 weight percent for Alloy 22 and from 15.0 to 17.0 weight percent for Alloy 686. It was important to determine how the corrosion rate of welded plates of Alloy 22 using Alloy 686 weld filler metal would change if heats of these alloys were prepared using several variations in the composition of the elements even though still in the range specified in B 575. All the material used in this report were especially prepared at Allegheny Ludlum Co. Seven heats of plate were welded with seven heats of wire. Immersion corrosion tests were conducted in a boiling solution of sulfuric acid plus ferric sulfate (ASTM G 28 A) using both as-welded (ASW) coupons and solution heat-treated (SHT) coupons. Results show that the corrosion rate was not affected by the chemistry of the materials in the range of the standards.
Methods to Calculate Corrosion Rates for Alloy 22 From Polarization Resistance Experiments
Authors: Wong Lana L. , Martin Sue I. , Rebak Rau´l B.
Published: July 2008

The general corrosion rate may be measured using immersion tests or electrochemical tests. The electrochemical tests are fast and can be used for a rapid screening of environmental effects such as temperature and electrolyte composition. The electrochemical tests are described in ASTM standards G 59 and G 102. The basis of these tests is to calculate the resistance to polarization (Rp) in a voltage vs. current plot and to convert these values to corrosion rates using the Faraday law. Commercial software can calculate the corrosion rate based on inputs from the operator. This paper discusses three ways of calculating the corrosion rate (Methods 1, 2 and 3) based on a fixed set of acquired data of voltage vs. current. The conclusions are that the way the corrosion rate is calculated does not impact greatly on the absolute value of the corrosion rate. Variations in the acquired data (current, potential) from one experiment to another seem more important that the manner the data is fitted with the Rp slope.
Long-Term Corrosion Behavior of Alloy 22 in 5 M CaCl2 at 120°C
Authors: Estill John C. , Hust Gary A. , Evans Kenneth J. , Stuart Marshall L. , Rebak Rau´l B.
Published: July 2008

In conditions where tight crevices exist in hot chloride containing solutions Alloy 22 may suffer crevice corrosion. The occurrence (or not) of crevice corrosion in a given environment (e.g. salt concentration and temperature), is governed by the values of the critical potential (Ecrit) for crevice corrosion and the corrosion potential (Ecorr). This paper discusses the evolution of Ecorr and corrosion rate (CR) of creviced Alloy 22 specimens in 5 M calcium chloride (CaCl2) at 120°C. Tested specimens included non-creviced rods and multiple creviced assemblies (MCA) both non-welded (wrought) and welded. Results show that Alloy 22 suffers crevice corrosion under the open circuit conditions in the aerated hot CaCl2 brine. However, after more than a year immersion the propagation of crevice corrosion was not significant. The general corrosion rate decreased or remained unchanged as the immersion time increased. For rods and MCA specimens, the corrosion rate was lower than 100 nm/year after more than a year immersion time.
Use of Class 1 Analysis to Aid Inservice Inspection
Authors: Vasquez Daniel J. , Shah Nitin J.
Published: July 2008

This paper describes an experience of utilization of ASME Section III Code Class 1 analysis to aid in inservice inspection (ISI). The pressurizer surge line weld to the pressurizer nozzle was targeted to be inspected under the ASME Section XI program and also to address Alloy 600 issues. The pipe close to the nozzle was encased by a source shield to protect the pressurizer and the pressurizer support from the effect of postulated longitudinal rupture of the pressurizer surge line. Consequently, the shield did not permit the access needed to perform ISI. The encasement was segmented with bolted joints for removal and installation. With the passage of time, the environmental condition around the encasement made the removal and replacement complex and dose intensive. A modification to the shield by permanent removal of a portion was considered as an attractive option to help provide access for the current inspection, as well as anticipated future inspections. This modification exposed a portion of the pipe which may have longitudinal rupture. ASME Class 1 analysis was performed for the portion of the exposed pipe. Analysis was performed in detail to establish that stress and cumulative usage factor is below the threshold level at which a break has to be postulated. The paper concludes that detailed use of stress analysis results in elimination of the postulated break. As a result, permanent access could be created for current and future inservice inspections of the pressurizer nozzle.
Probability of Burst in Steam Generator Tubes Using Monte Carlo Method
Authors: Lee Jae Bong , Park Jai Hak , Kim Hong-Deok , Chung Han-Sub , Kim Tae Ryong
Published: July 2008

