bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Research of AE Inspection on Stress Corrosion Crack for Small Pressure Vessel
Authors: Zhang Zhongzheng , Liang Hua , Ye Cheng , Cai Wensheng , Jiang Jun
Published: January 2014

To study acoustic emission (AE) signals characteristics of stress corrosion crack (SCC) on in-service pressure vessels. The small pressure vessel with a pre-crack, filled 6% ferric chloride solution was monitored by AE technique. Conventional parameter-based approach and signal-based analysis were combined to deal with recorded AE signals, and micromorphologic observation and ray detection were performed for further verification. The results showed that the Kaiser effect of Q345R material is obvious, AE hits rate and amplitude & energy of the first pressure cycling was higher. Signal band is mainly distributed in 40 ∼ 400 KHz, Signal waveform was mainly composed of high -frequency (>100 KHz) expansion wave with larger amplitude & energy and low-frequency (<100 KHz) flexural wave with lesser amplitude & energy. The research results have a certain reference value for AE test on SCC for practical in-service pressure vessel.
Biaxial Residual Stress Mapping in a PWR Dissimilar Metal Weld
Authors: Hill Michael R. , Olson Mitchell D.
Published: January 2014

This paper describes a sequence of residual stress measurements made to determine a two-dimensional map of biaxial residual stress in a dissimilar metal welded nozzle typical of a nuclear pressurized water reactor (PWR). The present experimental work follows on the numerical analysis reported earlier, in PVP2012-78885. The measurement subject is a cylindrical nozzle, removed from a PWR pressure vessel, having a nickel alloy weld joining a stainless steel safe end to a low-alloy steel vessel. Biaxial residual stress was determined in a series of experimental steps using strain gage measurements, the contour method, and slitting. Confirmatory measurements were also performed (including digital image correlation and neutron diffraction). The paper includes descriptions of the experimental steps, data reduction, and residual stress results, along with a comparison between measurements and output from a weld simulation. The measured hoop stress in the weld region is tensile near the OD (300 MPa) and compressive near the ID (−400 MPa); the measured axial stress is tensile near the OD (150 MPa) and compressive near the ID (−150 MPa).
Constitutive Modeling of High Temperature Uniaxial Creep-Fatigue and Creep-Ratcheting Responses of Alloy 617
Authors: Pritchard P. G. , Carroll L. , Hassan T.
Published: January 2014

Inconel Alloy 617 is a high temperature creep and corrosion resistant alloy and is a leading candidate for use in Intermediate Heat Exchangers (IHX) of the Next Generation Nuclear Plants (NGNP). The IHX of the NGNP is expected to experience operating temperatures in the range of 800°–950°C, which is in the creep regime of Alloy 617. A broad set of uniaxial, low-cycle fatigue, fatigue-creep, ratcheting, and ratcheting-creep experiments are conducted in order to study the fatigue and ratcheting responses, and their interactions with the creep response at high temperatures. A unified constitutive model developed at North Carolina State University is used to simulate these experimental responses. The model is developed based on the Chaboche viscoplastic model framework. It includes cyclic hardening/softening, strain rate dependence, strain range dependence, static and dynamic recovery modeling features. For simulation of the alloy 617 responses, new techniques of model parameter determination are developed for optimized simulations. This paper compares the experimental responses and model simulations for demonstrating the strengths and shortcomings of the model.
Fatigue and Ratcheting Experimental Responses of Alloy 617 Under High Temperature Multiaxial Loading
Authors: Quayyum Shahriar , Sengupta Mainak , Choi Gloria , Lissenden Clifford J. , Hassan Tasnim
Published: January 2014

Nickel based Alloy 617 is one of the leading candidate materials for intermediate heat exchanger (IHX) of the next generation nuclear plant (NGNP). The IHX is anticipated to operate at temperatures between 800–950°C, which is in the creep regime. In addition, system start-ups and shut-downs will induce low cycle fatigue (LCF) damages in the IHX components. Hence, designing IHX using Alloy 617 for NGNP construction will require a detailed understanding of the creep-fatigue and ratcheting responses. In this study, a broad set of multiaxial creep-fatigue and ratcheting experiments are performed and the results are critically evaluated. Experiments are conducted by prescribing multiaxial loading histories in axial and shear directions at 850°C and 950°C with different strain rates and strain amplitudes. Experimental results revealed that the axial strain ratcheting and cyclic hardening/softening responses of Alloy 617 vary significantly with temperature levels, strain rates and strain amplitudes indicating the dependence of creep-fatigue and ratcheting responses on these parameters. This necessitates the incorporation of strain rate and strain amplitude dependence and effect of loading non-proportionality and temperature in the unified constitutive modeling (UCM) for a better prediction of the material behavior. Development of a UCM is underway based on the experimental results developed.
Stress Classification for Tubesheet of Heat Exchanger With Semi-Ellipsoidal Heads
Authors: Yoshimura Naoki , Kataoka Shunji , Sato Takuya
Published: January 2014

A fixed tubesheet type heat exchanger with semi-ellipsoidal heads which is dealt with in this paper has been adopted for refrigerant heat exchange process in LNG Plant. Since the conventional design standards, e.g. ASME Sec VIII Div.1 and TEMA, are not meant to be used for such a special type of heat exchanger, FEA should be performed to determine minimum required thickness of the tubesheet.

