bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Evaluation Procedure for Calculating the Stress Intensity Factor of Flaws Beneath RPV Cladding During Pressurised Thermal Shock Events by FE Analysis
Authors: Sakamoto Hiroyuki , Hirota Takatoshi , Ogawa Naoki
Published: December 2016

Elastic-plastic finite element (FE) analysis is performed to determine the plastic behavior of the reactor pressure vessel (RPV) inner surface caused by rapid cooling during pressurized thermal shock (PTS) events. However, as the J-integral is not path-independent for elastic-plastic material in the unloading process, it is necessary to apply a suitable correction method using elastic material. In addition, it is also necessary to consider the effect of the welding residual stress appropriately.

Therefore, we investigated the stress intensity factor derived from FE analysis based on a model consisting of elastic-plastic cladding and linear elastic low-alloy steel with subsequent plastic zone correction, since the stress level of low-alloy steel remains within the elastic region except the crack front during a PTS event. Furthermore, we examined whether the stress mapping method is applicable for reflecting the effect of welding residual stress in FE analysis, even though the plastic strain generated during welding is ignored.
Failure Analysis of Spiral Water Wall Tube Cracking in Ultra-Supercritical Power Plant Boiler
Authors: Si Jun , Yan Zhenrong , Chen Jianjun
Published: December 2016

The efficiency of conventional boiler/steam turbine fossil power plants has strong relationship to the steam temperature and pressure. At present, steam temperatures of the most efficient fossil power plants are now in the 600°C range. Higher-strength materials are needed for upper water wall tube of boilers with steam pressure above 24 MPa. A high-strength 2.5%Cr steel recently approved by ASME code as T23 is the preferred candidate material for this application. Due to its superior properties, T23 steel is typically not post-weld heat treated. However, after several years running there are a lot of incident reports for T23 tubes especially the breakage of weldment in the ultra-supercritical power plant. This is cause for concern for T23 tubes weldment used under high temperature environments. Previous studies showed that the residual stress may play an important role to the performance of spiral water wall tube.

In this paper, the distribution of residual stress in T23 tube weldment has been investigated in detail. Inner wall cracks were found at the butt-jointed seam region of spiral water wall tubes by radiographic testing after one year’s operation. Failure analysis of the spiral water wall tube cracking was conducted by chemical composition analysis, mechanical testing and finite element analysis in this paper. It was found that localized residual stress after the weld process caused concentrated stress, which is the primary reason for failure. Our studies illustrate the necessity of post weld heat treatment for the T23 tubes used under high temperature.
Improvement of the LBB.ENG2 Circumferential Through-Wall Crack J-Estimation Scheme
Authors: Olson Richard , Kalyanam Sureshkumar , Park Jeong Soon , Brust Frederick W.
Published: December 2016

The LBB.ENG2[1] circumferential through-wall crack (TWC) J-estimation scheme forms the basis for the Extremely Low Probability of Rupture (xLPR)[2] probabilistic pipe fracture analysis for TWC elastic-plastic fracture mechanics (EPFM) stability assessment. The LBB.ENG2 methodology uses a reduced thickness pipe wall analogy to approximate the behavior of actual cracked pipe and sets the thickness of the reduced section by making the usual cracked pipe limit load assumption. Sometime during the original LBB.ENG2 development process, it was discovered that LBB.ENG2 was not as good as desired at predicting the maximum moment carrying capacity of pipe fracture experiments with longer cracks. Accordingly, the effective thickness equation was modified to be 1.0 at crack angles less than π/4, 4/π at angles greater than π/3, and linear between these values using a so-called ψ function.

When LBB.ENG2 was coded for the TWC stability module for xLPR, TWC_fail, the behavior described above was implemented. Quite unexpectedly, with the new coding, exploration of TWC_fail’s bounds uncovered two discontinuities in the complete moment-pressure-critical crack size failure surface. Subsequently, it was found that these discontinuities were caused by the discontinuity in the derivative of the ψ function.

This paper documents the approach used to smooth the TWC_fail moment-pressure-critical crack size surface by making a ψ function fit that minimizes the difference between J from LBB.ENG2 and J from finite element analyses results. The results of the finite element analyses and fitting methodology are described and the basic equations for the solution are presented. Following this, the new ψ function is applied to cases to evaluate the efficacy of the approach.
A Model for Probabilistic Seismic Risk Assessment of Process Plants
Authors: Caputo Antonio C.
Published: December 2016

