bluuebunny/crossref_metadata_2025 huggingface dataset:
FEM Analysis on Pressure Vessel Components Containing LTAs Against Seismic Load Using Combined Non-Linear Isotropic/Kinematic Hardening Model
Authors: Zhou Runze , Kojima Ikuo , Kaida Takuyo , Tsuji Hirokazu
Published: January 2014

Fitness-for-service (FFS) assessments are quantitative engineering evaluations that perform to demonstrate the integrity of an in-service component that may contain a flaw or damage [1]. It can be used to make run-repair-replace decisions to help determine if pressured equipment containing flaw that have been identified by inspection can continue to operate safety for some period of time.

This paper provides a FFS assessment on carbon steel pipe which contained a LTA (Local Thin Area) against seismic load by FEM (Finite Element Method) analysis. ABAQUS Ver. 6.10, which has the combined isotropic / kinematic hardening model [2], is used to simulate the LTA contained carbon steel pipe against seismic load. Material parameters in the hardening model are identified by a symmetric strain cycle experiment based on ASTM E606. Isotropic hardening component is introduced by specifying the equivalent stress defining the size of the yield surface, as a tabular function of the equivalent plastic strain. Kinematic hardening component is obtained from the stabilized cycle of a specimen that is subjected to symmetric stain cycles.

The authors introduced the way how to calibrate the material parameters of combined isotropic / kinematic hardening model. Then the authors calculated up to 100 cycles on carbon steel pipe which contained a Local Thin Area against seismic load at 300 degrees centigrade. The results comparison between FEM analysis and experiment shows that stress-strain hysteresis loop tendency and number of cycles to failure are predicted accurately.
European Project on Structural Integrity STYLE: Project Status
Authors: Keim Elisabeth , Nicak Tomas
Published: January 2014

The safety and reliability of all systems has to be maintained throughout the lifetime of a nuclear power plant. Continuous R&D work is needed in targeted areas to meet the challenges of long term operation of existing designs and for the GEN-III designs. A special focus is placed on reactor coolant pressure boundary (RCPB) components, because its integrity and functionality from the time of first operation until end of life is required to ensure plant safety.

The overall objective of STYLE is to assess, optimize and develop the use of advanced tools for the structural integrity assessment of RCPB components relevant to ageing and life time management and to support the integration of the knowledge created in the project into mainstream nuclear industry assessment codes.

The project concept is based on carefully selected research topics, which thematically cover the complex multidisciplinary character of structural assessment of RCPB components. The prioritization of the work reflects the needs of industrial end-users and assessment of currently available techniques and data at European and international level.

This paper describes the current status of the project STYLE and summarizes its main results achieved up to date (Feb 2013).

The project is coordinated by AREVA GmbH with 20 partner organizations from Europe, one collaborator from USA and one collaborator from Russia:

AREVA GmbH,

Germany (coordination, WP2 leader)

AREVA SAS, France

Bay Zoltan, Hungary

CEA, France (WP1 leader)

EDF, France

EDF Energy Ltd., UK (WP7 leader)

EK, Hungary

IdS, France

INR, Romania

IWM, Germany

JRC, Netherlands (WP4 leader)

NRI, Czech Republic

NRG, Netherlands

SCK-CEN, Belgium

AMEC, UK (WP3 and WP5 leader)

University of Bristol, UK

University of Manchester, UK

Tecnatom, Spain

Vattenfall, Sweden (WP6 leader)

VTT, Finland

ORNL, USA

NIKIET, Russia
Performance Study of the Simplified Theory of Plastic Zones for the Fatigue Check
Authors: Hübel Hartwig , Willuweit Adrian , Rudolph Jürgen , Ziegler Rainer , Lang Hermann , Rother Klemens , Deller Simon
Published: January 2014

As elastic-plastic fatigue analyses are still time consuming the simplified elastic-plastic analysis (e.g. ASME Section III, NB 3228.5, the French RCC-M code, paragraphs B 3234.3, B 3234.5 and B3234.6 and the German KTA rule 3201.2, paragraph 7.8.4) is often applied. Besides linearly elastic analyses and factorial plasticity correction (Ke-factors) direct methods are an option. In fact, calculation effort and accuracy of results are growing in the following graded scheme: a) linearly elastic analysis along with Ke correction, b) direct methods for the determination of stabilized elastic-plastic strain ranges and c) incremental elastic-plastic methods for the determination of stabilized elastic-plastic strain ranges.

The paper concentrates on option b) by substantiating the practical applicability of the simplified theory of plastic zones STPZ (based on Zarka’s method). Application relevant aspects are particularly addressed. Furthermore, the applicability of the STPZ for arbitrary load time histories in connection with an appropriate cycle counting method is discussed.