The elastic design procedure uses a stress classification methodology to guard against failure due to gross plastic deformation. According to the design standards, mechanical stresses in the tubesheet due to tube-side and/or shell-side pressure are defined as the primary membrane and bending stress and are evaluated by comparing with allowable values of the primary stress. For the special type of heat exchanger, however, stresses in the tubesheet obtained by FEA are actually complex combination of primary and secondary stresses. Application of this conventional design approach to the FEA-calculated stresses in tubesheet may lead to over-conservative design.

In helping to establish reliable and economical design of the tubesheet for such a special type of heat exchanger, authors conducted FEA investigation employing axisymmetric analysis model. Considering the geometric parameters, such as thickness of a tubesheet, heads type and shell dimension, the characteristics of tubesheet stresses was investigated and an appropriate stress classification was proposed.
Structural Integrity Analyses for a Preemptive Weld Overlay in a Pressurizer Surge Nozzle
Authors: Liu Ru-Feng , Huang Chin-Cheng
Published: January 2014

This paper is to present the structural integrity analyses for a preemptive weld overlay in a pressurizer surge nozzle. Based on ASME Code Case N-504-3 and MRP-169, the full structural weld overlay sizing calculation, residual stress improvement analysis, shrinkage evaluation, fatigue crack growth analysis and fatigue usage analysis were performed. After weld overlay installation, the welded nozzle structure has to be analyzed to measure the improvement in residual stresses around the inner surface of the original weld. The residual compressive stress distribution is thus addressed to be resistant to subsequent stress corrosion, the initiation of cracking, and the further crack growth. To ensure the structural integrity of the attached piping system, the weld induced displacement is measured and transformed to temperature gradient to simulate the shrinkage after overlay welding and to analyze the post-weld distortion and stress situations. Based on the further comparisons of fatigue crack growth with all of system operating cycles, two surface cracks in the original weld are conservatively postulated. Additionally, both the stress limits and cumulative fatigue usages of the nozzle with weld overlay are evaluated to meet the design requirements of ASME Code Section III. The present analysis results confirm the effectiveness of the procedure for analyzing the structural integrity of a nozzle with weld overlay.
Plastic Collapse Strength of Circumferentially Multiple Notched Stainless Piping Subjected to Combined Axial Tension and Bending
Authors: Yanagihara Seiji , Matsubara Masaaki , Suzuki Ryosuke
Published: January 2014

The present study examines the effects of the number of cracks and the crack interval on the plastic collapse strength of austenitic stainless steel (SUS304) piping with multiple cracks subjected to combined axial tension and bending. The goal of the present study is to simplify the structural integrity assessment of the stainless steel piping. Notches were cut in circumferential direction of the SUS304 pipes. The notch interval was 5 to 32 mm in the double-notched specimens. In the triple-notched specimens, the notches of the specimen were equally spaced. The notches at both ends of the triple-notched specimens were cut at the same interval as the double-notched specimens. The notched specimens were subjected to combined axial tension and bending. The plastic collapse strength of the notched specimens was dependent on the load history, and the plastic collapse strengths of the double- or triple-notched specimens was approximately equal to that of the single-notched specimens. These strengths were higher than the theoretical plastic collapse strength of the single-notched specimen based on an elastic-perfectly plastic material. Therefore, double or triple circumferential notches arranged in intervals of from 5 to 32 mm in SUS304 piping can be considered to be a single circumferential crack by applying the plastic collapse theory for an elastic-perfectly plastic material.
Corrosion Fatigue Evaluation of Austenitics Stainless Steels: The New Proposal to the Czech Standard in the Area of Nuclear Power Plants Type WWER
Authors: Vlcek Libor
Published: January 2014

In the Czech Republic the NTD A.M.E. (Normatively Technical Documentation of Association of Mechanical Engineers) standard [1] is recommended by the State Office for Nuclear Safety for assessment of components and piping in the nuclear power plants of WWER type. So far the fatigue life assessment is based on fatigue design curves or mathematical formulas which are based on experimental tests in air environment conditions only. The present paper is dealing with the new proposal of Czech approach in the area of corrosion fatigue interaction. Based on original Russian works the environmental aspects were taken into account for the case of fatigue life evaluation. The aim of this work is to clarify the main idea of the new proposal of appropriate part of NTD A.M.E. residual life section. In the frame of primary water corrosion fatigue interaction not only theoretical background, but also low-cycle fatigue tests in primary water are presented.
Mechanical Property Database Development and Creep Prediction of Candidate Generation IV SCWR Alloys
Authors: Xu S. , Jin S.-M. , Le Dreff-Kerwin P.
Published: January 2014