Seismic vulnerability of industrial plants processing hazardous substances is widely documented, and thousands of such facilities are located in areas of medium to high seismicity near population centers. Nevertheless, with the exception of the nuclear industry, national or international standards do not establish any procedure for the overall seismic risk assessment of industrial process plants located in earthquake-prone areas. Moreover, existing Probabilistic Seismic Risk Assessment (PSRA) methods developed by the nuclear industry are not readily applicable to process plants. In order to overcome this limitation, in this paper a novel general-purpose PSRA method is presented, able to systematically generate potential starting scenarios, deriving from simultaneous interactions of the earthquake with each separate equipment, and to account for propagation of effects between distinct equipment (i.e. Domino effects) keeping track of multiple simultaneous and possibly interacting chains of accidents. This allows to dynamically generate damage scenarios, and to rank their risk levels determining the critical process units that can be involved.
Effects of Hot Water and Holds on Fatigue of Stainless Steel
Authors: Solin Jussi , Alhainen Jouni , Karabaki Ertugrul , Mayinger Wolfgang
Published: December 2016

Direct strain controlled LCF data for solid specimens is still very rare. In PVP2013-97500 and PVP2014-28465 we reported results for niobium stabilized X6CrNiNb1810mod steel (type 347) fatigued in 325°C and 200°C PWR water according to VGB water chemistry specification. New data in this paper further confirms the conclusions: we are unable to repeat as high Fen factors or short lives as predicted according to NUREG/CR-6909.

The slowest strain rate used 4·10−6 in 325°C water would predict Fen > 12, i.e. laboratory specimen data below the current ASME design curve, but our results are superior for this steel generally used in German NPP’s. However, the difference is not necessarily grade specific. Use of 100% relevant fabricated material batch and standard LCF methodology are regarded to play an important role.

Notable hardening can be measured, when long duration holds in elevated temperatures are introduced between blocks of cyclic strains at lower temperatures. This is the case for thermal gradient loaded primary circuit components, e.g. the PWR pressurizer spray lines or surge line, which connects the pressurizer to primary coolant line. In PVP2011-57942 we reported improved endurances in fatigue tests aiming to roughly simulate steady state operation between fatigue transients in such NPP components. New test types have been introduced to generalize the results.

Mechanisms of time and temperature dependent relaxation of fatigue damage and/or improvement of material fatigue performance during holds are not yet fully revealed, but the rate controlling thermal activation energy is below shown to be near that for vacancy and interstitial atom diffusion. This allows us to draft a thermodynamic prediction model.

Improved accuracy of fatigue assessment helps in focusing optimally scheduled nondestructive testing to the most relevant locations and maintaining high level of reliability without excessive cost and radiation doses for inspection personnel.

This paper provides previously unpublished experimental results and proposes methods to improve transferability of laboratory test data to fatigue assessment of NPP components. The effects of material, water environment, temperature and service loading patterns are discussed.
Multi-Element Lamb Wave Transducers to Classify Damage Type and Characterize Size Based on Modal Content
Authors: Ren Baiyang , Lissenden Cliff J.
Published: December 2016

Assessing the structural integrity of PVP systems entails a hierarchical process to detect, locate, classify, and size damage in order to predict the remaining useful life of the system. Technologies to detect and locate damage have been researched intensely over the years, but classification and sizing of damage remains a challenging problem. In this work advanced sensing technology is employed to send and receive Lamb waves in plates. The receiver is a 16-element linear array that is made from PVDF; thus it is lightweight, low profile, flexible, inexpensive, and has minimal cross talk. The receiver has two novel capabilities that open new opportunities in diagnostics and prognostics: measurement of group velocity and determination of modal content. The actuator and receiver are intended to stay in place and function in a pitch-catch mode. The use of modal content to classify the type of damage as well as to size the defect is demonstrated.
Oore-Burns Function of Form Application in Numerical Treatment of Mode I Flat Crack Problem in Infinite Body
Authors: Orynyak Igor , Batura Anatolii , Oryniak Andrii , Lokhman Igor
Published: December 2016

The general approach of numerical treatment of integro-differential equation of the flat crack problem is considered. It consists in presenting the crack surface loading as the set of the polynomial functions of two Cartesian coordinates while the corresponding crack surface displacements are chosen as the similar polynomials multiplied by the function of form (FoF) which reflects the required singularity of their behavior. To find the relations matrixes between these two sets a new effective numerical procedure for the integration over the area of arbitrary shape crack is developed. In based on the classical hyper-singular method, i.e. Laplace operator is initially analytically applied to the integral part of equation and the resulting hyper singular equation is subsequently considered.

The presented approach can be implemented with any variant of FoF, but Oore-Burns FoF, which was earlier suggested in their famous 3D weight function method, is supposed to be the most accurate and universal. It takes into account all points of crack contour, which provides perfect physical conditionality of the solution, but such FoF is relatively heavy in implementation and of low computational speed. The special procedure is developed for the approximation of the crack contour of arbitrary shape by the circular and straight segments. It allows to easily obtain analytical expression for Oore-Burns FoF, which greatly increases the calculation speed and accuracy. The accuracy of the considered method is confirmed by the examples of the circular, elliptic, semicircular and square cracks at different polynomial laws of loading.