Note, that the STPZ is applicable both for the determination of (fatigue relevant) elastic-plastic strain ranges and (ratcheting relevant) locally accumulated strains. This paper concentrates on the performance of the method in terms of the determination of elastic-plastic strain ranges and fatigue usage factors. The additional performance in terms of locally accumulated strains and ratcheting will be discussed in a future publication.
Toughness Behavior of Through-Wall Cracks in Dissimilar Metal Welds
Authors: Rudland D. , Lukes R. , Shim D.-J. , Kalyanam S.
Published: January 2014

Over the years, J-estimation scheme procedures have been develop to predict the load-carrying capacity of through-wall cracks in nuclear grade piping materials. These procedures employ analytical or numerical procedures coupled with the fracture toughness of the material to predict the pipe response. For cracks in welds, the behavior has been shown to be related to the toughness of the weld and strength of the typically lower-strength base metal. However, with the advent of primary water stress corrosion cracking (PWSCC), flaws in dissimilar metal (DM) welds have occurred. These welds consist of a nickel-based weld joining stainless steel and carbon steel base metals.

Prior research has demonstrated that crack-driving force for through-wall circumferential cracks in DM welds is highly influenced by both the stainless steel and carbon steel base metals, and is related to the axial position of the flaw within the weld. This effect brings into question the accuracy of typical J-estimation scheme procedures for calculation of load carrying capacity for circumferential through-wall flaws in DM welds. In addition, it is unknown if the apparent toughness of the cracked pipe is also affected by the position of the crack in the weld.

Work is currently underway, sponsored by the NRC Office of Nuclear Regulatory Research, to investigate the behavior of through-wall and complex cracks in DM welds. In a prior paper, a series of full-scale pipe bend and laboratory-sized fracture experiments were documented. Initial analyses of those test results suggest that typical J-estimation scheme procedures could be used to predict the response if the weld toughness from a compact tension specimen and the appropriate material strength was used. In this paper, the fracture toughness from the DM weld is estimated from the pipe experiments using an η-factor solution and numerical techniques and these results are compared to the compact tension results. The results from this paper add insight into the effect of crack size and location within the DM weld on the apparent pipe toughness for through-wall cracks in DM welds.
Creep Relaxation Procedure for Achieving Uniform Clamp Load Distribution in Gasketed Bolted Joints Using Simultaneous Tightening
Authors: Abboud Antoine , Nassar Sayed A.
Published: January 2014

In this paper, a mathematical procedure is developed for achieving a uniform distribution of target steady-state clamp load level in a gasketed bolted flange model, using a mass-production version of a computer-controlled simultaneous multi-spindle tightening system. Closed form solutions are developed for the required initial clamp load distribution to achieve the target clamp load using a single cycle tightening, or the number of tightening cycles required to achieve the target uniform clamp load. The effect of the gasket thickness is investigated. An experimental procedure and test set-up are used to validate the proposed gasket model. Results show reasonable correlation between the analytical model and the experimental validation data.
Evaluation of Thermal and Mechanical Behaviors of Bolted Joints Made of Titanium and Titanium Alloy and its Application to Robust Joint Design
Authors: Fukuoka Toshimichi , Nomura Masataka , Takasugi Yusuke
Published: January 2014

Titanium and titanium alloys have some excellent characteristics when used for the parts and components of machines and structures. As for bolted joints, however, they are limitedly used mainly due to the high cost. Its specific characteristics, e.g., low weight and high resistance to corrosion, are highly attractive from the engineering point of view. In this paper, thermal and mechanical behaviors of the bolted joints made of titanium or titanium alloy are comprehensively evaluated by finite element analysis, aiming at its broader use by utilizing the distinctive features of small coefficient of linear expansion and Young’s modulus. As a first step, thermal contact coefficients at the interface composed of titanium, titanium alloys and other engineering materials are measured, and then the empirical equations for evaluating the coefficients are derived in the same form proposed in the previous papers. In the next place, numerical analyses are executed by incorporating the thermal contact coefficients into the finite element formulation. Numerical results suggest that threaded fasteners made of titanium alloys are favorably applied to the joints whose clamping forces are likely to decrease when subjected to thermal load. It was also found that the aforementioned threaded fasteners are effective, owing to its low Young’s modulus, for reducing the stress amplitude generated by alternating external forces.
Effect of Surface Finish and Loading Conditions on the Low Cycle Fatigue Life of Stainless Steel Welded Piping in PWR Environment
Authors: Fukuta Yuichi , Nomura Yuichiro , Asada Seiji
Published: January 2014

NUREG/CR-6909 of USA and JSME of Japan proposed new rules for evaluating environmental effects in fatigue analyses of reactors components. These rules were established from a lot of fatigue data with polished specimens under simple loading condition. The effects of surface finish or complex loading condition were reported in some papers, but these data were obtained with the simple shaped specimens.

In order to evaluate the effects of surface finish and loading condition and to confirm the applicability of the proposed rules to actual components, Low Cycle Fatigue tests are performed in PWR environment with the specimens cut from 316 austenitic stainless steel welded piping. The pipes are machined to have three levels of surface finish condition and the load pattern simulating the thermal stress is applied to specimens.