To contribute to the design and materials selection of the Generation IV SuperCritical Water Reactors (Gen IV SCWR), a high-temperature mechanical property database of candidate alloys has been developed and creep models have been applied to predict long-term creep strength. The alloys in the database include representative ferritic/martensitic (F/M) steels, stainless steels, iron-nickel–base alloys, Ni-base alloys, and oxide dispersion strengthened (ODS) alloys with an emphasis on candidate austenitic and super-austenitic stainless steels. The mechanical properties were evaluated and examined with reference to ASME Section III Subsection NH code and the preliminary fuel cladding requirements in Canadian and Japanese conceptual SCWR designs. Traditional creep prediction models (i.e., Monkman-Grant model and Larson-Miller parameter) and the recent Wilshire-Scharning model were assessed and the constants of creep models were obtained. The predicted average maximum allowable stresses at temperatures and lifetimes of interest to Gen IV SCWR fuel cladding applications are presented.
Nuclear Reactor Pressure Vessel Integrity Assessment: Enhancement Provided by 3D Modeling Flaw Stability Calculations
Authors: Arrieta-Ruiz Adolfo , Meister Eric , Churier Henriette
Published: January 2014

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main considerations regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Brittle fracture risk associated with the embrittlement of RPV steel in irradiated areas is the main potential damage.

In France, deterministic integrity assessment for RPV is based on the crack initiation stage. The stability of an under-clad postulated flaw in the core area is currently evaluated under a Pressurized Thermal Shock (PTS) through a fracture mechanics simplified method.

One of the axes of EDF’s implemented strategy for NPP lifetime extension is the improvement of the deterministic approach with regards to the input data and methods so as to reduce conservatisms. In this context, 3D finite element elastic-plastic calculations with flaw modelling have been carried out recently in order to quantify the enhancement provided by a more realistic approach in the most severe events.

The aim of this paper is to present both simplified and 3D modelling flaw stability evaluation methods and the results obtained by running a small break LOCA event.
Low-Constraint Toughness Testing: Results of a Round Robin on a Draft SE(T) Test Procedure
Authors: Tyson William R. , Gianetto James A.
Published: January 2014

Assessment of the effect of girth weld flaws on pipeline integrity requires knowledge of a number of factors: pipe geometry, applied loads, flaw size, and pipe mechanical properties. Of the latter, strength and toughness are the primary factors. Toughness has conventionally been measured using specimens tested in bending to maximize constraint. While this gives a conservative estimate of toughness, it would be better to use a test that would reveal the toughness in constraint conditions typical of girth weld flaws: namely, relatively shallow flaws loaded in tension. Consequently, there is a trend to evaluate toughness using pre-cracked single-edge-cracked tension (i.e. SE(T)) specimens, and one procedure has already been standardized. However, this procedure requires the use of multiple specimens to generate a resistance curve. With the objective of devising a more economical test, a single-specimen procedure has been developed at CANMET. The viability of this procedure has been assessed by means of a round robin involving test and research laboratories from around the world. In this presentation, the results of the round robin will be presented and discussed.
Research on Acoustic Emission Signals Characteristics of Pitting Corrosion on 304 Stainless Steel
Authors: Zhang Zhongzheng , Liang Hua , Ye Cheng , Cai Wensheng , Jiang Jun , Cui Qiang
Published: January 2014

In order to study acoustic emission (AE) signals waveform characteristics of pitting corrosion on 304 stainless steel under higher temperature than lower one, Pitting corrosion process on 304 stainless steel in 6% ferric chloride solution at 70°C was monitored by AE technology. Wavelet transform and mode acoustic emission technology were combined to deal with recorded AE signals, and micromorphologic observation was performed for further verification. The results showed that signal waveform was mainly composed of low-frequency (<100KHz) flexural wave with larger amplitude & energy and high-frequency (>100KHz) expansion wave with lesser amplitude & energy. The research results have some certain significance for AE monitoring of pitting corrosion on 304 stainless steel.
Investigation of Burst Pressure in Pipes With Square Wall Thinning by Using FEA and API579 FFS-1
Authors: Yamaguchi Atsushi
Published: January 2014

Boilers and pressure vessels are heavily used in chemical industrial plants and equipment is inspected periodically for damage. The most common type of damage is wall thinning due to Flow-Accelerated Corrosion (FAC) or corrosion under insulation (CUI). Any damage must be repaired or replaced as necessary. On the other hand, optimization of the time required in order to replace damaged equipment by evaluating the load carrying capacity of pipes with wall thinning is expected in chemical industrial field. In the present study, FE analysis is used in order to evaluate the load carrying capacity in pipes with wall thinning. Burst pressure is a measure of the load carrying capacity in pipes with wall thinning. The pipes subjected to burst testing are carbon steel tubes for pressure service STPG370 (JIS G3454). The examined wall thinning is rectangular, and the eroded depth is half the pipe wall thickness. The burst pressure is investigated by comparing the results of burst testing with the results of FE analysis. Moreover, the reduced maximum allowable working pressure (MAWPr), which is calculated by fitness-for-service (FFS) assessment, and the safety margin for burst pressure are investigated. The burst pressure calculated by FEA agrees well with the test results, except for square wall thinning for circumferential angles of less than 15°. Also, the safety margin of MAWPr based on FFS-1 Part 4 is over 4.0 times for burst pressure.
Reactor Pressure Vessel Nozzle Inner-Radius Examination
Authors: Glass S. W. , Thigpen B. , Guse G. , Brau E.
Published: January 2014

Reactor pressure vessel nozzle inner radius (NIR) areas are identified as a specific target for ultrasound examination (UT) by many regulatory codes. This region represents a particularly challenging geometry to examine. Typically the examination is performed from inside the vessel with at least the upper internals removed. Normally the inspection is on the critical path so minimizing the schedule and vessel occupation time is important to the utilities outage planning and ultimate financial performance.