The developed methods are used in the implemented procedure for crack growth simulation. It allows to model growth of crack of arbitrary shape at arbitrary polynomial loading, at that all contour points are taken into account and can expand with their own speeds each. Procedure has high accuracy and don’t need complex and high-cost re-meshing process between the iterations unlike FEM or other numerical methods. At that usage of Oore-Burns FoF provides high flexibility of the presented approach: unlike similar theoretical methods, where FoF calculation procedure is rigidly connected with the crack shape, which complicates the adequate crack growth modeling, the used FoF automatically takes into account all points of crack contour, even if its shape became complex during the growth. Presented crack growth procedure can be effectively used to test accuracy and correctness of correspondent numerical methods, including the newest XFEM approach.
Re-Evaluation of Long-Term Creep Strength of Base Metal of ASME Grade 91 Type Steel
Authors: Kimura Kazuhiro , Yaguchi Masatsugu
Published: December 2016

Creep rupture strength of ASME Grades 91, 92, 122 and 23 type steels were evaluated by the SHC committee in 2004 and 2005, and the Assessment Committee on Creep Data of High Chromium Steels in 2010. According to the evaluation of creep rupture strength, allowable stress of the steels was revised and weld strength reduction factor (WSRF) was established. In 2015, the creep rupture data of those steels was collected from materials producers, power plant manufacturers and institutes in Japan and a review of long-term creep rupture strength of the steels was conducted by the Assessment Committee on Creep Data of High Chromium Steels in reference to the previous evaluation. It has been confirmed with the latest dataset that re-evaluation of long-term creep rupture strength is not required for Grades 92, 122 and 23 type steels. On the other hand, lower creep rupture strength compared with the previous evaluation was recognized on the new creep rupture data of Grade 91 steels, therefore, re-evaluation of creep rupture strength was conducted on Grade 91 steels. Creep rupture strength was assessed by means of region splitting analysis method in consideration of 50% of 0.2% offset yield strength, in the same way as the previous study. According to the evaluation of long-term creep strength of the steels, allowable tensile stress was reviewed and proposed revision was concluded.
Environmental Fatigue and Fatigue Monitoring System in Korea
Authors: Boo Myung-Hwan , Lee Kyoung Soo , Kim Hyun-Su , Oh Chang-Kyun
Published: December 2016

In accordance with the recommendation of USNRC and the U.S. license renewal experiences, the effect of reactor coolant environment on the fatigue life has to be considered for the continued operation of operating nuclear power plants as well as for the design of new plants in Korea. The reason is that it is very important to maintain the structural integrity and reliability of the nuclear power plants against the fatigue failure during operation. Fatigue monitoring system has been considered as a practical way to ensure safe operation of the nuclear power plants in terms of the fatigue. The fatigue monitoring system evaluates various plant conditions and their effects on the monitored location to give quantified value that indicates accumulated fatigue damage up to date. From this, the authors have developed a fatigue monitoring system, named NuFMS (Nuclear Fatigue Monitoring System) in web environment and has been being applied widely to Korean nuclear plants. In this paper, overall configuration and characteristics of the NuFMS are described in detail.
Classification of the Extent of Wall Thinning in Pipes Based on Simulations in the Time and Frequency Domain
Authors: Alobaidi Wissam M. , Sandgren Eric
Published: December 2016

Numerical simulations created with Computer Simulation Technology (CST) modeling are used to classify and evaluate the microwave signal (waveform) in order to determine whether various parameters of pipe wall thinning (PWT) can be identified. Microwaves are used to carry out the measurement of PWT in 9 CST simulations using three cross-sectional profiles, three lengths of PWT, and three depths of PWT, to determine whether there are differences in waveforms that can be used to distinguish the parameters of unknown discontinuities (PWT). The modeled system uses the pipe as a circular waveguide (bandwidth 0.486GHz) with sweeping frequencies from 1.914GHz to 2.4GHz. Waveforms are found to be distinguishable based on the three parameters modeled in the study. This research establishes the possibility of creating a nondestructive testing system with which PWT discontinuities might be characterized using microwaves in the S11 and S21 scattering parametrics. The waveforms generated for known series of PWT cases, once cataloged, can be used in the future to identify discontinuities in test pipes, and to determine their degree of similarity to the standardized waveforms via pattern recognition algorithms.
Hydrogen Desorption From 6061 Aluminum Alloy During Deformation Detected by a New Apparatus
Authors: Zhang Lin , Zheng Jinyang , An Bai , Zhou Chengshuang
Published: December 2016

Hydrogen desorption from 6061 aluminum alloy during deformation was investigated by a new type of ultrahigh vacuum apparatus. The new apparatus which combined tension and outgassing experiments can be used to measure hydrogen desorption from the specimen during deformation. Outgassing corresponded to the deformation process, which initially released surface-adsorbed hydrogen. After elastic deformation, the as-received specimen released hydrogen because of the rupturing of the surface oxide layer. The hydrogen-charged specimen showed lower hydrogen concentration and hydrogen release rate than the as-received specimen. The second hydrogen release peak was due to the hydrogen accumulation at the interface between the oxide layer and matrix. The irregular sharp hydrogen release peaks resulted from the hydrogen bubble exposed to the surface during the rupture of the surface oxide layer.
Threshold for Hydrogen-Induced Fracture in 2.25Cr-1Mo Steel Used for Long-Term Service
Authors: Nakanishi Hiroki , Fujiki Wataru , Ohtani Hiroaki , Konosu Shinji
Published: December 2016

