bluuebunny/crossref_metadata_2025 huggingface dataset:
High Temperature Low Cycle Fatigue Behaviour of MarBN at 600 °C
Authors: Barrett Richard A. , O’Hara Eimear , O’Donoghue Padraic E. , Leen Sean B.
Published: November 2015

The changing face of fossil fuel power generation is such that next generation plants must be capable of operating under (i) flexible conditions to accommodate renewal sources of energy and (ii) higher steam pressures and temperatures to improve plant efficiency. These changes result in increased creep and fatigue degradation of plant components. The key limiting factor to achieving more efficient, flexible plant operation is the development of advanced materials capable of operating under such conditions. MarBN is a new precipitate strengthened 9Cr martensitic steel, with added boron and tungsten, designed to provide enhanced creep strength and precipitate stability at high temperature. Accurate characterisation of this material is necessary so that it can be used under flexible plant operating conditions with high temperature fatigue.

This paper presents a combined work program of experimental testing and computational modelling on a cast MarBN material. To characterise and assess the fatigue performance of MarBN, an experimental program of high temperature low cycle fatigue (HTLCF) tests is conducted at a temperature of 600 °C. MarBN is found to give an increased stress range compared to previous P91 steel experiments, as well as considerable cyclic softening. To characterise the constitutive behaviour of the cast MarBN material, a recently developed unified cyclic viscoplastic material model is calibrated and validated across a range of strain-rates and strain-ranges, with good correlation achieved with the measured data throughout.
The Effect of Streamwise Tube Motion on the Unsteady Fluid Forces in a Normal Triangle Tube Array
Authors: El Bouzidi Salim , Hassan Marwan
Published: November 2015

Fluidelastic instability is generally regarded as the most severe type of flow excitation mechanism. When this mechanism prevails, it could cause serious damage to tube arrays in a very short period of time. This mechanism is characterized by a critical flow velocity beyond which the tubes undergo unstable oscillations. Recently, a number of experimental investigations showed that it is possible to have instability in the streamwise direction; previously, it was believed that fluidelastic instability was only a concern in the direction transverse to the flow.

The purpose of this study is to characterize the flow in the channels surrounding a vibrating tube in a normal triangular bundle with P/d = 1.5. The tube is oscillating in the streamwise direction with a constant amplitude. Numerical simulations were conducted by solving the unsteady Reynolds Averaged Navier-Stokes equations (uRANS) cast in Arbitrary Lagrangian-Eulerian (ALE) form. The unsteady flow perturbation is estimated along the flow channel. The pressure perturbation is used to compute the streamwise unsteady force coefficients in the context of Chen’s model. The perturbation phase and decay are extracted and utilized in the framework of the Lever & Weaver model to study the stability of tube bundles due to tube motion in the streamwise direction.
High Temperature, Multi-Material, Cyclic Plasticity of a P91 Welded Branch-Header Connection Under Cyclic Pressure
Authors: Leen S. B. , Li M. , Barrett R. A. , Scully S. , Joyce D. , O’Donoghue P. E.
Published: November 2015

This paper presents a study on high temperature cyclic plasticity of a welded P91 T-joint under cyclic internal pressure, in the context of high temperature low cycle fatigue (HTLCF) performance of such connections. In the present work, attention is focused on the development of a multi-material model for high temperature cyclic plasticity, including the effects of the different weld-related material zones, namely, parent metal, weld metal and heat-affected zone. The cyclic plasticity behaviour of the three zones is identified from previously-published high temperature, low cycle fatigue test results on uniaxial test specimens, including parent metal, weld metal and cross-weld specimens, obtained from a specially fabricated pipe girth weld, using ex-service P91 material. The cyclic plasticity material model includes the effects of kinematic hardening and cyclic softening. A three-dimensional finite element model of the welded T-joint is developed, incorporating the three sets of identified cyclic plasticity constants. The study is limited to isothermal conditions of 500°C, with a view to understanding the complex effects of multiple material zones with inhomogeneous cyclic plasticity behaviour. The heat affected zone is shown to play a key role in the development of plastic strains and localised stresses. The particular T-joint geometry is the subject of an investigation due to premature failure in a combined cycle gas turbine plant.
Dynamic Finite Element Analysis of Cask Handling Accidents at Storage Sites
Authors: Zencker Uwe , Qiao Linan , Völzke Holger
Published: November 2015

The safety assessment of casks for radioactive material at interim storage facilities or in final repositories includes the investigation of possible handling accidents if clearly defined test conditions are not available from the regulations. Specific handling accidents usually are the drop of a cask onto the transport vehicle or the floor as well as the collision with the wall of the storage building or another cask. For such load cases an experimental demonstration of cask safety would be difficult. Therefore, numerical analyses of the entire load scenario are preferred. The lessons learnt from dynamic finite element analyses of accident scenarios with thick-walled cubical containers or cylindrical casks are presented. The dependency of calculation results on initial and boundary conditions, material models, and contact conditions is discussed. Parameter sets used should be verified by numerical simulation of experimentally investigated similar test scenarios. On the other hand, decisions have to be made whether a parameter or property is modeled in a realistic or conservative manner. For example, a very small variation of the initial impact angle of a container can cause significantly different stresses and strains. In sophisticated cases an investigation of simpler limit load scenarios could be advantageous instead of analyzing a very complicated load scenario.
Applying ASME and British Standard Welded Fatigue Methodologies to Thermal Fatigue Case Studies and Investigating Sensitivity to Fatigue Flaw Growth Models
Authors: Prueter Phillip E. , Brown Robert G.
Published: November 2015