Although some inspection vendors have traditional qualifications for this NIR examination under various codes, this paper addresses several advanced techniques have been developed to minimize the critical path inspection time. Technology advancements include:

• Stereo-vision with laser reference for precise VT sizing of any observed indication

• A Small 5 degree-of-freedom arm to precisely track a transducer set along the inner-radius surface for immersion ultrasonic examination

• A simple nozzle-only tool with a passive mechanism to track the nozzle inner-radius surface for contact ultrasonic examination

• Advanced software (3-D iMaV) coupled with a 5-axis robot to analyze and control transducer placements and coverage from the nozzle and shell outside (OD)

The net result is a more efficient examination with shorter schedules and lower overall outage costs.
Challenging Hypers Performance
Authors: Giacomelli Enzo
Published: January 2014

The production of LDPE may require huge heavy-duty reciprocating compressors to withstand the loads, deriving from the operating pressures, to satisfy the growing needs of the market. Safety, Performance and Reliability are normal expectations and therefore need a thorough evaluation of the specific service. The machine selection is based on positive experience in similar applications and cylinder performance. The cylinders are special pressure vessels, whose design and construction have to consider the extreme internal pressures and the process gas. The design must foresee all possible failure modes of each component, to have safe and smooth operation, thanks to innovative methods of modeling and simulation, like FEM and CFD, important for the design of cylinder parts.

Valves are simulated by mathematical models optimizing performance, to reach a correct mechanical behavior with minimum energy consumption and ensuring reliable operation.

The available technological improvements are a starting point, resulting from the developments of manufacturers and long experience of End Users.

The pulsation and vibration of the piping are usually investigated to keep the plant in operation without failures.

Many cylinder components are exposed to pressures fluctuating between suction and discharge and therefore to high fatigue loads. To reach high endurance capabilities they have to be pre-compressed to keep them operating under compressive stresses whenever possible. Special materials, shrink fitting and auto-frettage procedures are usually required.

The operation is the stage where all the parameters have to be kept under control and incipient problems have to be identified to minimize shut-downs and arrange various maintenance works. Automation, monitoring and diagnostic systems complete the efforts of operators to afford high safety levels, with increased availability and optimized maintenance interventions.

The continuing development of technology will help to challenge performance and high capacity demand of future plants.
Failure and Prevention of Pressure Vessels due to Instability of Process System
Authors: Chen Xuedong , Zhu Jianxin , Fan Zhichao , Ai Zhibin
Published: January 2014

From the analysis of engineering risks of petrochemical plants in recent years, it is found that the change and instability of the process systems have significant effect on the failure of pressure vessels, and the failure of pressure vessels takes place repeatedly due to the inadequate prediction of dynamic risk of the system in the design of pressure vessels. Starting from the analysis of systematic engineering risk methodology, several typical failure cases in petrochemical process systems due to the inadequacy of process design and interlock control are introduced and analyzed in this paper, and the corresponding measures for preventing the failure of pressure vessels caused by system instability at the design and the in-service stage are proposed. It is believed that the basic measures for preventing occurrence of such failure accidents are the analyzing the dynamic risk of the system during the determination of design parameters of pressure vessels at early design stage, verifying process changes and adjusting the configuration of interlock control system according to the design and operating parameters of pressure vessels at the in-service stage.
Study on the Relief Capacity and Safety Integrity of Multiple Relief Valves of Charge Gas Pipe in Ethylene-Cracking Plant
Authors: Zhu Jianxin , Chen Xuedong , Lu YunRong , Ai Zhibin , Guan Weihe
Published: January 2014

The shutdown of charge gas compressor in large-scale ethylene-cracking plant always involves emergency pressure relief of charge gas through multiple safety valves. The emergency relief capacity plays an important role on the safety of the overall plant. In this paper, by studying the difference between the configuration of the pressure relief system of two 1000 KTA ethylene-cracking plants (the inner diameters of the charge gas pipeline in both plants are 2m, while the number of same-sized relief valves are 28 and 19, respectively), the relief capacity of multiple relief valves is studied and compared with empirical calculation and numerical analysis. It is found that, due to the interruption of fluid flow when compressor is emergency shutdown, the upstream pressure of each relief valve increase steadily with the continuously make-up of the charge gas, but the difference between the inlet pressure of all relief valves can be neglected. With the increase of the upstream pressure, the opening of relief valves is determined mainly by the set pressure. In multiple valves pressure relief scenario, normally the downstream valves have greater relief capacity than those upstream valves if both relief valves have the same back pressure. Also, by analysis it is noted that the pressure relief capacities of multiple relief valves in both plants are sufficient. The minimum number of relief valves required for process safety is obtained. The maximum achievable Safety Integrity Level (SIL) of pressure relief system is determined by calculation of the reliability of the redundant relief valves. The analysis is used for determination of the SIL of the pressure relief system. The finding is also significant for determination of the required capacity of multiple relief valves.
Investigation of Adhesion Formation in New Stainless Steel Trim Spring Operated Pressure Relief Valves
Authors: Bukowski Julia V. , Gross Robert E. , Goble William M.
Published: January 2014