Structural materials employed for high-temperature and high-hydrogen-pressure service require excellent strength, and 2.25Cr-1Mo steel is widely used for such purposes. For instance, it is used in pressure vessels employed for hydro desulfurization, hydrocracking, and coal-liquefaction units. However, instances of hydrogen-related cracks occurring during a shutdown period have been reported when 2.25Cr-1Mo steel is used for long periods at high temperatures and high hydrogen pressures. As the risk of internal hydrogen embrittlement during shutdown, along with the detrimental effect of long-term temper-embrittlement, is a particular concern for the integrity and safe operation of pressure vessels, the combined effect of temper-embrittlement and hydrogen embrittlement in Cr-Mo steels was previously investigated using a step-cooling treatment, which is an accelerated temper-embrittlement treatment. In practical usage, it is important to ascertain the threshold stress-intensity factor at the onset of hydrogen-enhanced crack growth, KIH, of the material following long-term use. In the present study, we employed the offset potential-drop method to clarify the threshold stress-intensity factor, KIH for 2.25Cr-1Mo steel that had been used in actual equipment for a period of approximately 64,000 h at service temperatures (360–440 °C).
Prediction of Low-Cycle Fatigue Lives of Elbow and Tee Pipes Using Revised Universal Slope Method
Authors: Nagamori Hiun , Takahashi Koji
Published: December 2016

The stress states of elbow and tee pipes are complex and different from those of straight pipes. Several researchers have reported the low-cycle fatigue lives of elbows and tees under cyclic bending with internal pressure conditions. In this work, finite element analyses were carried out to simulate the reported experimental results of elbows and tees. The crack initiation area and the crack growth direction were successfully predicted by the analyses. The analytical results showed that the revised universal slope method can accurately predict the low-cycle fatigue lives of elbow and tee pipes under internal pressure conditions regardless of differences in shape and dimensions.
Trial Model Tests With Simulation Material to Obtain Failure Modes of Pipes Under Excessive Seismic Loads
Authors: Nakamura Izumi , Kasahara Naoto
Published: December 2016

Piping systems are one of the central components of NPP; It is well known that the major failure mode under seismic loads is likely to be fatigue failure. Other failure modes, however, such as ratchet-buckling failure, have been reported to occur under particular conditions. It is necessary to clarify the conditions that cause different failure modes of piping systems under very high seismic motion, but experimental studies with steel pipes are difficult to achieve, mainly due to the limitations of testing facilities and safety concerns. In order to overcome such difficulties, we propose a new experimental approach that uses pipes made of a simulation material instead of steel. Lead (Pb) pipes were used for the simulation material, and shaking table tests were conducted on lead elbow pipe specimens. Results showed that ratchet-collapse and overall deformation of pipe specimens were possible failure modes. The ratchet-collapse failure mode appeared to be affected not only by input acceleration level but also by the direction of gravity, the primary constant stress level of its own weight, and the frequencies of the input motion. The dynamic behaviors of pipes in the high inelastic region where a nearly fully plastic section was assumed were quite different from those in the elastic region, and those of the steel pipes in previous studies. We demonstrate that the proposed test approach is effective for qualitatively clarifying various kinds of failure behaviors with large plasticity under excessive seismic load.
Characterization of Interaction Between Elliptical Subsurface Flaws
Authors: Azuma Kisaburo , Li Yinsheng , Hasegawa Kunio
Published: December 2016

Multiple flaws are often observed in engineering structures and components. Interactions between multiple flaws can increase the stress intensity factors. Although fitness-for-service codes provide combination rules to account for these effects, they do not unify the criteria for flaw combinations. To establish a reasonable combination rule, we must identify the parameters that dominate the interaction. This study investigates the interactions of stress intensity factors in two coplanar subsurface flaws in a plate. The plate was subjected to a remote tension acting normal to the flaw surface. For varying shapes and distances of elliptical subsurface flaws, we solved the intensity factors by finite element analyses. Flaw distance and area were identified as important parameters for characterizing the interaction factor between two subsurface flaws.
Evaluation of a New Approach for Characterizing Environmental Stress Cracking Resistance (ESCR) of Polyethylene
Authors: Jar Ben , Zhang Yi
Published: December 2016