In this study, the effect of surface finish on fatigue life is included to be small for 316 austenitic stainless steel welded piping. Considering the insensitive region in the current evaluation rule, predicted accuracy is increased and possibility of improving the current rule is indicated.
Development of Seismic Design Method for Free Standing Rack
Authors: Iwasaki Akihisa , Nekomoto Yoshitsugu , Morita Hideyuki , Taniguchi Katsuhiko , Okuno Daisaku , Matsuoka Toshihiro , Chigusa Naoki
Published: January 2014

For high earthquake resistance and ease of installation, free standing racks which are not anchored to the pool floor or walls has been adopted in many countries.

Under the earthquake, the response of the free standing rack is highly nonlinear and involves a complex combination of motions (sliding, rocking, twisting, and turning) and impacts between the fuel assemblies and the fuel cell walls, rack-to-rack, and the pit floor and the rack pedestals. To obtain an accurate simulation of the free standing rack, the seismic analysis requires careful considerations of these complex phenomena (sliding, rocking, twisting, and turning), fluid coupling effects and frictional effects.

The important evaluation items while applying the free standing rack to the actual nuclear plants are maximum sliding displacement of the rack, maximum rocking displacement and maximum leg load under earthquake. When the sliding displacement increases, the rack may collide against the spent fuel pool wall. In addition, the free standing rack should not exhibit tilt sufficient to cause to the rack to overturn. The vibration tests were conducted in order to predict the rack behavior under earthquake, and the analysis method was validated by comparison to tests results. Furthermore, we developed the seismic design method to obtain the margin of safety for free standing rack.
Sealing Performance Evaluation in Bolted Flange Connections With Ring Joint Gasket Subjected to Internal Pressure
Authors: Kondo Koji , Sato Koji , Sawa Toshiyuki , Tsubaki Shota , Omiya Yuya
Published: January 2014

Bolted flange connections with ring type joint gaskets have been used to seal the inner fluid under higher pressure and higher temperature conditions when soft gaskets cannot be used in the connections. However, few researches on the characteristics and the sealing performance evaluation for the bolted flange connections with metal ring gasket have been conducted. Therefore, assembly procedures and tightening methods of the connection with ring type joint gaskets is empirically and not fully elucidated. It is important to know the characteristics such as the contact gasket stress distribution which governs the sealing performance prediction, the sealing performance and the sealing mechanism in the bolted flange connections for determining optimum tightening methods and the bolt preload. In this paper, the differences of the sealing performance for the bolted flange connections (3″) by the re-use octagonal and oval type ring gaskets are examined. In the FEM calculations the contact gasket stress distributions and the range of plastic deformation are examined and the sealing mechanism is discussed. It is found that the basic sealing mechanism is caused by the plastic deformation at the contact area of the gasket. In addition, the leakage tests for the bolted flange connections with the nominal diameter of 20″ with the octagonal ring type joint gaskets being inserted are conducted, where the bolt tightening for the connection is carried out according to both ASME PCC-1 and JIS B2251, respectively. Using these results, the optimum tightening methods for the connection with ring type joint gaskets are discussed.
Improvement of Reliability Assessment of Gas Pipeline Using Acoustic Emission Technique
Authors: Giunta Giuseppe , Budano Sergio , Lucci Antonio , Piancaldini Roberto , Prandi Luca
Published: January 2014

Among NDE techniques for monitoring damages on pipelines in service, the Acoustic Emission (AE) technique is effective to check initiation and propagation of critical defects under stress and exposed to aggressive environment. To investigate both reliability and applicability of the AE technique to pipelines used in Oil&Gas industry, different full scale tests have been designed and performed as significant items. A pilot line (48″ diameter and length 194m), formed from pipes made of both steels grade API 5L X80 and X100, has been buried and monitored for about 16 months by using AE technique. External defects (dent & gouge type) have been executed on each pipe. A pressure cycling test has been provided giving pressure in the range 135–150 bar for simulating gas transport operation over many years. By means of AE technique the source localization of defects and correlation between the damage growing and the acoustic transient energy have been analyzed. The growth in the crack areas has been also periodically controlled using NDT inspections (US and magnetic particles). The results provide good perspective for using AE technique as advanced methodology to improve the reliability of pipeline.
Residual Stress Study in Dissimilar Metal Welds of a PWR Pressurizer Surge Nozzle: Validation of Developed Fast Analysis Method and Examination of Safe-End Length Effect
Authors: Maekawa Akira , Kawahara Atsushi , Serizawa Hisashi , Murakawa Hidekazu
Published: January 2014