Examination of proof test data for new (not previously installed) stainless steel (SS) trim spring operated pressure relief valves (SOPRV) reveals that adhesions form between the seat and disc in about 46% of all such SOPRV. The forces needed to overcome these adhesions can be sufficiently large to cause the SOPRV to fail its proof test (FPT) prior to installation. Furthermore, a significant percentage of SOPRV which are found to FPT are also found to “fail to open” (FTO) meaning they would not relief excess pressure in the event of an overpressure event. The cases where adhesions result in FTO or FPT appear to be confined to SOPRV with diameters ≤ 1 in and set pressures < 150 psig and the FTO are estimated to occur in 0.31% to 2.00% of this subpopulation of SS trim SOPRV. The reliability and safety implications of these finding for end-users who do not perform pre-installation testing of SOPRV are discussed.
Acoustic Emission Testing of High Strength Steel LPG Spherical Tanks
Authors: Jiang Jun , Yi Rong , Que Lili
Published: January 2014

We use acoustic emission technique for the detecting of 1000m3 LPG spherical tank. The overall moitoring and local monitoring, as well as a combination of the two methods are applied. By lowering the threshold value, detection sensitivity is improved. 23 effective acoustic emission sources are discovered, in which 21 crack defects are retest.
Combined Measurement and Finite Element Analysis to Map Residual Stresses in Welded Components
Authors: Do Son , Serasli Karim , Smith David
Published: January 2014

Through thickness measurement of residual stresses is now undertaken routinely for complex welded components. To predict residual stress distributions finite element (FE) simulations of the welding of the component are also carried out using well established codes, with the simulations sometimes validated via measurements. Measurements are usually undertaken at locations where it is judged that the peak residual stresses occur. Therefore comparisons are often confined to limited locations. But this raises the question whether the simulated residual stresses at other locations are correct. To explore this, the work reported in this paper relies on introducing measured residual stresses into an elastic FE model of the welded component. These stresses are mapped into the model at the measurements locations. Then the FE analysis redistributes the initial stresses, with an iterative process introduced to ensure that the measured stresses are retained during redistribution. Examples are shown where agreement between measured and weld model predictions are good at the measurement locations and both the measured and weld model predictions satisfy global equilibrium. However, they do not agree at other locations. It is argued that additional measurements at other locations are required to validate the FE models of welding processes.
On the Whistling of Corrugated Pipes With Narrow Cavities
Authors: Golliard Joachim , Belfroid Stefan , Gonzalez Diez Nestor , Bendiksen Erik , Frimodt Casper
Published: January 2014

Pipes with a corrugated inner surface, as used in flexible pipes for gas production and transport, can be subject to Flow-Induced Pulsations when the flow velocities are higher than a certain onset velocity. The onset velocity for classical corrugated pipes can be predicted on basis of the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. A newly developed inner carcass design for flexible pipes features smaller corrugation cavities. The effect of narrow cavities on the whistling of corrugated cavities is evaluated.

In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as deeper and narrower cavities. These tests were performed in order to evaluate the validity of a prediction model for the onset of pulsations, for corrugated pipes with these kinds of atypical variations. The experimental results show that the validity of the model remains reasonable, except when the cavities are very narrow. In this case, the model becomes overly conservative. The deviation is attributed to the momentum thickness of the boundary layer, which is too large compared to the cavity width. In this case, any instability of the shear layer is destroyed, which prevents whistling. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, are considered.
Failure Assessment of Pipe Tee Element Using Continuum Damage Mechanics
Authors: Bonora Nicola , Gentile Domenico , Ruggiero Andrew , Testa Gabriel , Folgarait Paolo , Calatroni Andrea
Published: January 2014

In this work continuum damage mechanics was used to try to predict the occurrence of ductile rupture in a barred tee fitting subjected to pressure load. In order to account for the scatter in the material damage parameters, a stochastic definition was used. Ductile damage parameters were identified using failure data obtained from traction tests of round notched bar samples. The attention is concentrated on the possible failure of the grid since it occurrence can obstruct the pipe flow and drive the structural failure of the tee Numerical simulation indicates that the bars fail first but do not trigger the tee rupture. The location where ductile rupture is expected to initiate in the tee was found to be 30° out of the tee symmetry plane.
COD of Off-Centered Cracks in Pipes Under Bending: Experimental Measures and Model Validation
Authors: Gentile D. , Iannitti G. , Bonora N.
Published: January 2014