Predicting fatigue cracking at welded locations in fixed process equipment due to cyclic loading is of great interest to the chemical, petrochemical, and nuclear industries. Welded fatigue methodologies have been incorporated into both ASME and international pressure vessel Codes and Standards. These fatigue methodologies are based on welded fatigue tests. Some of the challenges associated with evaluating in-service equipment for susceptibility to fatigue failure are considering the overall scatter associated with the test data that forms the basis of the welded fatigue methodologies and using Code-based fatigue predictions to make practical recommendations relating to establishing inspection intervals and facilitating overall life cycle management. In this study, the Battelle Structural Stress welded fatigue methodology outlined in ASME Section VIII Division 2 is utilized. Additionally, the welded fatigue assessment techniques of British Standard PD 5500 are included for comparison.

In this paper, several case studies are investigated where transient thermal-mechanical finite element analysis (FEA) is used to develop fatigue predictions for several pieces of in-service equipment subjected to cyclic operation that experienced significant cracking in certain regions of the pressure boundary. These case studies focus on the thermal fatigue aspect of the observed cracking. In addition to Code-based fatigue methodologies, fracture mechanics calculations are performed to determine critical flaw sizes, and sub-critical fatigue flaw growth calculations are performed to investigate the propensity for a given initial flaw to propagate to critical dimensions. Furthermore, flaw propagation rate sensitivity to varying fatigue flaw growth models is quantified and discussed. This paper highlights several real-life examples of thermal fatigue cracking and how computational and analytical methods can be used to perform fatigue and flaw growth predictions to understand the root-cause of the observed damage and to determine the likelihood of fatigue crack propagation going forward.
Development of the Primary Stress Indices and Primary Plus Secondary Stress Indices for Pipe Cross Connection
Authors: Adams Timothy M. , Wen Jie
Published: November 2015

The current ASME Boiler Pressure Vessel Code doesn’t provide the primary stress indices (B2) and primary plus secondary stress indices (C2) for a pipe cross connection. In this study, two types of Finite Element Analysis (FEA) models were created to calculate the stress indices for such a configuration: the first was a 3D solid model to calculate the stress intensities and the second a simplified pipe model to calculate the bending moments to obtain the pipe nominal stresses. For both types of FEA models, loads were applied in one direction at either run pipe or branch pipe to ensure in-plane or out-of-plane bending moments were produced in the model. This analysis includes 28 cases for multiple combinations of loads and boundary conditions. As defined in NB-3682, stress indices are determined by B, C = σ/S where σ is elastic stress in the component and S is the nominal stress in the component. The B2 indices were calculated by two methods: method one which is the default solution in FEA program, all six stress components were applied to calculate the membrane plus bending stress; method two, axial and hoop normal stress components and torsional shear stress components were used to get the membrane plus bending stress. The results show that the method two for B2 indices are more reasonable and realistic. For C2 indices method one was determined to be more appropriate. This paper presents the results of the analysis, the basis for stress indices development and the resulting stress indices.
A Damage Assessment of Autofrettaged Tubes Exposed to Decompositions in an LDPE Facility
Authors: Cochran Jeffrey D. , Silfies Trace P. , Dobis Jonathan D.
Published: November 2015

The manufacture of low density polyethylene (LDPE) by radical polymerization regularly subjects components to extreme pressures exceeding 20 ksi and, possibly, to runaway decomposition reactions with temperatures exceeding 1500 °F and pressures above 30 ksi. Components subject to such extreme conditions are often autofrettaged to induce a beneficial residual stress distribution that retards crack growth and extends fatigue life. Three samples of autofrettaged tubes extracted from these components are examined here. Only one of these samples is known to have been exposed to multiple decompositions while in service. Measurements of the remaining residual stress were taken for each of these tube samples, and a number of other metallurgical tests were performed. The results show that the tube experiencing decompositions lost almost all of the beneficial residual stress induced by autofrettage and actually has a large, detrimental tensile stress at the inner surface. Corresponding to this is a band of embrittled material with a significantly altered microstructure that was most likely caused by thermal excursions. The tubes that experienced no decompositions showed no such alterations, and their residual stress distributions were relatively intact. An FFS assessment of crack-like flaws was performed on these tubes in accordance with API 579-1/ASME FFS-1 in order to determine the effect of this loss of residual stress on remaining life and quantify this loss in terms of a damage parameter.
My Pipes Are Corroding! When Should I Repair? Getting the Answers You Need for Maintaining Pipeline Integrity
Authors: Turnquist Michael
Published: November 2015

This case study exhibits how groundbreaking inspection methodologies combined with innovative computational analysis practices demonstrate the value of conducting fitness-for-service (FFS) assessments on sectional piping. In this instance, a fitness-for-service assessment was performed on two sections of piping experiencing external corrosion at the pipe-to-elbow seam welds.