It is necessary to establish properly reliable weld residual stress analysis methods for accurate crack initiation and growth assessment of primary water stress corrosion cracking, which may occur in nickel-based dissimilar metal welds in pressurized water reactors. The US Nuclear Regulatory Commission and the Electric Power Research Institute cooperatively conducted an international round robin for weld residual stress analysis to improve stress analysis methods and to examine the uncertainties involved in the calculated stress values. In this paper, the results from the authors’ participation in the round robin were reported. In the round robin, the weld residual stress in a nickel-based dissimilar metal weld of a pressurizer surge nozzle mock-up was computed under various analysis conditions. The residual stress analysis results computed by a welding simulation code currently being developed that uses the iterative substructure method were in good agreement with the measurements. Also, the effect of safe-end length on residual stress distribution was examined as an additional discussion point.
Benchmark on Residual Stress Modeling in Fracture Mechanics Assessment
Authors: Marie S. , Deschanels H. , Chapuliot S. , Le Delliou P.
Published: January 2014

In the frame of development in analytical defect assessment methods for the RSE-M and RCC-MRx codes, new work on the consideration of residual stresses is initiated by AREVA, CEA and EDF. The first step of this work is the realization of a database of F.E. reference cases.

To validate assumptions and develop a good practice guideline for the consideration of residual stresses in finite element calculations, a benchmark between AREVA, CEA and EDF is going-on. A first application presented in this paper focuses on the analysis of the crack initiation of aged duplex stainless steel pipes submitted to an increasing pressure loading. Residual stresses are related to pipe fabrication process and act as shell bending condition. Two tests were performed: the first with an internal longitudinal semi-elliptical crack and the second with an external crack.

The analysis first focuses on the ability to accurately estimate the measured pressure at the crack initiation of the two tests. For that purpose, the comparison of results obtained with different methods of taking into account the residual stresses (i.e. thermal fields or initial strain field). It then validates post-treatment procedures for J or G determination, and finally compares of the results obtained by the different partners.

It is then shown that the numerical models can integrate properly the impact of residual stresses on the crack initiation pressure. Then, an excellent agreement is obtained between the different numerical evaluations of G provided by the participants to the benchmark so that best practice and reference F.E. solutions for residual stresses consideration can be provided based on that work.
Evaluation of the Stratification Loads With the EDF Fatigue Assessment Device
Authors: Naudin Claire , Vidard Stéphane
Published: January 2014

A fatigue assessment device, Fatiguemètre, has been developed by EDF especially for sensitive zones of components of French PWR NPP. The main objective of this device is the evaluation of a realistic usage factor (damage criterion) by using operating data. Two requirements are to use as less specific transducers as possible and simplified thermomechanical methods for the calculation of stress variation. Some monitoring devices had nevertheless been necessary to get correlations between in service data, for instance flow rate and thermal stratification distribution. This instrumentation, called a stratimeter, consists of a ring of thermocouples installed around a section of a pipe.

The present studies were carried out on stabilized thermal stratification states and also on transients of different rates. These input data are always representative of the operating and design transient occurring on the FWL next to the connection with the steam generator. The first use of the Fatiguemètre device revealed the need of optimization on some thermomechanical methods. Investigating steady-state (stabilized) or slow enough transients of temperature stratifications, it was found that it is possible to calculate sufficiently accurate stresses without the use of any stress intensification factor, when applying temperatures from outer wall measurement as mean wall temperatures. The new discretization of Duhamel formula gives a satisfying evaluation of the local stratification stress value.
Ultrasonic Measurement of Residual Stresses in Welded Specimens and Structures
Authors: Kudryavtsev Yuri
Published: January 2014

The application of an ultrasonic non-destructive method for residual stress (RS) measurements has shown that, in many cases, this technique is very efficient and allows measuring the RS both in laboratory conditions and in real structures in field for a wide range of materials. Using this technique, one can measure the RS at the same points many times, studying for instance, the changes of RS under the action of service loading or effectiveness of stress-relieving techniques. An ultrasonic computerized complex (UCC) for non-destructive measurement of residual and applied stresses was developed recently. The complex includes a measurement unit with transducers, basic supporting software, an advanced database and an Expert System, housed in a laptop, for analysis of the influence of RS on the fatigue life of welded elements. In general, the ultrasonic method allows one to measure the RS in both cases: averaged through thickness or in surface layers. The present version of UCC allows measuring the averaged through thickness biaxial RS in plates 2–150 mm thick. The results of ultrasonic RS measurement in large scale welded specimens and structures are also discussed in this paper.
Crack Initiation Under Equibiaxial Fatigue, Development of a Particular Equibiaxial Fatigue Device
Authors: Bradaï S. , Gourdin C. , Courtin S. , Leroux J. C. , Gardin C.
Published: January 2014

Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures.

In some nuclear power plant components, the fatigue loading may be equi-biaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data on austenitic stainless steels is available. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. For this reason, a new experimental data must be obtained on the considered material with a strain tensor in equi-biaxial tension.