The leak area of circumferential part-through crack in pipe under bending depends on the location of the crack with respect to the bending plane. In LBB analysis, taking the crack symmetrically placed with respect to the bending plane no necessarily is a conservative assumption. In this work the COD distribution of circumferential cracks in pipes, off-centered placed with respect to the bending plane, was investigated experimentally. Thick and thin pipe geometries have been analyzed examining different crack lengths and off-axis angle values. The COD distributions have been measured by means of digital image correlation (DIC) technique and used to validate an analytical model (HCM Hodograph Cone Method) proposed by the authors.
Assessing Residual Strains in Nuclear Power Reactor Internal Components Weld Mockups of Nickel Alloys Using EBSD
Authors: Othon Michelle A. , Morra Martin M. , Ooki Suguru , Rebak Raul B.
Published: January 2014

The most common failure mode of commercial nuclear reactor internal components is environmentally assisted cracking (EAC). Environmentally cracking is promoted by the simultaneous effects of three affecting variables, namely (1) presence of tensile stresses and strains, (2) and aggressive environment and (3) a susceptible microstructure. If one or more of these affecting variables are removed, cracking will not occur or propagate. For example, EAC susceptibility and growth rate will be minimized if the residual tensile stresses or strains are controlled. Similarly, EAC may be minimized by controlling the chemistry of the weld metal, for example by increasing the content of chromium in the weld metal. The objective of the current research was to complete laboratory weldments of 76 mm thick plates of Alloy 600 using weld metal with three different compositions. Electron backscatter diffraction (EBSD) results of cross sections of the weld showed that approximately 10 to 15% of residual plastic strain existed at near the root of the weld and in the middle section (at approximately 38 mm); however, lower residual plastic strain existed near the top of the weld (last passes).
Vibration Suppression of Traffic Signal Pole by Generating Electrical Power
Authors: Matsuoka Taichi , Wada Takuya , Katakura Mizuki
Published: January 2014

The authors propose a damper that generates electrical power in order to not only suppress vibration and also get electrical energy when many traffic signal poles are oscillated by wind, traffic turbulence, and earthquake. The damper consists of a displacement magnifying mechanism by using levers, solenoid coils and rare-earth magnets. It is useful for small deformation between a beam and a column of the traffic pole. Vibration modes of the pole are analyzed by using FEM, and then a small scale model of the traffic pole is built up. The small scale model has 2.3 m high, consists of a steel column and a cantilever beam due to rescale about 1/3 of real scale one, and natural frequency is about 3.5 Hz. Trial damper is manufactured and a damping force, which is caused by the coils crossing magnetic field, is adjusted. Dynamic characteristics of the trial damper are measured by a shaking actuator. In order to confirm vibration reduction, both of seismic and harmonic vibration tests of small scale model when the trial damper is installed are carried out by using a shaking table. The experimental results of harmonic responses are compared with the calculated results by FEM, and effect of vibration suppression and efficiency of generating power are discussed experimentally and numerically.
Dynamic Coefficients Identification Using the POD Method
Authors: Ricciardi G. , Boccaccio E.
Published: January 2014

Earthquakes can irreversibly damage nuclear power plants especially in the core. Engineers need special tools to insure that the core will resist the worst conditions. Most of the models developed for industrial purpose account for the damping and added mass induced by the axial flow, and need to identify the related coefficients. Therefore, experiments on full scale fuel assemblies need to be performed. The LHC (Laboratory of Core and Circuit Hydrodynamics) has facilities to perform dynamical tests under axial flow of a fuel assembly. The displacement of one grid of the fuel assembly is imposed by a hydraulic jack with a force sensor, and the displacements of the other grids are measured. LDV measurements are also performed to give a description of the flow distribution in the fuel assembly. An identification based on a Proper Orthogonal Decomposition is proposed. Co-efficients obtained are given by unit of length, which means that they are directly available for models.
Fatigue Behavior of Cladding Material for Nuclear Components
Authors: Herter Karl-Heinz , Schuler Xaver , Hoffmann Michael , Kopp Peter , Mahlke Jan
Published: January 2014

To evaluate the fatigue behavior of the austenitic cladding of pressurized components, the fatigue design curves are usually based on experiments on specimens taken from plates, pipes or bars. Due to rapid heat transport into the ferritic base material, the cladding has a distinctive anisotropic structure that results from the manufacturing process. Therefore, it may not be assumed a priori that the fatigue curves of the various austenitic product forms used in the Safety Standards are also representative for the material of austenitic cladding. It is therefore necessary to determine and assure experimentally a fatigue curve of the cladding material and compare the results with the database of austenitic stainless steels used in German NPPs.