A statistical assessment model for structural integrity of steam generator tubes was proposed using Monte Carlo method. The growth of flaws in steam generator tubes was predicted using statistical approaches. The statistical parameters that represent the characteristics of flaw growth and initiation were derived from in-service inspection (ISI) non-destructive evaluation (NDE) data. Based on the statistical approaches, flaw growth models were proposed and applied to predict distribution of flaw size at the end of cycle (EOC). Because NDE measurement results differ from that of real ones in steam generator tubes, a simple method for predicting the physical number of flaws from periodic in-service inspection data was proposed. The probabilistic flaw growth rate was calculated from the in-service non-destructive inspection data. And the statistical growth of flaw was simulated using the Monte Carlo method. Probabilistic distributions of the flaw size and the probability of burst were obtained from numerously repeated simulations using the proposed assessment model.
Monitoring of a Radiation Embrittlement by a Reliable Fluence Evaluation With a Neutron Dosimetry in a Reactor Pressure Vessel
Authors: Lee SamLai , Kim ByoungChul , Yoo ChoonSung , Chang KeeOk
Published: July 2008

The assurance of a nuclear reactor pressure vessel integrity plays an important role in achieving a safety and extending the life of nuclear power plants. In the assessment of the state of an embrittlement of a pressure vessel in a pressurized light water reactor, an accurate evaluation of the neutron exposure of each of the materials comprising the beltline region of the vessel is required. The evaluation is performed through a neutron dosimetry analysis where a fluence calculation is done by both measurement of the dosimeter materials removed from surveillance capsules and a neutron transport calculation. Now that all the capsules have been completely removed from the reactor vessel and analyzed by a periodic monitoring schedule, four ex-vessel sensor sets are installed as a substitute capsule in an axial direction in the reactor cavity and then removed for an analysis in order to meet the regulation requirements. The results showed that the differences between the measurements and calculations are less than 20% for each capsule, which means these analyses satisfy the acceptable criterion required by Regulatory Guide 1.190, and they also provide an assurance that such an evaluation including an ex-vessel neutron dosimetry can be used to predict the fluence of a nuclear reactor vessel with a good reliability.
Evaluation of the Sealing Performance in Bolted Flange Connection Under Heat Condition and Internal Pressure: The Effect of Scatter in Bolt Preloads
Authors: Sawa Toshiyuki , Takagi Yoshio , Yamada Katsuhiro
Published: July 2008

It has been well known that a scatter in axial bolt forces of pipe flange connections tightened by the torque control method is substantial. It is necessary for evaluating the sealing performance of the pipe flange connections with the gaskets subjected to internal pressure to know the contact gasket stress distributions due to the scatter of the axial bolt forces in the connections tightened by the torque control method. Especially, when gases are used in the pipe flange connections with gaskets at a high temperature, it is necessary to evaluate the amount of gas leakage. In this study, when bolts and nuts in a pipe flange connection were tightened using a torque wrench, the axial bolt forces were measured and then the amount of gas leakage in the pipe flange connection at 50,100,150 and 200 °C was measured under internal pressure. Leakage tests were performed using Helium gases. In addition, the thermal stress distributions at the interfaces between pipe flanges and the gasket under heat condition (temperature 50,100,150 and 200 °C) and internal pressure were calculated by using the finite element method (FEM) taking into account hysteresis in the stress-strain curves of a spiral wound gasket. By using the calculated contact stress distributions and the results of the leakage tests, the sealing performance was evaluated.
New Tightening Diagram for Bolted Flange Gasket Joints
Authors: Ueno Yoshio , Nagata Satoshi , Kobayashi Takashi , Sawa Toshiyuki
Published: July 2008