A full external scan and spot ultrasonic thickness (UT) readings were used to create the corroded geometry and verify accurate measurement of the remaining thicknesses in various corroded locations. This allowed for the actual corroded profiles to be accurately modeled using finite element analysis (FEA).

Complications were present when modeling the observed metal loss. Through the use of innovative finite element mesh generation practices, the actual measured corroded geometry was modeled without the need for over-conservative geometric simplification. A Level 3 FFS assessment was then performed in addition to a remaining life assessment based on observed corrosion rates. The result of this analysis was that the piping could remain in service for at least two additional years before needing repair.
Validation of Friction Model Parameters Identified Using the Inverse Harmonic Balance Method
Authors: Hadji Abdallah , Mureithi Njuki
Published: November 2015

A hybrid friction model was recently developed by Azizian and Mureithi [1] to simulate the friction behavior of tube-support interaction. However, identification of the model parameters remains unresolved.

In previous work, the friction model parameters were identified using reverse the harmonic method, where the following quantities were indirectly obtained by measuring the vibration response of a beam: friction force, sliding speed of the force of impact and local displacement at the contact point.

In the present work, the simulation by the finite element method (FEM) of a beam clamped at one end and simply supported with the consideration of friction effect at the other is conducted. This beam is used to validate the inverse harmonic balance method and the parameters of the friction models identified previously.

Two static friction models (the Coulomb model and Stribeck model) are tested. The two models produce friction forces of the correct order of magnitude compared to the friction force calculated using the inverse harmonic balance method. However, the models cannot accurately reproduce the beam response; the Stribeck friction model is shown to give the response closer to experiments.

The results demonstrate some of the challenges associated with accurate friction model parameter identification using the inverse harmonic balance method. The present work is an intermediate step toward identification of the hybrid friction model parameters and, longer term, improved analysis of tube-support dynamic behavior under the influence of friction.
Cohesive Zone Modeling of Hydrogen Assisted Cracking in a 15-5 PH Steel and Comparison With Experiments
Authors: Bilotta Giovambattista , Arzaghi Mandana , Hénaff Gilbert , Benoit Guillaume , Moriconi Clara , Halm Damien
Published: November 2015

Gaseous hydrogen substantially reduces fracture properties such as threshold stress intensity factor and crack growth resistance in the precipitation-hardened martensitic stainless steel investigated in this study. Fatigue crack propagation tests were performed on CT specimens under different atmospheres (hydrogen pressures from 0.09 to 40 MPa) on the Hycomat test bench, at the Pprime Institute in Poitiers, France. A strongly enhanced crack growth regime was identified at high hydrogen pressure and low-frequency loading. Crack growth rates obtained at a constant load under same pressure levels suggest that a combination of tensile stresses above a threshold (KIscc) and fatigue cycles contribute to the hydrogen embrittlement at the crack tip.

These experimental results were compared to the finite element simulation results obtained by a recently developed cohesive zone model at the crack tip. A specifically developed traction-separation law which is suitable to describe the gradual degradation of cohesive stresses under monotonic and cyclic loadings, and which is furthermore sensitive to the hydrogen concentration was used. The effects of the different testing conditions, in terms of loading frequency and hydrogen pressure, on the modeling results are discussed. It was shown that the model qualitatively predicts the detrimental influence of gaseous hydrogen on the crack growth rates.
Modeling and Simulation for Pressing Process With Reconfigurable Punch and Die
Authors: Feng Zhengkun , Champliaud Henri
Published: November 2015

Pressing processes are widely used to reduce manufacturing cost by saving raw material when machining the deformed shapes and by reusing pressing tools. However, the conventional pressing process with matched punch and die is not suitable for flexible process when the shapes are variable and the production batches are small. In this paper, modeling of pressing process with reconfigurable punch and die is presented. The numerical results agree well with those obtained from the model of the conventional pressing process with matched punch and die.
Fatigue Monitoring and Assessment: Different Approaches Combined for Lifetime Extension Challenges
Authors: Gilman Tim , Gray Mark , Rudolph Jürgen , Heinz Benedikt
Published: November 2015

For plant lifetime extension programs, several products provide a customized solution for thermal load monitoring and fatigue calculation. Requirements like the consideration of Environmentally Assisted Fatigue (EAF) effects or flexible plant (e.g. load follow) operation have a crucial impact on the engineering practice of a detailed fatigue assessment considering the realistically occurring loads.