Flat specimens specially adapted to the geometric conditions were prepared out of the austenitic cladding of a RPV which had been manufactured according to nuclear specifications. To check a possible influence of the specimen geometry, flat specimens were prepared in advance from an austenitic pipe of known fatigue behavior and tested at different strain amplitudes. A comparison of the results with the fatigue curve determined with cylindrical specimens showed no influence at the higher strain amplitudes. Altogether, the fatigue data with flat specimens made of the austenitic cladding fit well into the scatter of the fatigue database of austenitic base materials tested with cylindrical specimens.
Fatigue Behavior of Dissimilar Welds Used for Nuclear Piping
Authors: Herter Karl-Heinz , Schuler Xaver , Hoffmann Michael , Kopp Peter
Published: January 2014

Due to specific requirements in NPP piping different materials are used and connected by dissimilar welds (DM). The fatigue behavior of such welds must be known for design and safety evaluations. The overall fatigue behavior of welds depends on the properties of the different weld sections and their interaction. The welding may influence the fatigue behavior of the base materials in the vicinity of the weld.

The investigation deals with the fatigue behavior of DM typical for German NPP: ferritic steel 20MnMoNi5-5 welded to austenitic steel X6CrNiNb18-10 using nickel based alloy for buttering. Fatigue specimens were taken from each region of the weld (ferritic steel near weld, buttering, connection weld, austenitic steel near weld). Additionally specimens were taken containing two adjacent material regions and the respective fusion line. For each position specimens were tested in fully reversed strain controlled conditions at room temperature and total strain amplitude of 0.25%. The results were compared with the best-fit curves for austenitic and ferritic steels.
Creep Damage Evaluation for Fine Grained HAZ of Mod. 9Cr Steels Under Multi-Axial Stress Conditions
Authors: Yoshida Kimiaki , Yatomi Masataka , Tabuchi Masaaki , Kobayashi Ken-ichi
Published: January 2014

This study is concerned with the creep damage evaluation for the fine grained heat affected zone (HAZ) of modified 9Cr steels under multi-axial stress conditions. Circumferentially notched bar creep rupture and interrupted tests have been conducted on the simulated HAZ specimens of modified 9Cr Steels. A metallographic examination has been carried out to quantify creep damage accumulation in the specimens. It has been found from void observation that growth of creep void correlates with maximum principle stress and stress triaxiality factor. Finite element predictions based on ductility exhaustion approach have also been performed to predict the creep rupture time and creep damage in notched specimens. It has been concluded that a ductility exhaustion approach with empirical model provides reasonable life predictability almost in a scatter band of a factor of 2.
Structural Assessment of Reactor Pressure Vessel Under Core Melting Conditions
Authors: Kim Seung-Hyun , Chang Yoon-Suk
Published: January 2014

The worst case scenario including melt-down of reactor core components has been recognized as one of the safety issues. Without any counter measure, this may lead to penetration of RPV (Reactor Pressure Vessel) due to significant thermal loads caused by the relocation of molten core debris into the lower plenum. The present paper shows applicability of ERVC (External Reactor Vessel Cooling), aimed at limiting radiological releases by adopting the in-vessel retention concept, under core melting conditions. Systematic numerical analyses were carried out by taking into account diverse melting progress mechanisms, properties and amounts of molten debris, and damage models. Consequences of the thermal loads under assumed core melting conditions, such as the critical locations and time to reach penetration of the RPV lower plenum, were compared as a part of sensitivity analyses. Also, influences of each parameter were examined and technical findings from the assessment were discussed to demonstrate effectiveness of the ERVC for severe accident mitigation features of new power plants.
Specimen Geometry and Size Effects on the Creep Crack Growth Behaviour of P91 Weldments
Authors: Mehmanparast A. , Maleki S. , Yatomi M. , Nikbin K. M.
Published: January 2014

The influence of specimen size and geometry on the creep crack growth (CCG) behaviour of P91 parent and weld materials at 600–625 °C has been examined. CCG tests have been performed on compact tension, C(T), specimens with an initial crack located in the heat affected zone (HAZ). Further tests have also been performed on specimens made of parent material (PM). Higher creep crack growth rates have been found in the HAZ material compared to the PM when the CCG rate is characterized using the C* fracture mechanics parameter. The experimental data from these tests are compared to those of available from specimens with different size and geometries. The results are discussed in terms of specimen geometry and constraint effects on the CCG behaviour of P91 weldments at elevated temperatures.
Small Scale Burst Facility: Experimental Investigation of Fluid-Structure Interaction in a PHWR
Authors: Baschuk J. J. , West Alan , Leitch B. W.
Published: January 2014