A study was conducted to develop a new approach for characterizing environmental stress cracking resistance (ESCR) of polyethylene (PE). The main objective is to reduce time for the testing, to be shorter than that required for the current standard ESCR tests. The new approach applies indentation to generate deflection in the central region of a PE plate, and uses time for crack generation under constant displacement, during the exposure to an aggressive agent, to characterize ESCR. The indentation introduces stretch to a central annular region around the indenter, in which PE molecules are increasingly oriented in the stretch direction. Since this annular region is subjected to bi-axial tension, exposure to aggressive agent increases its vulnerability to crack formation in the stretch direction. ESCR is characterized by the time needed for crack formation during the exposure to an aggressive agent (10% Igepal CO-630 solution). This paper presents the test set-up for the new approach, and compares time for the crack generation using this new approach with that from ASTM D1693, condition A.
An Improved Mechanism-Based Creep Constitutive Model Using Stress-Dependent Creep Ductility
Authors: Zhou Yu , Xuedong Chen , Fan Zhichao , Yichun Han
Published: December 2016

Creep ductility which is assumed to be constant at a given temperature in many creep constitutive models, actually varies with temperature, stress level and creep strain rate, etc. In this paper, the relationship between creep ductility and stress levels of ferritic steels has been briefly discussed from the perspective of failure mechanisms. It can be generally divided into three regimes, including the upper shelf, lower shelf and the transition regime. The four-parameter logistic model has been adopted to quantitatively describe the stress-dependent creep ductility. Furthermore, a modified mechanism-based continuum damage mechanics (CDM) model for ferrtic steels has been proposed using the stress-dependent creep ductility model. Uniaxial creep tests of 2.25Cr1Mo0.25V steel at three stress levels have been carried out and the experimental data points realistically reflecting the creep behavior have been carefully selected to fit the improved CDM model using genetic algorithm (GA). It is shown that the improved model has the capability to characterize the whole creep process of ferritic steels and the stress-dependent creep ductility over a wide range of applied stress.
Core Seismic Experiment of a Full-Scale Single Model for a Fast Reactor
Authors: Iwasaki Akihisa , Sawa Naoki , Matsubara Shinichiro , Kitamura Seiji , Okamura Shigeki
Published: December 2016

A fast reactor core consists of several hundred core elements, which are hexagonal flexible beams embedded at the lower support plate in a hexagonal arrangement, separated by small gaps, and immersed in a fluid. Core elements have no support for vertical fixing in order to avoid the influence of thermal expansion and swelling. These days, in Japan, larger earthquake vibrations are postulated in seismic evaluations. So, it is necessary to consider vertical displacements (rising) and horizontal displacements of the core elements simultaneously because vertical seismic vibrations are larger than the acceleration of gravity. The 3D vibration behavior is affected by the fluid force of the ambient coolant and contact with the surrounding core elements.

In this study, single-model vibration tests using a full-scale test model were conducted, and the basic characteristics of 3D vibration behavior of the core element were examined. In addition, structures restricting vertical displacements (dashpot structure) were devised, and their effectiveness was verified. As a result of the tests, the effects of the ambient condition (in air, in static water, and in flowing water), gap between the pads, vibration directions, vibration waves, and dashpot structures on the vibration behavior of the core element were examined. As regards the ambient condition, the vertical displacements were larger in flowing water that simulates the coolant flow than in air and in static water, because of upward fluid force in flowing water. As regards the gap between the pads, the larger the gaps was, the stronger the interferences due to horizontal displacements, and the smaller the vertical displacements were. The dashpot structure was verified to be suitable for reducing vertical displacements.
Stress Intensity Factor Solutions for Subsurface Flaws in Plates Subjected to Polynomial Stress Distributions
Authors: Lu Kai , Katsuyama Jinya , Li Yinsheng , Iwamatsu Fuminori
Published: December 2016

Stress intensity factor (SIF) solutions for subsurface flaws near the free surface in plates were numerically investigated based on the finite element analyses. The flaws with aspect ratios a/ℓ = 0, 0.1, 0.2, 0.3, 0.4 and 0.5, the normalized ratios a/d = 0, 0.1, 0.2, 0.4, 0.6 and 0.8 and d/t = 0.01 and 0.1 were taken into account, where a is the half flaw depth, ℓ is the flaw length, d is the distance from the center of the subsurface flaw to the nearest free surface and t is the wall thickness. Fourth-order polynomial stress distributions in the thickness direction were considered. Based on the results, it can be concluded that the numerical SIF solutions obtained in this study are useful in engineering applications.
The Law of Crack Growth Life Under Load Controlled Creep-Fatigue Conditions for W-Added 12% Cr Steel
Authors: Nagumo Yoshiko , Yokobori A. Toshimitsu , Fukuda Takahiro , Takahashi Yoshiki , Sugiura Ryuji
Published: December 2016

W-added 12% Cr ferritic heat resistant steel has been used as a steam turbine rotor material. The turbine rotor material is damaged by high temperature creep and fatigue due to starts and stops and changing load of power generation, which results in crack initiation and growth.