Several fatigue monitoring products are available on the market, some with local instrumentation added and some with transfer function approaches using existing plant instrumentation. The regulator in Germany requires thermal loading to be evaluated as realistically as practical, and thus additional instrumentation is typically added to measure the thermal response close to the monitored location. Elsewhere, and specifically in the U.S., the regulator has not required the addition of instrumentation, and thus utilities typically do not choose to add instruments.

It is one purpose of the paper to explain in detail the different engineering approaches and the methodology of fatigue assessment, also under consideration of Environmentally Assisted Fatigue (EAF) and the calculation of the complete six terms stress tensor for given load-time histories. Considering the fatigue analysis of given input data (stress-time-histories) the comparability of fatigue calculations constitutes a challenging item. Recommendations will be given how to harmonize the approaches based on the technical and regulatory requirements.

Finally, the issue of design code based fatigue monitoring guidelines and approaches is discussed. In this context, the German Nuclear Safety Standard KTA 3201.4 is addressed.
Further Insights on the Relationship Between J and CTOD for SE(B) and SE(T) Specimens Including Ductile Crack Propagation
Authors: Sarzosa Diego F. B. , Ruggieri Claudio
Published: November 2015

In structural assessment procedures the crack driving force is usually estimated numerically based on the J -Integral definition because its determination is well established in many finite element codes. The nuclear industry has extensive fracture toughness data expressed in terms of J-Integral and huge experience with its applications and limitations. On the other hand, material fracture toughness is typically measured by Crack Tip Opening Displacement (CTOD) parameter using the hinge plastic model or double clip gauge technique. The parameter CTOD has a wide acceptance in the Oil and Gas Industry (OGI). Also, the OGI has a lot of past data expressed in terms of CTOD and the people involved are very familiar with this parameter. Furthermore, the CTOD parameter is based on the physical deformation of the crack faces and can be visualized and understood in an easy way. There is a unique relationship between J and CTOD beyond the validity limits of Linear Elastic Fracture Mechanics (LEFM) for stationary cracks. However, if ductile crack propagation occurs, the crack tip deformation profile and stress-strain fields ahead of the crack tip will change significantly when compared to the static case. Thus, the stable crack propagation may change the well established relationship between J and CTOD for stationary cracks compromising the construction of resistance curves J-Δa from CTOD-Δa data or vice versa. This investigation is a complementary study on the relationship between J-Integral and CTOD under ductile crack propagation of a previous work. The theoretical definition of CTOD using the 90° method and the empirical expression used in the standard ASTM E1820 are analyzed under stable crack growth. Plane-strain finite element computations including stationary and growth analysis are conducted for 3P SE(B) and clamped SE(T) specimens having different notch length to specimen width ratios in the range of 0.1–0.5. For the growth analysis, the models are loaded to levels of J consistent to a crack growth resistance curve representative of a typical pipeline steel. A computational cell methodology to model Mode I crack extension in ductile materials is utilized to describe the evolution of J with a. Laboratory testing of an API 5L X70 steel at room temperature using standard, deeply cracked C(T) specimens is used to measure the crack growth resistance curve for the material and to calibrate the key cell parameter defined by the initial void fraction, f 0. The presented results provide additional understanding of the effects of ductile crack growth on the relationship between J-Integral and CTOD for standard and non-standard fracture specimens. Specific procedures for evaluation of CTOD-R curves using SE(T) and SE(B) specimens with direct application to structural integrity assessment and defect analysis in pipelines and risers will be proposed, yielding accurate and robust relations between J-Integral and CTOD.
Simplified Model for the Seismic Performance of Unanchored Liquid Storage Tanks
Authors: Vathi Maria , Karamanos Spyros A.
Published: November 2015

Ground-supported unanchored liquid-storage cylindrical tanks, when subjected to strong seismic loading may exhibit uplifting of their bottom plate, which has significant effects on their dynamic behavior and strength. Those effects mainly concern: (a) the increase of axial (meridional) compression at the tank base, resulting in premature buckling in the form of elephant’s foot and (b) the significant plastic deformation at the vicinity of the welded connection between the tank shell and the bottom plate that may cause failure of the welded connection due to fracture and fatigue. The present study focuses on base uplifting mechanics and tank performance with respect to the shell/plate welded connection through a numerical two-step methodology: (1) a detailed finite element shell model of the tank for incremental static analysis, capable of describing the state of stress and deformation at different levels of loading and (2) a simplified modeling of the tank as a spring-mass system for dynamic analysis, enhanced by a nonlinear spring at its base to account for the effects of uplifting. Two cylindrical liquid storage tanks of different aspect ratios are modeled and analyzed in terms of local performance of the welded connection. The results are aimed at better understanding of tank uplifting mechanics and motivating possible amendments in existing seismic design provisions.
Things to Concern for Finite Element Analyses
Authors: Shoji Yasumasa
Published: November 2015

Recently FEA (Finite Element Analysis) is used in various engineering fields such as for design, verification, validation trouble-shooting and other applications. As the more users are treating FEA, the quality of analyses has become the larger issue.