The Pressurized Heavy Water Reactor (PHWR) is based on natural uranium fuel and heavy water moderator. A unique feature of the PHWR is the horizontal fuel channel that allows for on-line re-fuelling and fuel management. A fuel channel consists of two concentric tubes, each approximately 6 meters long. The inner tube, known as the pressure tube, contains the uranium fuel bundles and the pressurized (∼10 MPa) primary coolant. The outer tube, known as the calandria tube, separates the heavy water moderator (∼70°C) from the pressure tube (∼300°C). A potential accident scenario is the bursting of a fuel channel. The escaping hot fluid generates a pressure wave in the moderator, which would interact with the adjacent pressure/calandria tube assemblies and the outer containment calandria vessel, potentially damaging components within the reactor core. To improve the understanding of channel bursts and associated fluid structure interaction, a 1:6 scale reactor vessel test facility (Small Scale Burst Facility) was constructed at the Atomic Energy of Canada Ltd, Chalk River Laboratories. The test facility allows for the measurement of transient pressures, the development and collapse of the steam bubble created by the burst tube, and resultant response of the neighboring tubes and scaled calandria vessel. A single bursting tube, or a single tube bursting within an array of neighboring tubes, can be tested. The results from recent tests are presented, which include a three-dimensional map of the pressure pulse from a single, bursting tube. Future work will include 3-D mapping of near wall bursts and modeling the experiments using Arbitary Lagrangian Eulerian methods in the finite element program, LS-DYNA. This work is part of the development of a next generation modeling tool for fuel channel phenomena.
Waterhammer in a Horizontal Pipe Induced by Slug Formation and Rapid Condensation
Authors: Martin C. Samuel
Published: January 2014

The phenomenon of condensation-induced waterhammer in an ammonia refrigeration system was investigated experimentally. Waterhammer was generated by introducing warm ammonia gas over static subcooled ammonia liquid placed in a horizontal 146.3 mm diameter carbon steel pipe approximately 6.0 m long. By means of fast response piezoelectric pressure transducers and a high speed data acquisition system rapid dynamic pressures were recorded whenever a condensation-induced event occurred. Employing top-mounted diaphragm pressure transducers to sense gas pressure the speed of liquid slugs propagating along the pipe was determined.

The occurrence of condensation-induced waterhammer depended upon three major variables; namely, (1) initial liquid depth, (2) liquid temperature, and (3) mass flow rate of warm gas. For given liquid depth and temperature, once the warm gas threshold conditions were exceeded, shocks occurred with greater magnitude as the mass flow rate of warm gas input was increased. With adequate subcooling condensation-induced waterhammer occurred for initial liquid depths ranging from 25% to 95% of internal pipe diameter. The threshold mass flow rate of warm gas necessary to initiate waterhammer was greater as the initial liquid depth was lowered. For numerous tests with sufficient gas mass flow rate a condensation-induced shock occurred at the end cap of the test pipe, generating an acoustic (pressure) wave that propagated at a modified speed of sound toward the gas-liquid interface at the back of the slug. Peak shock pressures could be correlated with the gas mass flow rate for various initial liquid depth and suction pressures and temperatures. As the initial liquid temperature and pressure were increased the hydraulic shocks became lower because of smaller subcooling.
Characterisation of Residual Stress Levels Retained in Fracture Mechanics Specimens Machined From Non-Stress Relieved Welds
Authors: McCluskey Robert J. A. , Zheng Gang , Sherry Andrew H. , Smith David J.
Published: January 2014

The structural integrity assessment of weldments in engineering components, including piping, is dependent upon the acquisition of valid fracture toughness data. Test standards provide guidance for the preparation of fracture mechanics specimens machined from welds, recognising that under some circumstances retained weld residual stress in the specimens may influence the test, for example, by impairing the ability to establish a valid fatigue pre-crack. To date, however, there are little experimental data quantifying the level and distribution of retained residual stress in fracture mechanics specimens.

This paper describes an experimental study characterising the residual stresses retained in single-edge notched bend specimens machined from a non stress-relieved, narrow-gap Tungsten Inert Gas welded pipe, manufactured from 304L stainless steel. The original weld residual stress field was characterised using neutron diffraction and deep hole drilling. The residual stress levels retained in the test specimens were subsequently quantified using deep hole drilling.

The results indicated that reasonable levels of residual stress are retained within specimens, although for high toughness, ductile steel, this is insufficient to influence the fracture toughness measurement. The results, however, have implications for testing non stress-relieved welds manufactured from low toughness materials, where retained residual stresses could unduly influence fracture toughness measurements.
Finite Element Analysis of Welding Residual Stress of the Ultra-Thick 13MnNiMoR Steel Cylinder of a Large EO Reactor Made in China
Authors: Wen Yongbin , Geng Luyang , Gong Jianming , Wang Yangfei , Tu Shantung
Published: January 2014

The finite element (FE) analysis was applied to investigate welding residual stresses generated in the weld region of the ultra-thick 13MnNiMoR steel cylinder of a large Ethylene Oxide (EO) reactor made in China, with an outer diameter of 6760mm and wall thickness of 110mm. The FE Analysis consists of the nonlinear thermal and thermo-mechanical axisymmetric numerical simulations. In the FE analysis, an alternating welding model was created for the double U-type groove welding. The residual stress distributions on the inside surface and the outside surface were obtained. The analyzed results show that the axial and hoop welding residual stresses on the inside surface and the outside surface are tensile in the weld zone and its vicinity. The residual stress distributions on the inside surface and the outside surface are very sensitive to the distance from the weld centerline. The effects of the temperature of PWHT on the welding residual stress were analyzed by taking into account PWHT at 600 °C, 620 °C and 640 °C. The simulated results show the residual stresses decrease with the increase in the temperature of PWHT, and an appropriate temperature of PWHT is 620 °C for the ultra-thick cylinder of the domestic EO reactor.