The aim of this paper is to present a new device “FABIME2” developed in the LISN in collaboration with EDF and AREVA. This new device allows accurate quantification of the effects of both equi-biaxial strain state as well as structure (such as mean stress) on the fatigue life. A Finite Element Modeling is also performed in order to obtain a precise description of the strain state in the specimen.
Ultrasonic Technique for Testing Cold Welding of Butt-Fusion Joints in Polyethylene Pipe
Authors: Guo Weican , Xu Huiting , Liu Zhongqiang , Shi Jianfeng
Published: January 2014

The butt-fusion process is an important method for connecting PE pipes, especially when the pipes are of large diameter and of thicker section. Since many different environmental factors can cause defects and flaws, the joints become the weak point that should be inspected before the pipes begin service. Especially cold welding caused by insufficient input of heat energy, which can not be detected by nondestructive test methods currently available, is one of the most dangerous defects in the butt-fusion joints of PE pipes. It has been discovered that there are three Eigen-lines in the butt-fusion joint of PE pipes by using the phased array ultrasonic focusing technique. Further research shows that the upper and lower Eigen-line indicates the solid-liquid interface and the middle Eigen-line indicates the initial butt interface. Based on a lot of experiments, it has been discovered that the distance between the upper and lower Eigen-line, is related with the input of heat energy during welding. So a new method called “Eigen-line method” is developed to assess cold welding by measuring the distance between the upper and lower Eigen-line. A set of experiments show that the method can detect cold welding in butt-fusion joints with the accuracy less than 6%, which can meet the testing requirement for welding joints in engineering.
A Novel Image Processing Method for ARCMAC Point to Point Optical Strain Measurement
Authors: Yang Haoliang , Davies Catrin Mair , Hooper Paul , Morris Andy , Dear John
Published: January 2014

The remaining life of high pressure steam pipes in power stations is heavily dependent upon material creep rates. Monitoring strain in these pipes is difficult due to demanding operational conditions and has resulted in the development of a rugged optical strain gauge system by E.ON UK. The E.ON UK auto-reference creep management and control (ARCMAC) gauge is a point-to-point biaxial creep strain measurement technique. Room temperature validation of the gauge was done using a UK National Physical Laboratory (NPL) extensometer calibration rig (ECR). These gauges have been successfully installed and measurements have been acquired on high temperature (∼600 °C) low-alloy ferritic steel power plant piping.

In conjunction with the ARCMAC gauges, research has been ongoing to seek effective methods to process the corresponding ARCMAC images. This paper describes a novel image processing method for the analysis of ARCMAC images. This method processes ARCMAC images with high efficiency and accuracy even if images were taken in demanding environmental conditions. This novel image processing method has been developed into a standalone software program named ARCMAC Assistant to assist both experiment and field work. Experiments involving calibration test work and in-situ creep tests have been used to validate its accuracy.
The Effect of Microstructure on the Hydrogen-Assisted Fatigue of Pipeline Steels
Authors: Slifka Andrew J. , Drexler Elizabeth S. , Stalheim Douglas G. , Amaro Robert L. , Lauria Damian S. , Stevenson April E. , Hayden Louis E.
Published: January 2014

Tests on the fatigue crack growth rate were conducted on four pipeline steels, two of grade API 5L-X52 and two API 5L-X70. One X52 material was manufactured in the mid-1960s and the other was manufactured in 2011. The two X70 materials had a similar vintage and chemistry, but the microstructure differs. The fatigue tests were performed in 5.5 and 34 MPa pressurized hydrogen gas, at 1 Hz and (load ratio) R = 0.5. At high pressures of hydrogen and high values of the stress intensity factor range (ΔK) there is no difference in the fatigue crack growth rates (da/dN), regardless of strength or microstructure. At low values of ΔK, however, significant differences in the da/dN are observed. The older X52 material has a ferrite-pearlite microstructure; whereas, the modern X52 has a mixture of polygonal and acicular ferrites. The X70 materials are both predominantly polygonal ferrite, but one has small amounts (∼5%) of upper bainite, and the other has small amounts of pearlite (<2%) and acicular ferrite (∼5%). We discuss the fatigue test results with respect to the different microstructures, with particular emphasis on the low ΔK regime.
Stress Intensification Factors for Fabricated Lateral Piping Connections
Authors: Mair David
Published: January 2014

Stress intensification factors (SIFs) are published in the piping codes for tees; branch connections where the branch intersects the header pipe at 90 degrees. These factors when multiplied by the nominal stress provide a measure of the increased local stresses at the junction of the two pipes. However, in cases where the branch pipe meets the header at an angle of other than 90 degrees, the main piping codes do not provide a method of calculating the SIFs. This presents a difficulty for the pipe stress engineer who must determine appropriate SIFs, usually in a conservative way and then manually enter these into the pipe stressing program.