Tightening diagrams have been well known and utilized to the design of bolted joints in wide applications. The tightening diagram is conceptually illustrated by using two lines. One represents the relationship between the bolt force and the bolt elongation, the other represents that of the clamping force and the compressive displacement of the clamped body. The tightening diagram also gives the changes of the bolt force and the compressive force when an external force exerts on the bolted joints after assembled. However, the tightening diagrams have a limitation in application only for the joints without gaskets. The tightening diagram is not possible to apply directly to the bolted flange gasket joints since the joint do not behave as non-gasketed joints due to the gasket inserted and the configurations bolts locate outside the ring gasket. This paper proposes a new tightening diagram for bolted flange gasket joints. The new tightening diagram consists of mainly three lines. Two lines represent the displacement of flange at the gasket reaction point due to pressure thrust and gasket load, respectively. The remaining shows the loading-unloading curve of the gasket. By the combination of these lines, the behavior of bolted flange gasket joint is conceptually illustrated and the changes of the bolt force and the gasket load is shown. The paper gives a detailed explanation of the new tightening diagram.
New Code Case to Substitute the Allowable Crack Angle in Rules on Fitness-for-Service
Authors: Machida Hideo , Kashima Koichi
Published: July 2008

This paper is a technical basis document of the new Code Case to substitute the allowable crack angle for a circumferential surface crack in “Rules on Fitness-for-Service (FFS)” published from The Japan Society of Mechanical Engineers (JSME). Until now, the angle of a circumferential surface crack was limited below 60°. This is the limitation with consideration to the stability of the crack if the crack penetrates wall of the pipe. Therefore, a long crack (such like an SCC) was obliged to repair or replace even if it was shallow enough. Weld Overlay (WOL) repair—strength of the original piping is not expected in it—is also inapplicable for the same reason. In order to solve this irrationality, the new Code Case applying to the crack stability assessment when the crack angle exceeds 60° was established, and allowable crack depth according to the crack angle were defined in it.
FE Modeling of the Orthotropic and Three-Layered Human Thoracic Aorta
Authors: Zhao Aihong , Pericevic Ian Owens , Digges Kennerly , Kan Cing-Dao , Moatamedi Moji , Augenstein Jeffrey S.
Published: July 2008

The human aorta consists of three layers: intima, media and adventitia from the inner to outer layer. Since aortic rupture of victims in vehicle crashes frequently occurs in the intima and the media, latent aortic injuries are difficult to detect at the crash scene or in the emergency room. It is necessary to develop a multi-layer aorta finite element (FE) model to identify and describe the potential mechanisms of injury in various impact modes. In this paper, a novel three-layer FE aortic model was created to study aortic ruptures under impact loading. The orthotropic material model [1] has been implemented into a user-defined material subroutine in the commercial dynamic finite element software LS-DYNA version 970 [2], which was adopted in the aorta FE model. The Arbitrary-Lagrangian Eulerian (ALE) approach was adopted to simulate the interaction between the fluid (blood) and the structure (aorta). Single element verifications for the user-defined subroutine were performed. The mechanical behaviors of aortic tissues under impact loading were simulated by the aorta FE model. The models successfully predicted the rupture of the layers separately. The results provide a basis for a more in-depth investigation of blunt traumatic aortic rupture (BTAR) in vehicle crashes.
On the Effect of Scattering of Bolt Forces on Gasket Stress
Authors: Schaaf Manfred , Schoeckle Friedrich , Bartonicek Jaroslav
Published: July 2008