In the studies done before, the law of crack growth life under creep-fatigue conditions was characterized and clarified that the characteristics of crack growth life of various load frequencies under different temperatures change from fatigue to creep behavior through an inflection region. The law of crack growth life under creep-fatigue interactive conditions has been reported and evaluated by monotonous linear law. On the other hand, it has been indicated that the characteristics of crack growth life under creep-fatigue condition can be represented mathematically by a three dimensional characteristic curved surface based on non-equilibrium science.

In this study, crack growth tests using standardized C(T) specimens of W-added 12% Cr ferritic heat resistant steel were conducted under various conditions of stress holding time, applied stress and temperature. To evaluate the effect of cycle dependent and time dependent mechanisms on crack growth life, a method of separate estimation of cycle dependent mechanism from the time dependent mechanism based on the concept of three dimensional characteristic curved surface based on non-equilibrium science were used. As a result, the effect of load frequency on crack growth life was characterized and the predictive law of crack growth life for W-added 12% Cr ferritic heat resistant steel under creep-fatigue interactive conditions based on the concept of Q* with the transition function of crack growth life was estimated.
A Combined Creep and Fatigue Damage Estimation Tool for Power-Plant Monitoring
Authors: Harrison Noel M. , Adams Adelina , O’Donoghue Padraic E. , Leen Sean B.
Published: December 2016

A user-friendly creep-fatigue damage calculation tool is developed in Visual Basic for Applications (VBA) with the familiar Microsoft Excel® user interface for power plant operators. Operational pressure and temperatures (steam and pipe exterior) are directly input and automatically converted to stress-time histories based on the summation of thermally- and mechanically-induced stresses. The stress history is automatically analysed and segregated into periods of sustained stress levels (creep range) and periods of fluctuating stress (fatigue range). Total damage is determined by summing the creep damage fraction (via Larson-Miller equation and Robinson’s rule) and fatigue damage fraction (via a rainflow cycle counting subroutine, the Smith-Watson-Topper fatigue parameter and Miner’s rule). Pre-existing damage fraction can be incorporated into the calculations. The remaining life estimates based on repetition of the load profile are outputted for the user. Finally, the estimated damage and remaining life are compared to that determined via the ASME, EN and TRD codes, where applicable.
Comparison of Header Flat End Plate Designs for Operation in the Creep Range
Authors: Cooch Michael , Dewees Dave , Komora George
Published: December 2016

Section I of the ASME Boiler and Pressure Vessel Code currently has a Code Case that provides rules for the construction of unstayed flat heads with integral flanges (butt welded hubs) from forged material. This Code Case is currently being considered for adoption into the Section I rules; therefore, the existing requirements of the Code Case are under review. In particular, feedback on the Code Case indicated that the required minimum hub length presents manufacturing challenges in certain situations, so the necessity of this hub is being reviewed.

As this type of flat head is commonly used in high temperature operation, evaluation of the expected creep behavior is critical, especially in the proposed weld area at the head junction to the attached shell (typically a header). Example geometries were developed using the current Code Case requirements and their suitability for high temperature operation was initially evaluated using elastic analysis. Detailed inelastic analysis was then performed to further quantify the expected time-dependent high temperature behavior.

Additionally, a series of failures of end plates designed to the TRD code was reported to have occurred in Europe in the 1990s. In order to assess the potential relevance of these failures to heads designed per the proposed Section I rules, additional examples were developed using the design rules of the TRD code rules. The predicted creep behavior and damage for these examples were then compared to the Code Case designed examples.
Reactor Pressure Vessel Integrity Assessment: French Simplified Analysis Method Applied to Underclad Postulated Defect in Nozzle
Authors: Arrieta-Ruiz Adolfo , Meister Eric , Vidard Stéphane
Published: December 2016

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main concerns regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Fast fracture risk is the main potential damage considered in the integrity assessment of RPV.

In France, deterministic integrity assessment for RPV vis-à-vis the brittle fracture risk is based on the crack initiation stage. As regards the core area in particular, the stability of an under-clad postulated flaw is currently evaluated under a Pressurized Thermal Shock (PTS) through a dedicated fracture mechanics simplified method called “beta method”. However, flaw stability analyses are also carried-out in several other areas of the RPV. Thence-forward performing uniform simplified inservice analyses of flaw stability is a major concern for EDF.

In this context, 3D finite element elastic-plastic calculations with flaw modelling in the nozzle have been carried out recently and the corresponding results have been compared to those provided by the beta method, codified in the French RSE-M code for under-clad defects in the core area, in the most severe events.

The purpose of this work is to validate the employment of the core area fracture mechanics simplified method as a conservative approach for the under-clad postulated flaw stability assessment in the complex geometry of the nozzle.