This paper summarizes some of the published methods of calculating SIFs for a limited range of lateral branch connections and makes recommendations based on comparisons with FEA studies. It also includes recommendations on how such FEA studies should be applied in order to provide suitable SIF values.
Linear Matching Method for Parametric Studies of Weldments Creep-Fatigue Endurance
Authors: Gorash Yevgen , Chen Haofeng
Published: January 2014

This paper presents parametric studies on creep-fatigue endurance of the steel AISI type 316N(L) weldments defined as types 1, 2 and 3 according to R5 Vol. 2/3 Procedure classification at 550°C. The study is implemented using the Linear Matching Method (LMM) and based upon previously developed creep-fatigue evaluation procedure considering time fraction rule. Several geometrical configurations of weldments with individual parameter sets, representing different fabrication cases, are developed. For each of configurations, the total number of cycles to failure N* in creep-fatigue conditions is assessed numerically for different loading cases. The obtained set of N* is extrapolated by the analytic function dependent on normalised bending moment M̃, dwell period Δt and geometrical parameters. Proposed function for N* shows good agreement with numerical results obtained by the LMM. Therefore, it is used for the identification of Fatigue Strength Reduction Factors (FSRFs) intended for design purposes and dependent on proposed variable parameters.
A Parametric Study Into the Competing Effects of Stress and Strain Rate in Environmental Fatigue Usage Calculations
Authors: Emslie Julian , Watson Chris
Published: January 2014

Data have emerged that indicate a Pressurised Water Reactor (PWR) environment can have a significant detrimental effect on the fatigue life of plant materials. Proposed methods for accounting for the PWR environment in an ASME III fatigue assessment are presented in ASME Code Case N-792 and NUREG/CR-6909, both of which use a fatigue penalty factor (Fen) approach that directly multiplies the Partial Usage Factor (PUF). Formulae are provided for the Fen factor which are dependent on strain rate, temperature and the dissolved oxygen content of the water. A slower strain rate provides for increased Fen values and therefore increased PUFs.

In stress analysis, defining the ramp of a thermal transient as a step change is pessimistic for thermal stress calculations. The dependence of the Fen factor on strain rate means that this approach may not be conservative when the stresses are carried through to a PWR environment enhanced ASME III fatigue calculation. An increased ramp time gives a lower stress, however this also provides for a slower strain rate, and therefore a larger Fen factor.

By a series of parametric studies using simple austenitic stainless steel 2D axisymmetric cylinder FE models, this paper examines the competing effects of reduced stress and increased Fen that an increased transient ramp time has upon a PWR environment enhanced ASME III calculated fatigue usage factor for stainless steel components.

It was found for thin walled sections that the assumption of a step to define the thermal transient is still pessimistic despite the competing effects. For thicker sections the results showed that this is not always the case, but the potential increase in PUF was found to be minimal.
Improvement of Jet Pump Inlet Mixer in Boiling Water Reactor for Mitigating Flow-Induced Vibration and Fouling
Authors: Watanabe Masanobu , Sayano Akio , Kinugasa Kunihiko , Mori Hajime , Hagiwara Tsuyoshi
Published: January 2014

Jet pumps in Boiling Water Reactor (BWR) have risk of damages by Flow-Induced Vibration (FIV) for when increasing the core flow rate for power uprating. Especially, the vibration by leakage flow at the slip joint between an inlet mixer and a diffuser can cause serious damage on jet pumps. It is one of the obstructive factors for power uprating. Another problem is crud deposition on the inside surface of the inlet mixer and nozzle. Thus fouling causes performance degradation of jet pumps.

To reduce the risk of an FIV problem, the gap flow passage of the slip joint was modified based on the leakage-flow-induced vibration theory. The effect and characteristic of vibration suppression for the improved design was confirmed by fundamental tests that simulated the slip joint configuration. To mitigate crud deposition, a sol-gel ceramic coating process using ZrTiO4, which generates electrostatic repulsion force to crud, was developed. The effect of the coating was confirmed by experiments using test pieces. These techniques for mitigating damage due to FIV and fouling were applied to inlet mixers of jet pumps for replacement in the actual BWR plant.
Automatic Fatigue Monitoring Based on Real Loads and Consideration of EAF: Live Demonstration
Authors: Bergholz Steffen , Jouan Benoit , Rudolph Jürgen , Heinz Benedikt
Published: January 2014

The fatigue assessment of power plant components based on local fatigue monitoring approaches is an essential part of the integrity concept and modern lifetime management. An integral approach like the AREVA Fatigue Concept (AFC) basically consists of two essential modules: realistic determination of occurring operational thermal loads by means of a high end fatigue monitoring system and related highly qualified fatigue assessment methods and tools. The fatigue monitoring system delivers continuously realistic load data at the fatigue relevant locations. Consequently, realistic operational load sequences are available as input data for all ensuing fatigue analyses. This way, realistic load data are available and qualified fatigue usage factors can be determined.

The mode of operation of the fatigue monitoring system will be explained in the framework of a live demonstration by means of the FAMOSi (i = integrated) demonstration wall. The workflow starts with the continuous online measurement of outer wall temperatures transients on a pipe. Visualization is implemented within the FAMOSi viewer software. In a second step, inner wall temperatures are directly calculated. In a third step, the resulting linearly elastic stress history will be calculated as the basis for subsequent code conforming fatigue assessment.