To guarantee integrity and tightness of bolted flanged connections a set of gasket characteristics (for tightness e.g. QMIN(L), QSMIN(L), tightness class L) has to be known. These characteristics are determined in simplified standardized tests with uniform gasket stress levels, in which the effect of the scattering of the bolt force is neglected. In this paper, results of Finite Element studies with real flange models are presented in which the local distribution of the gasket stress was determined in dependence of the scatter of the bolt forces. In the calculations, different models of the material characteristics are evaluated. A linear elastic approach, a nonlinear elastic approach and a non-linear elastic-plastic approach of the gasket behaviour is analysed. The results of the FEM studies demonstrated that elastic-plastic material laws are necessary for a realistic description of the material behaviour. The calculations in which the elastic-plastic gasket behaviour is considered give a nearly uniform gasket stress distribution along the gasket circumference despite a large scatter in the bolt force. This means that a non-uniform load transmission into the BFC is “damped” through the flange rings to a large degree and the gasket is compressed almost uniformly along the circumference. In radial direction an increase of the gasket stress from the inner to the outer diameter can be observed. Depending on the material law used, a lift-off of the flange ring from the gasket at the inner diameter (caused by the flange rotation) is obtained (linear elastic approach). Using a non-linear elastic or elastic-plastic approach for the gasket material the gasket stays in contact with the flange surfaces over the entire width of the gasket. These experiences can only partly be considered in analytical calculation codes such as EN 1591-1 (1). This is one reason why there are often discussions about the tightening factors of different mounting procedures and therefore difficulties in stress and tightness analysis can occur.
Low-Cycle Fatigue Evaluation Using the Weld Master S-N Curve
Authors: Dong P. , Cao Z. , Hong J. K.
Published: July 2008

In the context of fatigue evaluation in the low-cycle regime, the use of the master S-N curve in conjunction with elastic FE-based structural stress calculations is presented. An elastic pseudo structural stress estimation is introduced by assuming that Neuber’s rule applies in relating structural stress and strain concentration at a weld to the material’s cyclic stress-strain behavior. With the pseudo structural stress procedure, recent sources of recent full scale test data on pipe and vessel welds were analyzed as a validation of the proposed procedure. The estimated fatigue lives versus actual test lives show a reasonable agreement. Finally, the feasibility of using monotonic stress-strain curves as a first approximation is also examined for applications when cyclic stress-strain curve may not be readily found. The analysis results indicate that the life estimations using monotonic stress-strain curves are reasonable, with the recent test data falling within mean ± 2σ, where σ represents the standard deviation of the master S-N curve.
Maintenance Optimization of LWRs Based on PFM Analysis
Authors: Yoshimura Shinobu , Furuta Kazuo , Isobe Yoshihiro , Sagisaka Mitsuyuki , Noda Michiyasu , Wada Tetsuya , Akiba Hiroshi
Published: July 2008

We have been developing an integrated simulator for the maintenance optimization of LWRs (Light Water Reactors) based on PFM (Probabilistic Fracture Mechanics). As a typical example of the analysis, .an attempt was made to develop an economic evaluation model for the purpose of optimizing the maintenance activities of SG tubes in PWRs based on PFM approach, In the model, the probabilities of these risks were evaluated first and then the risk-benefit analysis was carried out to evaluate costs and profits as well during 60 years lifetime under various maintenance strategies. The model would be applied to pipes which are critical in terms of safety, availability and economy. The concept of the simulator is to provide a method to optimize maintenance activities for representative components and piping systems in nuclear power plants totally and quantitatively in terms of safety, availability and economic efficiency (both from cost and profit). The simulator will also provide a guideline regarding social acceptance of risk-based decision makings. This study has been conducted under “Innovative and Viable Nuclear Energy Technology (IVNET) Development Project” financially supported by Japanese METI.
High Grade Performance Proof on Gaskets for Bolted Flange Connections With Organic Fluids
Authors: Kockelmann H. , Hahn R.
Published: July 2008

For the “high grade performance proof” on gaskets for bolted flange connections according to TA Luft (German Clean Air Act) and VDI guideline 2440 “Emission Reduction - Mineral Oil Refineries” the pressure increase method was developed as an alternative method based on simple physical laws. The comparison of measuring results with results of the usual Helium mass spectrometry did show rather good agreement of both methods validating the pressure increase method. The advantage of the pressure increase method is the fact that a lot of volatile organic fluids can be used as test medium. It was shown that with Methanol and Ethanol the leakage rate criterion of VDI guideline 2200 for 40 bar internal pressure for a Graphite based sheet gasket often in use in chemical plants is met.