Finite Element Method (FEM) is just a calculation method to reproduce physical phenomena, and it has functional limitation in nature. As the software becomes more and more user-friendly, the limitation is hidden in the operation. However, as the limitation still exists in principle, users must be aware of it when using the FEA software.

This paper will address about the issues that we are easily trapped in modeling, such as element selection, boundary conditions and other conditions.
Benchmark of Elastic Plastic Seismic Response Analysis and Fatigue Evaluation for Piping
Authors: Otoyo Teruyoshi , Otani Akihito
Published: November 2015

This paper shows a benchmark result regarding elastic-plastic seismic response analysis and fatigue evaluation for of piping model excitation test. National Research Institute for Earth Science and Disaster Prevention (NIED) has a lot of experimental results of shaking table test of piping. To propose advance seismic evaluation method for piping under severe seismic event, a task in JSME Code committee performs benchmark activity for elastic plastic seismic response analysis and evaluation for piping by using NIED’s experimental results [1].

Authors are taking part in the task and have been performed a benchmark of seismic response analysis and seismic evaluation by comparing with the experimental results. For fatigue evaluation, the strain ranges and the cycles of each range obtained from strain time history were evaluated. The response acceleration and displacement was evaluated for plastic collapse.
Benchmarking of Pressurized Water Reactor Blowdown Analysis Using RELAP5 and ANSYS
Authors: Luke Olivia , Xu Heqin , Liszkai Tamas
Published: November 2015

Mechanical design bases for pressurized water reactors typically include various transients involving line breaches or valve actuations in high energy pressure boundaries. Due to the rapidly changing thermal hydraulic conditions and the resulting dynamic mechanical loads caused by the depressurization wave, blowdown events require special treatment from a mechanical analysis standpoint in order to meet the requirements of 10 CFR 50 Appendix A, General Design Criteria 4 and 14. Specifically, the fluid-structure interaction (FSI) is important for accurate prediction of dynamic mechanical loads, and must be evaluated to ensure that a reasonably bounding loading profile can be assured for all components, reactor vessel internals, and supports subject to the blowdown event.

This paper proposes a methodology to evaluate dynamic responses during blowdown events for mechanical design, using the code RELAP5-3D to simulate the thermal hydraulic conditions and subsequently the code ANSYS to simulate the FSI and resulting dynamic mechanical loads. Results from the German Heissdampf Reactor (HDR) blowdown experiments are used for methodology benchmarking. HDR benchmarking cases are studied to demonstrate that the capabilities of the thermal-hydraulic code RELAP5-3D and the multi-physics code ANSYS are sufficient to analyze high energy pressure boundary breaches. Thermal hydraulic boundary conditions are generated first using a RELAP5-3D model of the HDR break location for the selected study cases. The resulting time history data from RELAP5-3D are utilized in the ANSYS model, which is comprised of structural and acoustic elements. The use of essential, natural and acoustic impedance boundary conditions is investigated to determine the optimal method for simulating the fluid-structure interaction. Simulated displacements, strains, and differential pressure on the reactor vessel and reactor vessel internals are in excellent agreement with the experimental data for the time period of interest.
Hydrogen-Assisted Cracking of Cr-Mo Steel in Slow Strain Rate Tensile Test With High-Pressure Gaseous Hydrogen
Authors: Matsunaga Hisao , Yoshikawa Michio , Kondo Ryota , Itoga Hisatake , Yamabe Junichiro , Matsuoka Saburo
Published: November 2015

Slow strain rate tensile (SSRT) tests were performed using smooth specimens of quenched and tempered JIS-SCM435 steels with three different tensile strengths (TS), which are ranged from 824 to 1127 MPa. The tests were carried out in 115 MPa hydrogen gas and reference gases (air or 115 MPa nitrogen gas) at three different temperatures; 233 K, room temperature (RT) and 393 K. In the reference gases, the specimens exhibited the so-called cup-and-cone fracture at every temperature. On the other hand, in hydrogen gas, a number of cracks initiated at specimen surface and grew, which led to a marked reduction in ductility at every temperature. The crack growth curves were obtained as a function of true strain by observing the specimen surface of the fractured specimens. The true strain at which the hydrogen-assisted cracking starts was strongly dependent on the microstructure, strength level and test temperature. However, in all the materials tested at RT, the hydrogen-assisted cracking did not occur during the uniform deformation, but occurred in the necking process. Even at 233 K and 393 K, the material with a moderate strength did not exhibit the hydrogen-enhanced cracking before reaching the TS. The result ensured that the Cr-Mo steel with a moderate strength can maintain the TS even in 115 MPa hydrogen from the viewpoint of fracture mechanism.
Fracture Behavior of Pressurized Defective Pipes Subjected to Large Tensile Strains
Authors: Paredes Marcelo , Wierzbicki Tomasz
Published: November 2015