Subsequently, the related advanced fatigue assessment methods of the three staged AFC-approach are addressed.
Modelling Impacts Induced by Shoot Peening Techniques for the Assessment of Surface Integrity
Authors: Robin Vincent , Gilles Philippe , Chaise Thibaut , Li Jun , Nelias Daniel
Published: January 2014

During a manufacturing process, the shot peening technique can be used as the final surface treatment. The aim of this operation is to introduce surface compressive residual stresses in order to delay crack initiation and prevent its propagation. Although the numerical simulation method can predict the level of residual stresses in a peened part, the 3D modelling of the real process, in which many successive and shifted impacts take place, is very delicate to perform and costly in terms of computing time and resources. In the first part of this paper, a method which is applied in two steps is presented. The first step is based on the calculation of the averaged plastic strain tensor in a half-space by using a semi-analytical method. Secondly this plastic strain field is transferred to a finite element model in order to simulate the effects of the shot peening process in thin structures. The accuracy and advantages of the semi-analytical method are validated by a benchmark with several finite element codes. Experiments similar to the Almen test are performed on thin plates made of nickel base alloy. Numerical results in terms of distortions and residual stresses are compared with the experimental data. In the second part of the paper, some formulas based on digital plans of experiments are set up to obtain relevant information on the Process Affected Zone (PAZ) according to the impact parameters. For instance a relation between impact energy and indentation can be established to assess the surface roughness that is known to play a role on fatigue damage.
Solid-Liquid Slurry Flow Through an Expansion in a Rectangular Duct
Authors: Messa Gianandrea Vittorio , Malavasi Stefano
Published: January 2014

Duct flows of solid-liquid slurries are frequently encountered in many engineering applications. The literature about the behaviour of such mixtures in correspondence to hydraulic singularities — such as sudden variation of duct section, perforated plates and bar screens — is rather poor, despite they are integral part of the plants. The technical difficulties faced whilst performing experimental tests made CFD almost the only possible way to study the flow field in detail. In the present work the flow of sand-water mixtures through a sudden expansion in a rectangular horizontal duct is investigated by means of a two-fluid model. Due to the lack of experimental data available, a sensitivity analysis is performed to quantify the influence of the terms of the two-fluid model which proved negligible in the horizontal pipe case, topic of previous investigations. Computations were performed for either dilute or dense mixtures, in order to study the effect of the mean solids concentration on the flow field. Moreover, the effect of channel width is investigated to assess the validity of the hypothesis of two-dimensionality of the flow.
Constitutive Modeling of Haynes 230 for Anisothermal Thermo-Mechanical Fatigue and Multiaxial Creep-Ratcheting Responses
Authors: Ahmed Raasheduddin , Barrett Paul R. , Hassan Tasnim
Published: January 2014

Service life analysis and design of high temperature components, such as turbine engines, needs accurate estimation of stresses and strains at failure locations. The structural integrity under these high temperature environments can be evaluated through finite element structural analysis. This requires a robust constitutive model to predict local stresses and strains. A unified viscoplastic constitutive model based on the Chaboche type nonlinear kinematic hardening rule was developed including the added features of strain range dependence, rate dependence, temperature dependence, static recovery, and a mean stress evolution. The new constitutive model was validated through critical evaluation of the simulation of a broad set of stress and strain responses of a nickel-base superalloy Haynes 230. The experimental database encompasses uniaxial strain-controlled loading histories which include isothermal low cycle creep-fatigue and anisothermal thermo-mechanical fatigue experiments at temperatures ranging from 75°F to 1800°F. Simulations from the modified model are presented to demonstrate its strengths and weaknesses, and future work is needed for developing a robust constitutive model.
Analysis of Corrosion Areas in Pipelines Using Guided Wave Propagation: Numerical Simulations and Experimental Tests
Authors: Turcu Florin , Bertoncini Francesco , Giunta Giuseppe , Raugi Marco
Published: January 2014

Guided Waves (GW) have become widely used for the inspection of unpiggable and inaccessible pipelines because of the presence of coating, because of their position or because they are buried.

Among the possible anomalies, corrosion is the main integrity issue affecting pipelines. The effect that corrosion has on guided wave propagation is attenuation and increased coherent noise when it is generalized or reflection when corrosion is localized.

In this paper, the possibility to characterize corrosion areas affecting pipelines through long range guided wave inspection or monitoring is investigated. With this purpose field testing was performed and the results were used for the validation of numerical methods able to simulate the phenomenon.
Crack Growth Behavior and Preventive Maintenance for Reactor Internals With Cracks in Tokai-2 Nuclear Power Plant
Authors: Fujino Takushi , Terakado Takeshi , Dozaki Koji , Ito Nobuo , Hasegawa Kunihiro
Published: January 2014

Three cracks assumed to be caused by Stress Corrosion Cracking (SCC) were detected on shroud support of Tokai Daini Nuclear Power Plant (Tokai-2) in 2005. Additional inspections were performed in 2009 and 2011, and additional initiation and propagation of cracks were observed on core shroud and shroud support. Flaw evaluation was performed at each time. The results showed that these structures were allowed to use without repair.