This paper presents both simplified and 3D modelling flaw stability evaluation methods and the corresponding results obtained by running a PTS event. It shows that the employment of the “beta method” provides conservative results in comparison to those produced by elastic-plastic calculations for the cases here studied.
Consideration of Irradiation Effect in Components Design: Illustration of a Way to Introduce an Environmental Effect in the Design Process
Authors: Pétesch C. , Lebarbé T. , Pascal C. , Dubiez-Le Goff S.
Published: December 2016

During the last years, a particular attention has been paid to the consideration and evaluation of environmental effects in the design of mechanical components, particularly for the consequences of Pressure Water Reactors environment on fatigue damages. In the frame of RCC-MRx design code, developed for Sodium Fast Reactors (SFR), Research Reactors (RR) and Fusion Reactors (FR-ITER), the specific features are creep damage (covered by the design rules responding to the needs of fast breeder reactors and high temperatures) and irradiated material (covered by the design rules responding to the needs of research reactors developed for the JHR project).

The purpose of this document is to detail the way to consider an environmental effect such irradiation in the material design rules. It covers:

- the background for these rules, linked with the changes in materials behavior,

- their content, in term of damage impact,

- and the challenges to be met for their development to other applications.
A Hybrid Control Method to Reduce the Seismic Response of a Liquid Storage Tank
Authors: Luo Hao , Zhang Ruifu , Weng Dagen
Published: December 2016

In this study, a hybrid control method is proposed, in which both isolation bearings and an inertial mass damper (IMD) are used, to reduce the seismic response of a liquid storage tank. First, simplified models of the tank and IMD are illustrated. Next, to evaluate the effectiveness of the proposed method, three tanks, including a fixed tank, an isolated tank and an isolated tank with an IMD, are analyzed and compared. Last, parametric studies are conducted to investigate the effects of equivalent inertial mass and viscous damping of the IMD. It is observed that, compared with the fixed tank, the base shear of the isolated one is largely reduced, whereas the wave height is consequently amplified; for the isolated tank with an IMD, not only is the base shear more obviously reduced, but also the wave height is effectively controlled. What’s more, the base displacement of the isolated tank with an IMD is much lower than that of the isolated one. Therefore, the proposed method can be considered as an effective method to control the seismic response of the liquid storage tanks.
Proposal for an Improved Engineering Fatigue Lifetime Assessment Concept
Authors: Rudolph Jürgen , Wilhelm Paul , Roth Armin , Herbst Matthias , Kammerer Matthias C. , Schuler Xaver , Herter Karl-Heinz
Published: December 2016

Fatigue life assessment for pressurized components in nuclear power plants (NPPs) is an essential part of the aging management (AM) ensuring safe and long term operation (LTO). For fatigue life assessment different codes and standards provide a variety of methodologies with variable complexity. Major fatigue life influencing factors such as temperature, surface finish, multiaxiality, loading history and others are often considered in a more or less global way by combined overall reduction factors covering multiple mechanisms together. Other effects such as the environment or hold times are often considered not at all or otherwise with high levels of conservatism resulting in large discrepancies between calculated fatigue life and practical experience from power plant operation. In order to reduce this inadequacy a more accurate fatigue lifetime assessment concept including individual fatigue life influencing factors in a mechanistic manner is required. Nevertheless, these amendments are to fit into the existing basic engineering approach of design against fatigue failure as it is implemented in nuclear standards and design codes. In the framework of an ongoing three years German cooperation R&D project with participation of the Materials Testing Institute MPA University of Stuttgart and AREVA GmbH (Erlangen) it is the aim to both improve the state of the art based on an experimental program for some of the main fatigue life influencing factors and on the derivation of a practicable engineering fatigue assessment procedure. Within this fatigue assessment procedure the dominant fatigue life influencing factors are considered individually. The experimental program covers fatigue test results for austenitic and ferritic piping materials including a dissimilar metal weld. Within the testing program strain controlled fatigue tests were performed with and without hold-times in air and high temperature water environments. Smooth and notched specimens provide a database to study the influence of notches and multiaxiality. These results are used to state on the applicability of commonly used failure hypothesis like von Mises and Tresca in comparison to advanced fatigue damage parameters. In addition to constant amplitude strain controlled fatigue testing load spectra were investigated. Thereby fatigue cumulative damage models like Miner’s rule can be evaluated. This publication constitutes a follow-up to a previous paper [1] and targets at the presentation of experimental results in conjunction with potentials with an improved fatigue assessment concept. In addition the methodology of the concept is applied to experimental results on fatigue life assessments for piping materials published by other organizations. Requirements for further experimental investigations towards the verification of a closed concept are formulated.
Evaluation of the Lowest Temperature for Ductile Crack Initiation in an Irradiated RPV
Authors: Wilkowski G. , Brust F. W. , Uddin M. , Kalyanam S. , Lacroix V.
Published: December 2016

In this paper, work done for defining the lowest temperature for ductile fracture initiation in piping and fittings was extended to a sample reactor pressure vessel (RPV). The methodology used is called “Master Curve of Fracture Transition Temperatures” and was developed from correlations of thousands of laboratory tests and hundreds of pipe tests originally presented in 2005. Since then it has been extended to; low and high strength line-pipe steel base metals (oil/gas industry), blunt flaws as well as sharp cracks, girth welds for the oil/gas industry, fracture of pipe fittings/valves, and is the technical basis for the lowest temperature for ductile crack initiation in ferritic piping in Appendix C of ASME Section XI. Since the methodology is quite different than traditional approaches for nuclear component applications, the general methodology will be reviewed, as well as analysis results showing how surveillance capsule Charpy data could be used to predict the lowest temperature where ductile crack initiation would occur in RPVs. Once this temperature is established, then the upper-shelf toughness values can be used to determine if the failure is EPFM or limit-load, and the associated failure stresses. This temperature could be used for defining the pressure-temperature limits to assure that the RPV material has a high flaw tolerance. This methodology was proposed for the Doel 3 and Tihange 2 RPVs in Belgium.