In this work the tensile capacity of circumferentially pressurized cracked pipes with varying crack parameters and pipe dimensions are numerically investigated. The biaxial loading mode includes internal pressure and tensile load, which are applied in sequence. The present physics-inspired fracture model based upon the original Mohr-Coulomb criterion enables not only the computation of global fracture response of pipe subjected to complex loading condition but also a thorough determination of the local evolving stress state around the growing cracks.
Numerical Analysis of Weld Residual Stress in a Pressurizer Surge Nozzle Full-Scale Mockup: The Effect of Hardening Constitutive Model and Interpass Temperature
Authors: Tran Minh N. , Muránsky Ondrej , Hill Michael R. , Olson Mitchell D.
Published: November 2015

In an effort to shed light on accuracy and reliability of finite element (FE) weld modeling outputs, the U.S. Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) have been engaged in a program of cooperative research on weld residual stress (WRS) prediction. The current work presents numerical FE simulation of the WRS in a pressurizer surge nozzle full-scale mockup (Phase 2b), as a part of the broader NRC/EPRI program. Sequentially-coupled, thermo-mechanical FE analysis was performed, whereby the numerical solution from the thermal analysis was used as an input in the mechanical analysis. The thermal analysis made use of a dedicated weld modeling tool to accurately calibrate an ellipsoidal Gaussian volumetric heat source. The subsequent mechanical analysis utilized the isotropic and nonlinear kinematic hardening constitutive models to capture cyclic response of the material upon welding. The modeling results were then validated using a number of measurement techniques (deep hole drilling, contour method, slitting, and biaxial mapping). In addition, an effect of the interpass temperature (i.e. 24.5 °C, 150 °C, and 260 °C) on the final prediction of WRS is discussed.
Development of J-Integral Solutions for Semi-Elliptical Circumferential Cracked Pipes Subjected to Internal Pressure and Bending Moment
Authors: Udagawa Makoto , Katsuyama Jinya , Yamaguchi Yoshihito , Li Yinsheng , Onizawa Kunio
Published: November 2015

The J-integral solutions for cracked pipes are important in crack growth calculation and failure evaluation based on the elastic-plastic fracture mechanics. One of the most important crack types in structural integrity assessment for nuclear piping systems is circumferential semi-elliptical surface crack on the inside of the pipes. Although several J-integral solutions have been provided, no solutions were developed at both the deepest and the surface points of circumferential semi-elliptical surface cracks in pipes. In this study, with backgrounds described above, the J-integral solutions of circumferential semi-elliptical surface cracks on the inside of the pipe were developed by numerical finite element analyses. Three dimensional elastic-plastic analyses were performed considering different material properties, pipe sizes, crack dimensions and, especially, combined loading condition of internal pressure and bending moment which is a typical loading condition for nuclear piping systems. The J values at both the deepest and the surface points were extracted from finite element analysis results. Moreover, in order to benefit users in practical applications, a pair of convenient J-integral estimation equations were developed based on the calculated J values at the deepest and the surface points. Finally, the accuracy and applicability of the convenient equations were confirmed by comparing with the provided stress intensity factor solutions in elastic region and with finite element analysis results in elastic-plastic region.
Part Repair and Start/Stop Effects and Three Dimensional Residual Stress in Dissimilar Metal Welds
Authors: Brust F. W. , Punch E. , Kurth E.
Published: November 2015

PWR nuclear power plants have dissimilar metal (DM) welds at many junctions between the vessels and the piping. The DM welds are made with Alloy 82 filler materials between carbon steel and stainless steel. These are potentially susceptible to Primary Water Stress Corrosion Cracking (PWSCC). PWSCC is mainly driven by the tensile weld residual stresses (WRS) that develop during fabrication of the piping system. In particular, weld repairs that often occur during the weld fabrication process also play a strong role in the development of the weld residual stress state in and near the DM welds. Most weld residual stress analyses performed to date in order to characterize the weld residual stress state in DM welds for PWSCC crack growth, leakage, and subsequent failure used axis-symmetric assessments. The purpose of this work is to provide direct assessment of the appropriateness of this axis-symmetric assumption on the WRS by comparison with full three dimensional analyses of several nozzles. In particular, weld start stop effects on the original weld will be assessed. In addition, the effect of partial arc weld repairs will be included. Repair cases considered include 15% and 50% deep repairs of length 48-degree and 96-degree of the circumference, along with the baseline case with no repair. The more complex three dimensional WRS state from the three dimensional analyses are compared to the corresponding axis-symmetric solutions and guidelines regarding the appropriateness of 2D solutions are discussed. Finally, some limited calculations of stress intensity factors at locations along the repair are presented.
Technical Basis for the Assessment of Small Bore High Energy Piping With Lower Than Code Specified Design Minimum Thickness
Authors: Duan Xinjian
Published: November 2015