There has been a few inspection experiences in Japan, of successive SCC behavior in operating plants. In this paper, the change of crack shape and crack growth rate (CGR) was investigated. The result showed that cracks tend to change its shape as they grow and crack growth rate in an operating plant was below the crack growth disposition line of Japan Society of Mechanical Engineers (JSME) Code.

Water Jet Peening for core shroud with cracks was performed in 2011 and Noble Metal Chemical Addition is planned in next cycle to mitigate crack initiation and growth. These preventive maintenances are effective also in cracked surface. It is important to confirm that crack behavior and effect of preventive maintenances in successive inspections.
Effects of Multiple Factors on Crack Tip Constraint in Weld Joints and the Prediction of Weld Fracture Toughness
Authors: Chen Zhong-An , He Yuan-qing , Lam Poh-Sang , Chao Yuh J. , Jin X. S.
Published: January 2014

For assessing the safety of welded structural components, it is necessary to investigate the effects of multiple factors, which include the component geometry, load level, weld width, and weld strength mismatch, etc., on the crack tip constraint in weld joints, especially at high level of loading. Based on the J-A2 two-parameter fracture theory, a welding constraint parameter, A2w, is introduced such that the total constraint A2 is the sum of A2w and a geometry constraint A2g. The parameter A2w is developed to quantify the effects of material strength mismatch ratio and weld width, and is used to establish a dual constraint-parameters method (J-A2g-A2w) for characterizing the crack tip stress field in a welded joint. This method is validated by the finite element method (FEM), and the effects of material mismatch and weld width are analyzed. Using a critical crack opening stress as the fracture criterion, the fracture toughness of a welded joint can be predicted from the known fracture toughness value of another welded joint. The procedure and examples are given in this paper.
Sophisticated Procedures for Fatigue Evaluation in the Framework of German KTA Codes
Authors: Seichter Johannes , Reese Sven H. , Klucke Dietmar
Published: January 2014

German KTA consider the intensively discussed topic of environmentally assisted fatigue (EAF) by introducing so called attention thresholds for the cumulative fatigue usage factors (CUF). Threshold values for both austenitic steels and ferritic steels are defined. If the threshold value is exceeded, further measures like NDT, in-service inspections or detailed assessment procedures have to be performed. One way to handle those measures is to apply sophisticated procedures and to show that the numerically calculated CUF is below the defined attention thresholds. The article presents some examples to reduce calculated CUFs.

Fatigue analyses performed during design phase of NPP are based on specified loads consisting of conservatively determined reference transients, covering the whole lifetime including events with significantly fewer cycles than assumed during design phase as well as events with very low probability of occurrence at all. But there might be also operational loads which are not included in the load specifications. In general, there is a lot of potential to reduce computed CUFs in terms of considering realistic loading scenarios.

In German NPPs various temperature measurement planes are applied at fatigue relevant positions among others to calculate actual CUFs based on real loads. Detailed finite element (FE) calculations considering these loads can reduce computed CUFs considerably. Therefore detailed evaluation of temperature measurements in combination with FE calculations is carried out, reducing calculated CUFs below the threshold values given in German KTA.
Response Analysis of a Seismic Isolated Structure Considering the Nonlinearity of the Rubber Bearings
Authors: Borsoi Alexandre , Fujita Satoshi , Minagawa Keisuke
Published: January 2014

In Japan, the application of seismic isolation systems using rubber bearings to industrial structure and new generation Nuclear Power Plants have been considered in order to enhance seismic safety. However, the isolation performance will decline in case of huge earthquakes, because of the nonlinearity of both horizontal and vertical restoring characteristics of the rubber bearings. The horizontal restoring force has a hardening characteristic and the vertical restoring force has a softening characteristic. In addition, the horizontal nonlinearity depends on vertical load, so the interaction between the horizontal and vertical response is important. Consequently, in this paper, the analysis of the nonlinearity of the rubber bearings and the coupling between those two directions will be carried out. Then, after comparing these two approaches, the utility of considering this dependency will be estimated.

To do so, a simulation program, based on the Runge-Kutta-Gill’s method has been developed in order to evaluate the seismic response of the isolated structure composed of rubber bearings and oil dampers. The nonlinearity of the rubber bearings is considered, and the coupling of the vertical load and the horizontal hardening has been implemented.
PWR and WWER Steam Generator Tube Integrity Assessment
Authors: Krautschneider Roman
Published: January 2014

Paper is describing and comparing degradation mechanisms and integrity assessment of PWR and WWER type of steam generator tubes. Because of different design, different used materials and also different operating conditions, there are significant differences in degradation mechanisms. Therefore both steam generator types have their specific codes dealing with inspection, monitoring and maintenance.