One key concern for operation of RPVs is determining the lowest operating temperature where ductile crack initiation is still expected which can be based on studies of irradiation effects on the measured toughness from Charpy tests of material in surveillance capsules. With ductile crack initiation the flaw tolerance is quite high even with long-term irradiation damage to the material. In fact, if the toughness is closer to limit-load than LEFM in a FAD analysis, then as long as there is ductile initiation, the irradiation effects increase the strength which could increase the flaw tolerance. There are some ongoing efforts within the ASME Section XI activities to define the minimum temperature where ductile initiation occurs in fracture toughness testing (typically based on a mixture of Charpy and 1T CT specimen data); however, there are still thickness and constraint effects on the fracture toughness for more precise application to a thick-walled vessel with a postulated axial surface crack.
Molecular Dynamics Study of Energy Storage Device
Authors: Smith Sheriden , Park Young Ho
Published: December 2016

Currently, the dominating energy storage device remains the battery, particularly the lithium battery. Lithium/lithium-ion batteries are used for various applications. For example, lithium battery powered pipeline inspection tools are used by the oil and gas industry for internal inspection of pipelines. Lithium batteries are complex devices whose performance optimization requires a good understanding of physical processes that occur on multiple time and length scales. Optimization of the electrolyte, in particular, needs detailed, fundamental, molecular level understanding of the chemical and mechanical features that lead to stable electrolytes such as good interfacial lithium transport properties, thermal stability and safety. In this work, we use molecular dynamics (MD) computational technique to investigate thermodynamic and dynamics properties for various carbonate-based electrolyte systems of lithium-ion batteries.
High-Efficiency Remote Measurement of Pipe Defect Using RF/UT Technologies: A Theoretical Analysis Part One — Straight Beam UT
Authors: Alobaidi Wissam M. , Sandgren Eric
Published: December 2016

This analysis has established a new hybrid RF/UT system for non-destructive testing of pipe walls for pipe wall thinning (PWT) in order to predict location, and enable measurement of the depth of defect by combining the group velocity method and calibration condition. A simulation of microwave (MW) behavior in a 91% brass waveguide (762mm pipe, Young’s Modulus 102KN/mm2) was developed using Computer Simulation Technology (CST). The model included a frequency band of 1.283GHz for the TMnm mode (TM01 and TM21), with a sweeping frequency from 0.70GHZ to 2.00GHz. The model includes 14 instances of full-circumferential PWT, regularly spaced along the length of the waveguide with step-width of 50.8mm on center. For each we have modeled four cases of increasing PWT (5.08mm, 10.16mm, 15.24mm and 20.32mm). Considering the measurement with MW as a prediction of the location of the PWT, rather than a measurement, we can guide a straight-beam UT probe to the position predicted by MW, and use the appropriate signal velocity ultrasound to accurately measure the depth to defect from the outer surface of the pipe. The straight beam UT is found to be no better at determining the geometry of the defect than MW, but the accurate depth to defect (DDO) measurement would allow estimation of the volume of the PWT.
Multiple Reflection Theory for Fluid-Structure Interaction in Viscoelastic Vessels and Experimental Validation
Authors: Kroot J. M. B. , Giannopapa C. G.
Published: December 2016

Fluid-structure interaction in viscoelastic vessels is often modelled with the motivation to understand arterial blood flow. Traveling waves in flexible vessels have been analyzed and experiments have been performed by many researchers. Theoretical models often focus either on the flow of the liquid (assuming that the wall is rigid), or on the displacement of the wall (assuming that the wall is elastic). Analytical theories on the interaction between the fluid and the wall are limited; models are typically based on numerical techniques. For assessing the validity of analytical and numerical models well-defined in-vitro experiments are of great importance. The objective of this paper is to present a transmission line analytical theory and validate it against experimental data obtained for aortic analogues. Transition line theory allows for including non-uniformities of vessels by capturing them as several uniform segments. The analytical theory is set up by multiple sections and a formulation is derived that incorporates the multiple reflections and transmissions of propagating waves through the interfaces of these sections. The pressure, flow and wall distention results obtained from the analytical model are compared with experimental data from a straight uniform tube and a tapered one with aortic relevance. The analytical results and the experimental measurements were found to be in good agreement for both the uniform and tapered tubes.