Wall thinning by Flow Accelerated Corrosion (FAC), Erosion-Cavitation (E-C), and fretting has been observed in carbon steel piping. At some locations, the predicted end-of-life wall thickness could be below the design minimum thickness required by ASME B&PV Code Section III, which is an extremely conservative analysis method. To support the life extension without replacement or repair, it is essential to demonstrate the fitness for service of degraded piping components that satisfy the mandatory structural factors with uncertainties explicitly identified and addressed in an integrated manner. The present paper discusses the key technical basis for a sound assessment of small bore high energy Class 1 piping with lower than Code specified design minimum thickness, and proposes some future research activities to further enhance the technical basis.
A Review of the NeT TG4 International Weld Residual Stress Benchmark
Authors: Smith Mike C. , Smith Ann , Ohms Carsten , Wimpory Robert
Published: November 2015

The NeT international network has undertaken a number of round robin studies examining the prediction and measurement of weld residual stresses. NeT TG4 examined the case of a three-pass slot weld made from AISI 316L steel. The project started in 2007, and is now close to completion. This paper reviews the project as a whole, and presents its achievements.
Hydrogen Diffusion Analysis in the Fatigue Crack Growth Test Under High Pressure Hydrogen
Authors: Ishikawa Nobuyuki , Ohmi Toshihito , Yokobori A. Toshimitsu
Published: November 2015

Prevention of hydrogen embrittlement is one of the most important issues for the materials used in hydrogen environment. Various mechanisms for hydrogen embrittlement were proposed, such as the decohesion mechanism and hydrogen enhanced localized plasticity. However, the process of hydrogen diffusion and accumulation into the fracture point is necessary for understanding of hydrogen embrittlement. In this paper, hydrogen embrittlement behavior during the fatigue crack extension test under high pressure hydrogen was first conducted. Then, hydrogen diffusion and accumulation behavior in the crack tip region was analyzed by the numerical simulation based on the Fick’s diffusion theory. Alpha multiplication method which multiplies stress gradient induced terms was found to be valid to realize correct particle diffusion behaviors driven by the stress gradient term. The significance of the concept of alpha multiplication method for the numerical analysis was discussed by comparing to the experimental hydrogen embrittlement behavior.
Metal Magnetic Memory Testing Technique for Typical Defects in Pressure Vessels and Pipelines
Authors: Guan Weihe , Guo Pengju , Xuedong Chen
Published: November 2015

Metal magnetic memory technique has been extensively applied in different fields due to its unique advantages of time-saving, low cost, and high efficiency. However, very limited research has been carried out on studying the characteristics of metal magnetic memory signals of different defects except crack, and also the effect of orientation angle between testing direction and defect on magnetic memory signals. To promote study in this area, the magnetic memory signals of typical defects (such as crack, slag inclusion) are investigated as well as hydrogen-induced cracking. In addition, the characteristics of magnetic memory signals when measured with different angle between testing direction and defects were obtained. The results indicate that the metal magnetic memory technique is a promising method to detect typical defects of welding and also hydrogen-induced cracking. Moreover, the technique has high sensitivity on defects no matter the angle between testing direction and defect. However, further research is needed because it can only find the possible location of defects but cannot quantitatively describe the defect.
Crack Growth Evaluation for Cracked Carbon and Stainless Steel Pipes Under Large Seismic Cyclic Loading
Authors: Yamaguchi Yoshihito , Katsuyama Jinya , Li Yinsheng , Onizawa Kunio
Published: November 2015

Japanese nuclear power plants have recently experienced several large earthquakes beyond the previous design basis ground motion. In addition, cracks resulting from long-term operation have been detected in piping lines. Therefore, it is very important to establish a crack growth evaluation method for cracked pipes that are subjected to large seismic cyclic response loading. In our previous study, we proposed an evaluation method for crack growth during large earthquakes through experimental study using small specimens. In the present study, crack growth tests were conducted on pipes with a circumferential through-wall crack, considering large seismic cyclic response loading with complex wave forms. The predicted crack growth values are in good agreement with the experimental results for both stainless and carbon steel pipe specimens and the applicability of the proposed method was confirmed.
Buckling Strength of Towers Having Partial Metal Loss on Shell Under Overturning Moment
Authors: Ozaki Masayuki , Yamaguchi Atsushi , Kaida Takuyo , Nagata Satoshi
Published: November 2015

Reliability of Fitness-For-Service assessment has become more important especially for the aged pressure equipment such as towers in process plants put in service operation over decades. The effects of partial metal loss on buckling strength of the towers subject to overturning moment due to seismic or wind load are one of the critical issues to be clarified. The present paper simulates the buckling strength of towers under overturning moment by means of finite element analysis considering the condition that the shell has suffered from partial metal loss, and evaluates the validity of the buckling stress formulae of API 579-1/ASME FFS-1, NASA, and Donnell. It has been demonstrated that the buckling strength predicted by API formulae shows fairly good agreement with that simulated by finite element analysis. Finite element analysis results have shown that the axial length of metal loss does not affect the buckling stress very much while the buckling stress depends on the circumferential width of metal loss. It has been revealed that the API formulae underestimate the buckling stress when the width of metal loss is smaller than about 30 deg. The paper proposes the modification to the API formulae in this condition that gives more accurate buckling stress than the original formulae.
Core Mechanical Dynamics Experiment in the Phénix Reactor
Authors: Broc Daniel , Cardolaccia Jérome , Martin Laurent , Portier Jean Louis
Published: November 2015

ASTRID is a project for an industrial prototype of a 600 MWe sodium cooled Fast Reactor, led by CEA. A consequent program is in progress for the development and the validation of numerical tools for the simulation of the dynamic mechanical behavior of the Fast Reactor cores, with both experimental and numerical parts. The cores are constituted of Fuel Assemblies (or FA) and Neutronic Shields (or NS) immersed in the primary coolant (sodium), which circulates inside the Fluid Assemblies. The FA and the NS are slender structures, which may be considered as beams, from a mechanical point of view.

The dynamic behavior of this system has to be understood, for design and safety studies. Two main movements have to be considered: global horizontal movements under the effect of a seismic excitation, and a radial opening of the core. The fluid presence leads to complex interactions between the structures at a distance. The dynamic behavior of the core is strongly influenced by contacts between the beams and by the interactions with the sodium, which both limit their relative displacements. Numerical methods and models are built to describe and simulate this dynamic behavior. The validation of the numerical tools is based on the results of different experimental programs, already performed or in progress.

The paper presents the interpretation of tests performed in 2013 in the Phénix reactor. The French Phénix reactor was definitively shutdown in 2009 and is currently at an early stage of the decommissioning process. Before unloading the core, it has been decided to perform one last experimental campaign aimed at testing the mechanical dynamic behavior of the core. The interpretation of the tests highly contributes to the validation of the simulation methods. Relatively good comparisons have been obtained between the theoretical and experimental results, for the static excitation (stiffness of the bundle) and for the dynamic response (characteristic times). The tests confirm that the fluid leads to a significant decrease of the frequencies. Uncertainties remain on the significant damping which seems to be present, and may be due to the fluid or to the structures.
Failure Analysis of a High-Pressure Steam Pipeline
Authors: Shi Jin , Zhang Kai , Liu Wen , Xie Guoshan , Ye Guoqing , Li Wurong
Published: November 2015

In this paper, a failure analysis was performed on a high-pressure steam pipeline, which was burst after service in a chemical plant for 12 years. The burst field was investigated and the fragments were observed. Microstructures of the pipeline were analyzed by optical microscope (OM) and scanning electron microscope (SEM). The mechanical properties tests, including tensile testing and Charpy V notch impact testing, were performed on specimens removed from the high-pressure steam pipeline. The impact testing results showed that toughness of the material was poor and little resistance against cracking extension. According to further analysis, strain aging was the dominant mechanism of the failure. Some inspection approaches were recommended to prevent similar failures.
Development and Use of the Risk-Based Joint Integrity (RBJI) Assessment Methodology
Authors: Brown Warren
Published: November 2015

The ability to determine, using a uniform approach, which joints in a unit, plant or company represent the highest level of risk of leakage is extremely useful. Similarly to Risk-Based Inspection (RBI), Risk Based Joint Integrity (RBJI) allows the identification and allocation of resources to the joints that pose the greatest risk of failure. This ensures that the appropriate level of effort is placed in the most appropriate locations.

This paper outlines a quantitative methodology for assessing the probability of failure for any given pressure boundary bolted joint. It allows rapid calculation across a range of joints without resorting to the typical qualitative, reactive, experienced-based methods commonly employed to assess risk of joint leakage (i.e.: waiting for the joint to leak in order for it to be labelled a bad actor). This methodology has been successfully employed in a number of applications over the past three years, such as justification of heat exchanger replacement (demonstrating the expected improvement in joint integrity) and assessment of residual risk associated with historic joint assembly practices. Future applications include assessment of risk and definition of acceptable residual risk during the project design phase in order to eliminate problematic joints prior to fabrication and using the methodology to reduce the time associated with leak-testing of piping systems during maintenance turn-around activities.
A Probabilistic Life, Damage, and Uncertainty Assessment Method for Engineering Components and Systems
Authors: Wei Zhigang , Luo Limin , Guo Litang , Lin Shengbin (Burt)
Published: November 2015

Fatigue life and damage assessment is crucial to the durability and reliability performances of engineering components and systems, especially at early design and validation stages. However, durability and reliability assessment of engineering components and systems is difficult due to, partially, the large uncertainties introduced from many sources. How to quantitatively measure the uncertainties is an important task in engineering probabilistic analysis. Recently, based on fatigue failure data, a new procedure has been developed to assess the durability, reliability and uncertainty of components under constant amplitude loadings. An uncertainty measure, which is very similar to those used in computational complexity, classical statistical physics and information theory, has been proposed. In this paper, two new developments are reported: (1) the uncertainty measure is modified in such a way that the uncertainty measure can be normalized, (2) the durability, reliability and uncertainty analysis procedure is extended to system level. Several examples are provided to demonstrate the effectiveness of the new probabilistic life, damage, and uncertainty assessment approach.